- markus@cvs.openbsd.org 2002/01/14 13:55:55

[openssh.git] / channels.c

/*
 * 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"
RCSID("$OpenBSD: channels.c,v 1.159 2002/01/14 13:55:55 markus Exp $");

#include "ssh.h"
#include "ssh1.h"
#include "ssh2.h"
#include "packet.h"
#include "xmalloc.h"
#include "uidswap.h"
#include "log.h"
#include "misc.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 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. */
static ForwardPermission permitted_opens[SSH_MAX_FORWARDS_PER_DIRECTION];

/* Number of permitted host/port pairs in the array. */
static int num_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 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 char *x11_fake_data = NULL;
static u_int x11_fake_data_len;


/* -- agent forwarding */

#define NUM_SOCKS       10

/* Name and directory of socket for authentication agent forwarding. */
static char *auth_sock_name = NULL;
static char *auth_sock_dir = NULL;

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

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

/* -- channel core */

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

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

/*
 * 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->efd = efd;
        c->extended_usage = extusage;

        /* XXX ugly hack: nonblock is only set by the server */
        if (nonblock && isatty(c->rfd)) {
                debug("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;
        }

        /* 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,
    int window, int maxpack, int extusage, char *remote_name, int nonblock)
{
        int i, found;
        Channel *c;

        /* Do initial allocation if this is the first call. */
        if (channels_alloc == 0) {
                channels_alloc = 10;
                channels = xmalloc(channels_alloc * sizeof(Channel *));
                for (i = 0; i < channels_alloc; i++)
                        channels[i] = NULL;
                fatal_add_cleanup((void (*) (void *)) channel_free_all, 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 = i;
                        break;
                }
        if (found == -1) {
                /* There are no free slots.  Take last+1 slot and expand the array.  */
                found = channels_alloc;
                channels_alloc += 10;
                debug2("channel: expanding %d", channels_alloc);
                channels = xrealloc(channels, channels_alloc * sizeof(Channel *));
                for (i = found; i < channels_alloc; i++)
                        channels[i] = NULL;
        }
        /* Initialize and return new channel. */
        c = channels[found] = xmalloc(sizeof(Channel));
        memset(c, 0, 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 = remote_name;
        c->remote_window = 0;
        c->remote_maxpacket = 0;
        c->cb_fn = NULL;
        c->cb_arg = NULL;
        c->cb_event = 0;
        c->force_drain = 0;
        c->single_connection = 0;
        c->detach_user = NULL;
        c->input_filter = NULL;
        debug("channel %d: new [%s]", found, remote_name);
        return c;
}

static int
channel_find_maxfd(void)
{
        int i, 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_close_fds: channel %d: r %d w %d e %d",
            c->self, c->rfd, c->wfd, c->efd);

        channel_close_fd(&c->sock);
        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;
        int i, n;

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

        s = channel_open_message();
        debug3("channel_free: status: %s", s);
        xfree(s);

        if (c->sock != -1)
                shutdown(c->sock, 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;
        }
        channels[c->self] = NULL;
        xfree(c);
}

void
channel_free_all(void)
{
        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)
{
        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)
{
        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()) {
                                debug("channel %d: big input buffer %d",
                                    c->self, buffer_len(&c->input));
                                return 0;
                        }
#endif
                        if (buffer_len(&c->output) > packet_get_maxsize()) {
                                debug("channel %d: big output buffer %d > %d",
                                    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)
{
        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)
{
        int i;
        Channel *c;

        for (i = 0; i < channels_alloc; i++) {
                c = channels[i];
                if (c == NULL)
                        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;
        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)\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);
                        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) {
                log("channel_send_open: %d: bad id", id);
                return;
        }
        debug("send channel open %d", 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(int id, char *service, int wantconfirm)
{
        channel_request_start(id, service, wantconfirm);
        packet_send();
        debug("channel request %d: %s", id, service) ;
}
void
channel_request_start(int id, char *service, int wantconfirm)
{
        Channel *c = channel_lookup(id);
        if (c == NULL) {
                log("channel_request: %d: bad id", id);
                return;
        }
        packet_start(SSH2_MSG_CHANNEL_REQUEST);
        packet_put_int(c->remote_id);
        packet_put_cstring(service);
        packet_put_char(wantconfirm);
}
void
channel_register_callback(int id, int mtype, channel_callback_fn *fn, void *arg)
{
        Channel *c = channel_lookup(id);
        if (c == NULL) {
                log("channel_register_callback: %d: bad id", id);
                return;
        }
        c->cb_event = mtype;
        c->cb_fn = fn;
        c->cb_arg = arg;
}
void
channel_register_cleanup(int id, channel_callback_fn *fn)
{
        Channel *c = channel_lookup(id);
        if (c == NULL) {
                log("channel_register_cleanup: %d: bad id", id);
                return;
        }
        c->detach_user = fn;
}
void
channel_cancel_cleanup(int id)
{
        Channel *c = channel_lookup(id);
        if (c == NULL) {
                log("channel_cancel_cleanup: %d: bad id", id);
                return;
        }
        c->detach_user = NULL;
}
void
channel_register_filter(int id, channel_filter_fn *fn)
{
        Channel *c = channel_lookup(id);
        if (c == NULL) {
                log("channel_register_filter: %d: bad id", id);
                return;
        }
        c->input_filter = fn;
}

void
channel_set_fds(int id, int rfd, int wfd, int efd,
    int extusage, int nonblock)
{
        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;
        /* XXX window size? */
        c->local_window = c->local_window_max = c->local_maxpacket * 2;
        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];

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

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)
                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) {
                        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->extended_usage == CHAN_EXTENDED_READ &&
                    buffer_len(&c->extended) < c->remote_window)
                        FD_SET(c->efd, readset);
        }
}

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;
                debug("channel %d: closing after input drain.", c->self);
        }
}

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 {
                debug("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) {
                debug("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) {
                debug("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.
                 */
                log("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) {
                log("X11 connection rejected because of wrong authentication.");
                debug("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;
                debug("X11 closed %d i%d/o%d", c->self, c->istate, c->ostate);
        }
}

/* try to decode a socks4 header */
static int
channel_decode_socks4(Channel *c, fd_set * readset, fd_set * writeset)
{
        u_char *p, *host;
        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);

        debug("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, (char *)&s4_rsp, sizeof(s4_rsp));
        return 1;
}

/* dynamic port forwarding */
static void
channel_pre_dynamic(Channel *c, fd_set * readset, fd_set * writeset)
{
        u_char *p;
        int have, 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 < 4) {
                /* 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;
        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. */
static void
channel_post_x11_listener(Channel *c, fd_set * readset, fd_set * writeset)
{
        Channel *nc;
        struct sockaddr addr;
        int newsock, on = 1;
        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) {
                        debug("single_connection: closing X11 listener.");
                        channel_close_fd(&c->sock);
                        chan_mark_dead(c);
                }
                if (newsock < 0) {
                        error("accept: %.100s", strerror(errno));
                        return;
                }
                if (setsockopt(newsock, IPPROTO_TCP, TCP_NODELAY, &on,
                    sizeof on) == -1)
                        error("setsockopt TCP_NODELAY: %.100s",
                            strerror(errno));
                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, xstrdup(buf), 1);
                if (nc == NULL) {
                        close(newsock);
                        xfree(remote_ipaddr);
                        return;
                }
                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) {
                                debug("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);
        u_short 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(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);
}

/*
 * This socket is listening for connections to a forwarded TCP/IP port.
 */
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;
                }
                nc = channel_new(rtype,
                    nextstate, newsock, newsock, -1,
                    c->local_window_max, c->local_maxpacket,
                    0, xstrdup(rtype), 1);
                if (nc == NULL) {
                        error("channel_post_port_listener: no new channel:");
                        close(newsock);
                        return;
                }
                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.
 */
static void
channel_post_auth_listener(Channel *c, fd_set * readset, fd_set * writeset)
{
        Channel *nc;
        char *name;
        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;
                }
                name = xstrdup("accepted auth socket");
                nc = channel_new("accepted auth socket",
                    SSH_CHANNEL_OPENING, newsock, newsock, -1,
                    c->local_window_max, c->local_maxpacket,
                    0, name, 1);
                if (nc == NULL) {
                        error("channel_post_auth_listener: channel_new failed");
                        xfree(name);
                        close(newsock);
                }
                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();
        }
}

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

        if (FD_ISSET(c->sock, writeset)) {
                if (getsockopt(c->sock, SOL_SOCKET, SO_ERROR, (char *)&err,
                    &sz) < 0) {
                        err = errno;
                        error("getsockopt SO_ERROR failed");
                }
                if (err == 0) {
                        debug("channel %d: connected", c->self);
                        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: not connected: %s",
                            c->self, strerror(err));
                        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();
        }
}

static int
channel_handle_rfd(Channel *c, fd_set * readset, fd_set * writeset)
{
        char buf[16*1024];
        int len;

        if (c->rfd != -1 &&
            FD_ISSET(c->rfd, readset)) {
                len = read(c->rfd, buf, sizeof(buf));
                if (len < 0 && (errno == EINTR || errno == EAGAIN))
                        return 1;
                if (len <= 0) {
                        debug("channel %d: read<=0 rfd %d len %d",
                            c->self, c->rfd, len);
                        if (c->type != SSH_CHANNEL_OPEN) {
                                debug("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;
                                debug("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) {
                                debug("channel %d: filter stops", c->self);
                                chan_read_failed(c);
                        }
                } else {
                        buffer_append(&c->input, buf, len);
                }
        }
        return 1;
}
static int
channel_handle_wfd(Channel *c, fd_set * readset, fd_set * writeset)
{
        struct termios tio;
        u_char *data;
        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) {
                data = buffer_ptr(&c->output);
                dlen = buffer_len(&c->output);
                len = write(c->wfd, data, dlen);
                if (len < 0 && (errno == EINTR || errno == EAGAIN))
                        return 1;
                if (len <= 0) {
                        if (c->type != SSH_CHANNEL_OPEN) {
                                debug("channel %d: not open", c->self);
                                chan_mark_dead(c);
                                return -1;
                        } else if (compat13) {
                                buffer_clear(&c->output);
                                debug("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 && data[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 + data)
                                 */
                                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[16*1024];
        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 &&
                    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))
                                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;
}
static int
channel_check_window(Channel *c)
{
        if (c->type == SSH_CHANNEL_OPEN &&
            !(c->flags & (CHAN_CLOSE_SENT|CHAN_CLOSE_RCVD)) &&
            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_check_window(c);
}

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, 0))
                        return;
                debug("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;
                debug("channel %d: gc: user detached", c->self);
        }
        if (!chan_is_dead(c, 1))
                return;
        debug("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;
        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,
    int *nallocp, int rekeying)
{
        int n;
        u_int sz;

        n = MAX(*maxfdp, channel_max_fd);

        sz = howmany(n+1, NFDBITS) * sizeof(fd_mask);
        /* perhaps check sz < nalloc/2 and shrink? */
        if (*readsetp == NULL || sz > *nallocp) {
                *readsetp = xrealloc(*readsetp, sz);
                *writesetp = xrealloc(*writesetp, sz);
                *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)
{
        int len, i;
        Channel *c;

        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) {
                        /*
                         * 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
                         */
                        chan_ibuf_empty(c);
                }
                /* Send extended data, i.e. stderr */
                if (compat20 &&
                    c->remote_window > 0 &&
                    (len = buffer_len(&c->extended)) > 0 &&
                    c->extended_usage == CHAN_EXTENDED_READ) {
                        debug2("channel %d: rwin %d elen %d 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 */

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;

        /* same for protocol 1.5 if output end is no longer open */
        if (!compat13 && c->ostate != CHAN_OUTPUT_OPEN)
                return;

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

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

void
channel_input_extended_data(int type, u_int32_t seq, void *ctxt)
{
        int id;
        int tcode;
        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 extended_data for bad channel %d.", id);
        if (c->type != SSH_CHANNEL_OPEN) {
                log("channel %d: ext data for non open", id);
                return;
        }
        tcode = packet_get_int();
        if (c->efd == -1 ||
            c->extended_usage != CHAN_EXTENDED_WRITE ||
            tcode != SSH2_EXTENDED_DATA_STDERR) {
                log("channel %d: bad ext data", c->self);
                return;
        }
        data = packet_get_string(&data_len);
        packet_check_eom();
        if (data_len > c->local_window) {
                log("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);
}

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;
        }

}

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 */
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);
}

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);
}

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->cb_fn != NULL && c->cb_event == type) {
                        debug2("callback start");
                        c->cb_fn(c->self, c->cb_arg);
                        debug2("callback done");
                }
                debug("channel %d: open confirm rwindow %d rmax %d", 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";
}

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);
                }
                log("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);
}

void
channel_input_channel_request(int type, u_int32_t seq, void *ctxt)
{
        int id;
        Channel *c;

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

        if (c == NULL ||
            (c->type != SSH_CHANNEL_OPEN && c->type != SSH_CHANNEL_LARVAL))
                packet_disconnect("Received request for "
                    "non-open channel %d.", id);
        if (c->cb_fn != NULL && c->cb_event == type) {
                debug2("callback start");
                c->cb_fn(c->self, c->cb_arg);
                debug2("callback done");
        } else {
                char *service = packet_get_string(NULL);
                debug("channel %d: rcvd request for %s", c->self, service);
                debug("cb_fn %p cb_event %d", c->cb_fn , c->cb_event);
                xfree(service);
        }
}

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

        if (!compat20)
                return;

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

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

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, sock = -1;

        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();
        sock = channel_connect_to(host, host_port);
        if (sock != -1) {
                c = channel_new("connected socket",
                    SSH_CHANNEL_CONNECTING, sock, sock, -1, 0, 0, 0,
                    originator_string, 1);
                if (c == NULL) {
                        error("channel_input_port_open: channel_new failed");
                        close(sock);
                } else {
                        c->remote_id = remote_id;
                }
        }
        if (c == NULL) {
                packet_start(SSH_MSG_CHANNEL_OPEN_FAILURE);
                packet_put_int(remote_id);
                packet_send();
        }
        xfree(host);
}


/* -- tcp forwarding */

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

/*
 * Initiate forwarding of connections to local port "port" through the secure
 * channel to host:port from remote side.
 */
int
channel_request_local_forwarding(u_short listen_port, const char *host_to_connect,
    u_short port_to_connect, int gateway_ports)
{
        return channel_request_forwarding(
            NULL, listen_port,
            host_to_connect, port_to_connect,
            gateway_ports, /*remote_fwd*/ 0);
}

/*
 * If 'remote_fwd' is true we have a '-R style' listener for protocol 2
 * (SSH_CHANNEL_RPORT_LISTENER).
 */
int
channel_request_forwarding(
    const char *listen_address, u_short listen_port,
    const char *host_to_connect, u_short port_to_connect,
    int gateway_ports, int remote_fwd)
{
        Channel *c;
        int success, sock, on = 1, type;
        struct addrinfo hints, *ai, *aitop;
        char ntop[NI_MAXHOST], strport[NI_MAXSERV];
        const char *host;
        struct linger linger;

        success = 0;

        if (remote_fwd) {
                host = listen_address;
                type = SSH_CHANNEL_RPORT_LISTENER;
        } else {
                host = host_to_connect;
                type = SSH_CHANNEL_PORT_LISTENER;
        }

        if (strlen(host) > SSH_CHANNEL_PATH_LEN - 1) {
                error("Forward host name too long.");
                return success;
        }

        /* XXX listen_address is currently ignored */
        /*
         * 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 = gateway_ports ? AI_PASSIVE : 0;
        hints.ai_socktype = SOCK_STREAM;
        snprintf(strport, sizeof strport, "%d", listen_port);
        if (getaddrinfo(NULL, strport, &hints, &aitop) != 0)
                packet_disconnect("getaddrinfo: fatal error");

        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_request_forwarding: getnameinfo failed");
                        continue;
                }
                /* Create a port to listen for the host. */
                sock = socket(ai->ai_family, SOCK_STREAM, 0);
                if (sock < 0) {
                        /* this is no error since kernel may not support ipv6 */
                        verbose("socket: %.100s", strerror(errno));
                        continue;
                }
                /*
                 * Set socket options.  We would like the socket to disappear
                 * as soon as it has been closed for whatever reason.
                 */
                setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, (void *)&on, sizeof(on));
                linger.l_onoff = 1;
                linger.l_linger = 5;
                setsockopt(sock, SOL_SOCKET, SO_LINGER, (void *)&linger, sizeof(linger));
                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, 5) < 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, xstrdup("port listener"), 1);
                if (c == NULL) {
                        error("channel_request_forwarding: channel_new failed");
                        close(sock);
                        continue;
                }
                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_request_forwarding: cannot listen to port: %d",
                    listen_port);
        freeaddrinfo(aitop);
        return success;
}

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

void
channel_request_remote_forwarding(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 = "0.0.0.0";
                packet_start(SSH2_MSG_GLOBAL_REQUEST);
                packet_put_cstring("tcpip-forward");
                packet_put_char(0);                     /* 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:
                        log("Warning: Server denied remote port forwarding.");
                        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++;
        }
}

/*
 * 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).  This never returns if there was an error.
 */

void
channel_input_port_forward_request(int is_root, int gateway_ports)
{
        u_short port, host_port;
        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);
#endif
        /* Initiate forwarding */
        channel_request_local_forwarding(port, hostname, host_port, gateway_ports);

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

/*
 * 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_request_remote_forwarding: 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;
}

void
channel_clear_permitted_opens(void)
{
        int i;

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

}


/* return socket to remote host, port */
static int
connect_to(const char *host, u_short port)
{
        struct addrinfo hints, *ai, *aitop;
        char ntop[NI_MAXHOST], strport[NI_MAXSERV];
        int gaierr;
        int sock = -1;

        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, &aitop)) != 0) {
                error("connect_to %.100s: unknown host (%s)", host,
                    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;
                if (getnameinfo(ai->ai_addr, ai->ai_addrlen, ntop, sizeof(ntop),
                    strport, sizeof(strport), NI_NUMERICHOST|NI_NUMERICSERV) != 0) {
                        error("connect_to: getnameinfo failed");
                        continue;
                }
                sock = socket(ai->ai_family, SOCK_STREAM, 0);
                if (sock < 0) {
                        error("socket: %.100s", strerror(errno));
                        continue;
                }
                if (fcntl(sock, F_SETFL, O_NONBLOCK) < 0)
                        fatal("connect_to: F_SETFL: %s", strerror(errno));
                if (connect(sock, ai->ai_addr, ai->ai_addrlen) < 0 &&
                    errno != EINPROGRESS) {
                        error("connect_to %.100s port %s: %.100s", ntop, strport,
                            strerror(errno));
                        close(sock);
                        continue;       /* fail -- try next */
                }
                break; /* success */

        }
        freeaddrinfo(aitop);
        if (!ai) {
                error("connect_to %.100s port %d: failed.", host, port);
                return -1;
        }
        /* success */
        return sock;
}

int
channel_connect_by_listen_address(u_short listen_port)
{
        int i;

        for (i = 0; i < num_permitted_opens; i++)
                if (permitted_opens[i].listen_port == listen_port)
                        return connect_to(
                            permitted_opens[i].host_to_connect,
                            permitted_opens[i].port_to_connect);
        error("WARNING: Server requests forwarding for unknown listen_port %d",
            listen_port);
        return -1;
}

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

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

        }
        if (!permit) {
                log("Received request to connect to host %.100s port %d, "
                    "but the request was denied.", host, port);
                return -1;
        }
        return connect_to(host, port);
}

/* -- X11 forwarding */

/*
 * Creates an internet domain socket for listening for X11 connections.
 * Returns a suitable display number for the DISPLAY variable, or -1 if
 * an error occurs.
 */
int
x11_create_display_inet(int x11_display_offset, int gateway_ports,
    int single_connection)
{
        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];

        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 = gateway_ports ? AI_PASSIVE : 0;
                hints.ai_socktype = SOCK_STREAM;
                snprintf(strport, sizeof strport, "%d", port);
                if ((gaierr = getaddrinfo(NULL, strport, &hints, &aitop)) != 0) {
                        error("getaddrinfo: %.100s", 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, SOCK_STREAM, 0);
                        if (sock < 0) {
                                if ((errno != EINVAL) && (errno != EAFNOSUPPORT)) {
                                        error("socket: %.100s", strerror(errno));
                                        return -1;
                                } else {
                                        debug("x11_create_display_inet: Socket family %d not supported",
                                                 ai->ai_family);
                                        continue;
                                }
                        }
                        if (bind(sock, ai->ai_addr, ai->ai_addrlen) < 0) {
                                debug("bind port %d: %.100s", port, strerror(errno));
                                close(sock);

                                if (ai->ai_next)
                                        continue;

                                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
                        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, 5) < 0) {
                        error("listen: %.100s", strerror(errno));
                        close(sock);
                        return -1;
                }
        }

        /* Allocate a channel for each socket. */
        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, xstrdup("X11 inet listener"), 1);
                if (nc != NULL)
                        nc->single_connection = single_connection;
        }

        /* Return the display number for the DISPLAY environment variable. */
        return display_number;
}

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)
{
        int display_number, sock = 0, on = 1;
        const char *display;
        char buf[1024], *cp;
        struct addrinfo hints, *ai, *aitop;
        char strport[NI_MAXSERV];
        int gaierr;

        /* 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, "%d", &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, "%d", &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, "%d", 6000 + display_number);
        if ((gaierr = getaddrinfo(buf, strport, &hints, &aitop)) != 0) {
                error("%.100s: unknown host. (%s)", buf, gai_strerror(gaierr));
                return -1;
        }
        for (ai = aitop; ai; ai = ai->ai_next) {
                /* Create a socket. */
                sock = socket(ai->ai_family, SOCK_STREAM, 0);
                if (sock < 0) {
                        debug("socket: %.100s", strerror(errno));
                        continue;
                }
                /* Connect it to the display. */
                if (connect(sock, ai->ai_addr, ai->ai_addrlen) < 0) {
                        debug("connect %.100s port %d: %.100s", buf,
                            6000 + display_number, strerror(errno));
                        close(sock);
                        continue;
                }
                /* Success */
                break;
        }
        freeaddrinfo(aitop);
        if (!ai) {
                error("connect %.100s port %d: %.100s", buf, 6000 + display_number,
                    strerror(errno));
                return -1;
        }
        if (setsockopt(sock, IPPROTO_TCP, TCP_NODELAY, &on, sizeof on) == -1)
                error("setsockopt TCP_NODELAY: %.100s", strerror(errno));
        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.
 */

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);
                if (c == NULL) {
                        error("x11_input_open: channel_new failed");
                        close(sock);
                } else {
                        c->remote_id = remote_id;
                        c->force_drain = 1;
                }
        }
        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) */
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 *proto, const char *data)
{
        u_int data_len = (u_int) strlen(data) / 2;
        u_int i, value, len;
        char *new_data;
        int screen_number;
        const char *cp;
        u_int32_t rand = 0;

        cp = getenv("DISPLAY");
        if (cp)
                cp = strchr(cp, ':');
        if (cp)
                cp = strchr(cp, '.');
        if (cp)
                screen_number = atoi(cp + 1);
        else
                screen_number = 0;

        /* 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)
                        rand = arc4random();
                x11_saved_data[i] = value;
                x11_fake_data[i] = rand & 0xff;
                rand >>= 8;
        }
        x11_saved_data_len = data_len;
        x11_fake_data_len = data_len;

        /* Convert the fake data into hex. */
        len = 2 * data_len + 1;
        new_data = xmalloc(len);
        for (i = 0; i < data_len; i++)
                snprintf(new_data + 2 * i, len - 2 * i,
                    "%02x", (u_char) x11_fake_data[i]);

        /* 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();
}

/*
 * Returns the name of the forwarded authentication socket.  Returns NULL if
 * there is no forwarded authentication socket.  The returned value points to
 * a static buffer.
 */

char *
auth_get_socket_name(void)
{
        return auth_sock_name;
}

/* removes the agent forwarding socket */

void
auth_sock_cleanup_proc(void *_pw)
{
        struct passwd *pw = _pw;

        if (auth_sock_name) {
                temporarily_use_uid(pw);
                unlink(auth_sock_name);
                rmdir(auth_sock_dir);
                auth_sock_name = NULL;
                restore_uid();
        }
}

/*
 * This is called to process SSH_CMSG_AGENT_REQUEST_FORWARDING on the server.
 * This starts forwarding authentication requests.
 */

int
auth_input_request_forwarding(struct passwd * pw)
{
        Channel *nc;
        int sock;
        struct sockaddr_un sunaddr;

        if (auth_get_socket_name() != NULL) {
                error("authentication forwarding requested twice.");
                return 0;
        }

        /* Temporarily drop privileged uid for mkdir/bind. */
        temporarily_use_uid(pw);

        /* Allocate a buffer for the socket name, and format the name. */
        auth_sock_name = xmalloc(MAXPATHLEN);
        auth_sock_dir = xmalloc(MAXPATHLEN);
        strlcpy(auth_sock_dir, "/tmp/ssh-XXXXXXXX", MAXPATHLEN);

        /* Create private directory for socket */
        if (mkdtemp(auth_sock_dir) == NULL) {
                packet_send_debug("Agent forwarding disabled: "
                    "mkdtemp() failed: %.100s", strerror(errno));
                restore_uid();
                xfree(auth_sock_name);
                xfree(auth_sock_dir);
                auth_sock_name = NULL;
                auth_sock_dir = NULL;
                return 0;
        }
        snprintf(auth_sock_name, MAXPATHLEN, "%s/agent.%d",
                 auth_sock_dir, (int) getpid());

        /* delete agent socket on fatal() */
        fatal_add_cleanup(auth_sock_cleanup_proc, pw);

        /* Create the socket. */
        sock = socket(AF_UNIX, SOCK_STREAM, 0);
        if (sock < 0)
                packet_disconnect("socket: %.100s", strerror(errno));

        /* Bind it to the name. */
        memset(&sunaddr, 0, sizeof(sunaddr));
        sunaddr.sun_family = AF_UNIX;
        strlcpy(sunaddr.sun_path, auth_sock_name, sizeof(sunaddr.sun_path));

        if (bind(sock, (struct sockaddr *) & sunaddr, sizeof(sunaddr)) < 0)
                packet_disconnect("bind: %.100s", strerror(errno));

        /* Restore the privileged uid. */
        restore_uid();

        /* Start listening on the socket. */
        if (listen(sock, 5) < 0)
                packet_disconnect("listen: %.100s", strerror(errno));

        /* Allocate a channel for the authentication agent socket. */
        nc = channel_new("auth socket",
            SSH_CHANNEL_AUTH_SOCKET, sock, sock, -1,
            CHAN_X11_WINDOW_DEFAULT, CHAN_X11_PACKET_DEFAULT,
            0, xstrdup("auth socket"), 1);
        if (nc == NULL) {
                error("auth_input_request_forwarding: channel_new failed");
                auth_sock_cleanup_proc(pw);
                fatal_remove_cleanup(auth_sock_cleanup_proc, pw);
                close(sock);
                return 0;
        }
        strlcpy(nc->path, auth_sock_name, sizeof(nc->path));
        return 1;
}

/* This is called to process an SSH_SMSG_AGENT_OPEN message. */

void
auth_input_open_request(int type, u_int32_t seq, void *ctxt)
{
        Channel *c = NULL;
        int remote_id, sock;
        char *name;

        /* Read the remote channel number from the message. */
        remote_id = packet_get_int();
        packet_check_eom();

        /*
         * Get a connection to the local authentication agent (this may again
         * get forwarded).
         */
        sock = ssh_get_authentication_socket();

        /*
         * If we could not connect the agent, send an error message back to
         * the server. This should never happen unless the agent dies,
         * because authentication forwarding is only enabled if we have an
         * agent.
         */
        if (sock >= 0) {
                name = xstrdup("authentication agent connection");
                c = channel_new("", SSH_CHANNEL_OPEN, sock, sock,
                    -1, 0, 0, 0, name, 1);
                if (c == NULL) {
                        error("auth_input_open_request: channel_new failed");
                        xfree(name);
                        close(sock);
                } else {
                        c->remote_id = remote_id;
                        c->force_drain = 1;
                }
        }
        if (c == NULL) {
                packet_start(SSH_MSG_CHANNEL_OPEN_FAILURE);
                packet_put_int(remote_id);
        } else {
                /* Send a confirmation to the remote host. */
                debug("Forwarding authentication connection.");
                packet_start(SSH_MSG_CHANNEL_OPEN_CONFIRMATION);
                packet_put_int(remote_id);
                packet_put_int(c->self);
        }
        packet_send();
}