- djm@cvs.openbsd.org 2010/01/26 01:28:35

[channels.c channels.h clientloop.c clientloop.h mux.c nchan.c ssh.c]
     rewrite ssh(1) multiplexing code to a more sensible protocol.

     The new multiplexing code uses channels for the listener and
     accepted control sockets to make the mux master non-blocking, so
     no stalls when processing messages from a slave.

     avoid use of fatal() in mux master protocol parsing so an errant slave
     process cannot take down a running master.

     implement requesting of port-forwards over multiplexed sessions. Any
     port forwards requested by the slave are added to those the master has
     established.

     add support for stdio forwarding ("ssh -W host:port ...") in mux slaves.

     document master/slave mux protocol so that other tools can use it to
     control a running ssh(1). Note: there are no guarantees that this
     protocol won't be incompatibly changed (though it is versioned).

     feedback Salvador Fandino, dtucker@
     channel changes ok markus@

ChangeLog

@@ -8,6 +8,29 @@
      [roaming_client.c]
      s/long long unsigned/unsigned long long/, from tim via portable
      (Id sync only, change already in portable)
+   - djm@cvs.openbsd.org 2010/01/26 01:28:35
+     [channels.c channels.h clientloop.c clientloop.h mux.c nchan.c ssh.c]
+     rewrite ssh(1) multiplexing code to a more sensible protocol.
+     
+     The new multiplexing code uses channels for the listener and
+     accepted control sockets to make the mux master non-blocking, so
+     no stalls when processing messages from a slave.
+     
+     avoid use of fatal() in mux master protocol parsing so an errant slave
+     process cannot take down a running master.
+     
+     implement requesting of port-forwards over multiplexed sessions. Any
+     port forwards requested by the slave are added to those the master has
+     established.
+     
+     add support for stdio forwarding ("ssh -W host:port ...") in mux slaves.
+     
+     document master/slave mux protocol so that other tools can use it to
+     control a running ssh(1). Note: there are no guarantees that this
+     protocol won't be incompatibly changed (though it is versioned).
+     
+     feedback Salvador Fandino, dtucker@
+     channel changes ok markus@
 
 20100122
  - (tim) [configure.ac] Due to constraints in Windows Sockets in terms of

channels.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: channels.c,v 1.301 2010/01/11 01:39:46 dtucker Exp $ */
+/* $OpenBSD: channels.c,v 1.302 2010/01/26 01:28:35 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -239,7 +239,6 @@ channel_register_fds(Channel *c, int rfd, int wfd, int efd,
 	c->rfd = rfd;
 	c->wfd = wfd;
 	c->sock = (rfd == wfd) ? rfd : -1;
-	c->ctl_fd = -1; /* XXX: set elsewhere */
 	c->efd = efd;
 	c->extended_usage = extusage;
 
@@ -328,6 +327,9 @@ channel_new(char *ctype, int type, int rfd, int wfd, int efd,
 	c->output_filter = NULL;
 	c->filter_ctx = NULL;
 	c->filter_cleanup = NULL;
+	c->ctl_chan = -1;
+	c->mux_rcb = NULL;
+	c->mux_ctx = NULL;
 	c->delayed = 1;		/* prevent call to channel_post handler */
 	TAILQ_INIT(&c->status_confirms);
 	debug("channel %d: new [%s]", found, remote_name);
@@ -370,11 +372,10 @@ channel_close_fd(int *fdp)
 static void
 channel_close_fds(Channel *c)
 {
-	debug3("channel %d: close_fds r %d w %d e %d c %d",
+	debug3("channel %d: close_fds r %d w %d e %d",
-	    c->self, c->rfd, c->wfd, c->efd, c->ctl_fd);
+	    c->self, c->rfd, c->wfd, c->efd);
 
 	channel_close_fd(&c->sock);
-	channel_close_fd(&c->ctl_fd);
 	channel_close_fd(&c->rfd);
 	channel_close_fd(&c->wfd);
 	channel_close_fd(&c->efd);
@@ -400,8 +401,6 @@ channel_free(Channel *c)
 
 	if (c->sock != -1)
 		shutdown(c->sock, SHUT_RDWR);
-	if (c->ctl_fd != -1)
-		shutdown(c->ctl_fd, SHUT_RDWR);
 	channel_close_fds(c);
 	buffer_free(&c->input);
 	buffer_free(&c->output);
@@ -523,6 +522,7 @@ channel_still_open(void)
 		case SSH_CHANNEL_X11_LISTENER:
 		case SSH_CHANNEL_PORT_LISTENER:
 		case SSH_CHANNEL_RPORT_LISTENER:
+		case SSH_CHANNEL_MUX_LISTENER:
 		case SSH_CHANNEL_CLOSED:
 		case SSH_CHANNEL_AUTH_SOCKET:
 		case SSH_CHANNEL_DYNAMIC:
@@ -536,6 +536,7 @@ channel_still_open(void)
 		case SSH_CHANNEL_OPENING:
 		case SSH_CHANNEL_OPEN:
 		case SSH_CHANNEL_X11_OPEN:
+		case SSH_CHANNEL_MUX_CLIENT:
 			return 1;
 		case SSH_CHANNEL_INPUT_DRAINING:
 		case SSH_CHANNEL_OUTPUT_DRAINING:
@@ -567,6 +568,8 @@ channel_find_open(void)
 		case SSH_CHANNEL_X11_LISTENER:
 		case SSH_CHANNEL_PORT_LISTENER:
 		case SSH_CHANNEL_RPORT_LISTENER:
+		case SSH_CHANNEL_MUX_LISTENER:
+		case SSH_CHANNEL_MUX_CLIENT:
 		case SSH_CHANNEL_OPENING:
 		case SSH_CHANNEL_CONNECTING:
 		case SSH_CHANNEL_ZOMBIE:
@@ -617,6 +620,8 @@ channel_open_message(void)
 		case SSH_CHANNEL_CLOSED:
 		case SSH_CHANNEL_AUTH_SOCKET:
 		case SSH_CHANNEL_ZOMBIE:
+		case SSH_CHANNEL_MUX_CLIENT:
+		case SSH_CHANNEL_MUX_LISTENER:
 			continue;
 		case SSH_CHANNEL_LARVAL:
 		case SSH_CHANNEL_OPENING:
@@ -627,12 +632,12 @@ channel_open_message(void)
 		case SSH_CHANNEL_INPUT_DRAINING:
 		case SSH_CHANNEL_OUTPUT_DRAINING:
 			snprintf(buf, sizeof buf,
-			    "  #%d %.300s (t%d r%d i%d/%d o%d/%d fd %d/%d cfd %d)\r\n",
+			    "  #%d %.300s (t%d r%d i%d/%d o%d/%d fd %d/%d cc %d)\r\n",
 			    c->self, c->remote_name,
 			    c->type, c->remote_id,
 			    c->istate, buffer_len(&c->input),
 			    c->ostate, buffer_len(&c->output),
-			    c->rfd, c->wfd, c->ctl_fd);
+			    c->rfd, c->wfd, c->ctl_chan);
 			buffer_append(&buffer, buf, strlen(buf));
 			continue;
 		default:
@@ -839,9 +844,6 @@ channel_pre_open(Channel *c, fd_set *readset, fd_set *writeset)
 			FD_SET(c->efd, readset);
 	}
 	/* XXX: What about efd? races? */
-	if (compat20 && c->ctl_fd != -1 &&
-	    c->istate == CHAN_INPUT_OPEN && c->ostate == CHAN_OUTPUT_OPEN)
-		FD_SET(c->ctl_fd, readset);
 }
 
 /* ARGSUSED */
@@ -986,6 +988,28 @@ channel_pre_x11_open(Channel *c, fd_set *readset, fd_set *writeset)
 	}
 }
 
+static void
+channel_pre_mux_client(Channel *c, fd_set *readset, fd_set *writeset)
+{
+	if (c->istate == CHAN_INPUT_OPEN &&
+	    buffer_check_alloc(&c->input, CHAN_RBUF))
+		FD_SET(c->rfd, readset);
+	if (c->istate == CHAN_INPUT_WAIT_DRAIN) {
+		/* clear buffer immediately (discard any partial packet) */
+		buffer_clear(&c->input);
+		chan_ibuf_empty(c);
+		/* Start output drain. XXX just kill chan? */
+		chan_rcvd_oclose(c);
+	}
+	if (c->ostate == CHAN_OUTPUT_OPEN ||
+	    c->ostate == CHAN_OUTPUT_WAIT_DRAIN) {
+		if (buffer_len(&c->output) > 0)
+			FD_SET(c->wfd, writeset);
+		else if (c->ostate == CHAN_OUTPUT_WAIT_DRAIN)
+			chan_obuf_empty(c);
+	}
+}
+
 /* try to decode a socks4 header */
 /* ARGSUSED */
 static int
@@ -1218,19 +1242,14 @@ channel_decode_socks5(Channel *c, fd_set *readset, fd_set *writeset)
 }
 
 Channel *
-channel_connect_stdio_fwd(const char *host_to_connect, u_short port_to_connect)
+channel_connect_stdio_fwd(const char *host_to_connect, u_short port_to_connect,
+    int in, int out)
 {
 	Channel *c;
-	int in, out;
 
 	debug("channel_connect_stdio_fwd %s:%d", host_to_connect,
 	    port_to_connect);
 
-	in = dup(STDIN_FILENO);
-	out = dup(STDOUT_FILENO);
-	if (in < 0 || out < 0)
-		fatal("channel_connect_stdio_fwd: dup() in/out failed");
-
 	c = channel_new("stdio-forward", SSH_CHANNEL_OPENING, in, out,
 	    -1, CHAN_TCP_WINDOW_DEFAULT, CHAN_TCP_PACKET_DEFAULT,
 	    0, "stdio-forward", /*nonblock*/0);
@@ -1749,36 +1768,6 @@ channel_handle_efd(Channel *c, fd_set *readset, fd_set *writeset)
 	return 1;
 }
 
-/* ARGSUSED */
-static int
-channel_handle_ctl(Channel *c, fd_set *readset, fd_set *writeset)
-{
-	char buf[16];
-	int len;
-
-	/* Monitor control fd to detect if the slave client exits */
-	if (c->ctl_fd != -1 && FD_ISSET(c->ctl_fd, readset)) {
-		len = read(c->ctl_fd, buf, sizeof(buf));
-		if (len < 0 &&
-		    (errno == EINTR || errno == EAGAIN || errno == EWOULDBLOCK))
-			return 1;
-		if (len <= 0) {
-			debug2("channel %d: ctl read<=0", c->self);
-			if (c->type != SSH_CHANNEL_OPEN) {
-				debug2("channel %d: not open", c->self);
-				chan_mark_dead(c);
-				return -1;
-			} else {
-				chan_read_failed(c);
-				chan_write_failed(c);
-			}
-			return -1;
-		} else
-			fatal("%s: unexpected data on ctl fd", __func__);
-	}
-	return 1;
-}
-
 static int
 channel_check_window(Channel *c)
 {
@@ -1809,10 +1798,131 @@ channel_post_open(Channel *c, fd_set *readset, fd_set *writeset)
 	if (!compat20)
 		return;
 	channel_handle_efd(c, readset, writeset);
-	channel_handle_ctl(c, readset, writeset);
 	channel_check_window(c);
 }
 
+static u_int
+read_mux(Channel *c, u_int need)
+{
+	char buf[CHAN_RBUF];
+	int len;
+	u_int rlen;
+
+	if (buffer_len(&c->input) < need) {
+		rlen = need - buffer_len(&c->input);
+		len = read(c->rfd, buf, MIN(rlen, CHAN_RBUF));
+		if (len <= 0) {
+			if (errno != EINTR && errno != EAGAIN) {
+				debug2("channel %d: ctl read<=0 rfd %d len %d",
+				    c->self, c->rfd, len);
+				chan_read_failed(c);
+				return 0;
+			}
+		} else
+			buffer_append(&c->input, buf, len);
+	}
+	return buffer_len(&c->input);
+}
+
+static void
+channel_post_mux_client(Channel *c, fd_set *readset, fd_set *writeset)
+{
+	u_int need;
+	ssize_t len;
+
+	if (!compat20)
+		fatal("%s: entered with !compat20", __func__);
+
+	if (c->rfd != -1 && FD_ISSET(c->rfd, readset) &&
+	    (c->istate == CHAN_INPUT_OPEN ||
+	    c->istate == CHAN_INPUT_WAIT_DRAIN)) {
+		/*
+		 * Don't not read past the precise end of packets to
+		 * avoid disrupting fd passing.
+		 */
+		if (read_mux(c, 4) < 4) /* read header */
+			return;
+		need = get_u32(buffer_ptr(&c->input));
+#define CHANNEL_MUX_MAX_PACKET	(256 * 1024)
+		if (need > CHANNEL_MUX_MAX_PACKET) {
+			debug2("channel %d: packet too big %u > %u",
+			    c->self, CHANNEL_MUX_MAX_PACKET, need);
+			chan_rcvd_oclose(c);
+			return;
+		}
+		if (read_mux(c, need + 4) < need + 4) /* read body */
+			return;
+		if (c->mux_rcb(c) != 0) {
+			debug("channel %d: mux_rcb failed", c->self);
+			chan_mark_dead(c);
+			return;
+		}
+	}
+
+	if (c->wfd != -1 && FD_ISSET(c->wfd, writeset) &&
+	    buffer_len(&c->output) > 0) {
+		len = write(c->wfd, buffer_ptr(&c->output),
+		    buffer_len(&c->output));
+		if (len < 0 && (errno == EINTR || errno == EAGAIN))
+			return;
+		if (len <= 0) {
+			chan_mark_dead(c);
+			return;
+		}
+		buffer_consume(&c->output, len);
+	}
+}
+
+static void
+channel_post_mux_listener(Channel *c, fd_set *readset, fd_set *writeset)
+{
+	Channel *nc;
+	struct sockaddr_storage addr;
+	socklen_t addrlen;
+	int newsock;
+	uid_t euid;
+	gid_t egid;
+
+	if (!FD_ISSET(c->sock, readset))
+		return;
+
+	debug("multiplexing control connection");
+
+	/*
+	 * Accept connection on control socket
+	 */
+	memset(&addr, 0, sizeof(addr));
+	addrlen = sizeof(addr);
+	if ((newsock = accept(c->sock, (struct sockaddr*)&addr,
+	    &addrlen)) == -1) {
+		error("%s accept: %s", __func__, strerror(errno));
+		return;
+	}
+
+	if (getpeereid(newsock, &euid, &egid) < 0) {
+		error("%s getpeereid failed: %s", __func__,
+		    strerror(errno));
+		close(newsock);
+		return;
+	}
+	if ((euid != 0) && (getuid() != euid)) {
+		error("multiplex uid mismatch: peer euid %u != uid %u",
+		    (u_int)euid, (u_int)getuid());
+		close(newsock);
+		return;
+	}
+	nc = channel_new("multiplex client", SSH_CHANNEL_MUX_CLIENT,
+	    newsock, newsock, -1, c->local_window_max,
+	    c->local_maxpacket, 0, "mux-control", 1);
+	nc->mux_rcb = c->mux_rcb;
+	debug3("%s: new mux channel %d fd %d", __func__,
+	    nc->self, nc->sock);
+	/* establish state */
+	nc->mux_rcb(nc);
+	/* mux state transitions must not elicit protocol messages */
+	nc->flags |= CHAN_LOCAL;
+}
+
 /* ARGSUSED */
 static void
 channel_post_output_drain_13(Channel *c, fd_set *readset, fd_set *writeset)
@@ -1841,6 +1951,8 @@ channel_handler_init_20(void)
 	channel_pre[SSH_CHANNEL_AUTH_SOCKET] =		&channel_pre_listener;
 	channel_pre[SSH_CHANNEL_CONNECTING] =		&channel_pre_connecting;
 	channel_pre[SSH_CHANNEL_DYNAMIC] =		&channel_pre_dynamic;
+	channel_pre[SSH_CHANNEL_MUX_LISTENER] =		&channel_pre_listener;
+	channel_pre[SSH_CHANNEL_MUX_CLIENT] =		&channel_pre_mux_client;
 
 	channel_post[SSH_CHANNEL_OPEN] =		&channel_post_open;
 	channel_post[SSH_CHANNEL_PORT_LISTENER] =	&channel_post_port_listener;
@@ -1849,6 +1961,8 @@ channel_handler_init_20(void)
 	channel_post[SSH_CHANNEL_AUTH_SOCKET] =		&channel_post_auth_listener;
 	channel_post[SSH_CHANNEL_CONNECTING] =		&channel_post_connecting;
 	channel_post[SSH_CHANNEL_DYNAMIC] =		&channel_post_open;
+	channel_post[SSH_CHANNEL_MUX_LISTENER] =	&channel_post_mux_listener;
+	channel_post[SSH_CHANNEL_MUX_CLIENT] =		&channel_post_mux_client;
 }
 
 static void

channels.h

@@ -1,4 +1,4 @@
-/* $OpenBSD: channels.h,v 1.102 2010/01/11 01:39:46 dtucker Exp $ */
+/* $OpenBSD: channels.h,v 1.103 2010/01/26 01:28:35 djm Exp $ */
 
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
@@ -53,7 +53,9 @@
 #define SSH_CHANNEL_CONNECTING		12
 #define SSH_CHANNEL_DYNAMIC		13
 #define SSH_CHANNEL_ZOMBIE		14	/* Almost dead. */
-#define SSH_CHANNEL_MAX_TYPE		15
+#define SSH_CHANNEL_MUX_LISTENER	15	/* Listener for mux conn. */
+#define SSH_CHANNEL_MUX_CLIENT		16	/* Conn. to mux slave */
+#define SSH_CHANNEL_MAX_TYPE		17
 
 struct Channel;
 typedef struct Channel Channel;
@@ -81,6 +83,9 @@ struct channel_connect {
 	struct addrinfo *ai, *aitop;
 };
 
+/* Callbacks for mux channels back into client-specific code */
+typedef int mux_callback_fn(struct Channel *);
+
 struct Channel {
 	int     type;		/* channel type/state */
 	int     self;		/* my own channel identifier */
@@ -92,7 +97,7 @@ struct Channel {
 	int     wfd;		/* write fd */
 	int     efd;		/* extended fd */
 	int     sock;		/* sock fd */
-	int     ctl_fd;		/* control fd (client sharing) */
+	int     ctl_chan;	/* control channel (multiplexed connections) */
 	int     isatty;		/* rfd is a tty */
 	int     wfd_isatty;	/* wfd is a tty */
 	int	client_tty;	/* (client) TTY has been requested */
@@ -142,6 +147,10 @@ struct Channel {
 
 	/* non-blocking connect */
 	struct channel_connect	connect_ctx;
+
+	/* multiplexing protocol hook, called for each packet received */
+	mux_callback_fn		*mux_rcb;
+	void			*mux_ctx;
 };
 
 #define CHAN_EXTENDED_IGNORE		0
@@ -172,6 +181,7 @@ struct Channel {
 #define CHAN_CLOSE_RCVD			0x02
 #define CHAN_EOF_SENT			0x04
 #define CHAN_EOF_RCVD			0x08
+#define CHAN_LOCAL			0x10
 
 #define CHAN_RBUF	16*1024
 
@@ -243,7 +253,7 @@ void	 channel_clear_adm_permitted_opens(void);
 void 	 channel_print_adm_permitted_opens(void);
 int      channel_input_port_forward_request(int, int);
 Channel	*channel_connect_to(const char *, u_short, char *, char *);
-Channel	*channel_connect_stdio_fwd(const char*, u_short);
+Channel	*channel_connect_stdio_fwd(const char*, u_short, int, int);
 Channel	*channel_connect_by_listen_address(u_short, char *, char *);
 int	 channel_request_remote_forwarding(const char *, u_short,
 	     const char *, u_short);

clientloop.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: clientloop.c,v 1.216 2010/01/09 05:04:24 djm Exp $ */
+/* $OpenBSD: clientloop.c,v 1.217 2010/01/26 01:28:35 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -121,7 +121,7 @@ extern int stdin_null_flag;
 extern int no_shell_flag;
 
 /* Control socket */
-extern int muxserver_sock;
+extern int muxserver_sock; /* XXX use mux_client_cleanup() instead */
 
 /*
  * Name of the host we are connecting to.  This is the name given on the
@@ -146,7 +146,7 @@ static volatile sig_atomic_t received_signal = 0;
 static int in_non_blocking_mode = 0;
 
 /* Common data for the client loop code. */
-static volatile sig_atomic_t quit_pending; /* Set non-zero to quit the loop. */
+volatile sig_atomic_t quit_pending; /* Set non-zero to quit the loop. */
 static int escape_char1;	/* Escape character. (proto1 only) */
 static int escape_pending1;	/* Last character was an escape (proto1 only) */
 static int last_was_cr;		/* Last character was a newline. */
@@ -564,9 +564,6 @@ client_wait_until_can_do_something(fd_set **readsetp, fd_set **writesetp,
 	if (packet_have_data_to_write())
 		FD_SET(connection_out, *writesetp);
 
-	if (muxserver_sock != -1)
-		FD_SET(muxserver_sock, *readsetp);
-
 	/*
 	 * Wait for something to happen.  This will suspend the process until
 	 * some selected descriptor can be read, written, or has some other
@@ -695,7 +692,7 @@ client_status_confirm(int type, Channel *c, void *ctx)
 
 	/* XXX supress on mux _client_ quietmode */
 	tochan = options.log_level >= SYSLOG_LEVEL_ERROR &&
-	    c->ctl_fd != -1 && c->extended_usage == CHAN_EXTENDED_WRITE;
+	    c->ctl_chan != -1 && c->extended_usage == CHAN_EXTENDED_WRITE;
 
 	if (type == SSH2_MSG_CHANNEL_SUCCESS) {
 		debug2("%s request accepted on channel %d",
@@ -839,6 +836,7 @@ process_cmdline(void)
 	while (isspace(*++s))
 		;
 
+	/* XXX update list of forwards in options */
 	if (delete) {
 		cancel_port = 0;
 		cancel_host = hpdelim(&s);	/* may be NULL */
@@ -936,7 +934,7 @@ process_escapes(Channel *c, Buffer *bin, Buffer *bout, Buffer *berr,
 				    escape_char);
 				buffer_append(berr, string, strlen(string));
 
-				if (c && c->ctl_fd != -1) {
+				if (c && c->ctl_chan != -1) {
 					chan_read_failed(c);
 					chan_write_failed(c);
 					return 0;
@@ -946,7 +944,7 @@ process_escapes(Channel *c, Buffer *bin, Buffer *bout, Buffer *berr,
 
 			case 'Z' - 64:
 				/* XXX support this for mux clients */
-				if (c && c->ctl_fd != -1) {
+				if (c && c->ctl_chan != -1) {
  noescape:
 					snprintf(string, sizeof string,
 					    "%c%c escape not available to "
@@ -991,7 +989,7 @@ process_escapes(Channel *c, Buffer *bin, Buffer *bout, Buffer *berr,
 				continue;
 
 			case '&':
-				if (c && c->ctl_fd != -1)
+				if (c && c->ctl_chan != -1)
 					goto noescape;
 				/*
 				 * Detach the program (continue to serve
@@ -1042,7 +1040,7 @@ process_escapes(Channel *c, Buffer *bin, Buffer *bout, Buffer *berr,
 				continue;
 
 			case '?':
-				if (c && c->ctl_fd != -1) {
+				if (c && c->ctl_chan != -1) {
 					snprintf(string, sizeof string,
 "%c?\r\n\
 Supported escape sequences:\r\n\
@@ -1091,7 +1089,7 @@ Supported escape sequences:\r\n\
 				continue;
 
 			case 'C':
-				if (c && c->ctl_fd != -1)
+				if (c && c->ctl_chan != -1)
 					goto noescape;
 				process_cmdline();
 				continue;
@@ -1327,8 +1325,6 @@ client_loop(int have_pty, int escape_char_arg, int ssh2_chan_id)
 	connection_in = packet_get_connection_in();
 	connection_out = packet_get_connection_out();
 	max_fd = MAX(connection_in, connection_out);
-	if (muxserver_sock != -1)
-		max_fd = MAX(max_fd, muxserver_sock);
 
 	if (!compat20) {
 		/* enable nonblocking unless tty */
@@ -1446,12 +1442,6 @@ client_loop(int have_pty, int escape_char_arg, int ssh2_chan_id)
 		/* Buffer input from the connection.  */
 		client_process_net_input(readset);
 
-		/* Accept control connections.  */
-		if (muxserver_sock != -1 &&FD_ISSET(muxserver_sock, readset)) {
-			if (muxserver_accept_control())
-				quit_pending = 1;
-		}
-
 		if (quit_pending)
 			break;
 
@@ -1859,9 +1849,8 @@ client_input_channel_req(int type, u_int32_t seq, void *ctxt)
 		chan_rcvd_eow(c);
 	} else if (strcmp(rtype, "exit-status") == 0) {
 		exitval = packet_get_int();
-		if (c->ctl_fd != -1) {
+		if (c->ctl_chan != -1) {
-			/* Dispatch to mux client */
+			mux_exit_message(c, exitval);
-			atomicio(vwrite, c->ctl_fd, &exitval, sizeof(exitval));
 			success = 1;
 		} else if (id == session_ident) {
 			/* Record exit value of local session */

clientloop.h

@@ -1,4 +1,4 @@
-/* $OpenBSD: clientloop.h,v 1.22 2008/06/12 15:19:17 djm Exp $ */
+/* $OpenBSD: clientloop.h,v 1.23 2010/01/26 01:28:35 djm Exp $ */
 
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
@@ -56,18 +56,14 @@ typedef void global_confirm_cb(int, u_int32_t seq, void *);
 void	 client_register_global_confirm(global_confirm_cb *, void *);
 
 /* Multiplexing protocol version */
-#define SSHMUX_VER			2
+#define SSHMUX_VER			4
 
 /* Multiplexing control protocol flags */
 #define SSHMUX_COMMAND_OPEN		1	/* Open new connection */
 #define SSHMUX_COMMAND_ALIVE_CHECK	2	/* Check master is alive */
 #define SSHMUX_COMMAND_TERMINATE	3	/* Ask master to exit */
-
+#define SSHMUX_COMMAND_STDIO_FWD	4	/* Open stdio fwd (ssh -W) */
-#define SSHMUX_FLAG_TTY			(1)	/* Request tty on open */
-#define SSHMUX_FLAG_SUBSYS		(1<<1)	/* Subsystem request on open */
-#define SSHMUX_FLAG_X11_FWD		(1<<2)	/* Request X11 forwarding */
-#define SSHMUX_FLAG_AGENT_FWD		(1<<3)	/* Request agent forwarding */
 
 void	muxserver_listen(void);
-int	muxserver_accept_control(void);
 void	muxclient(const char *);
+void	mux_exit_message(Channel *, int);

nchan.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: nchan.c,v 1.62 2008/11/07 18:50:18 stevesk Exp $ */
+/* $OpenBSD: nchan.c,v 1.63 2010/01/26 01:28:35 djm Exp $ */
 /*
  * Copyright (c) 1999, 2000, 2001, 2002 Markus Friedl.  All rights reserved.
  *
@@ -161,7 +161,7 @@ chan_ibuf_empty(Channel *c)
 	switch (c->istate) {
 	case CHAN_INPUT_WAIT_DRAIN:
 		if (compat20) {
-			if (!(c->flags & CHAN_CLOSE_SENT))
+			if (!(c->flags & (CHAN_CLOSE_SENT|CHAN_LOCAL)))
 				chan_send_eof2(c);
 			chan_set_istate(c, CHAN_INPUT_CLOSED);
 		} else {
@@ -278,9 +278,12 @@ static void
 chan_rcvd_close2(Channel *c)
 {
 	debug2("channel %d: rcvd close", c->self);
-	if (c->flags & CHAN_CLOSE_RCVD)
+	if (!(c->flags & CHAN_LOCAL)) {
-		error("channel %d: protocol error: close rcvd twice", c->self);
+		if (c->flags & CHAN_CLOSE_RCVD)
-	c->flags |= CHAN_CLOSE_RCVD;
+			error("channel %d: protocol error: close rcvd twice",
+			    c->self);
+		c->flags |= CHAN_CLOSE_RCVD;
+	}
 	if (c->type == SSH_CHANNEL_LARVAL) {
 		/* tear down larval channels immediately */
 		chan_set_ostate(c, CHAN_OUTPUT_CLOSED);
@@ -302,11 +305,13 @@ chan_rcvd_close2(Channel *c)
 		chan_set_istate(c, CHAN_INPUT_CLOSED);
 		break;
 	case CHAN_INPUT_WAIT_DRAIN:
-		chan_send_eof2(c);
+		if (!(c->flags & CHAN_LOCAL))
+			chan_send_eof2(c);
 		chan_set_istate(c, CHAN_INPUT_CLOSED);
 		break;
 	}
 }
+
 void
 chan_rcvd_eow(Channel *c)
 {
@@ -454,6 +459,10 @@ chan_is_dead(Channel *c, int do_send)
 		    c->self, c->efd, buffer_len(&c->extended));
 		return 0;
 	}
+	if (c->flags & CHAN_LOCAL) {
+		debug2("channel %d: is dead (local)", c->self);
+		return 1;
+	}		
 	if (!(c->flags & CHAN_CLOSE_SENT)) {
 		if (do_send) {
 			chan_send_close2(c);

ssh.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: ssh.c,v 1.331 2010/01/11 01:39:46 dtucker Exp $ */
+/* $OpenBSD: ssh.c,v 1.332 2010/01/26 01:28:35 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -319,6 +319,11 @@ main(int ac, char **av)
 			options.gateway_ports = 1;
 			break;
 		case 'O':
+			if (stdio_forward_host != NULL)
+				fatal("Cannot specify multiplexing "
+				    "command with -W");
+			else if (muxclient_command != 0)
+				fatal("Multiplexing command already specified");
 			if (strcmp(optarg, "check") == 0)
 				muxclient_command = SSHMUX_COMMAND_ALIVE_CHECK;
 			else if (strcmp(optarg, "exit") == 0)
@@ -395,6 +400,10 @@ main(int ac, char **av)
 			}
 			break;
 		case 'W':
+			if (stdio_forward_host != NULL)
+				fatal("stdio forward already specified");
+			if (muxclient_command != 0)
+				fatal("Cannot specify stdio forward with -O");
 			if (parse_forward(&fwd, optarg, 1, 0)) {
 				stdio_forward_host = fwd.listen_host;
 				stdio_forward_port = fwd.listen_port;
@@ -902,11 +911,18 @@ static int
 client_setup_stdio_fwd(const char *host_to_connect, u_short port_to_connect)
 {
 	Channel *c;
+	int in, out;
 
 	debug3("client_setup_stdio_fwd %s:%d", host_to_connect,
 	    port_to_connect);
-	if ((c = channel_connect_stdio_fwd(host_to_connect, port_to_connect))
+
-	    == NULL)
+	in = dup(STDIN_FILENO);
+	out = dup(STDOUT_FILENO);
+	if (in < 0 || out < 0)
+		fatal("channel_connect_stdio_fwd: dup() in/out failed");
+
+	if ((c = channel_connect_stdio_fwd(host_to_connect, port_to_connect,
+	    in, out)) == NULL)
 		return 0;
 	channel_register_cleanup(c->self, client_cleanup_stdio_fwd, 0);
 	return 1;