- markus@cvs.openbsd.org 2006/10/11 12:38:03

[openssh-git.git] / serverloop.c

/* $OpenBSD: serverloop.c,v 1.145 2006/10/11 12:38:03 markus Exp $ */
/*
 * Author: Tatu Ylonen <ylo@cs.hut.fi>
 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
 *                    All rights reserved
 * Server main loop for handling the interactive session.
 *
 * 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"

#include <sys/types.h>
#include <sys/param.h>
#include <sys/wait.h>
#include <sys/socket.h>
#ifdef HAVE_SYS_TIME_H
# include <sys/time.h>
#endif

#include <netinet/in.h>

#include <errno.h>
#include <fcntl.h>
#include <pwd.h>
#include <signal.h>
#include <string.h>
#include <termios.h>
#include <unistd.h>
#include <stdarg.h>

#include "xmalloc.h"
#include "packet.h"
#include "buffer.h"
#include "log.h"
#include "servconf.h"
#include "canohost.h"
#include "sshpty.h"
#include "channels.h"
#include "compat.h"
#include "ssh1.h"
#include "ssh2.h"
#include "key.h"
#include "cipher.h"
#include "kex.h"
#include "hostfile.h"
#include "auth.h"
#include "session.h"
#include "dispatch.h"
#include "auth-options.h"
#include "serverloop.h"
#include "misc.h"

extern ServerOptions options;

/* XXX */
extern Kex *xxx_kex;
extern Authctxt *the_authctxt;
extern int use_privsep;

static Buffer stdin_buffer;     /* Buffer for stdin data. */
static Buffer stdout_buffer;    /* Buffer for stdout data. */
static Buffer stderr_buffer;    /* Buffer for stderr data. */
static int fdin;                /* Descriptor for stdin (for writing) */
static int fdout;               /* Descriptor for stdout (for reading);
                                   May be same number as fdin. */
static int fderr;               /* Descriptor for stderr.  May be -1. */
static long stdin_bytes = 0;    /* Number of bytes written to stdin. */
static long stdout_bytes = 0;   /* Number of stdout bytes sent to client. */
static long stderr_bytes = 0;   /* Number of stderr bytes sent to client. */
static long fdout_bytes = 0;    /* Number of stdout bytes read from program. */
static int stdin_eof = 0;       /* EOF message received from client. */
static int fdout_eof = 0;       /* EOF encountered reading from fdout. */
static int fderr_eof = 0;       /* EOF encountered readung from fderr. */
static int fdin_is_tty = 0;     /* fdin points to a tty. */
static int connection_in;       /* Connection to client (input). */
static int connection_out;      /* Connection to client (output). */
static int connection_closed = 0;       /* Connection to client closed. */
static u_int buffer_high;       /* "Soft" max buffer size. */
static int client_alive_timeouts = 0;

/*
 * This SIGCHLD kludge is used to detect when the child exits.  The server
 * will exit after that, as soon as forwarded connections have terminated.
 */

static volatile sig_atomic_t child_terminated = 0;      /* The child has terminated. */

/* Cleanup on signals (!use_privsep case only) */
static volatile sig_atomic_t received_sigterm = 0;

/* prototypes */
static void server_init_dispatch(void);

/*
 * we write to this pipe if a SIGCHLD is caught in order to avoid
 * the race between select() and child_terminated
 */
static int notify_pipe[2];
static void
notify_setup(void)
{
        if (pipe(notify_pipe) < 0) {
                error("pipe(notify_pipe) failed %s", strerror(errno));
        } else if ((fcntl(notify_pipe[0], F_SETFD, 1) == -1) ||
            (fcntl(notify_pipe[1], F_SETFD, 1) == -1)) {
                error("fcntl(notify_pipe, F_SETFD) failed %s", strerror(errno));
                close(notify_pipe[0]);
                close(notify_pipe[1]);
        } else {
                set_nonblock(notify_pipe[0]);
                set_nonblock(notify_pipe[1]);
                return;
        }
        notify_pipe[0] = -1;    /* read end */
        notify_pipe[1] = -1;    /* write end */
}
static void
notify_parent(void)
{
        if (notify_pipe[1] != -1)
                write(notify_pipe[1], "", 1);
}
static void
notify_prepare(fd_set *readset)
{
        if (notify_pipe[0] != -1)
                FD_SET(notify_pipe[0], readset);
}
static void
notify_done(fd_set *readset)
{
        char c;

        if (notify_pipe[0] != -1 && FD_ISSET(notify_pipe[0], readset))
                while (read(notify_pipe[0], &c, 1) != -1)
                        debug2("notify_done: reading");
}

/*ARGSUSED*/
static void
sigchld_handler(int sig)
{
        int save_errno = errno;
        child_terminated = 1;
#ifndef _UNICOS
        mysignal(SIGCHLD, sigchld_handler);
#endif
        notify_parent();
        errno = save_errno;
}

/*ARGSUSED*/
static void
sigterm_handler(int sig)
{
        received_sigterm = sig;
}

/*
 * Make packets from buffered stderr data, and buffer it for sending
 * to the client.
 */
static void
make_packets_from_stderr_data(void)
{
        u_int len;

        /* Send buffered stderr data to the client. */
        while (buffer_len(&stderr_buffer) > 0 &&
            packet_not_very_much_data_to_write()) {
                len = buffer_len(&stderr_buffer);
                if (packet_is_interactive()) {
                        if (len > 512)
                                len = 512;
                } else {
                        /* Keep the packets at reasonable size. */
                        if (len > packet_get_maxsize())
                                len = packet_get_maxsize();
                }
                packet_start(SSH_SMSG_STDERR_DATA);
                packet_put_string(buffer_ptr(&stderr_buffer), len);
                packet_send();
                buffer_consume(&stderr_buffer, len);
                stderr_bytes += len;
        }
}

/*
 * Make packets from buffered stdout data, and buffer it for sending to the
 * client.
 */
static void
make_packets_from_stdout_data(void)
{
        u_int len;

        /* Send buffered stdout data to the client. */
        while (buffer_len(&stdout_buffer) > 0 &&
            packet_not_very_much_data_to_write()) {
                len = buffer_len(&stdout_buffer);
                if (packet_is_interactive()) {
                        if (len > 512)
                                len = 512;
                } else {
                        /* Keep the packets at reasonable size. */
                        if (len > packet_get_maxsize())
                                len = packet_get_maxsize();
                }
                packet_start(SSH_SMSG_STDOUT_DATA);
                packet_put_string(buffer_ptr(&stdout_buffer), len);
                packet_send();
                buffer_consume(&stdout_buffer, len);
                stdout_bytes += len;
        }
}

static void
client_alive_check(void)
{
        int channel_id;

        /* timeout, check to see how many we have had */
        if (++client_alive_timeouts > options.client_alive_count_max) {
                logit("Timeout, client not responding.");
                cleanup_exit(255);
        }

        /*
         * send a bogus global/channel request with "wantreply",
         * we should get back a failure
         */
        if ((channel_id = channel_find_open()) == -1) {
                packet_start(SSH2_MSG_GLOBAL_REQUEST);
                packet_put_cstring("keepalive@openssh.com");
                packet_put_char(1);     /* boolean: want reply */
        } else {
                channel_request_start(channel_id, "keepalive@openssh.com", 1);
        }
        packet_send();
}

/*
 * Sleep in select() until we can do something.  This will initialize the
 * select masks.  Upon return, the masks will indicate which descriptors
 * have data or can accept data.  Optionally, a maximum time can be specified
 * for the duration of the wait (0 = infinite).
 */
static void
wait_until_can_do_something(fd_set **readsetp, fd_set **writesetp, int *maxfdp,
    u_int *nallocp, u_int max_time_milliseconds)
{
        struct timeval tv, *tvp;
        int ret;
        int client_alive_scheduled = 0;

        /*
         * if using client_alive, set the max timeout accordingly,
         * and indicate that this particular timeout was for client
         * alive by setting the client_alive_scheduled flag.
         *
         * this could be randomized somewhat to make traffic
         * analysis more difficult, but we're not doing it yet.
         */
        if (compat20 &&
            max_time_milliseconds == 0 && options.client_alive_interval) {
                client_alive_scheduled = 1;
                max_time_milliseconds = options.client_alive_interval * 1000;
        }

        /* Allocate and update select() masks for channel descriptors. */
        channel_prepare_select(readsetp, writesetp, maxfdp, nallocp, 0);

        if (compat20) {
#if 0
                /* wrong: bad condition XXX */
                if (channel_not_very_much_buffered_data())
#endif
                FD_SET(connection_in, *readsetp);
        } else {
                /*
                 * Read packets from the client unless we have too much
                 * buffered stdin or channel data.
                 */
                if (buffer_len(&stdin_buffer) < buffer_high &&
                    channel_not_very_much_buffered_data())
                        FD_SET(connection_in, *readsetp);
                /*
                 * If there is not too much data already buffered going to
                 * the client, try to get some more data from the program.
                 */
                if (packet_not_very_much_data_to_write()) {
                        if (!fdout_eof)
                                FD_SET(fdout, *readsetp);
                        if (!fderr_eof)
                                FD_SET(fderr, *readsetp);
                }
                /*
                 * If we have buffered data, try to write some of that data
                 * to the program.
                 */
                if (fdin != -1 && buffer_len(&stdin_buffer) > 0)
                        FD_SET(fdin, *writesetp);
        }
        notify_prepare(*readsetp);

        /*
         * If we have buffered packet data going to the client, mark that
         * descriptor.
         */
        if (packet_have_data_to_write())
                FD_SET(connection_out, *writesetp);

        /*
         * If child has terminated and there is enough buffer space to read
         * from it, then read as much as is available and exit.
         */
        if (child_terminated && packet_not_very_much_data_to_write())
                if (max_time_milliseconds == 0 || client_alive_scheduled)
                        max_time_milliseconds = 100;

        if (max_time_milliseconds == 0)
                tvp = NULL;
        else {
                tv.tv_sec = max_time_milliseconds / 1000;
                tv.tv_usec = 1000 * (max_time_milliseconds % 1000);
                tvp = &tv;
        }

        /* Wait for something to happen, or the timeout to expire. */
        ret = select((*maxfdp)+1, *readsetp, *writesetp, NULL, tvp);

        if (ret == -1) {
                memset(*readsetp, 0, *nallocp);
                memset(*writesetp, 0, *nallocp);
                if (errno != EINTR)
                        error("select: %.100s", strerror(errno));
        } else if (ret == 0 && client_alive_scheduled)
                client_alive_check();

        notify_done(*readsetp);
}

/*
 * Processes input from the client and the program.  Input data is stored
 * in buffers and processed later.
 */
static void
process_input(fd_set *readset)
{
        int len;
        char buf[16384];

        /* Read and buffer any input data from the client. */
        if (FD_ISSET(connection_in, readset)) {
                len = read(connection_in, buf, sizeof(buf));
                if (len == 0) {
                        verbose("Connection closed by %.100s",
                            get_remote_ipaddr());
                        connection_closed = 1;
                        if (compat20)
                                return;
                        cleanup_exit(255);
                } else if (len < 0) {
                        if (errno != EINTR && errno != EAGAIN) {
                                verbose("Read error from remote host "
                                    "%.100s: %.100s",
                                    get_remote_ipaddr(), strerror(errno));
                                cleanup_exit(255);
                        }
                } else {
                        /* Buffer any received data. */
                        packet_process_incoming(buf, len);
                }
        }
        if (compat20)
                return;

        /* Read and buffer any available stdout data from the program. */
        if (!fdout_eof && FD_ISSET(fdout, readset)) {
                errno = 0;
                len = read(fdout, buf, sizeof(buf));
                if (len < 0 && (errno == EINTR || errno == EAGAIN)) {
                        /* do nothing */
#ifndef PTY_ZEROREAD
                } else if (len <= 0) {
#else
                } else if ((!isatty(fdout) && len <= 0) ||
                    (isatty(fdout) && (len < 0 || (len == 0 && errno != 0)))) {
#endif
                        fdout_eof = 1;
                } else {
                        buffer_append(&stdout_buffer, buf, len);
                        fdout_bytes += len;
                }
        }
        /* Read and buffer any available stderr data from the program. */
        if (!fderr_eof && FD_ISSET(fderr, readset)) {
                errno = 0;
                len = read(fderr, buf, sizeof(buf));
                if (len < 0 && (errno == EINTR || errno == EAGAIN)) {
                        /* do nothing */
#ifndef PTY_ZEROREAD
                } else if (len <= 0) {
#else
                } else if ((!isatty(fderr) && len <= 0) ||
                    (isatty(fderr) && (len < 0 || (len == 0 && errno != 0)))) {
#endif
                        fderr_eof = 1;
                } else {
                        buffer_append(&stderr_buffer, buf, len);
                }
        }
}

/*
 * Sends data from internal buffers to client program stdin.
 */
static void
process_output(fd_set *writeset)
{
        struct termios tio;
        u_char *data;
        u_int dlen;
        int len;

        /* Write buffered data to program stdin. */
        if (!compat20 && fdin != -1 && FD_ISSET(fdin, writeset)) {
                data = buffer_ptr(&stdin_buffer);
                dlen = buffer_len(&stdin_buffer);
                len = write(fdin, data, dlen);
                if (len < 0 && (errno == EINTR || errno == EAGAIN)) {
                        /* do nothing */
                } else if (len <= 0) {
                        if (fdin != fdout)
                                close(fdin);
                        else
                                shutdown(fdin, SHUT_WR); /* We will no longer send. */
                        fdin = -1;
                } else {
                        /* Successful write. */
                        if (fdin_is_tty && dlen >= 1 && data[0] != '\r' &&
                            tcgetattr(fdin, &tio) == 0 &&
                            !(tio.c_lflag & ECHO) && (tio.c_lflag & ICANON)) {
                                /*
                                 * Simulate echo to reduce the impact of
                                 * traffic analysis
                                 */
                                packet_send_ignore(len);
                                packet_send();
                        }
                        /* Consume the data from the buffer. */
                        buffer_consume(&stdin_buffer, len);
                        /* Update the count of bytes written to the program. */
                        stdin_bytes += len;
                }
        }
        /* Send any buffered packet data to the client. */
        if (FD_ISSET(connection_out, writeset))
                packet_write_poll();
}

/*
 * Wait until all buffered output has been sent to the client.
 * This is used when the program terminates.
 */
static void
drain_output(void)
{
        /* Send any buffered stdout data to the client. */
        if (buffer_len(&stdout_buffer) > 0) {
                packet_start(SSH_SMSG_STDOUT_DATA);
                packet_put_string(buffer_ptr(&stdout_buffer),
                                  buffer_len(&stdout_buffer));
                packet_send();
                /* Update the count of sent bytes. */
                stdout_bytes += buffer_len(&stdout_buffer);
        }
        /* Send any buffered stderr data to the client. */
        if (buffer_len(&stderr_buffer) > 0) {
                packet_start(SSH_SMSG_STDERR_DATA);
                packet_put_string(buffer_ptr(&stderr_buffer),
                                  buffer_len(&stderr_buffer));
                packet_send();
                /* Update the count of sent bytes. */
                stderr_bytes += buffer_len(&stderr_buffer);
        }
        /* Wait until all buffered data has been written to the client. */
        packet_write_wait();
}

static void
process_buffered_input_packets(void)
{
        dispatch_run(DISPATCH_NONBLOCK, NULL, compat20 ? xxx_kex : NULL);
}

/*
 * Performs the interactive session.  This handles data transmission between
 * the client and the program.  Note that the notion of stdin, stdout, and
 * stderr in this function is sort of reversed: this function writes to
 * stdin (of the child program), and reads from stdout and stderr (of the
 * child program).
 */
void
server_loop(pid_t pid, int fdin_arg, int fdout_arg, int fderr_arg)
{
        fd_set *readset = NULL, *writeset = NULL;
        int max_fd = 0;
        u_int nalloc = 0;
        int wait_status;        /* Status returned by wait(). */
        pid_t wait_pid;         /* pid returned by wait(). */
        int waiting_termination = 0;    /* Have displayed waiting close message. */
        u_int max_time_milliseconds;
        u_int previous_stdout_buffer_bytes;
        u_int stdout_buffer_bytes;
        int type;

        debug("Entering interactive session.");

        /* Initialize the SIGCHLD kludge. */
        child_terminated = 0;
        mysignal(SIGCHLD, sigchld_handler);

        if (!use_privsep) {
                signal(SIGTERM, sigterm_handler);
                signal(SIGINT, sigterm_handler);
                signal(SIGQUIT, sigterm_handler);
        }

        /* Initialize our global variables. */
        fdin = fdin_arg;
        fdout = fdout_arg;
        fderr = fderr_arg;

        /* nonblocking IO */
        set_nonblock(fdin);
        set_nonblock(fdout);
        /* we don't have stderr for interactive terminal sessions, see below */
        if (fderr != -1)
                set_nonblock(fderr);

        if (!(datafellows & SSH_BUG_IGNOREMSG) && isatty(fdin))
                fdin_is_tty = 1;

        connection_in = packet_get_connection_in();
        connection_out = packet_get_connection_out();

        notify_setup();

        previous_stdout_buffer_bytes = 0;

        /* Set approximate I/O buffer size. */
        if (packet_is_interactive())
                buffer_high = 4096;
        else
                buffer_high = 64 * 1024;

#if 0
        /* Initialize max_fd to the maximum of the known file descriptors. */
        max_fd = MAX(connection_in, connection_out);
        max_fd = MAX(max_fd, fdin);
        max_fd = MAX(max_fd, fdout);
        if (fderr != -1)
                max_fd = MAX(max_fd, fderr);
#endif

        /* Initialize Initialize buffers. */
        buffer_init(&stdin_buffer);
        buffer_init(&stdout_buffer);
        buffer_init(&stderr_buffer);

        /*
         * If we have no separate fderr (which is the case when we have a pty
         * - there we cannot make difference between data sent to stdout and
         * stderr), indicate that we have seen an EOF from stderr.  This way
         * we don't need to check the descriptor everywhere.
         */
        if (fderr == -1)
                fderr_eof = 1;

        server_init_dispatch();

        /* Main loop of the server for the interactive session mode. */
        for (;;) {

                /* Process buffered packets from the client. */
                process_buffered_input_packets();

                /*
                 * If we have received eof, and there is no more pending
                 * input data, cause a real eof by closing fdin.
                 */
                if (stdin_eof && fdin != -1 && buffer_len(&stdin_buffer) == 0) {
                        if (fdin != fdout)
                                close(fdin);
                        else
                                shutdown(fdin, SHUT_WR); /* We will no longer send. */
                        fdin = -1;
                }
                /* Make packets from buffered stderr data to send to the client. */
                make_packets_from_stderr_data();

                /*
                 * Make packets from buffered stdout data to send to the
                 * client. If there is very little to send, this arranges to
                 * not send them now, but to wait a short while to see if we
                 * are getting more data. This is necessary, as some systems
                 * wake up readers from a pty after each separate character.
                 */
                max_time_milliseconds = 0;
                stdout_buffer_bytes = buffer_len(&stdout_buffer);
                if (stdout_buffer_bytes != 0 && stdout_buffer_bytes < 256 &&
                    stdout_buffer_bytes != previous_stdout_buffer_bytes) {
                        /* try again after a while */
                        max_time_milliseconds = 10;
                } else {
                        /* Send it now. */
                        make_packets_from_stdout_data();
                }
                previous_stdout_buffer_bytes = buffer_len(&stdout_buffer);

                /* Send channel data to the client. */
                if (packet_not_very_much_data_to_write())
                        channel_output_poll();

                /*
                 * Bail out of the loop if the program has closed its output
                 * descriptors, and we have no more data to send to the
                 * client, and there is no pending buffered data.
                 */
                if (fdout_eof && fderr_eof && !packet_have_data_to_write() &&
                    buffer_len(&stdout_buffer) == 0 && buffer_len(&stderr_buffer) == 0) {
                        if (!channel_still_open())
                                break;
                        if (!waiting_termination) {
                                const char *s = "Waiting for forwarded connections to terminate...\r\n";
                                char *cp;
                                waiting_termination = 1;
                                buffer_append(&stderr_buffer, s, strlen(s));

                                /* Display list of open channels. */
                                cp = channel_open_message();
                                buffer_append(&stderr_buffer, cp, strlen(cp));
                                xfree(cp);
                        }
                }
                max_fd = MAX(connection_in, connection_out);
                max_fd = MAX(max_fd, fdin);
                max_fd = MAX(max_fd, fdout);
                max_fd = MAX(max_fd, fderr);
                max_fd = MAX(max_fd, notify_pipe[0]);

                /* Sleep in select() until we can do something. */
                wait_until_can_do_something(&readset, &writeset, &max_fd,
                    &nalloc, max_time_milliseconds);

                if (received_sigterm) {
                        logit("Exiting on signal %d", received_sigterm);
                        /* Clean up sessions, utmp, etc. */
                        cleanup_exit(255);
                }

                /* Process any channel events. */
                channel_after_select(readset, writeset);

                /* Process input from the client and from program stdout/stderr. */
                process_input(readset);

                /* Process output to the client and to program stdin. */
                process_output(writeset);
        }
        if (readset)
                xfree(readset);
        if (writeset)
                xfree(writeset);

        /* Cleanup and termination code. */

        /* Wait until all output has been sent to the client. */
        drain_output();

        debug("End of interactive session; stdin %ld, stdout (read %ld, sent %ld), stderr %ld bytes.",
            stdin_bytes, fdout_bytes, stdout_bytes, stderr_bytes);

        /* Free and clear the buffers. */
        buffer_free(&stdin_buffer);
        buffer_free(&stdout_buffer);
        buffer_free(&stderr_buffer);

        /* Close the file descriptors. */
        if (fdout != -1)
                close(fdout);
        fdout = -1;
        fdout_eof = 1;
        if (fderr != -1)
                close(fderr);
        fderr = -1;
        fderr_eof = 1;
        if (fdin != -1)
                close(fdin);
        fdin = -1;

        channel_free_all();

        /* We no longer want our SIGCHLD handler to be called. */
        mysignal(SIGCHLD, SIG_DFL);

        while ((wait_pid = waitpid(-1, &wait_status, 0)) < 0)
                if (errno != EINTR)
                        packet_disconnect("wait: %.100s", strerror(errno));
        if (wait_pid != pid)
                error("Strange, wait returned pid %ld, expected %ld",
                    (long)wait_pid, (long)pid);

        /* Check if it exited normally. */
        if (WIFEXITED(wait_status)) {
                /* Yes, normal exit.  Get exit status and send it to the client. */
                debug("Command exited with status %d.", WEXITSTATUS(wait_status));
                packet_start(SSH_SMSG_EXITSTATUS);
                packet_put_int(WEXITSTATUS(wait_status));
                packet_send();
                packet_write_wait();

                /*
                 * Wait for exit confirmation.  Note that there might be
                 * other packets coming before it; however, the program has
                 * already died so we just ignore them.  The client is
                 * supposed to respond with the confirmation when it receives
                 * the exit status.
                 */
                do {
                        type = packet_read();
                }
                while (type != SSH_CMSG_EXIT_CONFIRMATION);

                debug("Received exit confirmation.");
                return;
        }
        /* Check if the program terminated due to a signal. */
        if (WIFSIGNALED(wait_status))
                packet_disconnect("Command terminated on signal %d.",
                                  WTERMSIG(wait_status));

        /* Some weird exit cause.  Just exit. */
        packet_disconnect("wait returned status %04x.", wait_status);
        /* NOTREACHED */
}

static void
collect_children(void)
{
        pid_t pid;
        sigset_t oset, nset;
        int status;

        /* block SIGCHLD while we check for dead children */
        sigemptyset(&nset);
        sigaddset(&nset, SIGCHLD);
        sigprocmask(SIG_BLOCK, &nset, &oset);
        if (child_terminated) {
                debug("Received SIGCHLD.");
                while ((pid = waitpid(-1, &status, WNOHANG)) > 0 ||
                    (pid < 0 && errno == EINTR))
                        if (pid > 0)
                                session_close_by_pid(pid, status);
                child_terminated = 0;
        }
        sigprocmask(SIG_SETMASK, &oset, NULL);
}

void
server_loop2(Authctxt *authctxt)
{
        fd_set *readset = NULL, *writeset = NULL;
        int rekeying = 0, max_fd, nalloc = 0;

        debug("Entering interactive session for SSH2.");

        mysignal(SIGCHLD, sigchld_handler);
        child_terminated = 0;
        connection_in = packet_get_connection_in();
        connection_out = packet_get_connection_out();

        if (!use_privsep) {
                signal(SIGTERM, sigterm_handler);
                signal(SIGINT, sigterm_handler);
                signal(SIGQUIT, sigterm_handler);
        }

        notify_setup();

        max_fd = MAX(connection_in, connection_out);
        max_fd = MAX(max_fd, notify_pipe[0]);

        server_init_dispatch();

        for (;;) {
                process_buffered_input_packets();

                rekeying = (xxx_kex != NULL && !xxx_kex->done);

                if (!rekeying && packet_not_very_much_data_to_write())
                        channel_output_poll();
                wait_until_can_do_something(&readset, &writeset, &max_fd,
                    &nalloc, 0);

                if (received_sigterm) {
                        logit("Exiting on signal %d", received_sigterm);
                        /* Clean up sessions, utmp, etc. */
                        cleanup_exit(255);
                }

                collect_children();
                if (!rekeying) {
                        channel_after_select(readset, writeset);
                        if (packet_need_rekeying()) {
                                debug("need rekeying");
                                xxx_kex->done = 0;
                                kex_send_kexinit(xxx_kex);
                        }
                }
                process_input(readset);
                if (connection_closed)
                        break;
                process_output(writeset);
        }
        collect_children();

        if (readset)
                xfree(readset);
        if (writeset)
                xfree(writeset);

        /* free all channels, no more reads and writes */
        channel_free_all();

        /* free remaining sessions, e.g. remove wtmp entries */
        session_destroy_all(NULL);
}

static void
server_input_keep_alive(int type, u_int32_t seq, void *ctxt)
{
        debug("Got %d/%u for keepalive", type, seq);
        /*
         * reset timeout, since we got a sane answer from the client.
         * even if this was generated by something other than
         * the bogus CHANNEL_REQUEST we send for keepalives.
         */
        client_alive_timeouts = 0;
}

static void
server_input_stdin_data(int type, u_int32_t seq, void *ctxt)
{
        char *data;
        u_int data_len;

        /* Stdin data from the client.  Append it to the buffer. */
        /* Ignore any data if the client has closed stdin. */
        if (fdin == -1)
                return;
        data = packet_get_string(&data_len);
        packet_check_eom();
        buffer_append(&stdin_buffer, data, data_len);
        memset(data, 0, data_len);
        xfree(data);
}

static void
server_input_eof(int type, u_int32_t seq, void *ctxt)
{
        /*
         * Eof from the client.  The stdin descriptor to the
         * program will be closed when all buffered data has
         * drained.
         */
        debug("EOF received for stdin.");
        packet_check_eom();
        stdin_eof = 1;
}

static void
server_input_window_size(int type, u_int32_t seq, void *ctxt)
{
        u_int row = packet_get_int();
        u_int col = packet_get_int();
        u_int xpixel = packet_get_int();
        u_int ypixel = packet_get_int();

        debug("Window change received.");
        packet_check_eom();
        if (fdin != -1)
                pty_change_window_size(fdin, row, col, xpixel, ypixel);
}

static Channel *
server_request_direct_tcpip(void)
{
        Channel *c;
        int sock;
        char *target, *originator;
        int target_port, originator_port;

        target = packet_get_string(NULL);
        target_port = packet_get_int();
        originator = packet_get_string(NULL);
        originator_port = packet_get_int();
        packet_check_eom();

        debug("server_request_direct_tcpip: originator %s port %d, target %s port %d",
            originator, originator_port, target, target_port);

        /* XXX check permission */
        sock = channel_connect_to(target, target_port);
        xfree(target);
        xfree(originator);
        if (sock < 0)
                return NULL;
        c = channel_new("direct-tcpip", SSH_CHANNEL_CONNECTING,
            sock, sock, -1, CHAN_TCP_WINDOW_DEFAULT,
            CHAN_TCP_PACKET_DEFAULT, 0, "direct-tcpip", 1);
        return c;
}

static Channel *
server_request_tun(void)
{
        Channel *c = NULL;
        int mode, tun;
        int sock;

        mode = packet_get_int();
        switch (mode) {
        case SSH_TUNMODE_POINTOPOINT:
        case SSH_TUNMODE_ETHERNET:
                break;
        default:
                packet_send_debug("Unsupported tunnel device mode.");
                return NULL;
        }
        if ((options.permit_tun & mode) == 0) {
                packet_send_debug("Server has rejected tunnel device "
                    "forwarding");
                return NULL;
        }

        tun = packet_get_int();
        if (forced_tun_device != -1) {
                if (tun != SSH_TUNID_ANY && forced_tun_device != tun)
                        goto done;
                tun = forced_tun_device;
        }
        sock = tun_open(tun, mode);
        if (sock < 0)
                goto done;
        c = channel_new("tun", SSH_CHANNEL_OPEN, sock, sock, -1,
            CHAN_TCP_WINDOW_DEFAULT, CHAN_TCP_PACKET_DEFAULT, 0, "tun", 1);
        c->datagram = 1;
#if defined(SSH_TUN_FILTER)
        if (mode == SSH_TUNMODE_POINTOPOINT)
                channel_register_filter(c->self, sys_tun_infilter,
                    sys_tun_outfilter);
#endif

 done:
        if (c == NULL)
                packet_send_debug("Failed to open the tunnel device.");
        return c;
}

static Channel *
server_request_session(void)
{
        Channel *c;

        debug("input_session_request");
        packet_check_eom();
        /*
         * A server session has no fd to read or write until a
         * CHANNEL_REQUEST for a shell is made, so we set the type to
         * SSH_CHANNEL_LARVAL.  Additionally, a callback for handling all
         * CHANNEL_REQUEST messages is registered.
         */
        c = channel_new("session", SSH_CHANNEL_LARVAL,
            -1, -1, -1, /*window size*/0, CHAN_SES_PACKET_DEFAULT,
            0, "server-session", 1);
        if (session_open(the_authctxt, c->self) != 1) {
                debug("session open failed, free channel %d", c->self);
                channel_free(c);
                return NULL;
        }
        channel_register_cleanup(c->self, session_close_by_channel, 0);
        return c;
}

static void
server_input_channel_open(int type, u_int32_t seq, void *ctxt)
{
        Channel *c = NULL;
        char *ctype;
        int rchan;
        u_int rmaxpack, rwindow, len;

        ctype = packet_get_string(&len);
        rchan = packet_get_int();
        rwindow = packet_get_int();
        rmaxpack = packet_get_int();

        debug("server_input_channel_open: ctype %s rchan %d win %d max %d",
            ctype, rchan, rwindow, rmaxpack);

        if (strcmp(ctype, "session") == 0) {
                c = server_request_session();
        } else if (strcmp(ctype, "direct-tcpip") == 0) {
                c = server_request_direct_tcpip();
        } else if (strcmp(ctype, "tun@openssh.com") == 0) {
                c = server_request_tun();
        }
        if (c != NULL) {
                debug("server_input_channel_open: confirm %s", ctype);
                c->remote_id = rchan;
                c->remote_window = rwindow;
                c->remote_maxpacket = rmaxpack;
                if (c->type != SSH_CHANNEL_CONNECTING) {
                        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);
                        packet_send();
                }
        } else {
                debug("server_input_channel_open: failure %s", ctype);
                packet_start(SSH2_MSG_CHANNEL_OPEN_FAILURE);
                packet_put_int(rchan);
                packet_put_int(SSH2_OPEN_ADMINISTRATIVELY_PROHIBITED);
                if (!(datafellows & SSH_BUG_OPENFAILURE)) {
                        packet_put_cstring("open failed");
                        packet_put_cstring("");
                }
                packet_send();
        }
        xfree(ctype);
}

static void
server_input_global_request(int type, u_int32_t seq, void *ctxt)
{
        char *rtype;
        int want_reply;
        int success = 0;

        rtype = packet_get_string(NULL);
        want_reply = packet_get_char();
        debug("server_input_global_request: rtype %s want_reply %d", rtype, want_reply);

        /* -R style forwarding */
        if (strcmp(rtype, "tcpip-forward") == 0) {
                struct passwd *pw;
                char *listen_address;
                u_short listen_port;

                pw = the_authctxt->pw;
                if (pw == NULL || !the_authctxt->valid)
                        fatal("server_input_global_request: no/invalid user");
                listen_address = packet_get_string(NULL);
                listen_port = (u_short)packet_get_int();
                debug("server_input_global_request: tcpip-forward listen %s port %d",
                    listen_address, listen_port);

                /* check permissions */
                if (!options.allow_tcp_forwarding ||
                    no_port_forwarding_flag
#ifndef NO_IPPORT_RESERVED_CONCEPT
                    || (listen_port < IPPORT_RESERVED && pw->pw_uid != 0)
#endif
                    ) {
                        success = 0;
                        packet_send_debug("Server has disabled port forwarding.");
                } else {
                        /* Start listening on the port */
                        success = channel_setup_remote_fwd_listener(
                            listen_address, listen_port, options.gateway_ports);
                }
                xfree(listen_address);
        } else if (strcmp(rtype, "cancel-tcpip-forward") == 0) {
                char *cancel_address;
                u_short cancel_port;

                cancel_address = packet_get_string(NULL);
                cancel_port = (u_short)packet_get_int();
                debug("%s: cancel-tcpip-forward addr %s port %d", __func__,
                    cancel_address, cancel_port);

                success = channel_cancel_rport_listener(cancel_address,
                    cancel_port);
                xfree(cancel_address);
        }
        if (want_reply) {
                packet_start(success ?
                    SSH2_MSG_REQUEST_SUCCESS : SSH2_MSG_REQUEST_FAILURE);
                packet_send();
                packet_write_wait();
        }
        xfree(rtype);
}

static void
server_input_channel_req(int type, u_int32_t seq, void *ctxt)
{
        Channel *c;
        int id, reply, success = 0;
        char *rtype;

        id = packet_get_int();
        rtype = packet_get_string(NULL);
        reply = packet_get_char();

        debug("server_input_channel_req: channel %d request %s reply %d",
            id, rtype, reply);

        if ((c = channel_lookup(id)) == NULL)
                packet_disconnect("server_input_channel_req: "
                    "unknown channel %d", id);
        if (c->type == SSH_CHANNEL_LARVAL || c->type == SSH_CHANNEL_OPEN)
                success = session_input_channel_req(c, rtype);
        if (reply) {
                packet_start(success ?
                    SSH2_MSG_CHANNEL_SUCCESS : SSH2_MSG_CHANNEL_FAILURE);
                packet_put_int(c->remote_id);
                packet_send();
        }
        xfree(rtype);
}

static void
server_init_dispatch_20(void)
{
        debug("server_init_dispatch_20");
        dispatch_init(&dispatch_protocol_error);
        dispatch_set(SSH2_MSG_CHANNEL_CLOSE, &channel_input_oclose);
        dispatch_set(SSH2_MSG_CHANNEL_DATA, &channel_input_data);
        dispatch_set(SSH2_MSG_CHANNEL_EOF, &channel_input_ieof);
        dispatch_set(SSH2_MSG_CHANNEL_EXTENDED_DATA, &channel_input_extended_data);
        dispatch_set(SSH2_MSG_CHANNEL_OPEN, &server_input_channel_open);
        dispatch_set(SSH2_MSG_CHANNEL_OPEN_CONFIRMATION, &channel_input_open_confirmation);
        dispatch_set(SSH2_MSG_CHANNEL_OPEN_FAILURE, &channel_input_open_failure);
        dispatch_set(SSH2_MSG_CHANNEL_REQUEST, &server_input_channel_req);
        dispatch_set(SSH2_MSG_CHANNEL_WINDOW_ADJUST, &channel_input_window_adjust);
        dispatch_set(SSH2_MSG_GLOBAL_REQUEST, &server_input_global_request);
        /* client_alive */
        dispatch_set(SSH2_MSG_CHANNEL_FAILURE, &server_input_keep_alive);
        dispatch_set(SSH2_MSG_REQUEST_SUCCESS, &server_input_keep_alive);
        dispatch_set(SSH2_MSG_REQUEST_FAILURE, &server_input_keep_alive);
        /* rekeying */
        dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit);
}
static void
server_init_dispatch_13(void)
{
        debug("server_init_dispatch_13");
        dispatch_init(NULL);
        dispatch_set(SSH_CMSG_EOF, &server_input_eof);
        dispatch_set(SSH_CMSG_STDIN_DATA, &server_input_stdin_data);
        dispatch_set(SSH_CMSG_WINDOW_SIZE, &server_input_window_size);
        dispatch_set(SSH_MSG_CHANNEL_CLOSE, &channel_input_close);
        dispatch_set(SSH_MSG_CHANNEL_CLOSE_CONFIRMATION, &channel_input_close_confirmation);
        dispatch_set(SSH_MSG_CHANNEL_DATA, &channel_input_data);
        dispatch_set(SSH_MSG_CHANNEL_OPEN_CONFIRMATION, &channel_input_open_confirmation);
        dispatch_set(SSH_MSG_CHANNEL_OPEN_FAILURE, &channel_input_open_failure);
        dispatch_set(SSH_MSG_PORT_OPEN, &channel_input_port_open);
}
static void
server_init_dispatch_15(void)
{
        server_init_dispatch_13();
        debug("server_init_dispatch_15");
        dispatch_set(SSH_MSG_CHANNEL_CLOSE, &channel_input_ieof);
        dispatch_set(SSH_MSG_CHANNEL_CLOSE_CONFIRMATION, &channel_input_oclose);
}
static void
server_init_dispatch(void)
{
        if (compat20)
                server_init_dispatch_20();
        else if (compat13)
                server_init_dispatch_13();
        else
                server_init_dispatch_15();
}