- djm@cvs.openbsd.org 2008/05/09 04:55:56

[openssh.git] / channels.c

/* $OpenBSD: channels.c,v 1.276 2008/05/09 04:55:56 djm Exp $ */
/*
 * Author: Tatu Ylonen <ylo@cs.hut.fi>
 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
 *                    All rights reserved
 * This file contains functions for generic socket connection forwarding.
 * There is also code for initiating connection forwarding for X11 connections,
 * arbitrary tcp/ip connections, and the authentication agent connection.
 *
 * As far as I am concerned, the code I have written for this software
 * can be used freely for any purpose.  Any derived versions of this
 * software must be clearly marked as such, and if the derived work is
 * incompatible with the protocol description in the RFC file, it must be
 * called by a name other than "ssh" or "Secure Shell".
 *
 * SSH2 support added by Markus Friedl.
 * Copyright (c) 1999, 2000, 2001, 2002 Markus Friedl.  All rights reserved.
 * Copyright (c) 1999 Dug Song.  All rights reserved.
 * Copyright (c) 1999 Theo de Raadt.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include "includes.h"

#include <sys/types.h>
#include <sys/ioctl.h>
#include <sys/un.h>
#include <sys/socket.h>
#ifdef HAVE_SYS_TIME_H
# include <sys/time.h>
#endif

#include <netinet/in.h>
#include <arpa/inet.h>

#include <errno.h>
#include <netdb.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <termios.h>
#include <unistd.h>
#include <stdarg.h>

#include "openbsd-compat/sys-queue.h"
#include "xmalloc.h"
#include "ssh.h"
#include "ssh1.h"
#include "ssh2.h"
#include "packet.h"
#include "log.h"
#include "misc.h"
#include "buffer.h"
#include "channels.h"
#include "compat.h"
#include "canohost.h"
#include "key.h"
#include "authfd.h"
#include "pathnames.h"

/* -- channel core */

/*
 * Pointer to an array containing all allocated channels.  The array is
 * dynamically extended as needed.
 */
static Channel **channels = NULL;

/*
 * Size of the channel array.  All slots of the array must always be
 * initialized (at least the type field); unused slots set to NULL
 */
static u_int channels_alloc = 0;

/*
 * Maximum file descriptor value used in any of the channels.  This is
 * updated in channel_new.
 */
static int channel_max_fd = 0;


/* -- tcp forwarding */

/*
 * Data structure for storing which hosts are permitted for forward requests.
 * The local sides of any remote forwards are stored in this array to prevent
 * a corrupt remote server from accessing arbitrary TCP/IP ports on our local
 * network (which might be behind a firewall).
 */
typedef struct {
        char *host_to_connect;          /* Connect to 'host'. */
        u_short port_to_connect;        /* Connect to 'port'. */
        u_short listen_port;            /* Remote side should listen port number. */
} ForwardPermission;

/* List of all permitted host/port pairs to connect by the user. */
static ForwardPermission permitted_opens[SSH_MAX_FORWARDS_PER_DIRECTION];

/* List of all permitted host/port pairs to connect by the admin. */
static ForwardPermission permitted_adm_opens[SSH_MAX_FORWARDS_PER_DIRECTION];

/* Number of permitted host/port pairs in the array permitted by the user. */
static int num_permitted_opens = 0;

/* Number of permitted host/port pair in the array permitted by the admin. */
static int num_adm_permitted_opens = 0;

/*
 * If this is true, all opens are permitted.  This is the case on the server
 * on which we have to trust the client anyway, and the user could do
 * anything after logging in anyway.
 */
static int all_opens_permitted = 0;


/* -- X11 forwarding */

/* Maximum number of fake X11 displays to try. */
#define MAX_DISPLAYS  1000

/* Saved X11 local (client) display. */
static char *x11_saved_display = NULL;

/* Saved X11 authentication protocol name. */
static char *x11_saved_proto = NULL;

/* Saved X11 authentication data.  This is the real data. */
static char *x11_saved_data = NULL;
static u_int x11_saved_data_len = 0;

/*
 * Fake X11 authentication data.  This is what the server will be sending us;
 * we should replace any occurrences of this by the real data.
 */
static u_char *x11_fake_data = NULL;
static u_int x11_fake_data_len;


/* -- agent forwarding */

#define NUM_SOCKS       10

/* AF_UNSPEC or AF_INET or AF_INET6 */
static int IPv4or6 = AF_UNSPEC;

/* helper */
static void port_open_helper(Channel *c, char *rtype);

/* non-blocking connect helpers */
static int connect_next(struct channel_connect *);
static void channel_connect_ctx_free(struct channel_connect *);

/* -- channel core */

Channel *
channel_by_id(int id)
{
        Channel *c;

        if (id < 0 || (u_int)id >= channels_alloc) {
                logit("channel_by_id: %d: bad id", id);
                return NULL;
        }
        c = channels[id];
        if (c == NULL) {
                logit("channel_by_id: %d: bad id: channel free", id);
                return NULL;
        }
        return c;
}

/*
 * Returns the channel if it is allowed to receive protocol messages.
 * Private channels, like listening sockets, may not receive messages.
 */
Channel *
channel_lookup(int id)
{
        Channel *c;

        if ((c = channel_by_id(id)) == NULL)
                return (NULL);

        switch (c->type) {
        case SSH_CHANNEL_X11_OPEN:
        case SSH_CHANNEL_LARVAL:
        case SSH_CHANNEL_CONNECTING:
        case SSH_CHANNEL_DYNAMIC:
        case SSH_CHANNEL_OPENING:
        case SSH_CHANNEL_OPEN:
        case SSH_CHANNEL_INPUT_DRAINING:
        case SSH_CHANNEL_OUTPUT_DRAINING:
                return (c);
        }
        logit("Non-public channel %d, type %d.", id, c->type);
        return (NULL);
}

/*
 * Register filedescriptors for a channel, used when allocating a channel or
 * when the channel consumer/producer is ready, e.g. shell exec'd
 */
static void
channel_register_fds(Channel *c, int rfd, int wfd, int efd,
    int extusage, int nonblock)
{
        /* Update the maximum file descriptor value. */
        channel_max_fd = MAX(channel_max_fd, rfd);
        channel_max_fd = MAX(channel_max_fd, wfd);
        channel_max_fd = MAX(channel_max_fd, efd);

        /* XXX set close-on-exec -markus */

        c->rfd = rfd;
        c->wfd = wfd;
        c->sock = (rfd == wfd) ? rfd : -1;
        c->ctl_fd = -1; /* XXX: set elsewhere */
        c->efd = efd;
        c->extended_usage = extusage;

        /* XXX ugly hack: nonblock is only set by the server */
        if (nonblock && isatty(c->rfd)) {
                debug2("channel %d: rfd %d isatty", c->self, c->rfd);
                c->isatty = 1;
                if (!isatty(c->wfd)) {
                        error("channel %d: wfd %d is not a tty?",
                            c->self, c->wfd);
                }
        } else {
                c->isatty = 0;
        }
        c->wfd_isatty = isatty(c->wfd);

        /* enable nonblocking mode */
        if (nonblock) {
                if (rfd != -1)
                        set_nonblock(rfd);
                if (wfd != -1)
                        set_nonblock(wfd);
                if (efd != -1)
                        set_nonblock(efd);
        }
}

/*
 * Allocate a new channel object and set its type and socket. This will cause
 * remote_name to be freed.
 */
Channel *
channel_new(char *ctype, int type, int rfd, int wfd, int efd,
    u_int window, u_int maxpack, int extusage, char *remote_name, int nonblock)
{
        int found;
        u_int i;
        Channel *c;

        /* Do initial allocation if this is the first call. */
        if (channels_alloc == 0) {
                channels_alloc = 10;
                channels = xcalloc(channels_alloc, sizeof(Channel *));
                for (i = 0; i < channels_alloc; i++)
                        channels[i] = NULL;
        }
        /* Try to find a free slot where to put the new channel. */
        for (found = -1, i = 0; i < channels_alloc; i++)
                if (channels[i] == NULL) {
                        /* Found a free slot. */
                        found = (int)i;
                        break;
                }
        if (found < 0) {
                /* There are no free slots.  Take last+1 slot and expand the array.  */
                found = channels_alloc;
                if (channels_alloc > 10000)
                        fatal("channel_new: internal error: channels_alloc %d "
                            "too big.", channels_alloc);
                channels = xrealloc(channels, channels_alloc + 10,
                    sizeof(Channel *));
                channels_alloc += 10;
                debug2("channel: expanding %d", channels_alloc);
                for (i = found; i < channels_alloc; i++)
                        channels[i] = NULL;
        }
        /* Initialize and return new channel. */
        c = channels[found] = xcalloc(1, sizeof(Channel));
        buffer_init(&c->input);
        buffer_init(&c->output);
        buffer_init(&c->extended);
        c->ostate = CHAN_OUTPUT_OPEN;
        c->istate = CHAN_INPUT_OPEN;
        c->flags = 0;
        channel_register_fds(c, rfd, wfd, efd, extusage, nonblock);
        c->self = found;
        c->type = type;
        c->ctype = ctype;
        c->local_window = window;
        c->local_window_max = window;
        c->local_consumed = 0;
        c->local_maxpacket = maxpack;
        c->remote_id = -1;
        c->remote_name = xstrdup(remote_name);
        c->remote_window = 0;
        c->remote_maxpacket = 0;
        c->force_drain = 0;
        c->single_connection = 0;
        c->detach_user = NULL;
        c->detach_close = 0;
        c->open_confirm = NULL;
        c->open_confirm_ctx = NULL;
        c->input_filter = NULL;
        c->output_filter = NULL;
        TAILQ_INIT(&c->status_confirms);
        debug("channel %d: new [%s]", found, remote_name);
        return c;
}

static int
channel_find_maxfd(void)
{
        u_int i;
        int max = 0;
        Channel *c;

        for (i = 0; i < channels_alloc; i++) {
                c = channels[i];
                if (c != NULL) {
                        max = MAX(max, c->rfd);
                        max = MAX(max, c->wfd);
                        max = MAX(max, c->efd);
                }
        }
        return max;
}

int
channel_close_fd(int *fdp)
{
        int ret = 0, fd = *fdp;

        if (fd != -1) {
                ret = close(fd);
                *fdp = -1;
                if (fd == channel_max_fd)
                        channel_max_fd = channel_find_maxfd();
        }
        return ret;
}

/* Close all channel fd/socket. */
static void
channel_close_fds(Channel *c)
{
        debug3("channel %d: close_fds r %d w %d e %d c %d",
            c->self, c->rfd, c->wfd, c->efd, c->ctl_fd);

        channel_close_fd(&c->sock);
        channel_close_fd(&c->ctl_fd);
        channel_close_fd(&c->rfd);
        channel_close_fd(&c->wfd);
        channel_close_fd(&c->efd);
}

/* Free the channel and close its fd/socket. */
void
channel_free(Channel *c)
{
        char *s;
        u_int i, n;
        struct channel_confirm *cc;

        for (n = 0, i = 0; i < channels_alloc; i++)
                if (channels[i])
                        n++;
        debug("channel %d: free: %s, nchannels %u", c->self,
            c->remote_name ? c->remote_name : "???", n);

        s = channel_open_message();
        debug3("channel %d: status: %s", c->self, s);
        xfree(s);

        if (c->sock != -1)
                shutdown(c->sock, SHUT_RDWR);
        if (c->ctl_fd != -1)
                shutdown(c->ctl_fd, SHUT_RDWR);
        channel_close_fds(c);
        buffer_free(&c->input);
        buffer_free(&c->output);
        buffer_free(&c->extended);
        if (c->remote_name) {
                xfree(c->remote_name);
                c->remote_name = NULL;
        }
        while ((cc = TAILQ_FIRST(&c->status_confirms)) != NULL) {
                if (cc->abandon_cb != NULL)
                        cc->abandon_cb(c, cc->ctx);
                TAILQ_REMOVE(&c->status_confirms, cc, entry);
                bzero(cc, sizeof(*cc));
                xfree(cc);
        }
        channels[c->self] = NULL;
        xfree(c);
}

void
channel_free_all(void)
{
        u_int i;

        for (i = 0; i < channels_alloc; i++)
                if (channels[i] != NULL)
                        channel_free(channels[i]);
}

/*
 * Closes the sockets/fds of all channels.  This is used to close extra file
 * descriptors after a fork.
 */
void
channel_close_all(void)
{
        u_int i;

        for (i = 0; i < channels_alloc; i++)
                if (channels[i] != NULL)
                        channel_close_fds(channels[i]);
}

/*
 * Stop listening to channels.
 */
void
channel_stop_listening(void)
{
        u_int i;
        Channel *c;

        for (i = 0; i < channels_alloc; i++) {
                c = channels[i];
                if (c != NULL) {
                        switch (c->type) {
                        case SSH_CHANNEL_AUTH_SOCKET:
                        case SSH_CHANNEL_PORT_LISTENER:
                        case SSH_CHANNEL_RPORT_LISTENER:
                        case SSH_CHANNEL_X11_LISTENER:
                                channel_close_fd(&c->sock);
                                channel_free(c);
                                break;
                        }
                }
        }
}

/*
 * Returns true if no channel has too much buffered data, and false if one or
 * more channel is overfull.
 */
int
channel_not_very_much_buffered_data(void)
{
        u_int i;
        Channel *c;

        for (i = 0; i < channels_alloc; i++) {
                c = channels[i];
                if (c != NULL && c->type == SSH_CHANNEL_OPEN) {
#if 0
                        if (!compat20 &&
                            buffer_len(&c->input) > packet_get_maxsize()) {
                                debug2("channel %d: big input buffer %d",
                                    c->self, buffer_len(&c->input));
                                return 0;
                        }
#endif
                        if (buffer_len(&c->output) > packet_get_maxsize()) {
                                debug2("channel %d: big output buffer %u > %u",
                                    c->self, buffer_len(&c->output),
                                    packet_get_maxsize());
                                return 0;
                        }
                }
        }
        return 1;
}

/* Returns true if any channel is still open. */
int
channel_still_open(void)
{
        u_int i;
        Channel *c;

        for (i = 0; i < channels_alloc; i++) {
                c = channels[i];
                if (c == NULL)
                        continue;
                switch (c->type) {
                case SSH_CHANNEL_X11_LISTENER:
                case SSH_CHANNEL_PORT_LISTENER:
                case SSH_CHANNEL_RPORT_LISTENER:
                case SSH_CHANNEL_CLOSED:
                case SSH_CHANNEL_AUTH_SOCKET:
                case SSH_CHANNEL_DYNAMIC:
                case SSH_CHANNEL_CONNECTING:
                case SSH_CHANNEL_ZOMBIE:
                        continue;
                case SSH_CHANNEL_LARVAL:
                        if (!compat20)
                                fatal("cannot happen: SSH_CHANNEL_LARVAL");
                        continue;
                case SSH_CHANNEL_OPENING:
                case SSH_CHANNEL_OPEN:
                case SSH_CHANNEL_X11_OPEN:
                        return 1;
                case SSH_CHANNEL_INPUT_DRAINING:
                case SSH_CHANNEL_OUTPUT_DRAINING:
                        if (!compat13)
                                fatal("cannot happen: OUT_DRAIN");
                        return 1;
                default:
                        fatal("channel_still_open: bad channel type %d", c->type);
                        /* NOTREACHED */
                }
        }
        return 0;
}

/* Returns the id of an open channel suitable for keepaliving */
int
channel_find_open(void)
{
        u_int i;
        Channel *c;

        for (i = 0; i < channels_alloc; i++) {
                c = channels[i];
                if (c == NULL || c->remote_id < 0)
                        continue;
                switch (c->type) {
                case SSH_CHANNEL_CLOSED:
                case SSH_CHANNEL_DYNAMIC:
                case SSH_CHANNEL_X11_LISTENER:
                case SSH_CHANNEL_PORT_LISTENER:
                case SSH_CHANNEL_RPORT_LISTENER:
                case SSH_CHANNEL_OPENING:
                case SSH_CHANNEL_CONNECTING:
                case SSH_CHANNEL_ZOMBIE:
                        continue;
                case SSH_CHANNEL_LARVAL:
                case SSH_CHANNEL_AUTH_SOCKET:
                case SSH_CHANNEL_OPEN:
                case SSH_CHANNEL_X11_OPEN:
                        return i;
                case SSH_CHANNEL_INPUT_DRAINING:
                case SSH_CHANNEL_OUTPUT_DRAINING:
                        if (!compat13)
                                fatal("cannot happen: OUT_DRAIN");
                        return i;
                default:
                        fatal("channel_find_open: bad channel type %d", c->type);
                        /* NOTREACHED */
                }
        }
        return -1;
}


/*
 * Returns a message describing the currently open forwarded connections,
 * suitable for sending to the client.  The message contains crlf pairs for
 * newlines.
 */
char *
channel_open_message(void)
{
        Buffer buffer;
        Channel *c;
        char buf[1024], *cp;
        u_int i;

        buffer_init(&buffer);
        snprintf(buf, sizeof buf, "The following connections are open:\r\n");
        buffer_append(&buffer, buf, strlen(buf));
        for (i = 0; i < channels_alloc; i++) {
                c = channels[i];
                if (c == NULL)
                        continue;
                switch (c->type) {
                case SSH_CHANNEL_X11_LISTENER:
                case SSH_CHANNEL_PORT_LISTENER:
                case SSH_CHANNEL_RPORT_LISTENER:
                case SSH_CHANNEL_CLOSED:
                case SSH_CHANNEL_AUTH_SOCKET:
                case SSH_CHANNEL_ZOMBIE:
                        continue;
                case SSH_CHANNEL_LARVAL:
                case SSH_CHANNEL_OPENING:
                case SSH_CHANNEL_CONNECTING:
                case SSH_CHANNEL_DYNAMIC:
                case SSH_CHANNEL_OPEN:
                case SSH_CHANNEL_X11_OPEN:
                case SSH_CHANNEL_INPUT_DRAINING:
                case SSH_CHANNEL_OUTPUT_DRAINING:
                        snprintf(buf, sizeof buf,
                            "  #%d %.300s (t%d r%d i%d/%d o%d/%d fd %d/%d cfd %d)\r\n",
                            c->self, c->remote_name,
                            c->type, c->remote_id,
                            c->istate, buffer_len(&c->input),
                            c->ostate, buffer_len(&c->output),
                            c->rfd, c->wfd, c->ctl_fd);
                        buffer_append(&buffer, buf, strlen(buf));
                        continue;
                default:
                        fatal("channel_open_message: bad channel type %d", c->type);
                        /* NOTREACHED */
                }
        }
        buffer_append(&buffer, "\0", 1);
        cp = xstrdup(buffer_ptr(&buffer));
        buffer_free(&buffer);
        return cp;
}

void
channel_send_open(int id)
{
        Channel *c = channel_lookup(id);

        if (c == NULL) {
                logit("channel_send_open: %d: bad id", id);
                return;
        }
        debug2("channel %d: send open", id);
        packet_start(SSH2_MSG_CHANNEL_OPEN);
        packet_put_cstring(c->ctype);
        packet_put_int(c->self);
        packet_put_int(c->local_window);
        packet_put_int(c->local_maxpacket);
        packet_send();
}

void
channel_request_start(int id, char *service, int wantconfirm)
{
        Channel *c = channel_lookup(id);

        if (c == NULL) {
                logit("channel_request_start: %d: unknown channel id", id);
                return;
        }
        debug2("channel %d: request %s confirm %d", id, service, wantconfirm);
        packet_start(SSH2_MSG_CHANNEL_REQUEST);
        packet_put_int(c->remote_id);
        packet_put_cstring(service);
        packet_put_char(wantconfirm);
}

void
channel_register_status_confirm(int id, channel_confirm_cb *cb,
    channel_confirm_abandon_cb *abandon_cb, void *ctx)
{
        struct channel_confirm *cc;
        Channel *c;

        if ((c = channel_lookup(id)) == NULL)
                fatal("channel_register_expect: %d: bad id", id);

        cc = xmalloc(sizeof(*cc));
        cc->cb = cb;
        cc->abandon_cb = abandon_cb;
        cc->ctx = ctx;
        TAILQ_INSERT_TAIL(&c->status_confirms, cc, entry);
}

void
channel_register_open_confirm(int id, channel_callback_fn *fn, void *ctx)
{
        Channel *c = channel_lookup(id);

        if (c == NULL) {
                logit("channel_register_open_comfirm: %d: bad id", id);
                return;
        }
        c->open_confirm = fn;
        c->open_confirm_ctx = ctx;
}

void
channel_register_cleanup(int id, channel_callback_fn *fn, int do_close)
{
        Channel *c = channel_by_id(id);

        if (c == NULL) {
                logit("channel_register_cleanup: %d: bad id", id);
                return;
        }
        c->detach_user = fn;
        c->detach_close = do_close;
}

void
channel_cancel_cleanup(int id)
{
        Channel *c = channel_by_id(id);

        if (c == NULL) {
                logit("channel_cancel_cleanup: %d: bad id", id);
                return;
        }
        c->detach_user = NULL;
        c->detach_close = 0;
}

void
channel_register_filter(int id, channel_infilter_fn *ifn,
    channel_outfilter_fn *ofn)
{
        Channel *c = channel_lookup(id);

        if (c == NULL) {
                logit("channel_register_filter: %d: bad id", id);
                return;
        }
        c->input_filter = ifn;
        c->output_filter = ofn;
}

void
channel_set_fds(int id, int rfd, int wfd, int efd,
    int extusage, int nonblock, u_int window_max)
{
        Channel *c = channel_lookup(id);

        if (c == NULL || c->type != SSH_CHANNEL_LARVAL)
                fatal("channel_activate for non-larval channel %d.", id);
        channel_register_fds(c, rfd, wfd, efd, extusage, nonblock);
        c->type = SSH_CHANNEL_OPEN;
        c->local_window = c->local_window_max = window_max;
        packet_start(SSH2_MSG_CHANNEL_WINDOW_ADJUST);
        packet_put_int(c->remote_id);
        packet_put_int(c->local_window);
        packet_send();
}

/*
 * 'channel_pre*' are called just before select() to add any bits relevant to
 * channels in the select bitmasks.
 */
/*
 * 'channel_post*': perform any appropriate operations for channels which
 * have events pending.
 */
typedef void chan_fn(Channel *c, fd_set *readset, fd_set *writeset);
chan_fn *channel_pre[SSH_CHANNEL_MAX_TYPE];
chan_fn *channel_post[SSH_CHANNEL_MAX_TYPE];

/* ARGSUSED */
static void
channel_pre_listener(Channel *c, fd_set *readset, fd_set *writeset)
{
        FD_SET(c->sock, readset);
}

/* ARGSUSED */
static void
channel_pre_connecting(Channel *c, fd_set *readset, fd_set *writeset)
{
        debug3("channel %d: waiting for connection", c->self);
        FD_SET(c->sock, writeset);
}

static void
channel_pre_open_13(Channel *c, fd_set *readset, fd_set *writeset)
{
        if (buffer_len(&c->input) < packet_get_maxsize())
                FD_SET(c->sock, readset);
        if (buffer_len(&c->output) > 0)
                FD_SET(c->sock, writeset);
}

static void
channel_pre_open(Channel *c, fd_set *readset, fd_set *writeset)
{
        u_int limit = compat20 ? c->remote_window : packet_get_maxsize();

        if (c->istate == CHAN_INPUT_OPEN &&
            limit > 0 &&
            buffer_len(&c->input) < limit &&
            buffer_check_alloc(&c->input, CHAN_RBUF))
                FD_SET(c->rfd, readset);
        if (c->ostate == CHAN_OUTPUT_OPEN ||
            c->ostate == CHAN_OUTPUT_WAIT_DRAIN) {
                if (buffer_len(&c->output) > 0) {
                        FD_SET(c->wfd, writeset);
                } else if (c->ostate == CHAN_OUTPUT_WAIT_DRAIN) {
                        if (CHANNEL_EFD_OUTPUT_ACTIVE(c))
                                debug2("channel %d: obuf_empty delayed efd %d/(%d)",
                                    c->self, c->efd, buffer_len(&c->extended));
                        else
                                chan_obuf_empty(c);
                }
        }
        /** XXX check close conditions, too */
        if (compat20 && c->efd != -1) {
                if (c->extended_usage == CHAN_EXTENDED_WRITE &&
                    buffer_len(&c->extended) > 0)
                        FD_SET(c->efd, writeset);
                else if (!(c->flags & CHAN_EOF_SENT) &&
                    c->extended_usage == CHAN_EXTENDED_READ &&
                    buffer_len(&c->extended) < c->remote_window)
                        FD_SET(c->efd, readset);
        }
        /* XXX: What about efd? races? */
        if (compat20 && c->ctl_fd != -1 &&
            c->istate == CHAN_INPUT_OPEN && c->ostate == CHAN_OUTPUT_OPEN)
                FD_SET(c->ctl_fd, readset);
}

/* ARGSUSED */
static void
channel_pre_input_draining(Channel *c, fd_set *readset, fd_set *writeset)
{
        if (buffer_len(&c->input) == 0) {
                packet_start(SSH_MSG_CHANNEL_CLOSE);
                packet_put_int(c->remote_id);
                packet_send();
                c->type = SSH_CHANNEL_CLOSED;
                debug2("channel %d: closing after input drain.", c->self);
        }
}

/* ARGSUSED */
static void
channel_pre_output_draining(Channel *c, fd_set *readset, fd_set *writeset)
{
        if (buffer_len(&c->output) == 0)
                chan_mark_dead(c);
        else
                FD_SET(c->sock, writeset);
}

/*
 * This is a special state for X11 authentication spoofing.  An opened X11
 * connection (when authentication spoofing is being done) remains in this
 * state until the first packet has been completely read.  The authentication
 * data in that packet is then substituted by the real data if it matches the
 * fake data, and the channel is put into normal mode.
 * XXX All this happens at the client side.
 * Returns: 0 = need more data, -1 = wrong cookie, 1 = ok
 */
static int
x11_open_helper(Buffer *b)
{
        u_char *ucp;
        u_int proto_len, data_len;

        /* Check if the fixed size part of the packet is in buffer. */
        if (buffer_len(b) < 12)
                return 0;

        /* Parse the lengths of variable-length fields. */
        ucp = buffer_ptr(b);
        if (ucp[0] == 0x42) {   /* Byte order MSB first. */
                proto_len = 256 * ucp[6] + ucp[7];
                data_len = 256 * ucp[8] + ucp[9];
        } else if (ucp[0] == 0x6c) {    /* Byte order LSB first. */
                proto_len = ucp[6] + 256 * ucp[7];
                data_len = ucp[8] + 256 * ucp[9];
        } else {
                debug2("Initial X11 packet contains bad byte order byte: 0x%x",
                    ucp[0]);
                return -1;
        }

        /* Check if the whole packet is in buffer. */
        if (buffer_len(b) <
            12 + ((proto_len + 3) & ~3) + ((data_len + 3) & ~3))
                return 0;

        /* Check if authentication protocol matches. */
        if (proto_len != strlen(x11_saved_proto) ||
            memcmp(ucp + 12, x11_saved_proto, proto_len) != 0) {
                debug2("X11 connection uses different authentication protocol.");
                return -1;
        }
        /* Check if authentication data matches our fake data. */
        if (data_len != x11_fake_data_len ||
            memcmp(ucp + 12 + ((proto_len + 3) & ~3),
                x11_fake_data, x11_fake_data_len) != 0) {
                debug2("X11 auth data does not match fake data.");
                return -1;
        }
        /* Check fake data length */
        if (x11_fake_data_len != x11_saved_data_len) {
                error("X11 fake_data_len %d != saved_data_len %d",
                    x11_fake_data_len, x11_saved_data_len);
                return -1;
        }
        /*
         * Received authentication protocol and data match
         * our fake data. Substitute the fake data with real
         * data.
         */
        memcpy(ucp + 12 + ((proto_len + 3) & ~3),
            x11_saved_data, x11_saved_data_len);
        return 1;
}

static void
channel_pre_x11_open_13(Channel *c, fd_set *readset, fd_set *writeset)
{
        int ret = x11_open_helper(&c->output);

        if (ret == 1) {
                /* Start normal processing for the channel. */
                c->type = SSH_CHANNEL_OPEN;
                channel_pre_open_13(c, readset, writeset);
        } else if (ret == -1) {
                /*
                 * We have received an X11 connection that has bad
                 * authentication information.
                 */
                logit("X11 connection rejected because of wrong authentication.");
                buffer_clear(&c->input);
                buffer_clear(&c->output);
                channel_close_fd(&c->sock);
                c->sock = -1;
                c->type = SSH_CHANNEL_CLOSED;
                packet_start(SSH_MSG_CHANNEL_CLOSE);
                packet_put_int(c->remote_id);
                packet_send();
        }
}

static void
channel_pre_x11_open(Channel *c, fd_set *readset, fd_set *writeset)
{
        int ret = x11_open_helper(&c->output);

        /* c->force_drain = 1; */

        if (ret == 1) {
                c->type = SSH_CHANNEL_OPEN;
                channel_pre_open(c, readset, writeset);
        } else if (ret == -1) {
                logit("X11 connection rejected because of wrong authentication.");
                debug2("X11 rejected %d i%d/o%d", c->self, c->istate, c->ostate);
                chan_read_failed(c);
                buffer_clear(&c->input);
                chan_ibuf_empty(c);
                buffer_clear(&c->output);
                /* for proto v1, the peer will send an IEOF */
                if (compat20)
                        chan_write_failed(c);
                else
                        c->type = SSH_CHANNEL_OPEN;
                debug2("X11 closed %d i%d/o%d", c->self, c->istate, c->ostate);
        }
}

/* try to decode a socks4 header */
/* ARGSUSED */
static int
channel_decode_socks4(Channel *c, fd_set *readset, fd_set *writeset)
{
        char *p, *host;
        u_int len, have, i, found;
        char username[256];
        struct {
                u_int8_t version;
                u_int8_t command;
                u_int16_t dest_port;
                struct in_addr dest_addr;
        } s4_req, s4_rsp;

        debug2("channel %d: decode socks4", c->self);

        have = buffer_len(&c->input);
        len = sizeof(s4_req);
        if (have < len)
                return 0;
        p = buffer_ptr(&c->input);
        for (found = 0, i = len; i < have; i++) {
                if (p[i] == '\0') {
                        found = 1;
                        break;
                }
                if (i > 1024) {
                        /* the peer is probably sending garbage */
                        debug("channel %d: decode socks4: too long",
                            c->self);
                        return -1;
                }
        }
        if (!found)
                return 0;
        buffer_get(&c->input, (char *)&s4_req.version, 1);
        buffer_get(&c->input, (char *)&s4_req.command, 1);
        buffer_get(&c->input, (char *)&s4_req.dest_port, 2);
        buffer_get(&c->input, (char *)&s4_req.dest_addr, 4);
        have = buffer_len(&c->input);
        p = buffer_ptr(&c->input);
        len = strlen(p);
        debug2("channel %d: decode socks4: user %s/%d", c->self, p, len);
        if (len > have)
                fatal("channel %d: decode socks4: len %d > have %d",
                    c->self, len, have);
        strlcpy(username, p, sizeof(username));
        buffer_consume(&c->input, len);
        buffer_consume(&c->input, 1);           /* trailing '\0' */

        host = inet_ntoa(s4_req.dest_addr);
        strlcpy(c->path, host, sizeof(c->path));
        c->host_port = ntohs(s4_req.dest_port);

        debug2("channel %d: dynamic request: socks4 host %s port %u command %u",
            c->self, host, c->host_port, s4_req.command);

        if (s4_req.command != 1) {
                debug("channel %d: cannot handle: socks4 cn %d",
                    c->self, s4_req.command);
                return -1;
        }
        s4_rsp.version = 0;                     /* vn: 0 for reply */
        s4_rsp.command = 90;                    /* cd: req granted */
        s4_rsp.dest_port = 0;                   /* ignored */
        s4_rsp.dest_addr.s_addr = INADDR_ANY;   /* ignored */
        buffer_append(&c->output, &s4_rsp, sizeof(s4_rsp));
        return 1;
}

/* try to decode a socks5 header */
#define SSH_SOCKS5_AUTHDONE     0x1000
#define SSH_SOCKS5_NOAUTH       0x00
#define SSH_SOCKS5_IPV4         0x01
#define SSH_SOCKS5_DOMAIN       0x03
#define SSH_SOCKS5_IPV6         0x04
#define SSH_SOCKS5_CONNECT      0x01
#define SSH_SOCKS5_SUCCESS      0x00

/* ARGSUSED */
static int
channel_decode_socks5(Channel *c, fd_set *readset, fd_set *writeset)
{
        struct {
                u_int8_t version;
                u_int8_t command;
                u_int8_t reserved;
                u_int8_t atyp;
        } s5_req, s5_rsp;
        u_int16_t dest_port;
        u_char *p, dest_addr[255+1];
        u_int have, need, i, found, nmethods, addrlen, af;

        debug2("channel %d: decode socks5", c->self);
        p = buffer_ptr(&c->input);
        if (p[0] != 0x05)
                return -1;
        have = buffer_len(&c->input);
        if (!(c->flags & SSH_SOCKS5_AUTHDONE)) {
                /* format: ver | nmethods | methods */
                if (have < 2)
                        return 0;
                nmethods = p[1];
                if (have < nmethods + 2)
                        return 0;
                /* look for method: "NO AUTHENTICATION REQUIRED" */
                for (found = 0, i = 2; i < nmethods + 2; i++) {
                        if (p[i] == SSH_SOCKS5_NOAUTH) {
                                found = 1;
                                break;
                        }
                }
                if (!found) {
                        debug("channel %d: method SSH_SOCKS5_NOAUTH not found",
                            c->self);
                        return -1;
                }
                buffer_consume(&c->input, nmethods + 2);
                buffer_put_char(&c->output, 0x05);              /* version */
                buffer_put_char(&c->output, SSH_SOCKS5_NOAUTH); /* method */
                FD_SET(c->sock, writeset);
                c->flags |= SSH_SOCKS5_AUTHDONE;
                debug2("channel %d: socks5 auth done", c->self);
                return 0;                               /* need more */
        }
        debug2("channel %d: socks5 post auth", c->self);
        if (have < sizeof(s5_req)+1)
                return 0;                       /* need more */
        memcpy(&s5_req, p, sizeof(s5_req));
        if (s5_req.version != 0x05 ||
            s5_req.command != SSH_SOCKS5_CONNECT ||
            s5_req.reserved != 0x00) {
                debug2("channel %d: only socks5 connect supported", c->self);
                return -1;
        }
        switch (s5_req.atyp){
        case SSH_SOCKS5_IPV4:
                addrlen = 4;
                af = AF_INET;
                break;
        case SSH_SOCKS5_DOMAIN:
                addrlen = p[sizeof(s5_req)];
                af = -1;
                break;
        case SSH_SOCKS5_IPV6:
                addrlen = 16;
                af = AF_INET6;
                break;
        default:
                debug2("channel %d: bad socks5 atyp %d", c->self, s5_req.atyp);
                return -1;
        }
        need = sizeof(s5_req) + addrlen + 2;
        if (s5_req.atyp == SSH_SOCKS5_DOMAIN)
                need++;
        if (have < need)
                return 0;
        buffer_consume(&c->input, sizeof(s5_req));
        if (s5_req.atyp == SSH_SOCKS5_DOMAIN)
                buffer_consume(&c->input, 1);    /* host string length */
        buffer_get(&c->input, (char *)&dest_addr, addrlen);
        buffer_get(&c->input, (char *)&dest_port, 2);
        dest_addr[addrlen] = '\0';
        if (s5_req.atyp == SSH_SOCKS5_DOMAIN)
                strlcpy(c->path, (char *)dest_addr, sizeof(c->path));
        else if (inet_ntop(af, dest_addr, c->path, sizeof(c->path)) == NULL)
                return -1;
        c->host_port = ntohs(dest_port);

        debug2("channel %d: dynamic request: socks5 host %s port %u command %u",
            c->self, c->path, c->host_port, s5_req.command);

        s5_rsp.version = 0x05;
        s5_rsp.command = SSH_SOCKS5_SUCCESS;
        s5_rsp.reserved = 0;                    /* ignored */
        s5_rsp.atyp = SSH_SOCKS5_IPV4;
        ((struct in_addr *)&dest_addr)->s_addr = INADDR_ANY;
        dest_port = 0;                          /* ignored */

        buffer_append(&c->output, &s5_rsp, sizeof(s5_rsp));
        buffer_append(&c->output, &dest_addr, sizeof(struct in_addr));
        buffer_append(&c->output, &dest_port, sizeof(dest_port));
        return 1;
}

/* dynamic port forwarding */
static void
channel_pre_dynamic(Channel *c, fd_set *readset, fd_set *writeset)
{
        u_char *p;
        u_int have;
        int ret;

        have = buffer_len(&c->input);
        c->delayed = 0;
        debug2("channel %d: pre_dynamic: have %d", c->self, have);
        /* buffer_dump(&c->input); */
        /* check if the fixed size part of the packet is in buffer. */
        if (have < 3) {
                /* need more */
                FD_SET(c->sock, readset);
                return;
        }
        /* try to guess the protocol */
        p = buffer_ptr(&c->input);
        switch (p[0]) {
        case 0x04:
                ret = channel_decode_socks4(c, readset, writeset);
                break;
        case 0x05:
                ret = channel_decode_socks5(c, readset, writeset);
                break;
        default:
                ret = -1;
                break;
        }
        if (ret < 0) {
                chan_mark_dead(c);
        } else if (ret == 0) {
                debug2("channel %d: pre_dynamic: need more", c->self);
                /* need more */
                FD_SET(c->sock, readset);
        } else {
                /* switch to the next state */
                c->type = SSH_CHANNEL_OPENING;
                port_open_helper(c, "direct-tcpip");
        }
}

/* This is our fake X11 server socket. */
/* ARGSUSED */
static void
channel_post_x11_listener(Channel *c, fd_set *readset, fd_set *writeset)
{
        Channel *nc;
        struct sockaddr addr;
        int newsock;
        socklen_t addrlen;
        char buf[16384], *remote_ipaddr;
        int remote_port;

        if (FD_ISSET(c->sock, readset)) {
                debug("X11 connection requested.");
                addrlen = sizeof(addr);
                newsock = accept(c->sock, &addr, &addrlen);
                if (c->single_connection) {
                        debug2("single_connection: closing X11 listener.");
                        channel_close_fd(&c->sock);
                        chan_mark_dead(c);
                }
                if (newsock < 0) {
                        error("accept: %.100s", strerror(errno));
                        return;
                }
                set_nodelay(newsock);
                remote_ipaddr = get_peer_ipaddr(newsock);
                remote_port = get_peer_port(newsock);
                snprintf(buf, sizeof buf, "X11 connection from %.200s port %d",
                    remote_ipaddr, remote_port);

                nc = channel_new("accepted x11 socket",
                    SSH_CHANNEL_OPENING, newsock, newsock, -1,
                    c->local_window_max, c->local_maxpacket, 0, buf, 1);
                if (compat20) {
                        packet_start(SSH2_MSG_CHANNEL_OPEN);
                        packet_put_cstring("x11");
                        packet_put_int(nc->self);
                        packet_put_int(nc->local_window_max);
                        packet_put_int(nc->local_maxpacket);
                        /* originator ipaddr and port */
                        packet_put_cstring(remote_ipaddr);
                        if (datafellows & SSH_BUG_X11FWD) {
                                debug2("ssh2 x11 bug compat mode");
                        } else {
                                packet_put_int(remote_port);
                        }
                        packet_send();
                } else {
                        packet_start(SSH_SMSG_X11_OPEN);
                        packet_put_int(nc->self);
                        if (packet_get_protocol_flags() &
                            SSH_PROTOFLAG_HOST_IN_FWD_OPEN)
                                packet_put_cstring(buf);
                        packet_send();
                }
                xfree(remote_ipaddr);
        }
}

static void
port_open_helper(Channel *c, char *rtype)
{
        int direct;
        char buf[1024];
        char *remote_ipaddr = get_peer_ipaddr(c->sock);
        int remote_port = get_peer_port(c->sock);

        direct = (strcmp(rtype, "direct-tcpip") == 0);

        snprintf(buf, sizeof buf,
            "%s: listening port %d for %.100s port %d, "
            "connect from %.200s port %d",
            rtype, c->listening_port, c->path, c->host_port,
            remote_ipaddr, remote_port);

        xfree(c->remote_name);
        c->remote_name = xstrdup(buf);

        if (compat20) {
                packet_start(SSH2_MSG_CHANNEL_OPEN);
                packet_put_cstring(rtype);
                packet_put_int(c->self);
                packet_put_int(c->local_window_max);
                packet_put_int(c->local_maxpacket);
                if (direct) {
                        /* target host, port */
                        packet_put_cstring(c->path);
                        packet_put_int(c->host_port);
                } else {
                        /* listen address, port */
                        packet_put_cstring(c->path);
                        packet_put_int(c->listening_port);
                }
                /* originator host and port */
                packet_put_cstring(remote_ipaddr);
                packet_put_int((u_int)remote_port);
                packet_send();
        } else {
                packet_start(SSH_MSG_PORT_OPEN);
                packet_put_int(c->self);
                packet_put_cstring(c->path);
                packet_put_int(c->host_port);
                if (packet_get_protocol_flags() &
                    SSH_PROTOFLAG_HOST_IN_FWD_OPEN)
                        packet_put_cstring(c->remote_name);
                packet_send();
        }
        xfree(remote_ipaddr);
}

static void
channel_set_reuseaddr(int fd)
{
        int on = 1;

        /*
         * Set socket options.
         * Allow local port reuse in TIME_WAIT.
         */
        if (setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) == -1)
                error("setsockopt SO_REUSEADDR fd %d: %s", fd, strerror(errno));
}

/*
 * This socket is listening for connections to a forwarded TCP/IP port.
 */
/* ARGSUSED */
static void
channel_post_port_listener(Channel *c, fd_set *readset, fd_set *writeset)
{
        Channel *nc;
        struct sockaddr addr;
        int newsock, nextstate;
        socklen_t addrlen;
        char *rtype;

        if (FD_ISSET(c->sock, readset)) {
                debug("Connection to port %d forwarding "
                    "to %.100s port %d requested.",
                    c->listening_port, c->path, c->host_port);

                if (c->type == SSH_CHANNEL_RPORT_LISTENER) {
                        nextstate = SSH_CHANNEL_OPENING;
                        rtype = "forwarded-tcpip";
                } else {
                        if (c->host_port == 0) {
                                nextstate = SSH_CHANNEL_DYNAMIC;
                                rtype = "dynamic-tcpip";
                        } else {
                                nextstate = SSH_CHANNEL_OPENING;
                                rtype = "direct-tcpip";
                        }
                }

                addrlen = sizeof(addr);
                newsock = accept(c->sock, &addr, &addrlen);
                if (newsock < 0) {
                        error("accept: %.100s", strerror(errno));
                        return;
                }
                set_nodelay(newsock);
                nc = channel_new(rtype, nextstate, newsock, newsock, -1,
                    c->local_window_max, c->local_maxpacket, 0, rtype, 1);
                nc->listening_port = c->listening_port;
                nc->host_port = c->host_port;
                strlcpy(nc->path, c->path, sizeof(nc->path));

                if (nextstate == SSH_CHANNEL_DYNAMIC) {
                        /*
                         * do not call the channel_post handler until
                         * this flag has been reset by a pre-handler.
                         * otherwise the FD_ISSET calls might overflow
                         */
                        nc->delayed = 1;
                } else {
                        port_open_helper(nc, rtype);
                }
        }
}

/*
 * This is the authentication agent socket listening for connections from
 * clients.
 */
/* ARGSUSED */
static void
channel_post_auth_listener(Channel *c, fd_set *readset, fd_set *writeset)
{
        Channel *nc;
        int newsock;
        struct sockaddr addr;
        socklen_t addrlen;

        if (FD_ISSET(c->sock, readset)) {
                addrlen = sizeof(addr);
                newsock = accept(c->sock, &addr, &addrlen);
                if (newsock < 0) {
                        error("accept from auth socket: %.100s", strerror(errno));
                        return;
                }
                nc = channel_new("accepted auth socket",
                    SSH_CHANNEL_OPENING, newsock, newsock, -1,
                    c->local_window_max, c->local_maxpacket,
                    0, "accepted auth socket", 1);
                if (compat20) {
                        packet_start(SSH2_MSG_CHANNEL_OPEN);
                        packet_put_cstring("auth-agent@openssh.com");
                        packet_put_int(nc->self);
                        packet_put_int(c->local_window_max);
                        packet_put_int(c->local_maxpacket);
                } else {
                        packet_start(SSH_SMSG_AGENT_OPEN);
                        packet_put_int(nc->self);
                }
                packet_send();
        }
}

/* ARGSUSED */
static void
channel_post_connecting(Channel *c, fd_set *readset, fd_set *writeset)
{
        int err = 0, sock;
        socklen_t sz = sizeof(err);

        if (FD_ISSET(c->sock, writeset)) {
                if (getsockopt(c->sock, SOL_SOCKET, SO_ERROR, &err, &sz) < 0) {
                        err = errno;
                        error("getsockopt SO_ERROR failed");
                }
                if (err == 0) {
                        debug("channel %d: connected to %s port %d",
                            c->self, c->connect_ctx.host, c->connect_ctx.port);
                        channel_connect_ctx_free(&c->connect_ctx);
                        c->type = SSH_CHANNEL_OPEN;
                        if (compat20) {
                                packet_start(SSH2_MSG_CHANNEL_OPEN_CONFIRMATION);
                                packet_put_int(c->remote_id);
                                packet_put_int(c->self);
                                packet_put_int(c->local_window);
                                packet_put_int(c->local_maxpacket);
                        } else {
                                packet_start(SSH_MSG_CHANNEL_OPEN_CONFIRMATION);
                                packet_put_int(c->remote_id);
                                packet_put_int(c->self);
                        }
                } else {
                        debug("channel %d: connection failed: %s",
                            c->self, strerror(err));
                        /* Try next address, if any */
                        if ((sock = connect_next(&c->connect_ctx)) > 0) {
                                close(c->sock);
                                c->sock = c->rfd = c->wfd = sock;
                                channel_max_fd = channel_find_maxfd();
                                return;
                        }
                        /* Exhausted all addresses */
                        error("connect_to %.100s port %d: failed.",
                            c->connect_ctx.host, c->connect_ctx.port);
                        channel_connect_ctx_free(&c->connect_ctx);
                        if (compat20) {
                                packet_start(SSH2_MSG_CHANNEL_OPEN_FAILURE);
                                packet_put_int(c->remote_id);
                                packet_put_int(SSH2_OPEN_CONNECT_FAILED);
                                if (!(datafellows & SSH_BUG_OPENFAILURE)) {
                                        packet_put_cstring(strerror(err));
                                        packet_put_cstring("");
                                }
                        } else {
                                packet_start(SSH_MSG_CHANNEL_OPEN_FAILURE);
                                packet_put_int(c->remote_id);
                        }
                        chan_mark_dead(c);
                }
                packet_send();
        }
}

/* ARGSUSED */
static int
channel_handle_rfd(Channel *c, fd_set *readset, fd_set *writeset)
{
        char buf[CHAN_RBUF];
        int len, force;

        force = c->isatty && c->detach_close && c->istate != CHAN_INPUT_CLOSED;
        if (c->rfd != -1 && (force || FD_ISSET(c->rfd, readset))) {
                errno = 0;
                len = read(c->rfd, buf, sizeof(buf));
                if (len < 0 && (errno == EINTR || (errno == EAGAIN && !force)))
                        return 1;
#ifndef PTY_ZEROREAD
                if (len <= 0) {
#else
                if ((!c->isatty && len <= 0) ||
                    (c->isatty && (len < 0 || (len == 0 && errno != 0)))) {
#endif
                        debug2("channel %d: read<=0 rfd %d len %d",
                            c->self, c->rfd, len);
                        if (c->type != SSH_CHANNEL_OPEN) {
                                debug2("channel %d: not open", c->self);
                                chan_mark_dead(c);
                                return -1;
                        } else if (compat13) {
                                buffer_clear(&c->output);
                                c->type = SSH_CHANNEL_INPUT_DRAINING;
                                debug2("channel %d: input draining.", c->self);
                        } else {
                                chan_read_failed(c);
                        }
                        return -1;
                }
                if (c->input_filter != NULL) {
                        if (c->input_filter(c, buf, len) == -1) {
                                debug2("channel %d: filter stops", c->self);
                                chan_read_failed(c);
                        }
                } else if (c->datagram) {
                        buffer_put_string(&c->input, buf, len);
                } else {
                        buffer_append(&c->input, buf, len);
                }
        }
        return 1;
}

/* ARGSUSED */
static int
channel_handle_wfd(Channel *c, fd_set *readset, fd_set *writeset)
{
        struct termios tio;
        u_char *data = NULL, *buf;
        u_int dlen;
        int len;

        /* Send buffered output data to the socket. */
        if (c->wfd != -1 &&
            FD_ISSET(c->wfd, writeset) &&
            buffer_len(&c->output) > 0) {
                if (c->output_filter != NULL) {
                        if ((buf = c->output_filter(c, &data, &dlen)) == NULL) {
                                debug2("channel %d: filter stops", c->self);
                                if (c->type != SSH_CHANNEL_OPEN)
                                        chan_mark_dead(c);
                                else
                                        chan_write_failed(c);
                                return -1;
                        }
                } else if (c->datagram) {
                        buf = data = buffer_get_string(&c->output, &dlen);
                } else {
                        buf = data = buffer_ptr(&c->output);
                        dlen = buffer_len(&c->output);
                }

                if (c->datagram) {
                        /* ignore truncated writes, datagrams might get lost */
                        c->local_consumed += dlen + 4;
                        len = write(c->wfd, buf, dlen);
                        xfree(data);
                        if (len < 0 && (errno == EINTR || errno == EAGAIN))
                                return 1;
                        if (len <= 0) {
                                if (c->type != SSH_CHANNEL_OPEN)
                                        chan_mark_dead(c);
                                else
                                        chan_write_failed(c);
                                return -1;
                        }
                        return 1;
                }
#ifdef _AIX
                /* XXX: Later AIX versions can't push as much data to tty */
                if (compat20 && c->wfd_isatty)
                        dlen = MIN(dlen, 8*1024);
#endif

                len = write(c->wfd, buf, dlen);
                if (len < 0 && (errno == EINTR || errno == EAGAIN))
                        return 1;
                if (len <= 0) {
                        if (c->type != SSH_CHANNEL_OPEN) {
                                debug2("channel %d: not open", c->self);
                                chan_mark_dead(c);
                                return -1;
                        } else if (compat13) {
                                buffer_clear(&c->output);
                                debug2("channel %d: input draining.", c->self);
                                c->type = SSH_CHANNEL_INPUT_DRAINING;
                        } else {
                                chan_write_failed(c);
                        }
                        return -1;
                }
                if (compat20 && c->isatty && dlen >= 1 && buf[0] != '\r') {
                        if (tcgetattr(c->wfd, &tio) == 0 &&
                            !(tio.c_lflag & ECHO) && (tio.c_lflag & ICANON)) {
                                /*
                                 * Simulate echo to reduce the impact of
                                 * traffic analysis. We need to match the
                                 * size of a SSH2_MSG_CHANNEL_DATA message
                                 * (4 byte channel id + buf)
                                 */
                                packet_send_ignore(4 + len);
                                packet_send();
                        }
                }
                buffer_consume(&c->output, len);
                if (compat20 && len > 0) {
                        c->local_consumed += len;
                }
        }
        return 1;
}

static int
channel_handle_efd(Channel *c, fd_set *readset, fd_set *writeset)
{
        char buf[CHAN_RBUF];
        int len;

/** XXX handle drain efd, too */
        if (c->efd != -1) {
                if (c->extended_usage == CHAN_EXTENDED_WRITE &&
                    FD_ISSET(c->efd, writeset) &&
                    buffer_len(&c->extended) > 0) {
                        len = write(c->efd, buffer_ptr(&c->extended),
                            buffer_len(&c->extended));
                        debug2("channel %d: written %d to efd %d",
                            c->self, len, c->efd);
                        if (len < 0 && (errno == EINTR || errno == EAGAIN))
                                return 1;
                        if (len <= 0) {
                                debug2("channel %d: closing write-efd %d",
                                    c->self, c->efd);
                                channel_close_fd(&c->efd);
                        } else {
                                buffer_consume(&c->extended, len);
                                c->local_consumed += len;
                        }
                } else if (c->extended_usage == CHAN_EXTENDED_READ &&
                    (c->detach_close || FD_ISSET(c->efd, readset))) {
                        len = read(c->efd, buf, sizeof(buf));
                        debug2("channel %d: read %d from efd %d",
                            c->self, len, c->efd);
                        if (len < 0 && (errno == EINTR ||
                            (errno == EAGAIN && !c->detach_close)))
                                return 1;
                        if (len <= 0) {
                                debug2("channel %d: closing read-efd %d",
                                    c->self, c->efd);
                                channel_close_fd(&c->efd);
                        } else {
                                buffer_append(&c->extended, buf, len);
                        }
                }
        }
        return 1;
}

/* ARGSUSED */
static int
channel_handle_ctl(Channel *c, fd_set *readset, fd_set *writeset)
{
        char buf[16];
        int len;

        /* Monitor control fd to detect if the slave client exits */
        if (c->ctl_fd != -1 && FD_ISSET(c->ctl_fd, readset)) {
                len = read(c->ctl_fd, buf, sizeof(buf));
                if (len < 0 && (errno == EINTR || errno == EAGAIN))
                        return 1;
                if (len <= 0) {
                        debug2("channel %d: ctl read<=0", c->self);
                        if (c->type != SSH_CHANNEL_OPEN) {
                                debug2("channel %d: not open", c->self);
                                chan_mark_dead(c);
                                return -1;
                        } else {
                                chan_read_failed(c);
                                chan_write_failed(c);
                        }
                        return -1;
                } else
                        fatal("%s: unexpected data on ctl fd", __func__);
        }
        return 1;
}

static int
channel_check_window(Channel *c)
{
        if (c->type == SSH_CHANNEL_OPEN &&
            !(c->flags & (CHAN_CLOSE_SENT|CHAN_CLOSE_RCVD)) &&
            ((c->local_window_max - c->local_window >
            c->local_maxpacket*3) ||
            c->local_window < c->local_window_max/2) &&
            c->local_consumed > 0) {
                packet_start(SSH2_MSG_CHANNEL_WINDOW_ADJUST);
                packet_put_int(c->remote_id);
                packet_put_int(c->local_consumed);
                packet_send();
                debug2("channel %d: window %d sent adjust %d",
                    c->self, c->local_window,
                    c->local_consumed);
                c->local_window += c->local_consumed;
                c->local_consumed = 0;
        }
        return 1;
}

static void
channel_post_open(Channel *c, fd_set *readset, fd_set *writeset)
{
        if (c->delayed)
                return;
        channel_handle_rfd(c, readset, writeset);
        channel_handle_wfd(c, readset, writeset);
        if (!compat20)
                return;
        channel_handle_efd(c, readset, writeset);
        channel_handle_ctl(c, readset, writeset);
        channel_check_window(c);
}

/* ARGSUSED */
static void
channel_post_output_drain_13(Channel *c, fd_set *readset, fd_set *writeset)
{
        int len;

        /* Send buffered output data to the socket. */
        if (FD_ISSET(c->sock, writeset) && buffer_len(&c->output) > 0) {
                len = write(c->sock, buffer_ptr(&c->output),
                            buffer_len(&c->output));
                if (len <= 0)
                        buffer_clear(&c->output);
                else
                        buffer_consume(&c->output, len);
        }
}

static void
channel_handler_init_20(void)
{
        channel_pre[SSH_CHANNEL_OPEN] =                 &channel_pre_open;
        channel_pre[SSH_CHANNEL_X11_OPEN] =             &channel_pre_x11_open;
        channel_pre[SSH_CHANNEL_PORT_LISTENER] =        &channel_pre_listener;
        channel_pre[SSH_CHANNEL_RPORT_LISTENER] =       &channel_pre_listener;
        channel_pre[SSH_CHANNEL_X11_LISTENER] =         &channel_pre_listener;
        channel_pre[SSH_CHANNEL_AUTH_SOCKET] =          &channel_pre_listener;
        channel_pre[SSH_CHANNEL_CONNECTING] =           &channel_pre_connecting;
        channel_pre[SSH_CHANNEL_DYNAMIC] =              &channel_pre_dynamic;

        channel_post[SSH_CHANNEL_OPEN] =                &channel_post_open;
        channel_post[SSH_CHANNEL_PORT_LISTENER] =       &channel_post_port_listener;
        channel_post[SSH_CHANNEL_RPORT_LISTENER] =      &channel_post_port_listener;
        channel_post[SSH_CHANNEL_X11_LISTENER] =        &channel_post_x11_listener;
        channel_post[SSH_CHANNEL_AUTH_SOCKET] =         &channel_post_auth_listener;
        channel_post[SSH_CHANNEL_CONNECTING] =          &channel_post_connecting;
        channel_post[SSH_CHANNEL_DYNAMIC] =             &channel_post_open;
}

static void
channel_handler_init_13(void)
{
        channel_pre[SSH_CHANNEL_OPEN] =                 &channel_pre_open_13;
        channel_pre[SSH_CHANNEL_X11_OPEN] =             &channel_pre_x11_open_13;
        channel_pre[SSH_CHANNEL_X11_LISTENER] =         &channel_pre_listener;
        channel_pre[SSH_CHANNEL_PORT_LISTENER] =        &channel_pre_listener;
        channel_pre[SSH_CHANNEL_AUTH_SOCKET] =          &channel_pre_listener;
        channel_pre[SSH_CHANNEL_INPUT_DRAINING] =       &channel_pre_input_draining;
        channel_pre[SSH_CHANNEL_OUTPUT_DRAINING] =      &channel_pre_output_draining;
        channel_pre[SSH_CHANNEL_CONNECTING] =           &channel_pre_connecting;
        channel_pre[SSH_CHANNEL_DYNAMIC] =              &channel_pre_dynamic;

        channel_post[SSH_CHANNEL_OPEN] =                &channel_post_open;
        channel_post[SSH_CHANNEL_X11_LISTENER] =        &channel_post_x11_listener;
        channel_post[SSH_CHANNEL_PORT_LISTENER] =       &channel_post_port_listener;
        channel_post[SSH_CHANNEL_AUTH_SOCKET] =         &channel_post_auth_listener;
        channel_post[SSH_CHANNEL_OUTPUT_DRAINING] =     &channel_post_output_drain_13;
        channel_post[SSH_CHANNEL_CONNECTING] =          &channel_post_connecting;
        channel_post[SSH_CHANNEL_DYNAMIC] =             &channel_post_open;
}

static void
channel_handler_init_15(void)
{
        channel_pre[SSH_CHANNEL_OPEN] =                 &channel_pre_open;
        channel_pre[SSH_CHANNEL_X11_OPEN] =             &channel_pre_x11_open;
        channel_pre[SSH_CHANNEL_X11_LISTENER] =         &channel_pre_listener;
        channel_pre[SSH_CHANNEL_PORT_LISTENER] =        &channel_pre_listener;
        channel_pre[SSH_CHANNEL_AUTH_SOCKET] =          &channel_pre_listener;
        channel_pre[SSH_CHANNEL_CONNECTING] =           &channel_pre_connecting;
        channel_pre[SSH_CHANNEL_DYNAMIC] =              &channel_pre_dynamic;

        channel_post[SSH_CHANNEL_X11_LISTENER] =        &channel_post_x11_listener;
        channel_post[SSH_CHANNEL_PORT_LISTENER] =       &channel_post_port_listener;
        channel_post[SSH_CHANNEL_AUTH_SOCKET] =         &channel_post_auth_listener;
        channel_post[SSH_CHANNEL_OPEN] =                &channel_post_open;
        channel_post[SSH_CHANNEL_CONNECTING] =          &channel_post_connecting;
        channel_post[SSH_CHANNEL_DYNAMIC] =             &channel_post_open;
}

static void
channel_handler_init(void)
{
        int i;

        for (i = 0; i < SSH_CHANNEL_MAX_TYPE; i++) {
                channel_pre[i] = NULL;
                channel_post[i] = NULL;
        }
        if (compat20)
                channel_handler_init_20();
        else if (compat13)
                channel_handler_init_13();
        else
                channel_handler_init_15();
}

/* gc dead channels */
static void
channel_garbage_collect(Channel *c)
{
        if (c == NULL)
                return;
        if (c->detach_user != NULL) {
                if (!chan_is_dead(c, c->detach_close))
                        return;
                debug2("channel %d: gc: notify user", c->self);
                c->detach_user(c->self, NULL);
                /* if we still have a callback */
                if (c->detach_user != NULL)
                        return;
                debug2("channel %d: gc: user detached", c->self);
        }
        if (!chan_is_dead(c, 1))
                return;
        debug2("channel %d: garbage collecting", c->self);
        channel_free(c);
}

static void
channel_handler(chan_fn *ftab[], fd_set *readset, fd_set *writeset)
{
        static int did_init = 0;
        u_int i;
        Channel *c;

        if (!did_init) {
                channel_handler_init();
                did_init = 1;
        }
        for (i = 0; i < channels_alloc; i++) {
                c = channels[i];
                if (c == NULL)
                        continue;
                if (ftab[c->type] != NULL)
                        (*ftab[c->type])(c, readset, writeset);
                channel_garbage_collect(c);
        }
}

/*
 * Allocate/update select bitmasks and add any bits relevant to channels in
 * select bitmasks.
 */
void
channel_prepare_select(fd_set **readsetp, fd_set **writesetp, int *maxfdp,
    u_int *nallocp, int rekeying)
{
        u_int n, sz, nfdset;

        n = MAX(*maxfdp, channel_max_fd);

        nfdset = howmany(n+1, NFDBITS);
        /* Explicitly test here, because xrealloc isn't always called */
        if (nfdset && SIZE_T_MAX / nfdset < sizeof(fd_mask))
                fatal("channel_prepare_select: max_fd (%d) is too large", n);
        sz = nfdset * sizeof(fd_mask);

        /* perhaps check sz < nalloc/2 and shrink? */
        if (*readsetp == NULL || sz > *nallocp) {
                *readsetp = xrealloc(*readsetp, nfdset, sizeof(fd_mask));
                *writesetp = xrealloc(*writesetp, nfdset, sizeof(fd_mask));
                *nallocp = sz;
        }
        *maxfdp = n;
        memset(*readsetp, 0, sz);
        memset(*writesetp, 0, sz);

        if (!rekeying)
                channel_handler(channel_pre, *readsetp, *writesetp);
}

/*
 * After select, perform any appropriate operations for channels which have
 * events pending.
 */
void
channel_after_select(fd_set *readset, fd_set *writeset)
{
        channel_handler(channel_post, readset, writeset);
}


/* If there is data to send to the connection, enqueue some of it now. */
void
channel_output_poll(void)
{
        Channel *c;
        u_int i, len;

        for (i = 0; i < channels_alloc; i++) {
                c = channels[i];
                if (c == NULL)
                        continue;

                /*
                 * We are only interested in channels that can have buffered
                 * incoming data.
                 */
                if (compat13) {
                        if (c->type != SSH_CHANNEL_OPEN &&
                            c->type != SSH_CHANNEL_INPUT_DRAINING)
                                continue;
                } else {
                        if (c->type != SSH_CHANNEL_OPEN)
                                continue;
                }
                if (compat20 &&
                    (c->flags & (CHAN_CLOSE_SENT|CHAN_CLOSE_RCVD))) {
                        /* XXX is this true? */
                        debug3("channel %d: will not send data after close", c->self);
                        continue;
                }

                /* Get the amount of buffered data for this channel. */
                if ((c->istate == CHAN_INPUT_OPEN ||
                    c->istate == CHAN_INPUT_WAIT_DRAIN) &&
                    (len = buffer_len(&c->input)) > 0) {
                        if (c->datagram) {
                                if (len > 0) {
                                        u_char *data;
                                        u_int dlen;

                                        data = buffer_get_string(&c->input,
                                            &dlen);
                                        packet_start(SSH2_MSG_CHANNEL_DATA);
                                        packet_put_int(c->remote_id);
                                        packet_put_string(data, dlen);
                                        packet_send();
                                        c->remote_window -= dlen + 4;
                                        xfree(data);
                                }
                                continue;
                        }
                        /*
                         * Send some data for the other side over the secure
                         * connection.
                         */
                        if (compat20) {
                                if (len > c->remote_window)
                                        len = c->remote_window;
                                if (len > c->remote_maxpacket)
                                        len = c->remote_maxpacket;
                        } else {
                                if (packet_is_interactive()) {
                                        if (len > 1024)
                                                len = 512;
                                } else {
                                        /* Keep the packets at reasonable size. */
                                        if (len > packet_get_maxsize()/2)
                                                len = packet_get_maxsize()/2;
                                }
                        }
                        if (len > 0) {
                                packet_start(compat20 ?
                                    SSH2_MSG_CHANNEL_DATA : SSH_MSG_CHANNEL_DATA);
                                packet_put_int(c->remote_id);
                                packet_put_string(buffer_ptr(&c->input), len);
                                packet_send();
                                buffer_consume(&c->input, len);
                                c->remote_window -= len;
                        }
                } else if (c->istate == CHAN_INPUT_WAIT_DRAIN) {
                        if (compat13)
                                fatal("cannot happen: istate == INPUT_WAIT_DRAIN for proto 1.3");
                        /*
                         * input-buffer is empty and read-socket shutdown:
                         * tell peer, that we will not send more data: send IEOF.
                         * hack for extended data: delay EOF if EFD still in use.
                         */
                        if (CHANNEL_EFD_INPUT_ACTIVE(c))
                                debug2("channel %d: ibuf_empty delayed efd %d/(%d)",
                                    c->self, c->efd, buffer_len(&c->extended));
                        else
                                chan_ibuf_empty(c);
                }
                /* Send extended data, i.e. stderr */
                if (compat20 &&
                    !(c->flags & CHAN_EOF_SENT) &&
                    c->remote_window > 0 &&
                    (len = buffer_len(&c->extended)) > 0 &&
                    c->extended_usage == CHAN_EXTENDED_READ) {
                        debug2("channel %d: rwin %u elen %u euse %d",
                            c->self, c->remote_window, buffer_len(&c->extended),
                            c->extended_usage);
                        if (len > c->remote_window)
                                len = c->remote_window;
                        if (len > c->remote_maxpacket)
                                len = c->remote_maxpacket;
                        packet_start(SSH2_MSG_CHANNEL_EXTENDED_DATA);
                        packet_put_int(c->remote_id);
                        packet_put_int(SSH2_EXTENDED_DATA_STDERR);
                        packet_put_string(buffer_ptr(&c->extended), len);
                        packet_send();
                        buffer_consume(&c->extended, len);
                        c->remote_window -= len;
                        debug2("channel %d: sent ext data %d", c->self, len);
                }
        }
}


/* -- protocol input */

/* ARGSUSED */
void
channel_input_data(int type, u_int32_t seq, void *ctxt)
{
        int id;
        char *data;
        u_int data_len;
        Channel *c;

        /* Get the channel number and verify it. */
        id = packet_get_int();
        c = channel_lookup(id);
        if (c == NULL)
                packet_disconnect("Received data for nonexistent channel %d.", id);

        /* Ignore any data for non-open channels (might happen on close) */
        if (c->type != SSH_CHANNEL_OPEN &&
            c->type != SSH_CHANNEL_X11_OPEN)
                return;

        /* Get the data. */
        data = packet_get_string_ptr(&data_len);

        /*
         * Ignore data for protocol > 1.3 if output end is no longer open.
         * For protocol 2 the sending side is reducing its window as it sends
         * data, so we must 'fake' consumption of the data in order to ensure
         * that window updates are sent back.  Otherwise the connection might
         * deadlock.
         */
        if (!compat13 && c->ostate != CHAN_OUTPUT_OPEN) {
                if (compat20) {
                        c->local_window -= data_len;
                        c->local_consumed += data_len;
                }
                return;
        }

        if (compat20) {
                if (data_len > c->local_maxpacket) {
                        logit("channel %d: rcvd big packet %d, maxpack %d",
                            c->self, data_len, c->local_maxpacket);
                }
                if (data_len > c->local_window) {
                        logit("channel %d: rcvd too much data %d, win %d",
                            c->self, data_len, c->local_window);
                        return;
                }
                c->local_window -= data_len;
        }
        if (c->datagram)
                buffer_put_string(&c->output, data, data_len);
        else
                buffer_append(&c->output, data, data_len);
        packet_check_eom();
}

/* ARGSUSED */
void
channel_input_extended_data(int type, u_int32_t seq, void *ctxt)
{
        int id;
        char *data;
        u_int data_len, tcode;
        Channel *c;

        /* Get the channel number and verify it. */
        id = packet_get_int();
        c = channel_lookup(id);

        if (c == NULL)
                packet_disconnect("Received extended_data for bad channel %d.", id);
        if (c->type != SSH_CHANNEL_OPEN) {
                logit("channel %d: ext data for non open", id);
                return;
        }
        if (c->flags & CHAN_EOF_RCVD) {
                if (datafellows & SSH_BUG_EXTEOF)
                        debug("channel %d: accepting ext data after eof", id);
                else
                        packet_disconnect("Received extended_data after EOF "
                            "on channel %d.", id);
        }
        tcode = packet_get_int();
        if (c->efd == -1 ||
            c->extended_usage != CHAN_EXTENDED_WRITE ||
            tcode != SSH2_EXTENDED_DATA_STDERR) {
                logit("channel %d: bad ext data", c->self);
                return;
        }
        data = packet_get_string(&data_len);
        packet_check_eom();
        if (data_len > c->local_window) {
                logit("channel %d: rcvd too much extended_data %d, win %d",
                    c->self, data_len, c->local_window);
                xfree(data);
                return;
        }
        debug2("channel %d: rcvd ext data %d", c->self, data_len);
        c->local_window -= data_len;
        buffer_append(&c->extended, data, data_len);
        xfree(data);
}

/* ARGSUSED */
void
channel_input_ieof(int type, u_int32_t seq, void *ctxt)
{
        int id;
        Channel *c;

        id = packet_get_int();
        packet_check_eom();
        c = channel_lookup(id);
        if (c == NULL)
                packet_disconnect("Received ieof for nonexistent channel %d.", id);
        chan_rcvd_ieof(c);

        /* XXX force input close */
        if (c->force_drain && c->istate == CHAN_INPUT_OPEN) {
                debug("channel %d: FORCE input drain", c->self);
                c->istate = CHAN_INPUT_WAIT_DRAIN;
                if (buffer_len(&c->input) == 0)
                        chan_ibuf_empty(c);
        }

}

/* ARGSUSED */
void
channel_input_close(int type, u_int32_t seq, void *ctxt)
{
        int id;
        Channel *c;

        id = packet_get_int();
        packet_check_eom();
        c = channel_lookup(id);
        if (c == NULL)
                packet_disconnect("Received close for nonexistent channel %d.", id);

        /*
         * Send a confirmation that we have closed the channel and no more
         * data is coming for it.
         */
        packet_start(SSH_MSG_CHANNEL_CLOSE_CONFIRMATION);
        packet_put_int(c->remote_id);
        packet_send();

        /*
         * If the channel is in closed state, we have sent a close request,
         * and the other side will eventually respond with a confirmation.
         * Thus, we cannot free the channel here, because then there would be
         * no-one to receive the confirmation.  The channel gets freed when
         * the confirmation arrives.
         */
        if (c->type != SSH_CHANNEL_CLOSED) {
                /*
                 * Not a closed channel - mark it as draining, which will
                 * cause it to be freed later.
                 */
                buffer_clear(&c->input);
                c->type = SSH_CHANNEL_OUTPUT_DRAINING;
        }
}

/* proto version 1.5 overloads CLOSE_CONFIRMATION with OCLOSE */
/* ARGSUSED */
void
channel_input_oclose(int type, u_int32_t seq, void *ctxt)
{
        int id = packet_get_int();
        Channel *c = channel_lookup(id);

        packet_check_eom();
        if (c == NULL)
                packet_disconnect("Received oclose for nonexistent channel %d.", id);
        chan_rcvd_oclose(c);
}

/* ARGSUSED */
void
channel_input_close_confirmation(int type, u_int32_t seq, void *ctxt)
{
        int id = packet_get_int();
        Channel *c = channel_lookup(id);

        packet_check_eom();
        if (c == NULL)
                packet_disconnect("Received close confirmation for "
                    "out-of-range channel %d.", id);
        if (c->type != SSH_CHANNEL_CLOSED)
                packet_disconnect("Received close confirmation for "
                    "non-closed channel %d (type %d).", id, c->type);
        channel_free(c);
}

/* ARGSUSED */
void
channel_input_open_confirmation(int type, u_int32_t seq, void *ctxt)
{
        int id, remote_id;
        Channel *c;

        id = packet_get_int();
        c = channel_lookup(id);

        if (c==NULL || c->type != SSH_CHANNEL_OPENING)
                packet_disconnect("Received open confirmation for "
                    "non-opening channel %d.", id);
        remote_id = packet_get_int();
        /* Record the remote channel number and mark that the channel is now open. */
        c->remote_id = remote_id;
        c->type = SSH_CHANNEL_OPEN;

        if (compat20) {
                c->remote_window = packet_get_int();
                c->remote_maxpacket = packet_get_int();
                if (c->open_confirm) {
                        debug2("callback start");
                        c->open_confirm(c->self, c->open_confirm_ctx);
                        debug2("callback done");
                }
                debug2("channel %d: open confirm rwindow %u rmax %u", c->self,
                    c->remote_window, c->remote_maxpacket);
        }
        packet_check_eom();
}

static char *
reason2txt(int reason)
{
        switch (reason) {
        case SSH2_OPEN_ADMINISTRATIVELY_PROHIBITED:
                return "administratively prohibited";
        case SSH2_OPEN_CONNECT_FAILED:
                return "connect failed";
        case SSH2_OPEN_UNKNOWN_CHANNEL_TYPE:
                return "unknown channel type";
        case SSH2_OPEN_RESOURCE_SHORTAGE:
                return "resource shortage";
        }
        return "unknown reason";
}

/* ARGSUSED */
void
channel_input_open_failure(int type, u_int32_t seq, void *ctxt)
{
        int id, reason;
        char *msg = NULL, *lang = NULL;
        Channel *c;

        id = packet_get_int();
        c = channel_lookup(id);

        if (c==NULL || c->type != SSH_CHANNEL_OPENING)
                packet_disconnect("Received open failure for "
                    "non-opening channel %d.", id);
        if (compat20) {
                reason = packet_get_int();
                if (!(datafellows & SSH_BUG_OPENFAILURE)) {
                        msg  = packet_get_string(NULL);
                        lang = packet_get_string(NULL);
                }
                logit("channel %d: open failed: %s%s%s", id,
                    reason2txt(reason), msg ? ": ": "", msg ? msg : "");
                if (msg != NULL)
                        xfree(msg);
                if (lang != NULL)
                        xfree(lang);
        }
        packet_check_eom();
        /* Free the channel.  This will also close the socket. */
        channel_free(c);
}

/* ARGSUSED */
void
channel_input_window_adjust(int type, u_int32_t seq, void *ctxt)
{
        Channel *c;
        int id;
        u_int adjust;

        if (!compat20)
                return;

        /* Get the channel number and verify it. */
        id = packet_get_int();
        c = channel_lookup(id);

        if (c == NULL) {
                logit("Received window adjust for non-open channel %d.", id);
                return;
        }
        adjust = packet_get_int();
        packet_check_eom();
        debug2("channel %d: rcvd adjust %u", id, adjust);
        c->remote_window += adjust;
}

/* ARGSUSED */
void
channel_input_port_open(int type, u_int32_t seq, void *ctxt)
{
        Channel *c = NULL;
        u_short host_port;
        char *host, *originator_string;
        int remote_id;

        remote_id = packet_get_int();
        host = packet_get_string(NULL);
        host_port = packet_get_int();

        if (packet_get_protocol_flags() & SSH_PROTOFLAG_HOST_IN_FWD_OPEN) {
                originator_string = packet_get_string(NULL);
        } else {
                originator_string = xstrdup("unknown (remote did not supply name)");
        }
        packet_check_eom();
        c = channel_connect_to(host, host_port,
            "connected socket", originator_string);
        xfree(originator_string);
        xfree(host);
        if (c == NULL) {
                packet_start(SSH_MSG_CHANNEL_OPEN_FAILURE);
                packet_put_int(remote_id);
                packet_send();
        } else
                c->remote_id = remote_id;
}

/* ARGSUSED */
void
channel_input_status_confirm(int type, u_int32_t seq, void *ctxt)
{
        Channel *c;
        struct channel_confirm *cc;
        int remote_id;

        /* Reset keepalive timeout */
        keep_alive_timeouts = 0;

        remote_id = packet_get_int();
        packet_check_eom();

        debug2("channel_input_confirm: type %d id %d", type, remote_id);

        if ((c = channel_lookup(remote_id)) == NULL) {
                logit("channel_input_success_failure: %d: unknown", remote_id);
                return;
        }       
        ;
        if ((cc = TAILQ_FIRST(&c->status_confirms)) == NULL)
                return;
        cc->cb(type, c, cc->ctx);
        TAILQ_REMOVE(&c->status_confirms, cc, entry);
        bzero(cc, sizeof(*cc));
        xfree(cc);
}

/* -- tcp forwarding */

void
channel_set_af(int af)
{
        IPv4or6 = af;
}

static int
channel_setup_fwd_listener(int type, const char *listen_addr, u_short listen_port,
    const char *host_to_connect, u_short port_to_connect, int gateway_ports)
{
        Channel *c;
        int sock, r, success = 0, wildcard = 0, is_client;
        struct addrinfo hints, *ai, *aitop;
        const char *host, *addr;
        char ntop[NI_MAXHOST], strport[NI_MAXSERV];

        host = (type == SSH_CHANNEL_RPORT_LISTENER) ?
            listen_addr : host_to_connect;
        is_client = (type == SSH_CHANNEL_PORT_LISTENER);

        if (host == NULL) {
                error("No forward host name.");
                return 0;
        }
        if (strlen(host) > SSH_CHANNEL_PATH_LEN - 1) {
                error("Forward host name too long.");
                return 0;
        }

        /*
         * Determine whether or not a port forward listens to loopback,
         * specified address or wildcard. On the client, a specified bind
         * address will always override gateway_ports. On the server, a
         * gateway_ports of 1 (``yes'') will override the client's
         * specification and force a wildcard bind, whereas a value of 2
         * (``clientspecified'') will bind to whatever address the client
         * asked for.
         *
         * Special-case listen_addrs are:
         *
         * "0.0.0.0"               -> wildcard v4/v6 if SSH_OLD_FORWARD_ADDR
         * "" (empty string), "*"  -> wildcard v4/v6
         * "localhost"             -> loopback v4/v6
         */
        addr = NULL;
        if (listen_addr == NULL) {
                /* No address specified: default to gateway_ports setting */
                if (gateway_ports)
                        wildcard = 1;
        } else if (gateway_ports || is_client) {
                if (((datafellows & SSH_OLD_FORWARD_ADDR) &&
                    strcmp(listen_addr, "0.0.0.0") == 0 && is_client == 0) ||
                    *listen_addr == '\0' || strcmp(listen_addr, "*") == 0 ||
                    (!is_client && gateway_ports == 1))
                        wildcard = 1;
                else if (strcmp(listen_addr, "localhost") != 0)
                        addr = listen_addr;
        }

        debug3("channel_setup_fwd_listener: type %d wildcard %d addr %s",
            type, wildcard, (addr == NULL) ? "NULL" : addr);

        /*
         * getaddrinfo returns a loopback address if the hostname is
         * set to NULL and hints.ai_flags is not AI_PASSIVE
         */
        memset(&hints, 0, sizeof(hints));
        hints.ai_family = IPv4or6;
        hints.ai_flags = wildcard ? AI_PASSIVE : 0;
        hints.ai_socktype = SOCK_STREAM;
        snprintf(strport, sizeof strport, "%d", listen_port);
        if ((r = getaddrinfo(addr, strport, &hints, &aitop)) != 0) {
                if (addr == NULL) {
                        /* This really shouldn't happen */
                        packet_disconnect("getaddrinfo: fatal error: %s",
                            ssh_gai_strerror(r));
                } else {
                        error("channel_setup_fwd_listener: "
                            "getaddrinfo(%.64s): %s", addr,
                            ssh_gai_strerror(r));
                }
                return 0;
        }

        for (ai = aitop; ai; ai = ai->ai_next) {
                if (ai->ai_family != AF_INET && ai->ai_family != AF_INET6)
                        continue;
                if (getnameinfo(ai->ai_addr, ai->ai_addrlen, ntop, sizeof(ntop),
                    strport, sizeof(strport), NI_NUMERICHOST|NI_NUMERICSERV) != 0) {
                        error("channel_setup_fwd_listener: getnameinfo failed");
                        continue;
                }
                /* Create a port to listen for the host. */
                sock = socket(ai->ai_family, ai->ai_socktype, ai->ai_protocol);
                if (sock < 0) {
                        /* this is no error since kernel may not support ipv6 */
                        verbose("socket: %.100s", strerror(errno));
                        continue;
                }

                channel_set_reuseaddr(sock);

                debug("Local forwarding listening on %s port %s.", ntop, strport);

                /* Bind the socket to the address. */
                if (bind(sock, ai->ai_addr, ai->ai_addrlen) < 0) {
                        /* address can be in use ipv6 address is already bound */
                        if (!ai->ai_next)
                                error("bind: %.100s", strerror(errno));
                        else
                                verbose("bind: %.100s", strerror(errno));

                        close(sock);
                        continue;
                }
                /* Start listening for connections on the socket. */
                if (listen(sock, SSH_LISTEN_BACKLOG) < 0) {
                        error("listen: %.100s", strerror(errno));
                        close(sock);
                        continue;
                }
                /* Allocate a channel number for the socket. */
                c = channel_new("port listener", type, sock, sock, -1,
                    CHAN_TCP_WINDOW_DEFAULT, CHAN_TCP_PACKET_DEFAULT,
                    0, "port listener", 1);
                strlcpy(c->path, host, sizeof(c->path));
                c->host_port = port_to_connect;
                c->listening_port = listen_port;
                success = 1;
        }
        if (success == 0)
                error("channel_setup_fwd_listener: cannot listen to port: %d",
                    listen_port);
        freeaddrinfo(aitop);
        return success;
}

int
channel_cancel_rport_listener(const char *host, u_short port)
{
        u_int i;
        int found = 0;

        for (i = 0; i < channels_alloc; i++) {
                Channel *c = channels[i];

                if (c != NULL && c->type == SSH_CHANNEL_RPORT_LISTENER &&
                    strncmp(c->path, host, sizeof(c->path)) == 0 &&
                    c->listening_port == port) {
                        debug2("%s: close channel %d", __func__, i);
                        channel_free(c);
                        found = 1;
                }
        }

        return (found);
}

/* protocol local port fwd, used by ssh (and sshd in v1) */
int
channel_setup_local_fwd_listener(const char *listen_host, u_short listen_port,
    const char *host_to_connect, u_short port_to_connect, int gateway_ports)
{
        return channel_setup_fwd_listener(SSH_CHANNEL_PORT_LISTENER,
            listen_host, listen_port, host_to_connect, port_to_connect,
            gateway_ports);
}

/* protocol v2 remote port fwd, used by sshd */
int
channel_setup_remote_fwd_listener(const char *listen_address,
    u_short listen_port, int gateway_ports)
{
        return channel_setup_fwd_listener(SSH_CHANNEL_RPORT_LISTENER,
            listen_address, listen_port, NULL, 0, gateway_ports);
}

/*
 * Initiate forwarding of connections to port "port" on remote host through
 * the secure channel to host:port from local side.
 */

int
channel_request_remote_forwarding(const char *listen_host, u_short listen_port,
    const char *host_to_connect, u_short port_to_connect)
{
        int type, success = 0;

        /* Record locally that connection to this host/port is permitted. */
        if (num_permitted_opens >= SSH_MAX_FORWARDS_PER_DIRECTION)
                fatal("channel_request_remote_forwarding: too many forwards");

        /* Send the forward request to the remote side. */
        if (compat20) {
                const char *address_to_bind;
                if (listen_host == NULL) {
                        if (datafellows & SSH_BUG_RFWD_ADDR)
                                address_to_bind = "127.0.0.1";
                        else
                                address_to_bind = "localhost";
                } else if (*listen_host == '\0' ||
                           strcmp(listen_host, "*") == 0) {
                        if (datafellows & SSH_BUG_RFWD_ADDR)
                                address_to_bind = "0.0.0.0";
                        else
                                address_to_bind = "";
                } else
                        address_to_bind = listen_host;

                packet_start(SSH2_MSG_GLOBAL_REQUEST);
                packet_put_cstring("tcpip-forward");
                packet_put_char(1);                     /* boolean: want reply */
                packet_put_cstring(address_to_bind);
                packet_put_int(listen_port);
                packet_send();
                packet_write_wait();
                /* Assume that server accepts the request */
                success = 1;
        } else {
                packet_start(SSH_CMSG_PORT_FORWARD_REQUEST);
                packet_put_int(listen_port);
                packet_put_cstring(host_to_connect);
                packet_put_int(port_to_connect);
                packet_send();
                packet_write_wait();

                /* Wait for response from the remote side. */
                type = packet_read();
                switch (type) {
                case SSH_SMSG_SUCCESS:
                        success = 1;
                        break;
                case SSH_SMSG_FAILURE:
                        break;
                default:
                        /* Unknown packet */
                        packet_disconnect("Protocol error for port forward request:"
                            "received packet type %d.", type);
                }
        }
        if (success) {
                permitted_opens[num_permitted_opens].host_to_connect = xstrdup(host_to_connect);
                permitted_opens[num_permitted_opens].port_to_connect = port_to_connect;
                permitted_opens[num_permitted_opens].listen_port = listen_port;
                num_permitted_opens++;
        }
        return (success ? 0 : -1);
}

/*
 * Request cancellation of remote forwarding of connection host:port from
 * local side.
 */
void
channel_request_rforward_cancel(const char *host, u_short port)
{
        int i;

        if (!compat20)
                return;

        for (i = 0; i < num_permitted_opens; i++) {
                if (permitted_opens[i].host_to_connect != NULL &&
                    permitted_opens[i].listen_port == port)
                        break;
        }
        if (i >= num_permitted_opens) {
                debug("%s: requested forward not found", __func__);
                return;
        }
        packet_start(SSH2_MSG_GLOBAL_REQUEST);
        packet_put_cstring("cancel-tcpip-forward");
        packet_put_char(0);
        packet_put_cstring(host == NULL ? "" : host);
        packet_put_int(port);
        packet_send();

        permitted_opens[i].listen_port = 0;
        permitted_opens[i].port_to_connect = 0;
        xfree(permitted_opens[i].host_to_connect);
        permitted_opens[i].host_to_connect = NULL;
}

/*
 * This is called after receiving CHANNEL_FORWARDING_REQUEST.  This initates
 * listening for the port, and sends back a success reply (or disconnect
 * message if there was an error).
 */
int
channel_input_port_forward_request(int is_root, int gateway_ports)
{
        u_short port, host_port;
        int success = 0;
        char *hostname;

        /* Get arguments from the packet. */
        port = packet_get_int();
        hostname = packet_get_string(NULL);
        host_port = packet_get_int();

#ifndef HAVE_CYGWIN
        /*
         * Check that an unprivileged user is not trying to forward a
         * privileged port.
         */
        if (port < IPPORT_RESERVED && !is_root)
                packet_disconnect(
                    "Requested forwarding of port %d but user is not root.",
                    port);
        if (host_port == 0)
                packet_disconnect("Dynamic forwarding denied.");
#endif

        /* Initiate forwarding */
        success = channel_setup_local_fwd_listener(NULL, port, hostname,
            host_port, gateway_ports);

        /* Free the argument string. */
        xfree(hostname);

        return (success ? 0 : -1);
}

/*
 * Permits opening to any host/port if permitted_opens[] is empty.  This is
 * usually called by the server, because the user could connect to any port
 * anyway, and the server has no way to know but to trust the client anyway.
 */
void
channel_permit_all_opens(void)
{
        if (num_permitted_opens == 0)
                all_opens_permitted = 1;
}

void
channel_add_permitted_opens(char *host, int port)
{
        if (num_permitted_opens >= SSH_MAX_FORWARDS_PER_DIRECTION)
                fatal("channel_add_permitted_opens: too many forwards");
        debug("allow port forwarding to host %s port %d", host, port);

        permitted_opens[num_permitted_opens].host_to_connect = xstrdup(host);
        permitted_opens[num_permitted_opens].port_to_connect = port;
        num_permitted_opens++;

        all_opens_permitted = 0;
}

int
channel_add_adm_permitted_opens(char *host, int port)
{
        if (num_adm_permitted_opens >= SSH_MAX_FORWARDS_PER_DIRECTION)
                fatal("channel_add_adm_permitted_opens: too many forwards");
        debug("config allows port forwarding to host %s port %d", host, port);

        permitted_adm_opens[num_adm_permitted_opens].host_to_connect
             = xstrdup(host);
        permitted_adm_opens[num_adm_permitted_opens].port_to_connect = port;
        return ++num_adm_permitted_opens;
}

void
channel_clear_permitted_opens(void)
{
        int i;

        for (i = 0; i < num_permitted_opens; i++)
                if (permitted_opens[i].host_to_connect != NULL)
                        xfree(permitted_opens[i].host_to_connect);
        num_permitted_opens = 0;
}

void
channel_clear_adm_permitted_opens(void)
{
        int i;

        for (i = 0; i < num_adm_permitted_opens; i++)
                if (permitted_adm_opens[i].host_to_connect != NULL)
                        xfree(permitted_adm_opens[i].host_to_connect);
        num_adm_permitted_opens = 0;
}

/* Try to start non-blocking connect to next host in cctx list */
static int
connect_next(struct channel_connect *cctx)
{
        int sock, saved_errno;
        char ntop[NI_MAXHOST], strport[NI_MAXSERV];

        for (; cctx->ai; cctx->ai = cctx->ai->ai_next) {
                if (cctx->ai->ai_family != AF_INET &&
                    cctx->ai->ai_family != AF_INET6)
                        continue;
                if (getnameinfo(cctx->ai->ai_addr, cctx->ai->ai_addrlen,
                    ntop, sizeof(ntop), strport, sizeof(strport),
                    NI_NUMERICHOST|NI_NUMERICSERV) != 0) {
                        error("connect_next: getnameinfo failed");
                        continue;
                }
                if ((sock = socket(cctx->ai->ai_family, cctx->ai->ai_socktype,
                    cctx->ai->ai_protocol)) == -1) {
                        if (cctx->ai->ai_next == NULL)
                                error("socket: %.100s", strerror(errno));
                        else
                                verbose("socket: %.100s", strerror(errno));
                        continue;
                }
                if (set_nonblock(sock) == -1)
                        fatal("%s: set_nonblock(%d)", __func__, sock);
                if (connect(sock, cctx->ai->ai_addr,
                    cctx->ai->ai_addrlen) == -1 && errno != EINPROGRESS) {
                        debug("connect_next: host %.100s ([%.100s]:%s): "
                            "%.100s", cctx->host, ntop, strport,
                            strerror(errno));
                        saved_errno = errno;
                        close(sock);
                        errno = saved_errno;
                        continue;       /* fail -- try next */
                }
                debug("connect_next: host %.100s ([%.100s]:%s) "
                    "in progress, fd=%d", cctx->host, ntop, strport, sock);
                cctx->ai = cctx->ai->ai_next;
                set_nodelay(sock);
                return sock;
        }
        return -1;
}

static void
channel_connect_ctx_free(struct channel_connect *cctx)
{
        xfree(cctx->host);
        if (cctx->aitop)
                freeaddrinfo(cctx->aitop);
        bzero(cctx, sizeof(*cctx));
        cctx->host = NULL;
        cctx->ai = cctx->aitop = NULL;
}

/* Return CONNECTING channel to remote host, port */
static Channel *
connect_to(const char *host, u_short port, char *ctype, char *rname)
{
        struct addrinfo hints;
        int gaierr;
        int sock = -1;
        char strport[NI_MAXSERV];
        struct channel_connect cctx;
        Channel *c;

        memset(&hints, 0, sizeof(hints));
        hints.ai_family = IPv4or6;
        hints.ai_socktype = SOCK_STREAM;
        snprintf(strport, sizeof strport, "%d", port);
        if ((gaierr = getaddrinfo(host, strport, &hints, &cctx.aitop)) != 0) {
                error("connect_to %.100s: unknown host (%s)", host,
                    ssh_gai_strerror(gaierr));
                return NULL;
        }

        cctx.host = xstrdup(host);
        cctx.port = port;
        cctx.ai = cctx.aitop;

        if ((sock = connect_next(&cctx)) == -1) {
                error("connect to %.100s port %d failed: %s",
                    host, port, strerror(errno));
                channel_connect_ctx_free(&cctx);
                return NULL;
        }
        c = channel_new(ctype, SSH_CHANNEL_CONNECTING, sock, sock, -1,
            CHAN_TCP_WINDOW_DEFAULT, CHAN_TCP_PACKET_DEFAULT, 0, rname, 1);
        c->connect_ctx = cctx;
        return c;
}

Channel *
channel_connect_by_listen_address(u_short listen_port, char *ctype, char *rname)
{
        int i;

        for (i = 0; i < num_permitted_opens; i++) {
                if (permitted_opens[i].host_to_connect != NULL &&
                    permitted_opens[i].listen_port == listen_port) {
                        return connect_to(
                            permitted_opens[i].host_to_connect,
                            permitted_opens[i].port_to_connect, ctype, rname);
                }
        }
        error("WARNING: Server requests forwarding for unknown listen_port %d",
            listen_port);
        return NULL;
}

/* Check if connecting to that port is permitted and connect. */
Channel *
channel_connect_to(const char *host, u_short port, char *ctype, char *rname)
{
        int i, permit, permit_adm = 1;

        permit = all_opens_permitted;
        if (!permit) {
                for (i = 0; i < num_permitted_opens; i++)
                        if (permitted_opens[i].host_to_connect != NULL &&
                            permitted_opens[i].port_to_connect == port &&
                            strcmp(permitted_opens[i].host_to_connect, host) == 0)
                                permit = 1;
        }

        if (num_adm_permitted_opens > 0) {
                permit_adm = 0;
                for (i = 0; i < num_adm_permitted_opens; i++)
                        if (permitted_adm_opens[i].host_to_connect != NULL &&
                            permitted_adm_opens[i].port_to_connect == port &&
                            strcmp(permitted_adm_opens[i].host_to_connect, host)
                            == 0)
                                permit_adm = 1;
        }

        if (!permit || !permit_adm) {
                logit("Received request to connect to host %.100s port %d, "
                    "but the request was denied.", host, port);
                return NULL;
        }
        return connect_to(host, port, ctype, rname);
}

void
channel_send_window_changes(void)
{
        u_int i;
        struct winsize ws;

        for (i = 0; i < channels_alloc; i++) {
                if (channels[i] == NULL || !channels[i]->client_tty ||
                    channels[i]->type != SSH_CHANNEL_OPEN)
                        continue;
                if (ioctl(channels[i]->rfd, TIOCGWINSZ, &ws) < 0)
                        continue;
                channel_request_start(i, "window-change", 0);
                packet_put_int((u_int)ws.ws_col);
                packet_put_int((u_int)ws.ws_row);
                packet_put_int((u_int)ws.ws_xpixel);
                packet_put_int((u_int)ws.ws_ypixel);
                packet_send();
        }
}

/* -- X11 forwarding */

/*
 * Creates an internet domain socket for listening for X11 connections.
 * Returns 0 and a suitable display number for the DISPLAY variable
 * stored in display_numberp , or -1 if an error occurs.
 */
int
x11_create_display_inet(int x11_display_offset, int x11_use_localhost,
    int single_connection, u_int *display_numberp, int **chanids)
{
        Channel *nc = NULL;
        int display_number, sock;
        u_short port;
        struct addrinfo hints, *ai, *aitop;
        char strport[NI_MAXSERV];
        int gaierr, n, num_socks = 0, socks[NUM_SOCKS];

        if (chanids == NULL)
                return -1;

        for (display_number = x11_display_offset;
            display_number < MAX_DISPLAYS;
            display_number++) {
                port = 6000 + display_number;
                memset(&hints, 0, sizeof(hints));
                hints.ai_family = IPv4or6;
                hints.ai_flags = x11_use_localhost ? 0: AI_PASSIVE;
                hints.ai_socktype = SOCK_STREAM;
                snprintf(strport, sizeof strport, "%d", port);
                if ((gaierr = getaddrinfo(NULL, strport, &hints, &aitop)) != 0) {
                        error("getaddrinfo: %.100s", ssh_gai_strerror(gaierr));
                        return -1;
                }
                for (ai = aitop; ai; ai = ai->ai_next) {
                        if (ai->ai_family != AF_INET && ai->ai_family != AF_INET6)
                                continue;
                        sock = socket(ai->ai_family, ai->ai_socktype,
                            ai->ai_protocol);
                        if (sock < 0) {
                                if ((errno != EINVAL) && (errno != EAFNOSUPPORT)) {
                                        error("socket: %.100s", strerror(errno));
                                        freeaddrinfo(aitop);
                                        return -1;
                                } else {
                                        debug("x11_create_display_inet: Socket family %d not supported",
                                                 ai->ai_family);
                                        continue;
                                }
                        }
#ifdef IPV6_V6ONLY
                        if (ai->ai_family == AF_INET6) {
                                int on = 1;
                                if (setsockopt(sock, IPPROTO_IPV6, IPV6_V6ONLY, &on, sizeof(on)) < 0)
                                        error("setsockopt IPV6_V6ONLY: %.100s", strerror(errno));
                        }
#endif
                        channel_set_reuseaddr(sock);
                        if (bind(sock, ai->ai_addr, ai->ai_addrlen) < 0) {
                                debug2("bind port %d: %.100s", port, strerror(errno));
                                close(sock);

                                for (n = 0; n < num_socks; n++) {
                                        close(socks[n]);
                                }
                                num_socks = 0;
                                break;
                        }
                        socks[num_socks++] = sock;
#ifndef DONT_TRY_OTHER_AF
                        if (num_socks == NUM_SOCKS)
                                break;
#else
                        if (x11_use_localhost) {
                                if (num_socks == NUM_SOCKS)
                                        break;
                        } else {
                                break;
                        }
#endif
                }
                freeaddrinfo(aitop);
                if (num_socks > 0)
                        break;
        }
        if (display_number >= MAX_DISPLAYS) {
                error("Failed to allocate internet-domain X11 display socket.");
                return -1;
        }
        /* Start listening for connections on the socket. */
        for (n = 0; n < num_socks; n++) {
                sock = socks[n];
                if (listen(sock, SSH_LISTEN_BACKLOG) < 0) {
                        error("listen: %.100s", strerror(errno));
                        close(sock);
                        return -1;
                }
        }

        /* Allocate a channel for each socket. */
        *chanids = xcalloc(num_socks + 1, sizeof(**chanids));
        for (n = 0; n < num_socks; n++) {
                sock = socks[n];
                nc = channel_new("x11 listener",
                    SSH_CHANNEL_X11_LISTENER, sock, sock, -1,
                    CHAN_X11_WINDOW_DEFAULT, CHAN_X11_PACKET_DEFAULT,
                    0, "X11 inet listener", 1);
                nc->single_connection = single_connection;
                (*chanids)[n] = nc->self;
        }
        (*chanids)[n] = -1;

        /* Return the display number for the DISPLAY environment variable. */
        *display_numberp = display_number;
        return (0);
}

static int
connect_local_xsocket(u_int dnr)
{
        int sock;
        struct sockaddr_un addr;

        sock = socket(AF_UNIX, SOCK_STREAM, 0);
        if (sock < 0)
                error("socket: %.100s", strerror(errno));
        memset(&addr, 0, sizeof(addr));
        addr.sun_family = AF_UNIX;
        snprintf(addr.sun_path, sizeof addr.sun_path, _PATH_UNIX_X, dnr);
        if (connect(sock, (struct sockaddr *)&addr, sizeof(addr)) == 0)
                return sock;
        close(sock);
        error("connect %.100s: %.100s", addr.sun_path, strerror(errno));
        return -1;
}

int
x11_connect_display(void)
{
        u_int display_number;
        const char *display;
        char buf[1024], *cp;
        struct addrinfo hints, *ai, *aitop;
        char strport[NI_MAXSERV];
        int gaierr, sock = 0;

        /* Try to open a socket for the local X server. */
        display = getenv("DISPLAY");
        if (!display) {
                error("DISPLAY not set.");
                return -1;
        }
        /*
         * Now we decode the value of the DISPLAY variable and make a
         * connection to the real X server.
         */

        /*
         * Check if it is a unix domain socket.  Unix domain displays are in
         * one of the following formats: unix:d[.s], :d[.s], ::d[.s]
         */
        if (strncmp(display, "unix:", 5) == 0 ||
            display[0] == ':') {
                /* Connect to the unix domain socket. */
                if (sscanf(strrchr(display, ':') + 1, "%u", &display_number) != 1) {
                        error("Could not parse display number from DISPLAY: %.100s",
                            display);
                        return -1;
                }
                /* Create a socket. */
                sock = connect_local_xsocket(display_number);
                if (sock < 0)
                        return -1;

                /* OK, we now have a connection to the display. */
                return sock;
        }
        /*
         * Connect to an inet socket.  The DISPLAY value is supposedly
         * hostname:d[.s], where hostname may also be numeric IP address.
         */
        strlcpy(buf, display, sizeof(buf));
        cp = strchr(buf, ':');
        if (!cp) {
                error("Could not find ':' in DISPLAY: %.100s", display);
                return -1;
        }
        *cp = 0;
        /* buf now contains the host name.  But first we parse the display number. */
        if (sscanf(cp + 1, "%u", &display_number) != 1) {
                error("Could not parse display number from DISPLAY: %.100s",
                    display);
                return -1;
        }

        /* Look up the host address */
        memset(&hints, 0, sizeof(hints));
        hints.ai_family = IPv4or6;
        hints.ai_socktype = SOCK_STREAM;
        snprintf(strport, sizeof strport, "%u", 6000 + display_number);
        if ((gaierr = getaddrinfo(buf, strport, &hints, &aitop)) != 0) {
                error("%.100s: unknown host. (%s)", buf,
                ssh_gai_strerror(gaierr));
                return -1;
        }
        for (ai = aitop; ai; ai = ai->ai_next) {
                /* Create a socket. */
                sock = socket(ai->ai_family, ai->ai_socktype, ai->ai_protocol);
                if (sock < 0) {
                        debug2("socket: %.100s", strerror(errno));
                        continue;
                }
                /* Connect it to the display. */
                if (connect(sock, ai->ai_addr, ai->ai_addrlen) < 0) {
                        debug2("connect %.100s port %u: %.100s", buf,
                            6000 + display_number, strerror(errno));
                        close(sock);
                        continue;
                }
                /* Success */
                break;
        }
        freeaddrinfo(aitop);
        if (!ai) {
                error("connect %.100s port %u: %.100s", buf, 6000 + display_number,
                    strerror(errno));
                return -1;
        }
        set_nodelay(sock);
        return sock;
}

/*
 * This is called when SSH_SMSG_X11_OPEN is received.  The packet contains
 * the remote channel number.  We should do whatever we want, and respond
 * with either SSH_MSG_OPEN_CONFIRMATION or SSH_MSG_OPEN_FAILURE.
 */

/* ARGSUSED */
void
x11_input_open(int type, u_int32_t seq, void *ctxt)
{
        Channel *c = NULL;
        int remote_id, sock = 0;
        char *remote_host;

        debug("Received X11 open request.");

        remote_id = packet_get_int();

        if (packet_get_protocol_flags() & SSH_PROTOFLAG_HOST_IN_FWD_OPEN) {
                remote_host = packet_get_string(NULL);
        } else {
                remote_host = xstrdup("unknown (remote did not supply name)");
        }
        packet_check_eom();

        /* Obtain a connection to the real X display. */
        sock = x11_connect_display();
        if (sock != -1) {
                /* Allocate a channel for this connection. */
                c = channel_new("connected x11 socket",
                    SSH_CHANNEL_X11_OPEN, sock, sock, -1, 0, 0, 0,
                    remote_host, 1);
                c->remote_id = remote_id;
                c->force_drain = 1;
        }
        xfree(remote_host);
        if (c == NULL) {
                /* Send refusal to the remote host. */
                packet_start(SSH_MSG_CHANNEL_OPEN_FAILURE);
                packet_put_int(remote_id);
        } else {
                /* Send a confirmation to the remote host. */
                packet_start(SSH_MSG_CHANNEL_OPEN_CONFIRMATION);
                packet_put_int(remote_id);
                packet_put_int(c->self);
        }
        packet_send();
}

/* dummy protocol handler that denies SSH-1 requests (agent/x11) */
/* ARGSUSED */
void
deny_input_open(int type, u_int32_t seq, void *ctxt)
{
        int rchan = packet_get_int();

        switch (type) {
        case SSH_SMSG_AGENT_OPEN:
                error("Warning: ssh server tried agent forwarding.");
                break;
        case SSH_SMSG_X11_OPEN:
                error("Warning: ssh server tried X11 forwarding.");
                break;
        default:
                error("deny_input_open: type %d", type);
                break;
        }
        error("Warning: this is probably a break-in attempt by a malicious server.");
        packet_start(SSH_MSG_CHANNEL_OPEN_FAILURE);
        packet_put_int(rchan);
        packet_send();
}

/*
 * Requests forwarding of X11 connections, generates fake authentication
 * data, and enables authentication spoofing.
 * This should be called in the client only.
 */
void
x11_request_forwarding_with_spoofing(int client_session_id, const char *disp,
    const char *proto, const char *data)
{
        u_int data_len = (u_int) strlen(data) / 2;
        u_int i, value;
        char *new_data;
        int screen_number;
        const char *cp;
        u_int32_t rnd = 0;

        if (x11_saved_display == NULL)
                x11_saved_display = xstrdup(disp);
        else if (strcmp(disp, x11_saved_display) != 0) {
                error("x11_request_forwarding_with_spoofing: different "
                    "$DISPLAY already forwarded");
                return;
        }

        cp = strchr(disp, ':');
        if (cp)
                cp = strchr(cp, '.');
        if (cp)
                screen_number = (u_int)strtonum(cp + 1, 0, 400, NULL);
        else
                screen_number = 0;

        if (x11_saved_proto == NULL) {
                /* Save protocol name. */
                x11_saved_proto = xstrdup(proto);
                /*
                 * Extract real authentication data and generate fake data
                 * of the same length.
                 */
                x11_saved_data = xmalloc(data_len);
                x11_fake_data = xmalloc(data_len);
                for (i = 0; i < data_len; i++) {
                        if (sscanf(data + 2 * i, "%2x", &value) != 1)
                                fatal("x11_request_forwarding: bad "
                                    "authentication data: %.100s", data);
                        if (i % 4 == 0)
                                rnd = arc4random();
                        x11_saved_data[i] = value;
                        x11_fake_data[i] = rnd & 0xff;
                        rnd >>= 8;
                }
                x11_saved_data_len = data_len;
                x11_fake_data_len = data_len;
        }

        /* Convert the fake data into hex. */
        new_data = tohex(x11_fake_data, data_len);

        /* Send the request packet. */
        if (compat20) {
                channel_request_start(client_session_id, "x11-req", 0);
                packet_put_char(0);     /* XXX bool single connection */
        } else {
                packet_start(SSH_CMSG_X11_REQUEST_FORWARDING);
        }
        packet_put_cstring(proto);
        packet_put_cstring(new_data);
        packet_put_int(screen_number);
        packet_send();
        packet_write_wait();
        xfree(new_data);
}


/* -- agent forwarding */

/* Sends a message to the server to request authentication fd forwarding. */

void
auth_request_forwarding(void)
{
        packet_start(SSH_CMSG_AGENT_REQUEST_FORWARDING);
        packet_send();
        packet_write_wait();
}