libopenssh/ssh/serverloop.c

/* $OpenBSD: serverloop.c,v 1.162 2012/06/20 04:42:58 djm 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 <sys/types.h>
#include <sys/wait.h>
#include <sys/socket.h>
#include <sys/time.h>
#include <sys/param.h>
#include <sys/queue.h>

#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"
#define PACKET_SKIP_COMPAT
#define PACKET_SKIP_COMPAT2
#include "packet.h"
#include "sshbuf.h"
#include "log.h"
#include "servconf.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"
#include "roaming.h"
#include "err.h"

extern ServerOptions options;

extern Authctxt *the_authctxt;
extern int use_privsep;

static struct sshbuf *stdin_buffer;	/* Buffer for stdin data. */
static struct sshbuf *stdout_buffer;	/* Buffer for stdout data. */
static struct sshbuf *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 size_t stdin_bytes = 0;	/* Number of bytes written to stdin. */
static size_t stdout_bytes = 0;	/* Number of stdout bytes sent to client. */
static size_t stderr_bytes = 0;	/* Number of stderr bytes sent to client. */
static size_t 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 no_more_sessions = 0; /* Disallow further sessions. */

/*
 * 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(struct ssh *);

/*
 * 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, FD_CLOEXEC) == -1) ||
	    (fcntl(notify_pipe[1], F_SETFD, FD_CLOEXEC) == -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;
	signal(SIGCHLD, sigchld_handler);
	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(struct ssh *ssh)
{
	size_t len;
	int r;

	/* Send buffered stderr data to the client. */
	while (sshbuf_len(stderr_buffer) > 0 &&
	    ssh_packet_not_very_much_data_to_write(ssh)) {
		len = sshbuf_len(stderr_buffer);
		if (ssh_packet_is_interactive(ssh)) {
			if (len > 512)
				len = 512;
		} else {
			/* Keep the packets at reasonable size. */
			if (len > ssh_packet_get_maxsize(ssh))
				len = ssh_packet_get_maxsize(ssh);
		}
		if ((r = sshpkt_start(ssh, SSH_SMSG_STDERR_DATA)) != 0 ||
		    (r = sshpkt_put_string(ssh, sshbuf_ptr(stderr_buffer),
		    len)) != 0 ||
		    (r = sshpkt_send(ssh)) != 0)
			fatal("%s: %s", __func__, ssh_err(r));
		if ((r = sshbuf_consume(stderr_buffer, len)) != 0)
			fatal("%s: buffer error: %s", __func__, ssh_err(r));
		stderr_bytes += len;
	}
}

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

	/* Send buffered stdout data to the client. */
	while (sshbuf_len(stdout_buffer) > 0 &&
	    ssh_packet_not_very_much_data_to_write(ssh)) {
		len = sshbuf_len(stdout_buffer);
		if (ssh_packet_is_interactive(ssh)) {
			if (len > 512)
				len = 512;
		} else {
			/* Keep the packets at reasonable size. */
			if (len > ssh_packet_get_maxsize(ssh))
				len = ssh_packet_get_maxsize(ssh);
		}
		if ((r = sshpkt_start(ssh, SSH_SMSG_STDOUT_DATA)) != 0 ||
		    (r = sshpkt_put_string(ssh, sshbuf_ptr(stdout_buffer),
		    len)) != 0 ||
		    (r = sshpkt_send(ssh)) != 0)
			fatal("%s: %s", __func__, ssh_err(r));
		if ((r = sshbuf_consume(stdout_buffer, len)) != 0)
			fatal("%s: buffer error: %s", __func__, ssh_err(r));
		stdout_bytes += len;
	}
}

static void
client_alive_check(struct ssh *ssh)
{
	int channel_id, r;

	/* timeout, check to see how many we have had */
	if (ssh_packet_inc_alive_timeouts(ssh) > 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) {
		if ((r = sshpkt_start(ssh, SSH2_MSG_GLOBAL_REQUEST)) != 0 ||
		    (r = sshpkt_put_cstring(ssh, "keepalive@openssh.com"))
		    != 0 ||
		    (r = sshpkt_put_u8(ssh, 1)) != 0) /* boolean: want reply */
			fatal("%s: %s", __func__, ssh_err(r));
	} else {
		channel_request_start(channel_id, "keepalive@openssh.com", 1);
	}
	if ((r = sshpkt_send(ssh)) != 0)
		fatal("%s: %s", __func__, ssh_err(r));
}

/*
 * 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(struct ssh *ssh, fd_set **readsetp, fd_set **writesetp,
    int *maxfdp, u_int *nallocp, u_int max_time_milliseconds)
{
	struct timeval tv, *tvp;
	int ret;
	time_t minwait_secs = 0;
	int client_alive_scheduled = 0;

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

	if (minwait_secs != 0)
		max_time_milliseconds = MIN(max_time_milliseconds,
		    (u_int)minwait_secs * 1000);

	/*
	 * 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;
	}

	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 (sshbuf_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 (ssh_packet_not_very_much_data_to_write(ssh)) {
			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 && sshbuf_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 (ssh_packet_have_data_to_write(ssh))
		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 && ssh_packet_not_very_much_data_to_write(ssh))
		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(ssh);

	notify_done(*readsetp);
}

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

	/* Read and buffer any input data from the client. */
	if (FD_ISSET(connection_in, readset)) {
		int cont = 0;
		len = roaming_read(connection_in, buf, sizeof(buf), &cont);
		if (len == 0) {
			if (cont)
				return;
			verbose("Connection closed by %.100s",
			    ssh_remote_ipaddr(ssh));
			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",
				    ssh_remote_ipaddr(ssh), strerror(errno));
				cleanup_exit(255);
			}
		} else {
			/* Buffer any received data. */
			ssh_packet_process_incoming(ssh, buf, len);
		}
	}
	if (compat20)
		return;

	/* Read and buffer any available stdout data from the program. */
	if (!fdout_eof && FD_ISSET(fdout, readset)) {
		len = read(fdout, buf, sizeof(buf));
		if (len < 0 && (errno == EINTR || errno == EAGAIN)) {
			/* do nothing */
		} else if (len <= 0) {
			fdout_eof = 1;
		} else {
			if ((r = sshbuf_put(stdout_buffer, buf, len)) != 0)
				fatal("%s: buffer error: %s",
				    __func__, ssh_err(r));
			fdout_bytes += len;
		}
	}
	/* Read and buffer any available stderr data from the program. */
	if (!fderr_eof && FD_ISSET(fderr, readset)) {
		len = read(fderr, buf, sizeof(buf));
		if (len < 0 && (errno == EINTR || errno == EAGAIN)) {
			/* do nothing */
		} else if (len <= 0) {
			fderr_eof = 1;
		} else {
			if ((r = sshbuf_put(stderr_buffer, buf, len)) != 0)
				fatal("%s: buffer error: %s",
				    __func__, ssh_err(r));
		}
	}
}

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

	/* Write buffered data to program stdin. */
	if (!compat20 && fdin != -1 && FD_ISSET(fdin, writeset)) {
		data = sshbuf_ptr(stdin_buffer);
		dlen = sshbuf_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
				 */
				ssh_packet_send_ignore(ssh, len);
				if ((r = sshpkt_send(ssh)) != 0)
					fatal("%s: %s", __func__, ssh_err(r));
			}
			/* Consume the data from the buffer. */
			if ((r = sshbuf_consume(stdin_buffer, len)) != 0)
				fatal("%s: buffer error: %s", __func__,
				    ssh_err(r));
			/* 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))
		ssh_packet_write_poll(ssh);
}

/*
 * Wait until all buffered output has been sent to the client.
 * This is used when the program terminates.
 */
static void
drain_output(struct ssh *ssh)
{
	int r;

	/* Send any buffered stdout data to the client. */
	if (sshbuf_len(stdout_buffer) > 0) {
		if ((r = sshpkt_start(ssh, SSH_SMSG_STDOUT_DATA)) != 0 ||
		    (r = sshpkt_put_string(ssh, sshbuf_ptr(stdout_buffer),
		    sshbuf_len(stdout_buffer))) != 0 ||
		    (r = sshpkt_send(ssh)) != 0)
			fatal("%s: %s", __func__, ssh_err(r));
		/* Update the count of sent bytes. */
		stdout_bytes += sshbuf_len(stdout_buffer);
	}
	/* Send any buffered stderr data to the client. */
	if (sshbuf_len(stderr_buffer) > 0) {
		if ((r = sshpkt_start(ssh, SSH_SMSG_STDERR_DATA)) != 0 ||
		    (r = sshpkt_put_string(ssh, sshbuf_ptr(stderr_buffer),
		    sshbuf_len(stderr_buffer))) != 0 ||
		    (r = sshpkt_send(ssh)) != 0)
		/* Update the count of sent bytes. */
		stderr_bytes += sshbuf_len(stderr_buffer);
	}
	/* Wait until all buffered data has been written to the client. */
	ssh_packet_write_wait(ssh);
}

static void
process_buffered_input_packets(struct ssh *ssh)
{
	int r;

	if ((r = ssh_dispatch_run(ssh, DISPATCH_NONBLOCK, NULL)) != 0)
		fatal("%s: %s", __func__, ssh_err(r));
}

/*
 * 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)
{
	struct ssh *ssh = active_state; /* XXX */
	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 r, type;

	debug("Entering interactive session.");

	/* Initialize the SIGCHLD kludge. */
	child_terminated = 0;
	signal(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 (!(ssh->compat & SSH_BUG_IGNOREMSG) && isatty(fdin))
		fdin_is_tty = 1;

	connection_in = ssh_packet_get_connection_in(ssh);
	connection_out = ssh_packet_get_connection_out(ssh);

	notify_setup();

	previous_stdout_buffer_bytes = 0;

	/* Set approximate I/O buffer size. */
	if (ssh_packet_is_interactive(ssh))
		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. */
	if ((stdin_buffer = sshbuf_new()) == NULL)
		fatal("%s: sshbuf_new failed", __func__);
	if ((stdout_buffer = sshbuf_new()) == NULL)
		fatal("%s: sshbuf_new failed", __func__);
	if ((stderr_buffer = sshbuf_new()) == NULL)
		fatal("%s: sshbuf_new failed", __func__);

	/*
	 * 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(ssh);

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

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

		/*
		 * 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 && sshbuf_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(ssh);

		/*
		 * 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 = sshbuf_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(ssh);
		}
		previous_stdout_buffer_bytes = sshbuf_len(stdout_buffer);

		/* Send channel data to the client. */
		if (ssh_packet_not_very_much_data_to_write(ssh))
			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 && !ssh_packet_have_data_to_write(ssh) &&
		    sshbuf_len(stdout_buffer) == 0 && sshbuf_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 = channel_open_message();

				waiting_termination = 1;
				/* Display list of open channels. */
				if ((r = sshbuf_put(stderr_buffer,
				    s, strlen(s))) != 0 ||
				    (r = sshbuf_put(stderr_buffer,
				    s, strlen(s))) != 0)
					fatal("%s: buffer error: %s",
					    __func__, ssh_err(r));
				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(ssh, &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(ssh, readset);

		/* Process output to the client and to program stdin. */
		process_output(ssh, 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(ssh);

	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. */
	sshbuf_free(stdin_buffer);
	sshbuf_free(stdout_buffer);
	sshbuf_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. */
	signal(SIGCHLD, SIG_DFL);

	while ((wait_pid = waitpid(-1, &wait_status, 0)) < 0)
		if (errno != EINTR)
			ssh_packet_disconnect(ssh, "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));
		if ((r = sshpkt_start(ssh, SSH_SMSG_EXITSTATUS)) != 0 ||
		    (r = sshpkt_put_u32(ssh, WEXITSTATUS(wait_status))) != 0 ||
		    (r = sshpkt_send(ssh)) != 0)
			fatal("%s: %s", __func__, ssh_err(r));
		ssh_packet_write_wait(ssh);

		/*
		 * 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 = ssh_packet_read(ssh);
		}
		while (type != SSH_CMSG_EXIT_CONFIRMATION);

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

	/* Some weird exit cause.  Just exit. */
	ssh_packet_disconnect(ssh, "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(struct ssh *ssh)
{
	fd_set *readset = NULL, *writeset = NULL;
	int r, rekeying = 0, max_fd, nalloc = 0;

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

	signal(SIGCHLD, sigchld_handler);
	child_terminated = 0;
	connection_in = ssh_packet_get_connection_in(ssh);
	connection_out = ssh_packet_get_connection_out(ssh);

	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(ssh);

	for (;;) {
		process_buffered_input_packets(ssh);

		rekeying = (ssh->kex != NULL &&
			    !ssh->kex->done);

		if (!rekeying && ssh_packet_not_very_much_data_to_write(ssh))
			channel_output_poll();
		wait_until_can_do_something(ssh, &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 (ssh_packet_need_rekeying(ssh)) {
				debug("need rekeying");
				ssh->kex->done = 0;
				if ((r = kex_send_kexinit(ssh)) != 0) {
					fatal("%s: kex_send_kexinit: %s",
					    __func__, ssh_err(r));
				}
			}
		}
		process_input(ssh, readset);
		if (connection_closed)
			break;
		process_output(ssh, 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 int
server_input_keep_alive(int type, u_int32_t seq, struct ssh *ssh)
{
	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.
	 */
	ssh_packet_set_alive_timeouts(ssh, 0);
	return 0;
}

static int
server_input_stdin_data(int type, u_int32_t seq, struct ssh *ssh)
{
	u_char *data = NULL;
	size_t data_len;
	int r;

	/* Stdin data from the client.  Append it to the buffer. */
	/* Ignore any data if the client has closed stdin. */
	if (fdin == -1)
		return 0;
	if ((r = sshpkt_get_string(ssh, &data, &data_len)) != 0 ||
	    (r = sshpkt_get_end(ssh)) != 0 ||
	    (r = sshbuf_put(stdin_buffer, data, data_len)) != 0)
		goto out;
	r = 0;
 out:
	if (data) {
		memset(data, 0, data_len);
		free(data);
	}
	return r;
}

static int
server_input_eof(int type, u_int32_t seq, struct ssh *ssh)
{
	int r;

	/*
	 * Eof from the client.  The stdin descriptor to the
	 * program will be closed when all buffered data has
	 * drained.
	 */
	debug("EOF received for stdin.");
	r = sshpkt_get_end(ssh);
	stdin_eof = 1;
	return r;
}

static int
server_input_window_size(int type, u_int32_t seq, struct ssh *ssh)
{
	u_int row, col, xpixel, ypixel;
	int r;

	if ((r = sshpkt_get_u32(ssh, &row)) != 0 ||
	    (r = sshpkt_get_u32(ssh, &col)) != 0 ||
	    (r = sshpkt_get_u32(ssh, &xpixel)) != 0 ||
	    (r = sshpkt_get_u32(ssh, &ypixel)) != 0 ||
	    (r = sshpkt_get_end(ssh)))
		return r;

	debug("Window change received.");
	if (fdin != -1)
		pty_change_window_size(fdin, row, col, xpixel, ypixel);
	return 0;
}

static Channel *
server_request_direct_tcpip(struct ssh *ssh)
{
	Channel *c;
	char *target, *originator;
	u_int target_port, originator_port;
	int r;

	if ((r = sshpkt_get_cstring(ssh, &target, NULL)) != 0 ||
	    (r = sshpkt_get_u32(ssh, &target_port)) != 0 ||
	    (r = sshpkt_get_cstring(ssh, &originator, NULL)) != 0 ||
	    (r = sshpkt_get_u32(ssh, &originator_port)) != 0 ||
	    (r = sshpkt_get_end(ssh)) != 0)
		fatal("%s: %s", __func__, ssh_err(r));

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

	/* XXX check permission */
	c = channel_connect_to(target, target_port,
	    "direct-tcpip", "direct-tcpip");

	xfree(originator);
	xfree(target);

	return c;
}

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

	if ((r = sshpkt_get_u32(ssh, &mode)) != 0 ||
	    (r = sshpkt_get_u32(ssh, &tun)) != 0)
		fatal("%s: %s", __func__, ssh_err(r));
	switch (mode) {
	case SSH_TUNMODE_POINTOPOINT:
	case SSH_TUNMODE_ETHERNET:
		break;
	default:
		ssh_packet_send_debug(ssh, "Unsupported tunnel device mode.");
		return NULL;
	}
	if ((options.permit_tun & mode) == 0) {
		ssh_packet_send_debug(ssh, "Server has rejected tunnel device "
		    "forwarding");
		return NULL;
	}
	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;

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

static Channel *
server_request_session(struct ssh *ssh)
{
	Channel *c;
	int r;

	debug("input_session_request");
	if ((r = sshpkt_get_end(ssh)) != 0)
		fatal("%s: %s", __func__, ssh_err(r));

	if (no_more_sessions) {
		ssh_packet_disconnect(ssh,
		    "Possible attack: attempt to open a session "
		    "after additional sessions disabled");
	}

	/*
	 * 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(ssh, 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 int
server_input_channel_open(int type, u_int32_t seq, struct ssh *ssh)
{
	Channel *c = NULL;
	char *ctype = 0;
	int r, rchan;
	u_int rmaxpack, rwindow;
	size_t len;

	if ((r = sshpkt_get_cstring(ssh, &ctype, &len)) != 0 ||
	    (r = sshpkt_get_u32(ssh, &rchan)) != 0 ||
	    (r = sshpkt_get_u32(ssh, &rwindow)) != 0 ||
	    (r = sshpkt_get_u32(ssh, &rmaxpack)) != 0)
		goto out;

	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(ssh);
	} else if (strcmp(ctype, "direct-tcpip") == 0) {
		c = server_request_direct_tcpip(ssh);
	} else if (strcmp(ctype, "tun@openssh.com") == 0) {
		c = server_request_tun(ssh);
	}
	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) {
			if ((r = sshpkt_start(ssh,
			    SSH2_MSG_CHANNEL_OPEN_CONFIRMATION)) != 0 ||
			    (r = sshpkt_put_u32(ssh, c->remote_id)) != 0 ||
			    (r = sshpkt_put_u32(ssh, c->self)) != 0 ||
			    (r = sshpkt_put_u32(ssh, c->local_window)) != 0 ||
			    (r = sshpkt_put_u32(ssh, c->local_maxpacket)) != 0||
			    (r = sshpkt_send(ssh)) != 0)
				goto out;
		}
	} else {
		debug("server_input_channel_open: failure %s", ctype);
		if ((r = sshpkt_start(ssh, SSH2_MSG_CHANNEL_OPEN_FAILURE)) != 0 ||
		    (r = sshpkt_put_u32(ssh, rchan)) != 0 ||
		    (r = sshpkt_put_u32(ssh,
		    SSH2_OPEN_ADMINISTRATIVELY_PROHIBITED)) != 0 ||
		    (!(ssh->compat & SSH_BUG_OPENFAILURE) &&
		    (r = sshpkt_put_cstring(ssh, "open failed")) != 0) ||
		    (!(ssh->compat & SSH_BUG_OPENFAILURE) &&
		    (r = sshpkt_put_cstring(ssh, "")) != 0) ||
		    (r = sshpkt_send(ssh)) != 0)
			goto out;
	}
	r = 0;
 out:
	free(ctype);
	return r;
}

static int
server_input_global_request(int type, u_int32_t seq, struct ssh *ssh)
{
	char *rtype = NULL, *listen_address = NULL, *cancel_address = NULL;
	char want_reply;
	u_int listen_port, cancel_port;
	int r, success = 0, allocated_listen_port = 0;

	if ((r = sshpkt_get_cstring(ssh, &rtype, NULL)) != 0 ||
	    (r = sshpkt_get_u8(ssh, &want_reply)) != 0)
		goto out;
	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;

		pw = the_authctxt->pw;
		if (pw == NULL || !the_authctxt->valid)
			fatal("server_input_global_request: no/invalid user");
		if ((r = sshpkt_get_cstring(ssh, &listen_address, NULL)) != 0 ||
		    (r = sshpkt_get_u32(ssh, &listen_port)) != 0)
			goto out;
		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 ||
		    (!want_reply && listen_port == 0) ||
		    (listen_port != 0 && listen_port < IPPORT_RESERVED &&
		    pw->pw_uid != 0)) {
			success = 0;
			ssh_packet_send_debug(ssh,
			    "Server has disabled port forwarding.");
		} else {
			/* Start listening on the port */
			success = channel_setup_remote_fwd_listener(
			    listen_address, listen_port,
			    &allocated_listen_port, options.gateway_ports);
		}
	} else if (strcmp(rtype, "cancel-tcpip-forward") == 0) {
		if ((r = sshpkt_get_cstring(ssh, &cancel_address, NULL)) != 0 ||
		    (r = sshpkt_get_u32(ssh, &cancel_port)) != 0)
			goto out;
		debug("%s: cancel-tcpip-forward addr %s port %d", __func__,
		    cancel_address, cancel_port);
		success = channel_cancel_rport_listener(cancel_address,
		    cancel_port);
	} else if (strcmp(rtype, "no-more-sessions@openssh.com") == 0) {
		no_more_sessions = 1;
		success = 1;
	}
	if (want_reply) {
		if ((r = sshpkt_start(ssh, success ?
		    SSH2_MSG_REQUEST_SUCCESS : SSH2_MSG_REQUEST_FAILURE)) != 0 ||
		    (success && allocated_listen_port > 0 &&
		    (r = sshpkt_put_u32(ssh, allocated_listen_port)) != 0) ||
		    (r = sshpkt_send(ssh)) != 0) 
			goto out;
		ssh_packet_write_wait(ssh);
	}
	r = 0;
 out:
	free(rtype);
	free(listen_address);
	free(cancel_address);
	return r;
}

static int
server_input_channel_req(int type, u_int32_t seq, struct ssh *ssh)
{
	Channel *c;
	int r, id, success = 0;
	char *rtype = NULL, reply;

	if ((r = sshpkt_get_u32(ssh, &id)) != 0 ||
	    (r = sshpkt_get_cstring(ssh, &rtype, NULL)) != 0 ||
	    (r = sshpkt_get_u8(ssh, &reply)) != 0)
		goto out;

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

	if ((c = channel_lookup(id)) == NULL)
		ssh_packet_disconnect(ssh, "server_input_channel_req: "
		    "unknown channel %d", id);
	if (!strcmp(rtype, "eow@openssh.com")) {
		if ((r = sshpkt_get_end(ssh)) != 0)
			goto out;
		chan_rcvd_eow(c);
	} else if ((c->type == SSH_CHANNEL_LARVAL ||
	    c->type == SSH_CHANNEL_OPEN) && strcmp(c->ctype, "session") == 0)
		success = session_input_channel_req(c, rtype);
	if (reply) {
		if ((r = sshpkt_start(ssh, success ? SSH2_MSG_CHANNEL_SUCCESS :
		    SSH2_MSG_CHANNEL_FAILURE)) != 0 ||
		    (r = sshpkt_put_u32(ssh, c->remote_id)) != 0 ||
		    (r = sshpkt_send(ssh)) != 0)
			goto out;
	}
	r = 0;
 out:
	if (rtype)
		free(rtype);
	return r;
}

static void
server_init_dispatch_20(struct ssh *ssh)
{
	debug("server_init_dispatch_20");
	ssh_dispatch_init(ssh, &dispatch_protocol_error);
	ssh_dispatch_set(ssh, SSH2_MSG_CHANNEL_CLOSE, &channel_input_oclose);
	ssh_dispatch_set(ssh, SSH2_MSG_CHANNEL_DATA, &channel_input_data);
	ssh_dispatch_set(ssh, SSH2_MSG_CHANNEL_EOF, &channel_input_ieof);
	ssh_dispatch_set(ssh, SSH2_MSG_CHANNEL_EXTENDED_DATA,
	    &channel_input_extended_data);
	ssh_dispatch_set(ssh, SSH2_MSG_CHANNEL_OPEN,
	    &server_input_channel_open);
	ssh_dispatch_set(ssh, SSH2_MSG_CHANNEL_OPEN_CONFIRMATION,
	    &channel_input_open_confirmation);
	ssh_dispatch_set(ssh, SSH2_MSG_CHANNEL_OPEN_FAILURE,
	    &channel_input_open_failure);
	ssh_dispatch_set(ssh, SSH2_MSG_CHANNEL_REQUEST,
	    &server_input_channel_req);
	ssh_dispatch_set(ssh, SSH2_MSG_CHANNEL_WINDOW_ADJUST,
	    &channel_input_window_adjust);
	ssh_dispatch_set(ssh, SSH2_MSG_GLOBAL_REQUEST,
	    &server_input_global_request);
	/* client_alive */
	ssh_dispatch_set(ssh, SSH2_MSG_CHANNEL_SUCCESS,
	    &server_input_keep_alive);
	ssh_dispatch_set(ssh, SSH2_MSG_CHANNEL_FAILURE,
	    &server_input_keep_alive);
	ssh_dispatch_set(ssh, SSH2_MSG_REQUEST_SUCCESS,
	    &server_input_keep_alive);
	ssh_dispatch_set(ssh, SSH2_MSG_REQUEST_FAILURE,
	    &server_input_keep_alive);
	/* rekeying */
	ssh_dispatch_set(ssh, SSH2_MSG_KEXINIT, &kex_input_kexinit);
}
static void
server_init_dispatch_13(struct ssh *ssh)
{
	debug("server_init_dispatch_13");
	ssh_dispatch_init(ssh, NULL);
	ssh_dispatch_set(ssh, SSH_CMSG_EOF, &server_input_eof);
	ssh_dispatch_set(ssh, SSH_CMSG_STDIN_DATA, &server_input_stdin_data);
	ssh_dispatch_set(ssh, SSH_CMSG_WINDOW_SIZE, &server_input_window_size);
	ssh_dispatch_set(ssh, SSH_MSG_CHANNEL_CLOSE, &channel_input_close);
	ssh_dispatch_set(ssh, SSH_MSG_CHANNEL_CLOSE_CONFIRMATION,
	    &channel_input_close_confirmation);
	ssh_dispatch_set(ssh, SSH_MSG_CHANNEL_DATA, &channel_input_data);
	ssh_dispatch_set(ssh, SSH_MSG_CHANNEL_OPEN_CONFIRMATION,
	    &channel_input_open_confirmation);
	ssh_dispatch_set(ssh, SSH_MSG_CHANNEL_OPEN_FAILURE,
	    &channel_input_open_failure);
	ssh_dispatch_set(ssh, SSH_MSG_PORT_OPEN, &channel_input_port_open);
}
static void
server_init_dispatch_15(struct ssh *ssh)
{
	server_init_dispatch_13(ssh);
	debug("server_init_dispatch_15");
	ssh_dispatch_set(ssh, SSH_MSG_CHANNEL_CLOSE,
	    &channel_input_ieof);
	ssh_dispatch_set(ssh, SSH_MSG_CHANNEL_CLOSE_CONFIRMATION,
	    &channel_input_oclose);
}
static void
server_init_dispatch(struct ssh *ssh)
{
	if (compat20)
		server_init_dispatch_20(ssh);
	else if (compat13)
		server_init_dispatch_13(ssh);
	else
		server_init_dispatch_15(ssh);
}