add a "ControlPersist" option that automatically starts a background

ssh(1) multiplex master when connecting. This connection can stay alive
indefinitely, or can be set to automatically close after a user-specified
duration of inactivity. bz#1330 - patch by dwmw2 AT infradead.org, but
further hacked on by wmertens AT cisco.com, apb AT cequrux.com,
martin-mindrot-bugzilla AT earth.li and myself; "looks ok" markus@

5 files changed, 215 insertions, 31 deletions

diff --git a/usr.bin/ssh/clientloop.c b/usr.bin/ssh/clientloop.c
index be01467e9d4..263e41943c0 100644
--- a/usr.bin/ssh/clientloop.c
+++ b/usr.bin/ssh/clientloop.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: clientloop.c,v 1.221 2010/06/25 23:15:36 djm Exp $ */
+/* $OpenBSD: clientloop.c,v 1.222 2010/07/19 09:15:12 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -137,6 +137,9 @@ static volatile sig_atomic_t received_signal = 0;
 /* Flag indicating whether the user's terminal is in non-blocking mode. */
 static int in_non_blocking_mode = 0;
 
+/* Time when backgrounded control master using ControlPersist should exit */
+static time_t control_persist_exit_time = 0;
+
 /* Common data for the client loop code. */
 volatile sig_atomic_t quit_pending; /* Set non-zero to quit the loop. */
 static int escape_char1;	/* Escape character. (proto1 only) */
@@ -244,6 +247,34 @@ get_current_time(void)
 	return (double) tv.tv_sec + (double) tv.tv_usec / 1000000.0;
 }
 
+/*
+ * Sets control_persist_exit_time to the absolute time when the
+ * backgrounded control master should exit due to expiry of the
+ * ControlPersist timeout.  Sets it to 0 if we are not a backgrounded
+ * control master process, or if there is no ControlPersist timeout.
+ */
+static void
+set_control_persist_exit_time(void)
+{
+	if (muxserver_sock == -1 || !options.control_persist
+	    || options.control_persist_timeout == 0)
+		/* not using a ControlPersist timeout */
+		control_persist_exit_time = 0;
+	else if (channel_still_open()) {
+		/* some client connections are still open */
+		if (control_persist_exit_time > 0)
+			debug2("%s: cancel scheduled exit", __func__);
+		control_persist_exit_time = 0;
+	} else if (control_persist_exit_time <= 0) {
+		/* a client connection has recently closed */
+		control_persist_exit_time = time(NULL) +
+			(time_t)options.control_persist_timeout;
+		debug2("%s: schedule exit in %d seconds", __func__,
+		    options.control_persist_timeout);
+	}
+	/* else we are already counting down to the timeout */
+}
+
 #define SSH_X11_PROTO "MIT-MAGIC-COOKIE-1"
 void
 client_x11_get_proto(const char *display, const char *xauth_path,
@@ -525,6 +556,7 @@ client_wait_until_can_do_something(fd_set **readsetp, fd_set **writesetp,
     int *maxfdp, u_int *nallocp, int rekeying)
 {
 	struct timeval tv, *tvp;
+	int timeout_secs;
 	int ret;
 
 	/* Add any selections by the channel mechanism. */
@@ -568,16 +600,27 @@ client_wait_until_can_do_something(fd_set **readsetp, fd_set **writesetp,
 	/*
 	 * Wait for something to happen.  This will suspend the process until
 	 * some selected descriptor can be read, written, or has some other
-	 * event pending.
+	 * event pending, or a timeout expires.
 	 */
 
-	if (options.server_alive_interval == 0 || !compat20)
+	timeout_secs = INT_MAX; /* we use INT_MAX to mean no timeout */
+	if (options.server_alive_interval > 0 && compat20)
+		timeout_secs = options.server_alive_interval;
+	set_control_persist_exit_time();
+	if (control_persist_exit_time > 0) {
+		timeout_secs = MIN(timeout_secs,
+			control_persist_exit_time - time(NULL));
+		if (timeout_secs < 0)
+			timeout_secs = 0;
+	}
+	if (timeout_secs == INT_MAX)
 		tvp = NULL;
 	else {
-		tv.tv_sec = options.server_alive_interval;
+		tv.tv_sec = timeout_secs;
 		tv.tv_usec = 0;
 		tvp = &tv;
 	}
+
 	ret = select((*maxfdp)+1, *readsetp, *writesetp, NULL, tvp);
 	if (ret < 0) {
 		char buf[100];
@@ -1466,6 +1509,18 @@ client_loop(int have_pty, int escape_char_arg, int ssh2_chan_id)
 		 */
 		if (FD_ISSET(connection_out, writeset))
 			packet_write_poll();
+
+		/*
+		 * If we are a backgrounded control master, and the
+		 * timeout has expired without any active client
+		 * connections, then quit.
+		 */
+		if (control_persist_exit_time > 0) {
+			if (time(NULL) >= control_persist_exit_time) {
+				debug("ControlPersist timeout expired");
+				break;
+			}
+		}
 	}
 	if (readset)
 		xfree(readset);
diff --git a/usr.bin/ssh/readconf.c b/usr.bin/ssh/readconf.c
index da717e6462c..56f37b7786b 100644
--- a/usr.bin/ssh/readconf.c
+++ b/usr.bin/ssh/readconf.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: readconf.c,v 1.186 2010/06/25 23:15:36 djm Exp $ */
+/* $OpenBSD: readconf.c,v 1.187 2010/07/19 09:15:12 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -125,7 +125,8 @@ typedef enum {
 	oEnableSSHKeysign, oRekeyLimit, oVerifyHostKeyDNS, oConnectTimeout,
 	oAddressFamily, oGssAuthentication, oGssDelegateCreds,
 	oServerAliveInterval, oServerAliveCountMax, oIdentitiesOnly,
-	oSendEnv, oControlPath, oControlMaster, oHashKnownHosts,
+	oSendEnv, oControlPath, oControlMaster, oControlPersist,
+	oHashKnownHosts,
 	oTunnel, oTunnelDevice, oLocalCommand, oPermitLocalCommand,
 	oVisualHostKey, oUseRoaming, oZeroKnowledgePasswordAuthentication,
 	oDeprecated, oUnsupported
@@ -222,6 +223,7 @@ static struct {
 	{ "sendenv", oSendEnv },
 	{ "controlpath", oControlPath },
 	{ "controlmaster", oControlMaster },
+	{ "controlpersist", oControlPersist },
 	{ "hashknownhosts", oHashKnownHosts },
 	{ "tunnel", oTunnel },
 	{ "tunneldevice", oTunnelDevice },
@@ -878,6 +880,30 @@ parse_int:
 			*intptr = value;
 		break;
 
+	case oControlPersist:
+		/* no/false/yes/true, or a time spec */
+		intptr = &options->control_persist;
+		arg = strdelim(&s);
+		if (!arg || *arg == '\0')
+			fatal("%.200s line %d: Missing ControlPersist"
+			    " argument.", filename, linenum);
+		value = 0;
+		value2 = 0;	/* timeout */
+		if (strcmp(arg, "no") == 0 || strcmp(arg, "false") == 0)
+			value = 0;
+		else if (strcmp(arg, "yes") == 0 || strcmp(arg, "true") == 0)
+			value = 1;
+		else if ((value2 = convtime(arg)) >= 0)
+			value = 1;
+		else
+			fatal("%.200s line %d: Bad ControlPersist argument.",
+			    filename, linenum);
+		if (*activep && *intptr == -1) {
+			*intptr = value;
+			options->control_persist_timeout = value2;
+		}
+		break;
+
 	case oHashKnownHosts:
 		intptr = &options->hash_known_hosts;
 		goto parse_flag;
@@ -1079,6 +1105,8 @@ initialize_options(Options * options)
 	options->num_send_env = 0;
 	options->control_path = NULL;
 	options->control_master = -1;
+	options->control_persist = -1;
+	options->control_persist_timeout = 0;
 	options->hash_known_hosts = -1;
 	options->tun_open = -1;
 	options->tun_local = -1;
@@ -1214,6 +1242,10 @@ fill_default_options(Options * options)
 		options->server_alive_count_max = 3;
 	if (options->control_master == -1)
 		options->control_master = 0;
+	if (options->control_persist == -1) {
+		options->control_persist = 0;
+		options->control_persist_timeout = 0;
+	}
 	if (options->hash_known_hosts == -1)
 		options->hash_known_hosts = 0;
 	if (options->tun_open == -1)
diff --git a/usr.bin/ssh/readconf.h b/usr.bin/ssh/readconf.h
index 66acafdefa1..95d10467472 100644
--- a/usr.bin/ssh/readconf.h
+++ b/usr.bin/ssh/readconf.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: readconf.h,v 1.85 2010/06/25 23:15:36 djm Exp $ */
+/* $OpenBSD: readconf.h,v 1.86 2010/07/19 09:15:12 djm Exp $ */
 
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
@@ -114,6 +114,8 @@ typedef struct {
 
 	char	*control_path;
 	int	control_master;
+	int     control_persist; /* ControlPersist flag */
+	int     control_persist_timeout; /* ControlPersist timeout (seconds) */
 
 	int	hash_known_hosts;
 
diff --git a/usr.bin/ssh/ssh.c b/usr.bin/ssh/ssh.c
index 2aab1048a31..0c18fec527b 100644
--- a/usr.bin/ssh/ssh.c
+++ b/usr.bin/ssh/ssh.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: ssh.c,v 1.343 2010/07/12 22:41:13 djm Exp $ */
+/* $OpenBSD: ssh.c,v 1.344 2010/07/19 09:15:12 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -119,6 +119,15 @@ int no_shell_flag = 0;
 int stdin_null_flag = 0;
 
 /*
+ * Flag indicating that the current process should be backgrounded and
+ * a new slave launched in the foreground for ControlPersist.
+ */
+int need_controlpersist_detach = 0;
+
+/* Copies of flags for ControlPersist foreground slave */
+int ostdin_null_flag, ono_shell_flag, ono_tty_flag, otty_flag;
+
+/*
  * Flag indicating that ssh should fork after authentication.  This is useful
  * so that the passphrase can be entered manually, and then ssh goes to the
  * background.
@@ -858,6 +867,50 @@ main(int ac, char **av)
 	return exit_status;
 }
 
+static void
+control_persist_detach(void)
+{
+	pid_t pid;
+
+	debug("%s: backgrounding master process", __func__);
+
+ 	/*
+ 	 * master (current process) into the background, and make the
+ 	 * foreground process a client of the backgrounded master.
+ 	 */
+	switch ((pid = fork())) {
+	case -1:
+		fatal("%s: fork: %s", __func__, strerror(errno));
+	case 0:
+		/* Child: master process continues mainloop */
+ 		break;
+ 	default:
+		/* Parent: set up mux slave to connect to backgrounded master */
+		debug2("%s: background process is %ld", __func__, (long)pid);
+		stdin_null_flag = ostdin_null_flag;
+		no_shell_flag = ono_shell_flag;
+		no_tty_flag = ono_tty_flag;
+		tty_flag = otty_flag;
+ 		close(muxserver_sock);
+ 		muxserver_sock = -1;
+ 		muxclient(options.control_path);
+		/* muxclient() doesn't return on success. */
+ 		fatal("Failed to connect to new control master");
+ 	}
+}
+
+/* Do fork() after authentication. Used by "ssh -f" */
+static void
+fork_postauth(void)
+{
+	if (need_controlpersist_detach)
+		control_persist_detach();
+	debug("forking to background");
+	fork_after_authentication_flag = 0;
+	if (daemon(1, 1) < 0)
+		fatal("daemon() failed: %.200s", strerror(errno));
+}
+
 /* Callback for remote forward global requests */
 static void
 ssh_confirm_remote_forward(int type, u_int32_t seq, void *ctxt)
@@ -885,12 +938,8 @@ ssh_confirm_remote_forward(int type, u_int32_t seq, void *ctxt)
 	}
 	if (++remote_forward_confirms_received == options.num_remote_forwards) {
 		debug("All remote forwarding requests processed");
-		if (fork_after_authentication_flag) {
-			fork_after_authentication_flag = 0;
-			if (daemon(1, 1) < 0)
-				fatal("daemon() failed: %.200s",
-				    strerror(errno));
-		}
+		if (fork_after_authentication_flag)
+			fork_postauth();
 	}
 }
 
@@ -1134,12 +1183,13 @@ ssh_session(void)
 	 * If requested and we are not interested in replies to remote
 	 * forwarding requests, then let ssh continue in the background.
 	 */
-	if (fork_after_authentication_flag &&
-	    (!options.exit_on_forward_failure ||
-	    options.num_remote_forwards == 0)) {
-		fork_after_authentication_flag = 0;
-		if (daemon(1, 1) < 0)
-			fatal("daemon() failed: %.200s", strerror(errno));
+	if (fork_after_authentication_flag) {
+		if (options.exit_on_forward_failure &&
+		    options.num_remote_forwards > 0) {
+			debug("deferring postauth fork until remote forward "
+			    "confirmation received");
+		} else
+			fork_postauth();
 	}
 
 	/*
@@ -1262,6 +1312,31 @@ ssh_session2(void)
 	/* XXX should be pre-session */
 	ssh_init_forwarding();
 
+	/* Start listening for multiplex clients */
+	muxserver_listen();
+
+ 	/*
+	 * If we are in control persist mode, then prepare to background
+	 * ourselves and have a foreground client attach as a control
+	 * slave. NB. we must save copies of the flags that we override for
+	 * the backgrounding, since we defer attachment of the slave until
+	 * after the connection is fully established (in particular,
+	 * async rfwd replies have been received for ExitOnForwardFailure).
+	 */
+ 	if (options.control_persist && muxserver_sock != -1) {
+		ostdin_null_flag = stdin_null_flag;
+		ono_shell_flag = no_shell_flag;
+		ono_tty_flag = no_tty_flag;
+		otty_flag = tty_flag;
+ 		stdin_null_flag = 1;
+ 		no_shell_flag = 1;
+ 		no_tty_flag = 1;
+ 		tty_flag = 0;
+		if (!fork_after_authentication_flag)
+			need_controlpersist_detach = 1;
+		fork_after_authentication_flag = 1;
+ 	}
+
 	if (!no_shell_flag || (datafellows & SSH_BUG_DUMMYCHAN))
 		id = ssh_session2_open();
 
@@ -1280,19 +1355,17 @@ ssh_session2(void)
 	    options.permit_local_command)
 		ssh_local_cmd(options.local_command);
 
-	/* Start listening for multiplex clients */
-	muxserver_listen();
-
 	/*
 	 * If requested and we are not interested in replies to remote
 	 * forwarding requests, then let ssh continue in the background.
 	 */
-	if (fork_after_authentication_flag &&
-	    (!options.exit_on_forward_failure ||
-	    options.num_remote_forwards == 0)) {
-		fork_after_authentication_flag = 0;
-		if (daemon(1, 1) < 0)
-			fatal("daemon() failed: %.200s", strerror(errno));
+	if (fork_after_authentication_flag) {
+		if (options.exit_on_forward_failure &&
+		    options.num_remote_forwards > 0) {
+			debug("deferring postauth fork until remote forward "
+			    "confirmation received");
+		} else
+			fork_postauth();
 	}
 
 	if (options.use_roaming)
diff --git a/usr.bin/ssh/ssh_config.5 b/usr.bin/ssh/ssh_config.5
index e7bb21ebb43..04df8184c13 100644
--- a/usr.bin/ssh/ssh_config.5
+++ b/usr.bin/ssh/ssh_config.5
@@ -34,8 +34,8 @@
 .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 .\"
-.\" $OpenBSD: ssh_config.5,v 1.136 2010/07/12 22:41:13 djm Exp $
-.Dd $Mdocdate: July 12 2010 $
+.\" $OpenBSD: ssh_config.5,v 1.137 2010/07/19 09:15:12 djm Exp $
+.Dd $Mdocdate: July 19 2010 $
 .Dt SSH_CONFIG 5
 .Os
 .Sh NAME
@@ -319,6 +319,28 @@ It is recommended that any
 used for opportunistic connection sharing include
 at least %h, %p, and %r.
 This ensures that shared connections are uniquely identified.
+.It Cm ControlPersist
+When used in conjunction with
+.Cm ControlMaster ,
+specifies that the master connection should remain open
+in the background (waiting for future client connections)
+after the initial client connection has been closed.
+If set to
+.Dq no ,
+then the master connection will not be placed into the background,
+and will close as soon as the initial client connection is closed.
+If set to
+.Dq yes ,
+then the master connection will remain in the background indefinitely
+(until killed or closed via a mechanism such as the
+.Xr ssh 1
+.Dq Fl O No exit
+option).
+If set to a time in seconds, or a time in any of the formats documented in
+.Xr sshd_config 5 ,
+then the backgrounded master connection will automatically terminate
+after it has remained idle (with no client connections) for the
+specified time.
 .It Cm DynamicForward
 Specifies that a TCP port on the local machine be forwarded
 over the secure channel, and the application