OpenBSD-4.6/usr.bin/ssh/mux.c
/* $OpenBSD: mux.c,v 1.7 2008/06/13 17:21:20 dtucker Exp $ */
/*
* Copyright (c) 2002-2008 Damien Miller <djm@openbsd.org>
*
* Permission to use, copy, modify, and distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
/* ssh session multiplexing support */
/*
* TODO:
* 1. partial reads in muxserver_accept_control (maybe make channels
* from accepted connections)
* 2. Better signalling from master to slave, especially passing of
* error messages
* 3. Better fall-back from mux slave error to new connection.
* 3. Add/delete forwardings via slave
* 4. ExitOnForwardingFailure (after #3 obviously)
* 5. Maybe extension mechanisms for multi-X11/multi-agent forwarding
* 6. Document the mux mini-protocol somewhere.
* 7. Support ~^Z in mux slaves.
* 8. Inspect or control sessions in master.
* 9. If we ever support the "signal" channel request, send signals on
* sessions in master.
*/
#include <sys/types.h>
#include <sys/param.h>
#include <sys/queue.h>
#include <sys/stat.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <errno.h>
#include <fcntl.h>
#include <signal.h>
#include <stdarg.h>
#include <stddef.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <util.h>
#include <paths.h>
#include "xmalloc.h"
#include "log.h"
#include "ssh.h"
#include "pathnames.h"
#include "misc.h"
#include "match.h"
#include "buffer.h"
#include "channels.h"
#include "msg.h"
#include "packet.h"
#include "monitor_fdpass.h"
#include "sshpty.h"
#include "key.h"
#include "readconf.h"
#include "clientloop.h"
/* from ssh.c */
extern int tty_flag;
extern Options options;
extern int stdin_null_flag;
extern char *host;
int subsystem_flag;
extern Buffer command;
/* Context for session open confirmation callback */
struct mux_session_confirm_ctx {
int want_tty;
int want_subsys;
int want_x_fwd;
int want_agent_fwd;
Buffer cmd;
char *term;
struct termios tio;
char **env;
};
/* fd to control socket */
int muxserver_sock = -1;
/* Multiplexing control command */
u_int muxclient_command = 0;
/* Set when signalled. */
static volatile sig_atomic_t muxclient_terminate = 0;
/* PID of multiplex server */
static u_int muxserver_pid = 0;
/* ** Multiplexing master support */
/* Prepare a mux master to listen on a Unix domain socket. */
void
muxserver_listen(void)
{
struct sockaddr_un addr;
mode_t old_umask;
if (options.control_path == NULL ||
options.control_master == SSHCTL_MASTER_NO)
return;
debug("setting up multiplex master socket");
memset(&addr, '\0', sizeof(addr));
addr.sun_family = AF_UNIX;
addr.sun_len = offsetof(struct sockaddr_un, sun_path) +
strlen(options.control_path) + 1;
if (strlcpy(addr.sun_path, options.control_path,
sizeof(addr.sun_path)) >= sizeof(addr.sun_path))
fatal("ControlPath too long");
if ((muxserver_sock = socket(PF_UNIX, SOCK_STREAM, 0)) < 0)
fatal("%s socket(): %s", __func__, strerror(errno));
old_umask = umask(0177);
if (bind(muxserver_sock, (struct sockaddr *)&addr, addr.sun_len) == -1) {
muxserver_sock = -1;
if (errno == EINVAL || errno == EADDRINUSE) {
error("ControlSocket %s already exists, "
"disabling multiplexing", options.control_path);
close(muxserver_sock);
muxserver_sock = -1;
xfree(options.control_path);
options.control_path = NULL;
options.control_master = SSHCTL_MASTER_NO;
return;
} else
fatal("%s bind(): %s", __func__, strerror(errno));
}
umask(old_umask);
if (listen(muxserver_sock, 64) == -1)
fatal("%s listen(): %s", __func__, strerror(errno));
set_nonblock(muxserver_sock);
}
/* Callback on open confirmation in mux master for a mux client session. */
static void
mux_session_confirm(int id, void *arg)
{
struct mux_session_confirm_ctx *cctx = arg;
const char *display;
Channel *c;
int i;
if (cctx == NULL)
fatal("%s: cctx == NULL", __func__);
if ((c = channel_lookup(id)) == NULL)
fatal("%s: no channel for id %d", __func__, id);
display = getenv("DISPLAY");
if (cctx->want_x_fwd && options.forward_x11 && display != NULL) {
char *proto, *data;
/* Get reasonable local authentication information. */
client_x11_get_proto(display, options.xauth_location,
options.forward_x11_trusted, &proto, &data);
/* Request forwarding with authentication spoofing. */
debug("Requesting X11 forwarding with authentication spoofing.");
x11_request_forwarding_with_spoofing(id, display, proto, data);
/* XXX wait for reply */
}
if (cctx->want_agent_fwd && options.forward_agent) {
debug("Requesting authentication agent forwarding.");
channel_request_start(id, "auth-agent-req@openssh.com", 0);
packet_send();
}
client_session2_setup(id, cctx->want_tty, cctx->want_subsys,
cctx->term, &cctx->tio, c->rfd, &cctx->cmd, cctx->env);
c->open_confirm_ctx = NULL;
buffer_free(&cctx->cmd);
xfree(cctx->term);
if (cctx->env != NULL) {
for (i = 0; cctx->env[i] != NULL; i++)
xfree(cctx->env[i]);
xfree(cctx->env);
}
xfree(cctx);
}
/*
* Accept a connection on the mux master socket and process the
* client's request. Returns flag indicating whether mux master should
* begin graceful close.
*/
int
muxserver_accept_control(void)
{
Buffer m;
Channel *c;
int client_fd, new_fd[3], ver, allowed, window, packetmax;
socklen_t addrlen;
struct sockaddr_storage addr;
struct mux_session_confirm_ctx *cctx;
char *cmd;
u_int i, j, len, env_len, mux_command, flags, escape_char;
uid_t euid;
gid_t egid;
int start_close = 0;
/*
* Accept connection on control socket
*/
memset(&addr, 0, sizeof(addr));
addrlen = sizeof(addr);
if ((client_fd = accept(muxserver_sock,
(struct sockaddr*)&addr, &addrlen)) == -1) {
error("%s accept: %s", __func__, strerror(errno));
return 0;
}
if (getpeereid(client_fd, &euid, &egid) < 0) {
error("%s getpeereid failed: %s", __func__, strerror(errno));
close(client_fd);
return 0;
}
if ((euid != 0) && (getuid() != euid)) {
error("control mode uid mismatch: peer euid %u != uid %u",
(u_int) euid, (u_int) getuid());
close(client_fd);
return 0;
}
/* XXX handle asynchronously */
unset_nonblock(client_fd);
/* Read command */
buffer_init(&m);
if (ssh_msg_recv(client_fd, &m) == -1) {
error("%s: client msg_recv failed", __func__);
close(client_fd);
buffer_free(&m);
return 0;
}
if ((ver = buffer_get_char(&m)) != SSHMUX_VER) {
error("%s: wrong client version %d", __func__, ver);
buffer_free(&m);
close(client_fd);
return 0;
}
allowed = 1;
mux_command = buffer_get_int(&m);
flags = buffer_get_int(&m);
buffer_clear(&m);
switch (mux_command) {
case SSHMUX_COMMAND_OPEN:
if (options.control_master == SSHCTL_MASTER_ASK ||
options.control_master == SSHCTL_MASTER_AUTO_ASK)
allowed = ask_permission("Allow shared connection "
"to %s? ", host);
/* continue below */
break;
case SSHMUX_COMMAND_TERMINATE:
if (options.control_master == SSHCTL_MASTER_ASK ||
options.control_master == SSHCTL_MASTER_AUTO_ASK)
allowed = ask_permission("Terminate shared connection "
"to %s? ", host);
if (allowed)
start_close = 1;
/* FALLTHROUGH */
case SSHMUX_COMMAND_ALIVE_CHECK:
/* Reply for SSHMUX_COMMAND_TERMINATE and ALIVE_CHECK */
buffer_clear(&m);
buffer_put_int(&m, allowed);
buffer_put_int(&m, getpid());
if (ssh_msg_send(client_fd, SSHMUX_VER, &m) == -1) {
error("%s: client msg_send failed", __func__);
close(client_fd);
buffer_free(&m);
return start_close;
}
buffer_free(&m);
close(client_fd);
return start_close;
default:
error("Unsupported command %d", mux_command);
buffer_free(&m);
close(client_fd);
return 0;
}
/* Reply for SSHMUX_COMMAND_OPEN */
buffer_clear(&m);
buffer_put_int(&m, allowed);
buffer_put_int(&m, getpid());
if (ssh_msg_send(client_fd, SSHMUX_VER, &m) == -1) {
error("%s: client msg_send failed", __func__);
close(client_fd);
buffer_free(&m);
return 0;
}
if (!allowed) {
error("Refused control connection");
close(client_fd);
buffer_free(&m);
return 0;
}
buffer_clear(&m);
if (ssh_msg_recv(client_fd, &m) == -1) {
error("%s: client msg_recv failed", __func__);
close(client_fd);
buffer_free(&m);
return 0;
}
if ((ver = buffer_get_char(&m)) != SSHMUX_VER) {
error("%s: wrong client version %d", __func__, ver);
buffer_free(&m);
close(client_fd);
return 0;
}
cctx = xcalloc(1, sizeof(*cctx));
cctx->want_tty = (flags & SSHMUX_FLAG_TTY) != 0;
cctx->want_subsys = (flags & SSHMUX_FLAG_SUBSYS) != 0;
cctx->want_x_fwd = (flags & SSHMUX_FLAG_X11_FWD) != 0;
cctx->want_agent_fwd = (flags & SSHMUX_FLAG_AGENT_FWD) != 0;
cctx->term = buffer_get_string(&m, &len);
escape_char = buffer_get_int(&m);
cmd = buffer_get_string(&m, &len);
buffer_init(&cctx->cmd);
buffer_append(&cctx->cmd, cmd, strlen(cmd));
env_len = buffer_get_int(&m);
env_len = MIN(env_len, 4096);
debug3("%s: receiving %d env vars", __func__, env_len);
if (env_len != 0) {
cctx->env = xcalloc(env_len + 1, sizeof(*cctx->env));
for (i = 0; i < env_len; i++)
cctx->env[i] = buffer_get_string(&m, &len);
cctx->env[i] = NULL;
}
debug2("%s: accepted tty %d, subsys %d, cmd %s", __func__,
cctx->want_tty, cctx->want_subsys, cmd);
xfree(cmd);
/* Gather fds from client */
for(i = 0; i < 3; i++) {
if ((new_fd[i] = mm_receive_fd(client_fd)) == -1) {
error("%s: failed to receive fd %d from slave",
__func__, i);
for (j = 0; j < i; j++)
close(new_fd[j]);
for (j = 0; j < env_len; j++)
xfree(cctx->env[j]);
if (env_len > 0)
xfree(cctx->env);
xfree(cctx->term);
buffer_free(&cctx->cmd);
close(client_fd);
xfree(cctx);
return 0;
}
}
debug2("%s: got fds stdin %d, stdout %d, stderr %d", __func__,
new_fd[0], new_fd[1], new_fd[2]);
/* Try to pick up ttymodes from client before it goes raw */
if (cctx->want_tty && tcgetattr(new_fd[0], &cctx->tio) == -1)
error("%s: tcgetattr: %s", __func__, strerror(errno));
/* This roundtrip is just for synchronisation of ttymodes */
buffer_clear(&m);
if (ssh_msg_send(client_fd, SSHMUX_VER, &m) == -1) {
error("%s: client msg_send failed", __func__);
close(client_fd);
close(new_fd[0]);
close(new_fd[1]);
close(new_fd[2]);
buffer_free(&m);
xfree(cctx->term);
if (env_len != 0) {
for (i = 0; i < env_len; i++)
xfree(cctx->env[i]);
xfree(cctx->env);
}
return 0;
}
buffer_free(&m);
/* enable nonblocking unless tty */
if (!isatty(new_fd[0]))
set_nonblock(new_fd[0]);
if (!isatty(new_fd[1]))
set_nonblock(new_fd[1]);
if (!isatty(new_fd[2]))
set_nonblock(new_fd[2]);
set_nonblock(client_fd);
window = CHAN_SES_WINDOW_DEFAULT;
packetmax = CHAN_SES_PACKET_DEFAULT;
if (cctx->want_tty) {
window >>= 1;
packetmax >>= 1;
}
c = channel_new("session", SSH_CHANNEL_OPENING,
new_fd[0], new_fd[1], new_fd[2], window, packetmax,
CHAN_EXTENDED_WRITE, "client-session", /*nonblock*/0);
c->ctl_fd = client_fd;
if (cctx->want_tty && escape_char != 0xffffffff) {
channel_register_filter(c->self,
client_simple_escape_filter, NULL,
client_filter_cleanup,
client_new_escape_filter_ctx((int)escape_char));
}
debug3("%s: channel_new: %d", __func__, c->self);
channel_send_open(c->self);
channel_register_open_confirm(c->self, mux_session_confirm, cctx);
return 0;
}
/* ** Multiplexing client support */
/* Exit signal handler */
static void
control_client_sighandler(int signo)
{
muxclient_terminate = signo;
}
/*
* Relay signal handler - used to pass some signals from mux client to
* mux master.
*/
static void
control_client_sigrelay(int signo)
{
int save_errno = errno;
if (muxserver_pid > 1)
kill(muxserver_pid, signo);
errno = save_errno;
}
/* Check mux client environment variables before passing them to mux master. */
static int
env_permitted(char *env)
{
int i, ret;
char name[1024], *cp;
if ((cp = strchr(env, '=')) == NULL || cp == env)
return (0);
ret = snprintf(name, sizeof(name), "%.*s", (int)(cp - env), env);
if (ret <= 0 || (size_t)ret >= sizeof(name))
fatal("env_permitted: name '%.100s...' too long", env);
for (i = 0; i < options.num_send_env; i++)
if (match_pattern(name, options.send_env[i]))
return (1);
return (0);
}
/* Multiplex client main loop. */
void
muxclient(const char *path)
{
struct sockaddr_un addr;
int i, r, fd, sock, exitval[2], num_env;
Buffer m;
char *term;
extern char **environ;
u_int allowed, flags;
if (muxclient_command == 0)
muxclient_command = SSHMUX_COMMAND_OPEN;
switch (options.control_master) {
case SSHCTL_MASTER_AUTO:
case SSHCTL_MASTER_AUTO_ASK:
debug("auto-mux: Trying existing master");
/* FALLTHROUGH */
case SSHCTL_MASTER_NO:
break;
default:
return;
}
memset(&addr, '\0', sizeof(addr));
addr.sun_family = AF_UNIX;
addr.sun_len = offsetof(struct sockaddr_un, sun_path) +
strlen(path) + 1;
if (strlcpy(addr.sun_path, path,
sizeof(addr.sun_path)) >= sizeof(addr.sun_path))
fatal("ControlPath too long");
if ((sock = socket(PF_UNIX, SOCK_STREAM, 0)) < 0)
fatal("%s socket(): %s", __func__, strerror(errno));
if (connect(sock, (struct sockaddr *)&addr, addr.sun_len) == -1) {
if (muxclient_command != SSHMUX_COMMAND_OPEN) {
fatal("Control socket connect(%.100s): %s", path,
strerror(errno));
}
if (errno == ENOENT)
debug("Control socket \"%.100s\" does not exist", path);
else {
error("Control socket connect(%.100s): %s", path,
strerror(errno));
}
close(sock);
return;
}
if (stdin_null_flag) {
if ((fd = open(_PATH_DEVNULL, O_RDONLY)) == -1)
fatal("open(/dev/null): %s", strerror(errno));
if (dup2(fd, STDIN_FILENO) == -1)
fatal("dup2: %s", strerror(errno));
if (fd > STDERR_FILENO)
close(fd);
}
term = getenv("TERM");
flags = 0;
if (tty_flag)
flags |= SSHMUX_FLAG_TTY;
if (subsystem_flag)
flags |= SSHMUX_FLAG_SUBSYS;
if (options.forward_x11)
flags |= SSHMUX_FLAG_X11_FWD;
if (options.forward_agent)
flags |= SSHMUX_FLAG_AGENT_FWD;
signal(SIGPIPE, SIG_IGN);
buffer_init(&m);
/* Send our command to server */
buffer_put_int(&m, muxclient_command);
buffer_put_int(&m, flags);
if (ssh_msg_send(sock, SSHMUX_VER, &m) == -1) {
error("%s: msg_send", __func__);
muxerr:
close(sock);
buffer_free(&m);
if (muxclient_command != SSHMUX_COMMAND_OPEN)
cleanup_exit(255);
logit("Falling back to non-multiplexed connection");
xfree(options.control_path);
options.control_path = NULL;
options.control_master = SSHCTL_MASTER_NO;
return;
}
buffer_clear(&m);
/* Get authorisation status and PID of controlee */
if (ssh_msg_recv(sock, &m) == -1) {
error("%s: Did not receive reply from master", __func__);
goto muxerr;
}
if (buffer_get_char(&m) != SSHMUX_VER) {
error("%s: Master replied with wrong version", __func__);
goto muxerr;
}
if (buffer_get_int_ret(&allowed, &m) != 0) {
error("%s: bad server reply", __func__);
goto muxerr;
}
if (allowed != 1) {
error("Connection to master denied");
goto muxerr;
}
muxserver_pid = buffer_get_int(&m);
buffer_clear(&m);
switch (muxclient_command) {
case SSHMUX_COMMAND_ALIVE_CHECK:
fprintf(stderr, "Master running (pid=%d)\r\n",
muxserver_pid);
exit(0);
case SSHMUX_COMMAND_TERMINATE:
fprintf(stderr, "Exit request sent.\r\n");
exit(0);
case SSHMUX_COMMAND_OPEN:
buffer_put_cstring(&m, term ? term : "");
if (options.escape_char == SSH_ESCAPECHAR_NONE)
buffer_put_int(&m, 0xffffffff);
else
buffer_put_int(&m, options.escape_char);
buffer_append(&command, "\0", 1);
buffer_put_cstring(&m, buffer_ptr(&command));
if (options.num_send_env == 0 || environ == NULL) {
buffer_put_int(&m, 0);
} else {
/* Pass environment */
num_env = 0;
for (i = 0; environ[i] != NULL; i++) {
if (env_permitted(environ[i]))
num_env++; /* Count */
}
buffer_put_int(&m, num_env);
for (i = 0; environ[i] != NULL && num_env >= 0; i++) {
if (env_permitted(environ[i])) {
num_env--;
buffer_put_cstring(&m, environ[i]);
}
}
}
break;
default:
fatal("unrecognised muxclient_command %d", muxclient_command);
}
if (ssh_msg_send(sock, SSHMUX_VER, &m) == -1) {
error("%s: msg_send", __func__);
goto muxerr;
}
if (mm_send_fd(sock, STDIN_FILENO) == -1 ||
mm_send_fd(sock, STDOUT_FILENO) == -1 ||
mm_send_fd(sock, STDERR_FILENO) == -1) {
error("%s: send fds failed", __func__);
goto muxerr;
}
/*
* Mux errors are non-recoverable from this point as the master
* has ownership of the session now.
*/
/* Wait for reply, so master has a chance to gather ttymodes */
buffer_clear(&m);
if (ssh_msg_recv(sock, &m) == -1)
fatal("%s: msg_recv", __func__);
if (buffer_get_char(&m) != SSHMUX_VER)
fatal("%s: wrong version", __func__);
buffer_free(&m);
signal(SIGHUP, control_client_sighandler);
signal(SIGINT, control_client_sighandler);
signal(SIGTERM, control_client_sighandler);
signal(SIGWINCH, control_client_sigrelay);
if (tty_flag)
enter_raw_mode();
/*
* Stick around until the controlee closes the client_fd.
* Before it does, it is expected to write this process' exit
* value (one int). This process must read the value and wait for
* the closure of the client_fd; if this one closes early, the
* multiplex master will terminate early too (possibly losing data).
*/
exitval[0] = 0;
for (i = 0; !muxclient_terminate && i < (int)sizeof(exitval);) {
r = read(sock, (char *)exitval + i, sizeof(exitval) - i);
if (r == 0) {
debug2("Received EOF from master");
break;
}
if (r == -1) {
if (errno == EINTR)
continue;
fatal("%s: read %s", __func__, strerror(errno));
}
i += r;
}
close(sock);
leave_raw_mode();
if (i > (int)sizeof(int))
fatal("%s: master returned too much data (%d > %lu)",
__func__, i, (u_long)sizeof(int));
if (muxclient_terminate) {
debug2("Exiting on signal %d", muxclient_terminate);
exitval[0] = 255;
} else if (i < (int)sizeof(int)) {
debug2("Control master terminated unexpectedly");
exitval[0] = 255;
} else
debug2("Received exit status from master %d", exitval[0]);
if (tty_flag && options.log_level != SYSLOG_LEVEL_QUIET)
fprintf(stderr, "Shared connection to %s closed.\r\n", host);
exit(exitval[0]);
}