- stevesk@cvs.openbsd.org 2006/02/20 16:36:15

[openssh.git] / session.c

/*
 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
 *                    All rights reserved
 *
 * 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 by Markus Friedl.
 * Copyright (c) 2000, 2001 Markus Friedl.  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: session.c,v 1.194 2006/02/20 16:36:14 stevesk Exp $");

#include <sys/types.h>
#include <sys/wait.h>
#include <sys/un.h>

#include <paths.h>

#include "ssh.h"
#include "ssh1.h"
#include "ssh2.h"
#include "xmalloc.h"
#include "sshpty.h"
#include "packet.h"
#include "buffer.h"
#include "match.h"
#include "uidswap.h"
#include "compat.h"
#include "channels.h"
#include "bufaux.h"
#include "auth.h"
#include "auth-options.h"
#include "pathnames.h"
#include "log.h"
#include "servconf.h"
#include "sshlogin.h"
#include "serverloop.h"
#include "canohost.h"
#include "session.h"
#include "kex.h"
#include "monitor_wrap.h"

#if defined(KRB5) && defined(USE_AFS)
#include <kafs.h>
#endif

#ifdef GSSAPI
#include "ssh-gss.h"
#endif

/* func */

Session *session_new(void);
void    session_set_fds(Session *, int, int, int);
void    session_pty_cleanup(Session *);
void    session_proctitle(Session *);
int     session_setup_x11fwd(Session *);
void    do_exec_pty(Session *, const char *);
void    do_exec_no_pty(Session *, const char *);
void    do_exec(Session *, const char *);
void    do_login(Session *, const char *);
#ifdef LOGIN_NEEDS_UTMPX
static void     do_pre_login(Session *s);
#endif
void    do_child(Session *, const char *);
void    do_motd(void);
int     check_quietlogin(Session *, const char *);

static void do_authenticated1(Authctxt *);
static void do_authenticated2(Authctxt *);

static int session_pty_req(Session *);

/* import */
extern ServerOptions options;
extern char *__progname;
extern int log_stderr;
extern int debug_flag;
extern u_int utmp_len;
extern int startup_pipe;
extern void destroy_sensitive_data(void);
extern Buffer loginmsg;

/* original command from peer. */
const char *original_command = NULL;

/* data */
#define MAX_SESSIONS 10
Session sessions[MAX_SESSIONS];

#ifdef HAVE_LOGIN_CAP
login_cap_t *lc;
#endif

static int is_child = 0;

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

/* removes the agent forwarding socket */

static void
auth_sock_cleanup_proc(struct passwd *pw)
{
        if (auth_sock_name != NULL) {
                temporarily_use_uid(pw);
                unlink(auth_sock_name);
                rmdir(auth_sock_dir);
                auth_sock_name = NULL;
                restore_uid();
        }
}

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

        if (auth_sock_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-XXXXXXXXXX", 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.%ld",
                 auth_sock_dir, (long) getpid());

        /* 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, SSH_LISTEN_BACKLOG) < 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, "auth socket", 1);
        strlcpy(nc->path, auth_sock_name, sizeof(nc->path));
        return 1;
}

static void
display_loginmsg(void)
{
        if (buffer_len(&loginmsg) > 0) {
                buffer_append(&loginmsg, "\0", 1);
                printf("%s", (char *)buffer_ptr(&loginmsg));
                buffer_clear(&loginmsg);
        }
}

void
do_authenticated(Authctxt *authctxt)
{
        setproctitle("%s", authctxt->pw->pw_name);

        /* setup the channel layer */
        if (!no_port_forwarding_flag && options.allow_tcp_forwarding)
                channel_permit_all_opens();

        if (compat20)
                do_authenticated2(authctxt);
        else
                do_authenticated1(authctxt);

        do_cleanup(authctxt);
}

/*
 * Prepares for an interactive session.  This is called after the user has
 * been successfully authenticated.  During this message exchange, pseudo
 * terminals are allocated, X11, TCP/IP, and authentication agent forwardings
 * are requested, etc.
 */
static void
do_authenticated1(Authctxt *authctxt)
{
        Session *s;
        char *command;
        int success, type, screen_flag;
        int enable_compression_after_reply = 0;
        u_int proto_len, data_len, dlen, compression_level = 0;

        s = session_new();
        if (s == NULL) {
                error("no more sessions");
                return;
        }
        s->authctxt = authctxt;
        s->pw = authctxt->pw;

        /*
         * We stay in this loop until the client requests to execute a shell
         * or a command.
         */
        for (;;) {
                success = 0;

                /* Get a packet from the client. */
                type = packet_read();

                /* Process the packet. */
                switch (type) {
                case SSH_CMSG_REQUEST_COMPRESSION:
                        compression_level = packet_get_int();
                        packet_check_eom();
                        if (compression_level < 1 || compression_level > 9) {
                                packet_send_debug("Received invalid compression level %d.",
                                    compression_level);
                                break;
                        }
                        if (options.compression == COMP_NONE) {
                                debug2("compression disabled");
                                break;
                        }
                        /* Enable compression after we have responded with SUCCESS. */
                        enable_compression_after_reply = 1;
                        success = 1;
                        break;

                case SSH_CMSG_REQUEST_PTY:
                        success = session_pty_req(s);
                        break;

                case SSH_CMSG_X11_REQUEST_FORWARDING:
                        s->auth_proto = packet_get_string(&proto_len);
                        s->auth_data = packet_get_string(&data_len);

                        screen_flag = packet_get_protocol_flags() &
                            SSH_PROTOFLAG_SCREEN_NUMBER;
                        debug2("SSH_PROTOFLAG_SCREEN_NUMBER: %d", screen_flag);

                        if (packet_remaining() == 4) {
                                if (!screen_flag)
                                        debug2("Buggy client: "
                                            "X11 screen flag missing");
                                s->screen = packet_get_int();
                        } else {
                                s->screen = 0;
                        }
                        packet_check_eom();
                        success = session_setup_x11fwd(s);
                        if (!success) {
                                xfree(s->auth_proto);
                                xfree(s->auth_data);
                                s->auth_proto = NULL;
                                s->auth_data = NULL;
                        }
                        break;

                case SSH_CMSG_AGENT_REQUEST_FORWARDING:
                        if (no_agent_forwarding_flag || compat13) {
                                debug("Authentication agent forwarding not permitted for this authentication.");
                                break;
                        }
                        debug("Received authentication agent forwarding request.");
                        success = auth_input_request_forwarding(s->pw);
                        break;

                case SSH_CMSG_PORT_FORWARD_REQUEST:
                        if (no_port_forwarding_flag) {
                                debug("Port forwarding not permitted for this authentication.");
                                break;
                        }
                        if (!options.allow_tcp_forwarding) {
                                debug("Port forwarding not permitted.");
                                break;
                        }
                        debug("Received TCP/IP port forwarding request.");
                        channel_input_port_forward_request(s->pw->pw_uid == 0, options.gateway_ports);
                        success = 1;
                        break;

                case SSH_CMSG_MAX_PACKET_SIZE:
                        if (packet_set_maxsize(packet_get_int()) > 0)
                                success = 1;
                        break;

                case SSH_CMSG_EXEC_SHELL:
                case SSH_CMSG_EXEC_CMD:
                        if (type == SSH_CMSG_EXEC_CMD) {
                                command = packet_get_string(&dlen);
                                debug("Exec command '%.500s'", command);
                                do_exec(s, command);
                                xfree(command);
                        } else {
                                do_exec(s, NULL);
                        }
                        packet_check_eom();
                        session_close(s);
                        return;

                default:
                        /*
                         * Any unknown messages in this phase are ignored,
                         * and a failure message is returned.
                         */
                        logit("Unknown packet type received after authentication: %d", type);
                }
                packet_start(success ? SSH_SMSG_SUCCESS : SSH_SMSG_FAILURE);
                packet_send();
                packet_write_wait();

                /* Enable compression now that we have replied if appropriate. */
                if (enable_compression_after_reply) {
                        enable_compression_after_reply = 0;
                        packet_start_compression(compression_level);
                }
        }
}

/*
 * This is called to fork and execute a command when we have no tty.  This
 * will call do_child from the child, and server_loop from the parent after
 * setting up file descriptors and such.
 */
void
do_exec_no_pty(Session *s, const char *command)
{
        pid_t pid;

#ifdef USE_PIPES
        int pin[2], pout[2], perr[2];
        /* Allocate pipes for communicating with the program. */
        if (pipe(pin) < 0 || pipe(pout) < 0 || pipe(perr) < 0)
                packet_disconnect("Could not create pipes: %.100s",
                                  strerror(errno));
#else /* USE_PIPES */
        int inout[2], err[2];
        /* Uses socket pairs to communicate with the program. */
        if (socketpair(AF_UNIX, SOCK_STREAM, 0, inout) < 0 ||
            socketpair(AF_UNIX, SOCK_STREAM, 0, err) < 0)
                packet_disconnect("Could not create socket pairs: %.100s",
                                  strerror(errno));
#endif /* USE_PIPES */
        if (s == NULL)
                fatal("do_exec_no_pty: no session");

        session_proctitle(s);

#if defined(USE_PAM)
        if (options.use_pam && !use_privsep)
                do_pam_setcred(1);
#endif /* USE_PAM */

        /* Fork the child. */
        if ((pid = fork()) == 0) {
                is_child = 1;

                /* Child.  Reinitialize the log since the pid has changed. */
                log_init(__progname, options.log_level, options.log_facility, log_stderr);

                /*
                 * Create a new session and process group since the 4.4BSD
                 * setlogin() affects the entire process group.
                 */
                if (setsid() < 0)
                        error("setsid failed: %.100s", strerror(errno));

#ifdef USE_PIPES
                /*
                 * Redirect stdin.  We close the parent side of the socket
                 * pair, and make the child side the standard input.
                 */
                close(pin[1]);
                if (dup2(pin[0], 0) < 0)
                        perror("dup2 stdin");
                close(pin[0]);

                /* Redirect stdout. */
                close(pout[0]);
                if (dup2(pout[1], 1) < 0)
                        perror("dup2 stdout");
                close(pout[1]);

                /* Redirect stderr. */
                close(perr[0]);
                if (dup2(perr[1], 2) < 0)
                        perror("dup2 stderr");
                close(perr[1]);
#else /* USE_PIPES */
                /*
                 * Redirect stdin, stdout, and stderr.  Stdin and stdout will
                 * use the same socket, as some programs (particularly rdist)
                 * seem to depend on it.
                 */
                close(inout[1]);
                close(err[1]);
                if (dup2(inout[0], 0) < 0)      /* stdin */
                        perror("dup2 stdin");
                if (dup2(inout[0], 1) < 0)      /* stdout.  Note: same socket as stdin. */
                        perror("dup2 stdout");
                if (dup2(err[0], 2) < 0)        /* stderr */
                        perror("dup2 stderr");
#endif /* USE_PIPES */

#ifdef _UNICOS
                cray_init_job(s->pw); /* set up cray jid and tmpdir */
#endif

                /* Do processing for the child (exec command etc). */
                do_child(s, command);
                /* NOTREACHED */
        }
#ifdef _UNICOS
        signal(WJSIGNAL, cray_job_termination_handler);
#endif /* _UNICOS */
#ifdef HAVE_CYGWIN
        if (is_winnt)
                cygwin_set_impersonation_token(INVALID_HANDLE_VALUE);
#endif
        if (pid < 0)
                packet_disconnect("fork failed: %.100s", strerror(errno));
        s->pid = pid;
        /* Set interactive/non-interactive mode. */
        packet_set_interactive(s->display != NULL);
#ifdef USE_PIPES
        /* We are the parent.  Close the child sides of the pipes. */
        close(pin[0]);
        close(pout[1]);
        close(perr[1]);

        if (compat20) {
                if (s->is_subsystem) {
                        close(perr[0]);
                        perr[0] = -1;
                }
                session_set_fds(s, pin[1], pout[0], perr[0]);
        } else {
                /* Enter the interactive session. */
                server_loop(pid, pin[1], pout[0], perr[0]);
                /* server_loop has closed pin[1], pout[0], and perr[0]. */
        }
#else /* USE_PIPES */
        /* We are the parent.  Close the child sides of the socket pairs. */
        close(inout[0]);
        close(err[0]);

        /*
         * Clear loginmsg, since it's the child's responsibility to display
         * it to the user, otherwise multiple sessions may accumulate
         * multiple copies of the login messages.
         */
        buffer_clear(&loginmsg);

        /*
         * Enter the interactive session.  Note: server_loop must be able to
         * handle the case that fdin and fdout are the same.
         */
        if (compat20) {
                session_set_fds(s, inout[1], inout[1], s->is_subsystem ? -1 : err[1]);
        } else {
                server_loop(pid, inout[1], inout[1], err[1]);
                /* server_loop has closed inout[1] and err[1]. */
        }
#endif /* USE_PIPES */
}

/*
 * This is called to fork and execute a command when we have a tty.  This
 * will call do_child from the child, and server_loop from the parent after
 * setting up file descriptors, controlling tty, updating wtmp, utmp,
 * lastlog, and other such operations.
 */
void
do_exec_pty(Session *s, const char *command)
{
        int fdout, ptyfd, ttyfd, ptymaster;
        pid_t pid;

        if (s == NULL)
                fatal("do_exec_pty: no session");
        ptyfd = s->ptyfd;
        ttyfd = s->ttyfd;

#if defined(USE_PAM)
        if (options.use_pam) {
                do_pam_set_tty(s->tty);
                if (!use_privsep)
                        do_pam_setcred(1);
        }
#endif

        /* Fork the child. */
        if ((pid = fork()) == 0) {
                is_child = 1;

                /* Child.  Reinitialize the log because the pid has changed. */
                log_init(__progname, options.log_level, options.log_facility, log_stderr);
                /* Close the master side of the pseudo tty. */
                close(ptyfd);

                /* Make the pseudo tty our controlling tty. */
                pty_make_controlling_tty(&ttyfd, s->tty);

                /* Redirect stdin/stdout/stderr from the pseudo tty. */
                if (dup2(ttyfd, 0) < 0)
                        error("dup2 stdin: %s", strerror(errno));
                if (dup2(ttyfd, 1) < 0)
                        error("dup2 stdout: %s", strerror(errno));
                if (dup2(ttyfd, 2) < 0)
                        error("dup2 stderr: %s", strerror(errno));

                /* Close the extra descriptor for the pseudo tty. */
                close(ttyfd);

                /* record login, etc. similar to login(1) */
#ifndef HAVE_OSF_SIA
                if (!(options.use_login && command == NULL)) {
#ifdef _UNICOS
                        cray_init_job(s->pw); /* set up cray jid and tmpdir */
#endif /* _UNICOS */
                        do_login(s, command);
                }
# ifdef LOGIN_NEEDS_UTMPX
                else
                        do_pre_login(s);
# endif
#endif

                /* Do common processing for the child, such as execing the command. */
                do_child(s, command);
                /* NOTREACHED */
        }
#ifdef _UNICOS
        signal(WJSIGNAL, cray_job_termination_handler);
#endif /* _UNICOS */
#ifdef HAVE_CYGWIN
        if (is_winnt)
                cygwin_set_impersonation_token(INVALID_HANDLE_VALUE);
#endif
        if (pid < 0)
                packet_disconnect("fork failed: %.100s", strerror(errno));
        s->pid = pid;

        /* Parent.  Close the slave side of the pseudo tty. */
        close(ttyfd);

        /*
         * Create another descriptor of the pty master side for use as the
         * standard input.  We could use the original descriptor, but this
         * simplifies code in server_loop.  The descriptor is bidirectional.
         */
        fdout = dup(ptyfd);
        if (fdout < 0)
                packet_disconnect("dup #1 failed: %.100s", strerror(errno));

        /* we keep a reference to the pty master */
        ptymaster = dup(ptyfd);
        if (ptymaster < 0)
                packet_disconnect("dup #2 failed: %.100s", strerror(errno));
        s->ptymaster = ptymaster;

        /* Enter interactive session. */
        packet_set_interactive(1);
        if (compat20) {
                session_set_fds(s, ptyfd, fdout, -1);
        } else {
                server_loop(pid, ptyfd, fdout, -1);
                /* server_loop _has_ closed ptyfd and fdout. */
        }
}

#ifdef LOGIN_NEEDS_UTMPX
static void
do_pre_login(Session *s)
{
        socklen_t fromlen;
        struct sockaddr_storage from;
        pid_t pid = getpid();

        /*
         * Get IP address of client. If the connection is not a socket, let
         * the address be 0.0.0.0.
         */
        memset(&from, 0, sizeof(from));
        fromlen = sizeof(from);
        if (packet_connection_is_on_socket()) {
                if (getpeername(packet_get_connection_in(),
                    (struct sockaddr *) & from, &fromlen) < 0) {
                        debug("getpeername: %.100s", strerror(errno));
                        cleanup_exit(255);
                }
        }

        record_utmp_only(pid, s->tty, s->pw->pw_name,
            get_remote_name_or_ip(utmp_len, options.use_dns),
            (struct sockaddr *)&from, fromlen);
}
#endif

/*
 * This is called to fork and execute a command.  If another command is
 * to be forced, execute that instead.
 */
void
do_exec(Session *s, const char *command)
{
        if (forced_command) {
                original_command = command;
                command = forced_command;
                debug("Forced command '%.900s'", command);
        }

#ifdef SSH_AUDIT_EVENTS
        if (command != NULL)
                PRIVSEP(audit_run_command(command));
        else if (s->ttyfd == -1) {
                char *shell = s->pw->pw_shell;

                if (shell[0] == '\0')   /* empty shell means /bin/sh */
                        shell =_PATH_BSHELL;
                PRIVSEP(audit_run_command(shell));
        }
#endif

        if (s->ttyfd != -1)
                do_exec_pty(s, command);
        else
                do_exec_no_pty(s, command);

        original_command = NULL;

        /*
         * Clear loginmsg: it's the child's responsibility to display
         * it to the user, otherwise multiple sessions may accumulate
         * multiple copies of the login messages.
         */
        buffer_clear(&loginmsg);
}

/* administrative, login(1)-like work */
void
do_login(Session *s, const char *command)
{
        socklen_t fromlen;
        struct sockaddr_storage from;
        struct passwd * pw = s->pw;
        pid_t pid = getpid();

        /*
         * Get IP address of client. If the connection is not a socket, let
         * the address be 0.0.0.0.
         */
        memset(&from, 0, sizeof(from));
        fromlen = sizeof(from);
        if (packet_connection_is_on_socket()) {
                if (getpeername(packet_get_connection_in(),
                    (struct sockaddr *) & from, &fromlen) < 0) {
                        debug("getpeername: %.100s", strerror(errno));
                        cleanup_exit(255);
                }
        }

        /* Record that there was a login on that tty from the remote host. */
        if (!use_privsep)
                record_login(pid, s->tty, pw->pw_name, pw->pw_uid,
                    get_remote_name_or_ip(utmp_len,
                    options.use_dns),
                    (struct sockaddr *)&from, fromlen);

#ifdef USE_PAM
        /*
         * If password change is needed, do it now.
         * This needs to occur before the ~/.hushlogin check.
         */
        if (options.use_pam && !use_privsep && s->authctxt->force_pwchange) {
                display_loginmsg();
                do_pam_chauthtok();
                s->authctxt->force_pwchange = 0;
                /* XXX - signal [net] parent to enable forwardings */
        }
#endif

        if (check_quietlogin(s, command))
                return;

        display_loginmsg();

        do_motd();
}

/*
 * Display the message of the day.
 */
void
do_motd(void)
{
        FILE *f;
        char buf[256];

        if (options.print_motd) {
#ifdef HAVE_LOGIN_CAP
                f = fopen(login_getcapstr(lc, "welcome", "/etc/motd",
                    "/etc/motd"), "r");
#else
                f = fopen("/etc/motd", "r");
#endif
                if (f) {
                        while (fgets(buf, sizeof(buf), f))
                                fputs(buf, stdout);
                        fclose(f);
                }
        }
}


/*
 * Check for quiet login, either .hushlogin or command given.
 */
int
check_quietlogin(Session *s, const char *command)
{
        char buf[256];
        struct passwd *pw = s->pw;
        struct stat st;

        /* Return 1 if .hushlogin exists or a command given. */
        if (command != NULL)
                return 1;
        snprintf(buf, sizeof(buf), "%.200s/.hushlogin", pw->pw_dir);
#ifdef HAVE_LOGIN_CAP
        if (login_getcapbool(lc, "hushlogin", 0) || stat(buf, &st) >= 0)
                return 1;
#else
        if (stat(buf, &st) >= 0)
                return 1;
#endif
        return 0;
}

/*
 * Sets the value of the given variable in the environment.  If the variable
 * already exists, its value is overriden.
 */
void
child_set_env(char ***envp, u_int *envsizep, const char *name,
        const char *value)
{
        char **env;
        u_int envsize;
        u_int i, namelen;

        /*
         * If we're passed an uninitialized list, allocate a single null
         * entry before continuing.
         */
        if (*envp == NULL && *envsizep == 0) {
                *envp = xmalloc(sizeof(char *));
                *envp[0] = NULL;
                *envsizep = 1;
        }

        /*
         * Find the slot where the value should be stored.  If the variable
         * already exists, we reuse the slot; otherwise we append a new slot
         * at the end of the array, expanding if necessary.
         */
        env = *envp;
        namelen = strlen(name);
        for (i = 0; env[i]; i++)
                if (strncmp(env[i], name, namelen) == 0 && env[i][namelen] == '=')
                        break;
        if (env[i]) {
                /* Reuse the slot. */
                xfree(env[i]);
        } else {
                /* New variable.  Expand if necessary. */
                envsize = *envsizep;
                if (i >= envsize - 1) {
                        if (envsize >= 1000)
                                fatal("child_set_env: too many env vars");
                        envsize += 50;
                        env = (*envp) = xrealloc(env, envsize * sizeof(char *));
                        *envsizep = envsize;
                }
                /* Need to set the NULL pointer at end of array beyond the new slot. */
                env[i + 1] = NULL;
        }

        /* Allocate space and format the variable in the appropriate slot. */
        env[i] = xmalloc(strlen(name) + 1 + strlen(value) + 1);
        snprintf(env[i], strlen(name) + 1 + strlen(value) + 1, "%s=%s", name, value);
}

/*
 * Reads environment variables from the given file and adds/overrides them
 * into the environment.  If the file does not exist, this does nothing.
 * Otherwise, it must consist of empty lines, comments (line starts with '#')
 * and assignments of the form name=value.  No other forms are allowed.
 */
static void
read_environment_file(char ***env, u_int *envsize,
        const char *filename)
{
        FILE *f;
        char buf[4096];
        char *cp, *value;
        u_int lineno = 0;

        f = fopen(filename, "r");
        if (!f)
                return;

        while (fgets(buf, sizeof(buf), f)) {
                if (++lineno > 1000)
                        fatal("Too many lines in environment file %s", filename);
                for (cp = buf; *cp == ' ' || *cp == '\t'; cp++)
                        ;
                if (!*cp || *cp == '#' || *cp == '\n')
                        continue;
                if (strchr(cp, '\n'))
                        *strchr(cp, '\n') = '\0';
                value = strchr(cp, '=');
                if (value == NULL) {
                        fprintf(stderr, "Bad line %u in %.100s\n", lineno,
                            filename);
                        continue;
                }
                /*
                 * Replace the equals sign by nul, and advance value to
                 * the value string.
                 */
                *value = '\0';
                value++;
                child_set_env(env, envsize, cp, value);
        }
        fclose(f);
}

#ifdef HAVE_ETC_DEFAULT_LOGIN
/*
 * Return named variable from specified environment, or NULL if not present.
 */
static char *
child_get_env(char **env, const char *name)
{
        int i;
        size_t len;

        len = strlen(name);
        for (i=0; env[i] != NULL; i++)
                if (strncmp(name, env[i], len) == 0 && env[i][len] == '=')
                        return(env[i] + len + 1);
        return NULL;
}

/*
 * Read /etc/default/login.
 * We pick up the PATH (or SUPATH for root) and UMASK.
 */
static void
read_etc_default_login(char ***env, u_int *envsize, uid_t uid)
{
        char **tmpenv = NULL, *var;
        u_int i, tmpenvsize = 0;
        u_long mask;

        /*
         * We don't want to copy the whole file to the child's environment,
         * so we use a temporary environment and copy the variables we're
         * interested in.
         */
        read_environment_file(&tmpenv, &tmpenvsize, "/etc/default/login");

        if (tmpenv == NULL)
                return;

        if (uid == 0)
                var = child_get_env(tmpenv, "SUPATH");
        else
                var = child_get_env(tmpenv, "PATH");
        if (var != NULL)
                child_set_env(env, envsize, "PATH", var);

        if ((var = child_get_env(tmpenv, "UMASK")) != NULL)
                if (sscanf(var, "%5lo", &mask) == 1)
                        umask((mode_t)mask);

        for (i = 0; tmpenv[i] != NULL; i++)
                xfree(tmpenv[i]);
        xfree(tmpenv);
}
#endif /* HAVE_ETC_DEFAULT_LOGIN */

void
copy_environment(char **source, char ***env, u_int *envsize)
{
        char *var_name, *var_val;
        int i;

        if (source == NULL)
                return;

        for(i = 0; source[i] != NULL; i++) {
                var_name = xstrdup(source[i]);
                if ((var_val = strstr(var_name, "=")) == NULL) {
                        xfree(var_name);
                        continue;
                }
                *var_val++ = '\0';

                debug3("Copy environment: %s=%s", var_name, var_val);
                child_set_env(env, envsize, var_name, var_val);

                xfree(var_name);
        }
}

static char **
do_setup_env(Session *s, const char *shell)
{
        char buf[256];
        u_int i, envsize;
        char **env, *laddr, *path = NULL;
        struct passwd *pw = s->pw;

        /* Initialize the environment. */
        envsize = 100;
        env = xmalloc(envsize * sizeof(char *));
        env[0] = NULL;

#ifdef HAVE_CYGWIN
        /*
         * The Windows environment contains some setting which are
         * important for a running system. They must not be dropped.
         */
        {
                char **p;

                p = fetch_windows_environment();
                copy_environment(p, &env, &envsize);
                free_windows_environment(p);
        }
#endif

#ifdef GSSAPI
        /* Allow any GSSAPI methods that we've used to alter
         * the childs environment as they see fit
         */
        ssh_gssapi_do_child(&env, &envsize);
#endif

        if (!options.use_login) {
                /* Set basic environment. */
                for (i = 0; i < s->num_env; i++)
                        child_set_env(&env, &envsize, s->env[i].name,
                            s->env[i].val);

                child_set_env(&env, &envsize, "USER", pw->pw_name);
                child_set_env(&env, &envsize, "LOGNAME", pw->pw_name);
#ifdef _AIX
                child_set_env(&env, &envsize, "LOGIN", pw->pw_name);
#endif
                child_set_env(&env, &envsize, "HOME", pw->pw_dir);
#ifdef HAVE_LOGIN_CAP
                if (setusercontext(lc, pw, pw->pw_uid, LOGIN_SETPATH) < 0)
                        child_set_env(&env, &envsize, "PATH", _PATH_STDPATH);
                else
                        child_set_env(&env, &envsize, "PATH", getenv("PATH"));
#else /* HAVE_LOGIN_CAP */
# ifndef HAVE_CYGWIN
                /*
                 * There's no standard path on Windows. The path contains
                 * important components pointing to the system directories,
                 * needed for loading shared libraries. So the path better
                 * remains intact here.
                 */
#  ifdef HAVE_ETC_DEFAULT_LOGIN
                read_etc_default_login(&env, &envsize, pw->pw_uid);
                path = child_get_env(env, "PATH");
#  endif /* HAVE_ETC_DEFAULT_LOGIN */
                if (path == NULL || *path == '\0') {
                        child_set_env(&env, &envsize, "PATH",
                            s->pw->pw_uid == 0 ?
                                SUPERUSER_PATH : _PATH_STDPATH);
                }
# endif /* HAVE_CYGWIN */
#endif /* HAVE_LOGIN_CAP */

                snprintf(buf, sizeof buf, "%.200s/%.50s",
                         _PATH_MAILDIR, pw->pw_name);
                child_set_env(&env, &envsize, "MAIL", buf);

                /* Normal systems set SHELL by default. */
                child_set_env(&env, &envsize, "SHELL", shell);
        }
        if (getenv("TZ"))
                child_set_env(&env, &envsize, "TZ", getenv("TZ"));

        /* Set custom environment options from RSA authentication. */
        if (!options.use_login) {
                while (custom_environment) {
                        struct envstring *ce = custom_environment;
                        char *str = ce->s;

                        for (i = 0; str[i] != '=' && str[i]; i++)
                                ;
                        if (str[i] == '=') {
                                str[i] = 0;
                                child_set_env(&env, &envsize, str, str + i + 1);
                        }
                        custom_environment = ce->next;
                        xfree(ce->s);
                        xfree(ce);
                }
        }

        /* SSH_CLIENT deprecated */
        snprintf(buf, sizeof buf, "%.50s %d %d",
            get_remote_ipaddr(), get_remote_port(), get_local_port());
        child_set_env(&env, &envsize, "SSH_CLIENT", buf);

        laddr = get_local_ipaddr(packet_get_connection_in());
        snprintf(buf, sizeof buf, "%.50s %d %.50s %d",
            get_remote_ipaddr(), get_remote_port(), laddr, get_local_port());
        xfree(laddr);
        child_set_env(&env, &envsize, "SSH_CONNECTION", buf);

        if (s->ttyfd != -1)
                child_set_env(&env, &envsize, "SSH_TTY", s->tty);
        if (s->term)
                child_set_env(&env, &envsize, "TERM", s->term);
        if (s->display)
                child_set_env(&env, &envsize, "DISPLAY", s->display);
        if (original_command)
                child_set_env(&env, &envsize, "SSH_ORIGINAL_COMMAND",
                    original_command);

#ifdef _UNICOS
        if (cray_tmpdir[0] != '\0')
                child_set_env(&env, &envsize, "TMPDIR", cray_tmpdir);
#endif /* _UNICOS */

        /*
         * Since we clear KRB5CCNAME at startup, if it's set now then it
         * must have been set by a native authentication method (eg AIX or
         * SIA), so copy it to the child.
         */
        {
                char *cp;

                if ((cp = getenv("KRB5CCNAME")) != NULL)
                        child_set_env(&env, &envsize, "KRB5CCNAME", cp);
        }

#ifdef _AIX
        {
                char *cp;

                if ((cp = getenv("AUTHSTATE")) != NULL)
                        child_set_env(&env, &envsize, "AUTHSTATE", cp);
                read_environment_file(&env, &envsize, "/etc/environment");
        }
#endif
#ifdef KRB5
        if (s->authctxt->krb5_ccname)
                child_set_env(&env, &envsize, "KRB5CCNAME",
                    s->authctxt->krb5_ccname);
#endif
#ifdef USE_PAM
        /*
         * Pull in any environment variables that may have
         * been set by PAM.
         */
        if (options.use_pam) {
                char **p;

                p = fetch_pam_child_environment();
                copy_environment(p, &env, &envsize);
                free_pam_environment(p);

                p = fetch_pam_environment();
                copy_environment(p, &env, &envsize);
                free_pam_environment(p);
        }
#endif /* USE_PAM */

        if (auth_sock_name != NULL)
                child_set_env(&env, &envsize, SSH_AUTHSOCKET_ENV_NAME,
                    auth_sock_name);

        /* read $HOME/.ssh/environment. */
        if (options.permit_user_env && !options.use_login) {
                snprintf(buf, sizeof buf, "%.200s/.ssh/environment",
                    strcmp(pw->pw_dir, "/") ? pw->pw_dir : "");
                read_environment_file(&env, &envsize, buf);
        }
        if (debug_flag) {
                /* dump the environment */
                fprintf(stderr, "Environment:\n");
                for (i = 0; env[i]; i++)
                        fprintf(stderr, "  %.200s\n", env[i]);
        }
        return env;
}

/*
 * Run $HOME/.ssh/rc, /etc/ssh/sshrc, or xauth (whichever is found
 * first in this order).
 */
static void
do_rc_files(Session *s, const char *shell)
{
        FILE *f = NULL;
        char cmd[1024];
        int do_xauth;
        struct stat st;

        do_xauth =
            s->display != NULL && s->auth_proto != NULL && s->auth_data != NULL;

        /* ignore _PATH_SSH_USER_RC for subsystems */
        if (!s->is_subsystem && (stat(_PATH_SSH_USER_RC, &st) >= 0)) {
                snprintf(cmd, sizeof cmd, "%s -c '%s %s'",
                    shell, _PATH_BSHELL, _PATH_SSH_USER_RC);
                if (debug_flag)
                        fprintf(stderr, "Running %s\n", cmd);
                f = popen(cmd, "w");
                if (f) {
                        if (do_xauth)
                                fprintf(f, "%s %s\n", s->auth_proto,
                                    s->auth_data);
                        pclose(f);
                } else
                        fprintf(stderr, "Could not run %s\n",
                            _PATH_SSH_USER_RC);
        } else if (stat(_PATH_SSH_SYSTEM_RC, &st) >= 0) {
                if (debug_flag)
                        fprintf(stderr, "Running %s %s\n", _PATH_BSHELL,
                            _PATH_SSH_SYSTEM_RC);
                f = popen(_PATH_BSHELL " " _PATH_SSH_SYSTEM_RC, "w");
                if (f) {
                        if (do_xauth)
                                fprintf(f, "%s %s\n", s->auth_proto,
                                    s->auth_data);
                        pclose(f);
                } else
                        fprintf(stderr, "Could not run %s\n",
                            _PATH_SSH_SYSTEM_RC);
        } else if (do_xauth && options.xauth_location != NULL) {
                /* Add authority data to .Xauthority if appropriate. */
                if (debug_flag) {
                        fprintf(stderr,
                            "Running %.500s remove %.100s\n",
                            options.xauth_location, s->auth_display);
                        fprintf(stderr,
                            "%.500s add %.100s %.100s %.100s\n",
                            options.xauth_location, s->auth_display,
                            s->auth_proto, s->auth_data);
                }
                snprintf(cmd, sizeof cmd, "%s -q -",
                    options.xauth_location);
                f = popen(cmd, "w");
                if (f) {
                        fprintf(f, "remove %s\n",
                            s->auth_display);
                        fprintf(f, "add %s %s %s\n",
                            s->auth_display, s->auth_proto,
                            s->auth_data);
                        pclose(f);
                } else {
                        fprintf(stderr, "Could not run %s\n",
                            cmd);
                }
        }
}

static void
do_nologin(struct passwd *pw)
{
        FILE *f = NULL;
        char buf[1024];

#ifdef HAVE_LOGIN_CAP
        if (!login_getcapbool(lc, "ignorenologin", 0) && pw->pw_uid)
                f = fopen(login_getcapstr(lc, "nologin", _PATH_NOLOGIN,
                    _PATH_NOLOGIN), "r");
#else
        if (pw->pw_uid)
                f = fopen(_PATH_NOLOGIN, "r");
#endif
        if (f) {
                /* /etc/nologin exists.  Print its contents and exit. */
                logit("User %.100s not allowed because %s exists",
                    pw->pw_name, _PATH_NOLOGIN);
                while (fgets(buf, sizeof(buf), f))
                        fputs(buf, stderr);
                fclose(f);
                fflush(NULL);
                exit(254);
        }
}

/* Set login name, uid, gid, and groups. */
void
do_setusercontext(struct passwd *pw)
{
#ifndef HAVE_CYGWIN
        if (getuid() == 0 || geteuid() == 0)
#endif /* HAVE_CYGWIN */
        {

#ifdef HAVE_SETPCRED
                if (setpcred(pw->pw_name, (char **)NULL) == -1)
                        fatal("Failed to set process credentials");
#endif /* HAVE_SETPCRED */
#ifdef HAVE_LOGIN_CAP
# ifdef __bsdi__
                setpgid(0, 0);
# endif
#ifdef GSSAPI
                if (options.gss_authentication) {
                        temporarily_use_uid(pw);
                        ssh_gssapi_storecreds();
                        restore_uid();
                }
#endif
# ifdef USE_PAM
                if (options.use_pam) {
                        do_pam_session();
                        do_pam_setcred(0);
                }
# endif /* USE_PAM */
                if (setusercontext(lc, pw, pw->pw_uid,
                    (LOGIN_SETALL & ~LOGIN_SETPATH)) < 0) {
                        perror("unable to set user context");
                        exit(1);
                }
#else
# if defined(HAVE_GETLUID) && defined(HAVE_SETLUID)
                /* Sets login uid for accounting */
                if (getluid() == -1 && setluid(pw->pw_uid) == -1)
                        error("setluid: %s", strerror(errno));
# endif /* defined(HAVE_GETLUID) && defined(HAVE_SETLUID) */

                if (setlogin(pw->pw_name) < 0)
                        error("setlogin failed: %s", strerror(errno));
                if (setgid(pw->pw_gid) < 0) {
                        perror("setgid");
                        exit(1);
                }
                /* Initialize the group list. */
                if (initgroups(pw->pw_name, pw->pw_gid) < 0) {
                        perror("initgroups");
                        exit(1);
                }
                endgrent();
#ifdef GSSAPI
                if (options.gss_authentication) {
                        temporarily_use_uid(pw);
                        ssh_gssapi_storecreds();
                        restore_uid();
                }
#endif
# ifdef USE_PAM
                /*
                 * PAM credentials may take the form of supplementary groups.
                 * These will have been wiped by the above initgroups() call.
                 * Reestablish them here.
                 */
                if (options.use_pam) {
                        do_pam_session();
                        do_pam_setcred(0);
                }
# endif /* USE_PAM */
# if defined(WITH_IRIX_PROJECT) || defined(WITH_IRIX_JOBS) || defined(WITH_IRIX_ARRAY)
                irix_setusercontext(pw);
#  endif /* defined(WITH_IRIX_PROJECT) || defined(WITH_IRIX_JOBS) || defined(WITH_IRIX_ARRAY) */
# ifdef _AIX
                aix_usrinfo(pw);
# endif /* _AIX */
#if defined(HAVE_LIBIAF)  &&  !defined(BROKEN_LIBIAF)
                if (set_id(pw->pw_name) != 0) {
                        exit(1);
                }
#endif /* HAVE_LIBIAF  && !BROKEN_LIBIAF */
                /* Permanently switch to the desired uid. */
                permanently_set_uid(pw);
#endif
        }

#ifdef HAVE_CYGWIN
        if (is_winnt)
#endif
        if (getuid() != pw->pw_uid || geteuid() != pw->pw_uid)
                fatal("Failed to set uids to %u.", (u_int) pw->pw_uid);
}

static void
do_pwchange(Session *s)
{
        fflush(NULL);
        fprintf(stderr, "WARNING: Your password has expired.\n");
        if (s->ttyfd != -1) {
                fprintf(stderr,
                    "You must change your password now and login again!\n");
#ifdef PASSWD_NEEDS_USERNAME
                execl(_PATH_PASSWD_PROG, "passwd", s->pw->pw_name,
                    (char *)NULL);
#else
                execl(_PATH_PASSWD_PROG, "passwd", (char *)NULL);
#endif
                perror("passwd");
        } else {
                fprintf(stderr,
                    "Password change required but no TTY available.\n");
        }
        exit(1);
}

static void
launch_login(struct passwd *pw, const char *hostname)
{
        /* Launch login(1). */

        execl(LOGIN_PROGRAM, "login", "-h", hostname,
#ifdef xxxLOGIN_NEEDS_TERM
                    (s->term ? s->term : "unknown"),
#endif /* LOGIN_NEEDS_TERM */
#ifdef LOGIN_NO_ENDOPT
            "-p", "-f", pw->pw_name, (char *)NULL);
#else
            "-p", "-f", "--", pw->pw_name, (char *)NULL);
#endif

        /* Login couldn't be executed, die. */

        perror("login");
        exit(1);
}

static void
child_close_fds(void)
{
        int i;

        if (packet_get_connection_in() == packet_get_connection_out())
                close(packet_get_connection_in());
        else {
                close(packet_get_connection_in());
                close(packet_get_connection_out());
        }
        /*
         * Close all descriptors related to channels.  They will still remain
         * open in the parent.
         */
        /* XXX better use close-on-exec? -markus */
        channel_close_all();

        /*
         * Close any extra file descriptors.  Note that there may still be
         * descriptors left by system functions.  They will be closed later.
         */
        endpwent();

        /*
         * Close any extra open file descriptors so that we don't have them
         * hanging around in clients.  Note that we want to do this after
         * initgroups, because at least on Solaris 2.3 it leaves file
         * descriptors open.
         */
        for (i = 3; i < 64; i++)
                close(i);
}

/*
 * Performs common processing for the child, such as setting up the
 * environment, closing extra file descriptors, setting the user and group
 * ids, and executing the command or shell.
 */
void
do_child(Session *s, const char *command)
{
        extern char **environ;
        char **env;
        char *argv[10];
        const char *shell, *shell0, *hostname = NULL;
        struct passwd *pw = s->pw;

        /* remove hostkey from the child's memory */
        destroy_sensitive_data();

        /* Force a password change */
        if (s->authctxt->force_pwchange) {
                do_setusercontext(pw);
                child_close_fds();
                do_pwchange(s);
                exit(1);
        }

        /* login(1) is only called if we execute the login shell */
        if (options.use_login && command != NULL)
                options.use_login = 0;

#ifdef _UNICOS
        cray_setup(pw->pw_uid, pw->pw_name, command);
#endif /* _UNICOS */

        /*
         * Login(1) does this as well, and it needs uid 0 for the "-h"
         * switch, so we let login(1) to this for us.
         */
        if (!options.use_login) {
#ifdef HAVE_OSF_SIA
                session_setup_sia(pw, s->ttyfd == -1 ? NULL : s->tty);
                if (!check_quietlogin(s, command))
                        do_motd();
#else /* HAVE_OSF_SIA */
                /* When PAM is enabled we rely on it to do the nologin check */
                if (!options.use_pam)
                        do_nologin(pw);
                do_setusercontext(pw);
                /*
                 * PAM session modules in do_setusercontext may have
                 * generated messages, so if this in an interactive
                 * login then display them too.
                 */
                if (!check_quietlogin(s, command))
                        display_loginmsg();
#endif /* HAVE_OSF_SIA */
        }

#ifdef USE_PAM
        if (options.use_pam && !options.use_login && !is_pam_session_open()) {
                debug3("PAM session not opened, exiting");
                display_loginmsg();
                exit(254);
        }
#endif

        /*
         * Get the shell from the password data.  An empty shell field is
         * legal, and means /bin/sh.
         */
        shell = (pw->pw_shell[0] == '\0') ? _PATH_BSHELL : pw->pw_shell;

        /*
         * Make sure $SHELL points to the shell from the password file,
         * even if shell is overridden from login.conf
         */
        env = do_setup_env(s, shell);

#ifdef HAVE_LOGIN_CAP
        shell = login_getcapstr(lc, "shell", (char *)shell, (char *)shell);
#endif

        /* we have to stash the hostname before we close our socket. */
        if (options.use_login)
                hostname = get_remote_name_or_ip(utmp_len,
                    options.use_dns);
        /*
         * Close the connection descriptors; note that this is the child, and
         * the server will still have the socket open, and it is important
         * that we do not shutdown it.  Note that the descriptors cannot be
         * closed before building the environment, as we call
         * get_remote_ipaddr there.
         */
        child_close_fds();

        /*
         * Must take new environment into use so that .ssh/rc,
         * /etc/ssh/sshrc and xauth are run in the proper environment.
         */
        environ = env;

#if defined(KRB5) && defined(USE_AFS)
        /*
         * At this point, we check to see if AFS is active and if we have
         * a valid Kerberos 5 TGT. If so, it seems like a good idea to see
         * if we can (and need to) extend the ticket into an AFS token. If
         * we don't do this, we run into potential problems if the user's
         * home directory is in AFS and it's not world-readable.
         */

        if (options.kerberos_get_afs_token && k_hasafs() &&
            (s->authctxt->krb5_ctx != NULL)) {
                char cell[64];

                debug("Getting AFS token");

                k_setpag();

                if (k_afs_cell_of_file(pw->pw_dir, cell, sizeof(cell)) == 0)
                        krb5_afslog(s->authctxt->krb5_ctx,
                            s->authctxt->krb5_fwd_ccache, cell, NULL);

                krb5_afslog_home(s->authctxt->krb5_ctx,
                    s->authctxt->krb5_fwd_ccache, NULL, NULL, pw->pw_dir);
        }
#endif

        /* Change current directory to the user's home directory. */
        if (chdir(pw->pw_dir) < 0) {
                fprintf(stderr, "Could not chdir to home directory %s: %s\n",
                    pw->pw_dir, strerror(errno));
#ifdef HAVE_LOGIN_CAP
                if (login_getcapbool(lc, "requirehome", 0))
                        exit(1);
#endif
        }

        if (!options.use_login)
                do_rc_files(s, shell);

        /* restore SIGPIPE for child */
        signal(SIGPIPE,  SIG_DFL);

        if (options.use_login) {
                launch_login(pw, hostname);
                /* NEVERREACHED */
        }

        /* Get the last component of the shell name. */
        if ((shell0 = strrchr(shell, '/')) != NULL)
                shell0++;
        else
                shell0 = shell;

        /*
         * If we have no command, execute the shell.  In this case, the shell
         * name to be passed in argv[0] is preceded by '-' to indicate that
         * this is a login shell.
         */
        if (!command) {
                char argv0[256];

                /* Start the shell.  Set initial character to '-'. */
                argv0[0] = '-';

                if (strlcpy(argv0 + 1, shell0, sizeof(argv0) - 1)
                    >= sizeof(argv0) - 1) {
                        errno = EINVAL;
                        perror(shell);
                        exit(1);
                }

                /* Execute the shell. */
                argv[0] = argv0;
                argv[1] = NULL;
                execve(shell, argv, env);

                /* Executing the shell failed. */
                perror(shell);
                exit(1);
        }
        /*
         * Execute the command using the user's shell.  This uses the -c
         * option to execute the command.
         */
        argv[0] = (char *) shell0;
        argv[1] = "-c";
        argv[2] = (char *) command;
        argv[3] = NULL;
        execve(shell, argv, env);
        perror(shell);
        exit(1);
}

Session *
session_new(void)
{
        int i;
        static int did_init = 0;
        if (!did_init) {
                debug("session_new: init");
                for (i = 0; i < MAX_SESSIONS; i++) {
                        sessions[i].used = 0;
                }
                did_init = 1;
        }
        for (i = 0; i < MAX_SESSIONS; i++) {
                Session *s = &sessions[i];
                if (! s->used) {
                        memset(s, 0, sizeof(*s));
                        s->chanid = -1;
                        s->ptyfd = -1;
                        s->ttyfd = -1;
                        s->used = 1;
                        s->self = i;
                        s->x11_chanids = NULL;
                        debug("session_new: session %d", i);
                        return s;
                }
        }
        return NULL;
}

static void
session_dump(void)
{
        int i;
        for (i = 0; i < MAX_SESSIONS; i++) {
                Session *s = &sessions[i];
                debug("dump: used %d session %d %p channel %d pid %ld",
                    s->used,
                    s->self,
                    s,
                    s->chanid,
                    (long)s->pid);
        }
}

int
session_open(Authctxt *authctxt, int chanid)
{
        Session *s = session_new();
        debug("session_open: channel %d", chanid);
        if (s == NULL) {
                error("no more sessions");
                return 0;
        }
        s->authctxt = authctxt;
        s->pw = authctxt->pw;
        if (s->pw == NULL || !authctxt->valid)
                fatal("no user for session %d", s->self);
        debug("session_open: session %d: link with channel %d", s->self, chanid);
        s->chanid = chanid;
        return 1;
}

Session *
session_by_tty(char *tty)
{
        int i;
        for (i = 0; i < MAX_SESSIONS; i++) {
                Session *s = &sessions[i];
                if (s->used && s->ttyfd != -1 && strcmp(s->tty, tty) == 0) {
                        debug("session_by_tty: session %d tty %s", i, tty);
                        return s;
                }
        }
        debug("session_by_tty: unknown tty %.100s", tty);
        session_dump();
        return NULL;
}

static Session *
session_by_channel(int id)
{
        int i;
        for (i = 0; i < MAX_SESSIONS; i++) {
                Session *s = &sessions[i];
                if (s->used && s->chanid == id) {
                        debug("session_by_channel: session %d channel %d", i, id);
                        return s;
                }
        }
        debug("session_by_channel: unknown channel %d", id);
        session_dump();
        return NULL;
}

static Session *
session_by_x11_channel(int id)
{
        int i, j;

        for (i = 0; i < MAX_SESSIONS; i++) {
                Session *s = &sessions[i];

                if (s->x11_chanids == NULL || !s->used)
                        continue;
                for (j = 0; s->x11_chanids[j] != -1; j++) {
                        if (s->x11_chanids[j] == id) {
                                debug("session_by_x11_channel: session %d "
                                    "channel %d", s->self, id);
                                return s;
                        }
                }
        }
        debug("session_by_x11_channel: unknown channel %d", id);
        session_dump();
        return NULL;
}

static Session *
session_by_pid(pid_t pid)
{
        int i;
        debug("session_by_pid: pid %ld", (long)pid);
        for (i = 0; i < MAX_SESSIONS; i++) {
                Session *s = &sessions[i];
                if (s->used && s->pid == pid)
                        return s;
        }
        error("session_by_pid: unknown pid %ld", (long)pid);
        session_dump();
        return NULL;
}

static int
session_window_change_req(Session *s)
{
        s->col = packet_get_int();
        s->row = packet_get_int();
        s->xpixel = packet_get_int();
        s->ypixel = packet_get_int();
        packet_check_eom();
        pty_change_window_size(s->ptyfd, s->row, s->col, s->xpixel, s->ypixel);
        return 1;
}

static int
session_pty_req(Session *s)
{
        u_int len;
        int n_bytes;

        if (no_pty_flag) {
                debug("Allocating a pty not permitted for this authentication.");
                return 0;
        }
        if (s->ttyfd != -1) {
                packet_disconnect("Protocol error: you already have a pty.");
                return 0;
        }

        s->term = packet_get_string(&len);

        if (compat20) {
                s->col = packet_get_int();
                s->row = packet_get_int();
        } else {
                s->row = packet_get_int();
                s->col = packet_get_int();
        }
        s->xpixel = packet_get_int();
        s->ypixel = packet_get_int();

        if (strcmp(s->term, "") == 0) {
                xfree(s->term);
                s->term = NULL;
        }

        /* Allocate a pty and open it. */
        debug("Allocating pty.");
        if (!PRIVSEP(pty_allocate(&s->ptyfd, &s->ttyfd, s->tty, sizeof(s->tty)))) {
                if (s->term)
                        xfree(s->term);
                s->term = NULL;
                s->ptyfd = -1;
                s->ttyfd = -1;
                error("session_pty_req: session %d alloc failed", s->self);
                return 0;
        }
        debug("session_pty_req: session %d alloc %s", s->self, s->tty);

        /* for SSH1 the tty modes length is not given */
        if (!compat20)
                n_bytes = packet_remaining();
        tty_parse_modes(s->ttyfd, &n_bytes);

        if (!use_privsep)
                pty_setowner(s->pw, s->tty);

        /* Set window size from the packet. */
        pty_change_window_size(s->ptyfd, s->row, s->col, s->xpixel, s->ypixel);

        packet_check_eom();
        session_proctitle(s);
        return 1;
}

static int
session_subsystem_req(Session *s)
{
        struct stat st;
        u_int len;
        int success = 0;
        char *cmd, *subsys = packet_get_string(&len);
        u_int i;

        packet_check_eom();
        logit("subsystem request for %.100s", subsys);

        for (i = 0; i < options.num_subsystems; i++) {
                if (strcmp(subsys, options.subsystem_name[i]) == 0) {
                        cmd = options.subsystem_command[i];
                        if (stat(cmd, &st) < 0) {
                                error("subsystem: cannot stat %s: %s", cmd,
                                    strerror(errno));
                                break;
                        }
                        debug("subsystem: exec() %s", cmd);
                        s->is_subsystem = 1;
                        do_exec(s, cmd);
                        success = 1;
                        break;
                }
        }

        if (!success)
                logit("subsystem request for %.100s failed, subsystem not found",
                    subsys);

        xfree(subsys);
        return success;
}

static int
session_x11_req(Session *s)
{
        int success;

        if (s->auth_proto != NULL || s->auth_data != NULL) {
                error("session_x11_req: session %d: "
                    "x11 forwarding already active", s->self);
                return 0;
        }
        s->single_connection = packet_get_char();
        s->auth_proto = packet_get_string(NULL);
        s->auth_data = packet_get_string(NULL);
        s->screen = packet_get_int();
        packet_check_eom();

        success = session_setup_x11fwd(s);
        if (!success) {
                xfree(s->auth_proto);
                xfree(s->auth_data);
                s->auth_proto = NULL;
                s->auth_data = NULL;
        }
        return success;
}

static int
session_shell_req(Session *s)
{
        packet_check_eom();
        do_exec(s, NULL);
        return 1;
}

static int
session_exec_req(Session *s)
{
        u_int len;
        char *command = packet_get_string(&len);
        packet_check_eom();
        do_exec(s, command);
        xfree(command);
        return 1;
}

static int
session_break_req(Session *s)
{

        packet_get_int();       /* ignored */
        packet_check_eom();

        if (s->ttyfd == -1 ||
            tcsendbreak(s->ttyfd, 0) < 0)
                return 0;
        return 1;
}

static int
session_env_req(Session *s)
{
        char *name, *val;
        u_int name_len, val_len, i;

        name = packet_get_string(&name_len);
        val = packet_get_string(&val_len);
        packet_check_eom();

        /* Don't set too many environment variables */
        if (s->num_env > 128) {
                debug2("Ignoring env request %s: too many env vars", name);
                goto fail;
        }

        for (i = 0; i < options.num_accept_env; i++) {
                if (match_pattern(name, options.accept_env[i])) {
                        debug2("Setting env %d: %s=%s", s->num_env, name, val);
                        s->env = xrealloc(s->env, sizeof(*s->env) *
                            (s->num_env + 1));
                        s->env[s->num_env].name = name;
                        s->env[s->num_env].val = val;
                        s->num_env++;
                        return (1);
                }
        }
        debug2("Ignoring env request %s: disallowed name", name);

 fail:
        xfree(name);
        xfree(val);
        return (0);
}

static int
session_auth_agent_req(Session *s)
{
        static int called = 0;
        packet_check_eom();
        if (no_agent_forwarding_flag) {
                debug("session_auth_agent_req: no_agent_forwarding_flag");
                return 0;
        }
        if (called) {
                return 0;
        } else {
                called = 1;
                return auth_input_request_forwarding(s->pw);
        }
}

int
session_input_channel_req(Channel *c, const char *rtype)
{
        int success = 0;
        Session *s;

        if ((s = session_by_channel(c->self)) == NULL) {
                logit("session_input_channel_req: no session %d req %.100s",
                    c->self, rtype);
                return 0;
        }
        debug("session_input_channel_req: session %d req %s", s->self, rtype);

        /*
         * a session is in LARVAL state until a shell, a command
         * or a subsystem is executed
         */
        if (c->type == SSH_CHANNEL_LARVAL) {
                if (strcmp(rtype, "shell") == 0) {
                        success = session_shell_req(s);
                } else if (strcmp(rtype, "exec") == 0) {
                        success = session_exec_req(s);
                } else if (strcmp(rtype, "pty-req") == 0) {
                        success =  session_pty_req(s);
                } else if (strcmp(rtype, "x11-req") == 0) {
                        success = session_x11_req(s);
                } else if (strcmp(rtype, "auth-agent-req@openssh.com") == 0) {
                        success = session_auth_agent_req(s);
                } else if (strcmp(rtype, "subsystem") == 0) {
                        success = session_subsystem_req(s);
                } else if (strcmp(rtype, "env") == 0) {
                        success = session_env_req(s);
                }
        }
        if (strcmp(rtype, "window-change") == 0) {
                success = session_window_change_req(s);
        } else if (strcmp(rtype, "break") == 0) {
                success = session_break_req(s);
        }

        return success;
}

void
session_set_fds(Session *s, int fdin, int fdout, int fderr)
{
        if (!compat20)
                fatal("session_set_fds: called for proto != 2.0");
        /*
         * now that have a child and a pipe to the child,
         * we can activate our channel and register the fd's
         */
        if (s->chanid == -1)
                fatal("no channel for session %d", s->self);
        channel_set_fds(s->chanid,
            fdout, fdin, fderr,
            fderr == -1 ? CHAN_EXTENDED_IGNORE : CHAN_EXTENDED_READ,
            1,
            CHAN_SES_WINDOW_DEFAULT);
}

/*
 * Function to perform pty cleanup. Also called if we get aborted abnormally
 * (e.g., due to a dropped connection).
 */
void
session_pty_cleanup2(Session *s)
{
        if (s == NULL) {
                error("session_pty_cleanup: no session");
                return;
        }
        if (s->ttyfd == -1)
                return;

        debug("session_pty_cleanup: session %d release %s", s->self, s->tty);

        /* Record that the user has logged out. */
        if (s->pid != 0)
                record_logout(s->pid, s->tty, s->pw->pw_name);

        /* Release the pseudo-tty. */
        if (getuid() == 0)
                pty_release(s->tty);

        /*
         * Close the server side of the socket pairs.  We must do this after
         * the pty cleanup, so that another process doesn't get this pty
         * while we're still cleaning up.
         */
        if (close(s->ptymaster) < 0)
                error("close(s->ptymaster/%d): %s", s->ptymaster, strerror(errno));

        /* unlink pty from session */
        s->ttyfd = -1;
}

void
session_pty_cleanup(Session *s)
{
        PRIVSEP(session_pty_cleanup2(s));
}

static char *
sig2name(int sig)
{
#define SSH_SIG(x) if (sig == SIG ## x) return #x
        SSH_SIG(ABRT);
        SSH_SIG(ALRM);
        SSH_SIG(FPE);
        SSH_SIG(HUP);
        SSH_SIG(ILL);
        SSH_SIG(INT);
        SSH_SIG(KILL);
        SSH_SIG(PIPE);
        SSH_SIG(QUIT);
        SSH_SIG(SEGV);
        SSH_SIG(TERM);
        SSH_SIG(USR1);
        SSH_SIG(USR2);
#undef  SSH_SIG
        return "SIG@openssh.com";
}

static void
session_close_x11(int id)
{
        Channel *c;

        if ((c = channel_by_id(id)) == NULL) {
                debug("session_close_x11: x11 channel %d missing", id);
        } else {
                /* Detach X11 listener */
                debug("session_close_x11: detach x11 channel %d", id);
                channel_cancel_cleanup(id);
                if (c->ostate != CHAN_OUTPUT_CLOSED)
                        chan_mark_dead(c);
        }
}

static void
session_close_single_x11(int id, void *arg)
{
        Session *s;
        u_int i;

        debug3("session_close_single_x11: channel %d", id);
        channel_cancel_cleanup(id);
        if ((s  = session_by_x11_channel(id)) == NULL)
                fatal("session_close_single_x11: no x11 channel %d", id);
        for (i = 0; s->x11_chanids[i] != -1; i++) {
                debug("session_close_single_x11: session %d: "
                    "closing channel %d", s->self, s->x11_chanids[i]);
                /*
                 * The channel "id" is already closing, but make sure we
                 * close all of its siblings.
                 */
                if (s->x11_chanids[i] != id)
                        session_close_x11(s->x11_chanids[i]);
        }
        xfree(s->x11_chanids);
        s->x11_chanids = NULL;
        if (s->display) {
                xfree(s->display);
                s->display = NULL;
        }
        if (s->auth_proto) {
                xfree(s->auth_proto);
                s->auth_proto = NULL;
        }
        if (s->auth_data) {
                xfree(s->auth_data);
                s->auth_data = NULL;
        }
        if (s->auth_display) {
                xfree(s->auth_display);
                s->auth_display = NULL;
        }
}

static void
session_exit_message(Session *s, int status)
{
        Channel *c;

        if ((c = channel_lookup(s->chanid)) == NULL)
                fatal("session_exit_message: session %d: no channel %d",
                    s->self, s->chanid);
        debug("session_exit_message: session %d channel %d pid %ld",
            s->self, s->chanid, (long)s->pid);

        if (WIFEXITED(status)) {
                channel_request_start(s->chanid, "exit-status", 0);
                packet_put_int(WEXITSTATUS(status));
                packet_send();
        } else if (WIFSIGNALED(status)) {
                channel_request_start(s->chanid, "exit-signal", 0);
                packet_put_cstring(sig2name(WTERMSIG(status)));
#ifdef WCOREDUMP
                packet_put_char(WCOREDUMP(status));
#else /* WCOREDUMP */
                packet_put_char(0);
#endif /* WCOREDUMP */
                packet_put_cstring("");
                packet_put_cstring("");
                packet_send();
        } else {
                /* Some weird exit cause.  Just exit. */
                packet_disconnect("wait returned status %04x.", status);
        }

        /* disconnect channel */
        debug("session_exit_message: release channel %d", s->chanid);

        /*
         * Adjust cleanup callback attachment to send close messages when
         * the channel gets EOF. The session will be then be closed 
         * by session_close_by_channel when the childs close their fds.
         */
        channel_register_cleanup(c->self, session_close_by_channel, 1);

        /*
         * emulate a write failure with 'chan_write_failed', nobody will be
         * interested in data we write.
         * Note that we must not call 'chan_read_failed', since there could
         * be some more data waiting in the pipe.
         */
        if (c->ostate != CHAN_OUTPUT_CLOSED)
                chan_write_failed(c);
}

void
session_close(Session *s)
{
        u_int i;

        debug("session_close: session %d pid %ld", s->self, (long)s->pid);
        if (s->ttyfd != -1)
                session_pty_cleanup(s);
        if (s->term)
                xfree(s->term);
        if (s->display)
                xfree(s->display);
        if (s->x11_chanids)
                xfree(s->x11_chanids);
        if (s->auth_display)
                xfree(s->auth_display);
        if (s->auth_data)
                xfree(s->auth_data);
        if (s->auth_proto)
                xfree(s->auth_proto);
        s->used = 0;
        for (i = 0; i < s->num_env; i++) {
                xfree(s->env[i].name);
                xfree(s->env[i].val);
        }
        if (s->env != NULL)
                xfree(s->env);
        session_proctitle(s);
}

void
session_close_by_pid(pid_t pid, int status)
{
        Session *s = session_by_pid(pid);
        if (s == NULL) {
                debug("session_close_by_pid: no session for pid %ld",
                    (long)pid);
                return;
        }
        if (s->chanid != -1)
                session_exit_message(s, status);
        if (s->ttyfd != -1)
                session_pty_cleanup(s);
        s->pid = 0;
}

/*
 * this is called when a channel dies before
 * the session 'child' itself dies
 */
void
session_close_by_channel(int id, void *arg)
{
        Session *s = session_by_channel(id);
        u_int i;

        if (s == NULL) {
                debug("session_close_by_channel: no session for id %d", id);
                return;
        }
        debug("session_close_by_channel: channel %d child %ld",
            id, (long)s->pid);
        if (s->pid != 0) {
                debug("session_close_by_channel: channel %d: has child", id);
                /*
                 * delay detach of session, but release pty, since
                 * the fd's to the child are already closed
                 */
                if (s->ttyfd != -1)
                        session_pty_cleanup(s);
                return;
        }
        /* detach by removing callback */
        channel_cancel_cleanup(s->chanid);

        /* Close any X11 listeners associated with this session */
        if (s->x11_chanids != NULL) {
                for (i = 0; s->x11_chanids[i] != -1; i++) {
                        session_close_x11(s->x11_chanids[i]);
                        s->x11_chanids[i] = -1;
                }
        }

        s->chanid = -1;
        session_close(s);
}

void
session_destroy_all(void (*closefunc)(Session *))
{
        int i;
        for (i = 0; i < MAX_SESSIONS; i++) {
                Session *s = &sessions[i];
                if (s->used) {
                        if (closefunc != NULL)
                                closefunc(s);
                        else
                                session_close(s);
                }
        }
}

static char *
session_tty_list(void)
{
        static char buf[1024];
        int i;
        char *cp;

        buf[0] = '\0';
        for (i = 0; i < MAX_SESSIONS; i++) {
                Session *s = &sessions[i];
                if (s->used && s->ttyfd != -1) {

                        if (strncmp(s->tty, "/dev/", 5) != 0) {
                                cp = strrchr(s->tty, '/');
                                cp = (cp == NULL) ? s->tty : cp + 1;
                        } else
                                cp = s->tty + 5;

                        if (buf[0] != '\0')
                                strlcat(buf, ",", sizeof buf);
                        strlcat(buf, cp, sizeof buf);
                }
        }
        if (buf[0] == '\0')
                strlcpy(buf, "notty", sizeof buf);
        return buf;
}

void
session_proctitle(Session *s)
{
        if (s->pw == NULL)
                error("no user for session %d", s->self);
        else
                setproctitle("%s@%s", s->pw->pw_name, session_tty_list());
}

int
session_setup_x11fwd(Session *s)
{
        struct stat st;
        char display[512], auth_display[512];
        char hostname[MAXHOSTNAMELEN];
        u_int i;

        if (no_x11_forwarding_flag) {
                packet_send_debug("X11 forwarding disabled in user configuration file.");
                return 0;
        }
        if (!options.x11_forwarding) {
                debug("X11 forwarding disabled in server configuration file.");
                return 0;
        }
        if (!options.xauth_location ||
            (stat(options.xauth_location, &st) == -1)) {
                packet_send_debug("No xauth program; cannot forward with spoofing.");
                return 0;
        }
        if (options.use_login) {
                packet_send_debug("X11 forwarding disabled; "
                    "not compatible with UseLogin=yes.");
                return 0;
        }
        if (s->display != NULL) {
                debug("X11 display already set.");
                return 0;
        }
        if (x11_create_display_inet(options.x11_display_offset,
            options.x11_use_localhost, s->single_connection,
            &s->display_number, &s->x11_chanids) == -1) {
                debug("x11_create_display_inet failed.");
                return 0;
        }
        for (i = 0; s->x11_chanids[i] != -1; i++) {
                channel_register_cleanup(s->x11_chanids[i],
                    session_close_single_x11, 0);
        }

        /* Set up a suitable value for the DISPLAY variable. */
        if (gethostname(hostname, sizeof(hostname)) < 0)
                fatal("gethostname: %.100s", strerror(errno));
        /*
         * auth_display must be used as the displayname when the
         * authorization entry is added with xauth(1).  This will be
         * different than the DISPLAY string for localhost displays.
         */
        if (options.x11_use_localhost) {
                snprintf(display, sizeof display, "localhost:%u.%u",
                    s->display_number, s->screen);
                snprintf(auth_display, sizeof auth_display, "unix:%u.%u",
                    s->display_number, s->screen);
                s->display = xstrdup(display);
                s->auth_display = xstrdup(auth_display);
        } else {
#ifdef IPADDR_IN_DISPLAY
                struct hostent *he;
                struct in_addr my_addr;

                he = gethostbyname(hostname);
                if (he == NULL) {
                        error("Can't get IP address for X11 DISPLAY.");
                        packet_send_debug("Can't get IP address for X11 DISPLAY.");
                        return 0;
                }
                memcpy(&my_addr, he->h_addr_list[0], sizeof(struct in_addr));
                snprintf(display, sizeof display, "%.50s:%u.%u", inet_ntoa(my_addr),
                    s->display_number, s->screen);
#else
                snprintf(display, sizeof display, "%.400s:%u.%u", hostname,
                    s->display_number, s->screen);
#endif
                s->display = xstrdup(display);
                s->auth_display = xstrdup(display);
        }

        return 1;
}

static void
do_authenticated2(Authctxt *authctxt)
{
        server_loop2(authctxt);
}

void
do_cleanup(Authctxt *authctxt)
{
        static int called = 0;

        debug("do_cleanup");

        /* no cleanup if we're in the child for login shell */
        if (is_child)
                return;

        /* avoid double cleanup */
        if (called)
                return;
        called = 1;

        if (authctxt == NULL)
                return;
#ifdef KRB5
        if (options.kerberos_ticket_cleanup &&
            authctxt->krb5_ctx)
                krb5_cleanup_proc(authctxt);
#endif

#ifdef GSSAPI
        if (compat20 && options.gss_cleanup_creds)
                ssh_gssapi_cleanup_creds();
#endif

#ifdef USE_PAM
        if (options.use_pam) {
                sshpam_cleanup();
                sshpam_thread_cleanup();
        }
#endif

        /* remove agent socket */
        auth_sock_cleanup_proc(authctxt->pw);

        /*
         * Cleanup ptys/utmp only if privsep is disabled,
         * or if running in monitor.
         */
        if (!use_privsep || mm_is_monitor())
                session_destroy_all(session_pty_cleanup2);
}