- markus@cvs.openbsd.org 2010/05/16 12:55:51

[PROTOCOL.mux clientloop.h mux.c readconf.c readconf.h ssh.1 ssh.c]
     mux support for remote forwarding with dynamic port allocation,
     use with
        LPORT=`ssh -S muxsocket -R0:localhost:25 -O forward somehost`
     feedback and ok djm@

ChangeLog

@@ -23,6 +23,12 @@
      the server.
      
      motivated by and with feedback from markus@
+   - markus@cvs.openbsd.org 2010/05/16 12:55:51
+     [PROTOCOL.mux clientloop.h mux.c readconf.c readconf.h ssh.1 ssh.c]
+     mux support for remote forwarding with dynamic port allocation,
+     use with
+        LPORT=`ssh -S muxsocket -R0:localhost:25 -O forward somehost`
+     feedback and ok djm@
 
 20100511
  - (dtucker) [Makefile.in] Bug #1770: Link libopenbsd-compat twice to solve

PROTOCOL.mux

@@ -109,8 +109,14 @@ A client may request the master to establish a port forward:
 
 forwarding type may be MUX_FWD_LOCAL, MUX_FWD_REMOTE, MUX_FWD_DYNAMIC.
 
-A server may reply with a MUX_S_OK, a MUX_S_PERMISSION_DENIED or a
+A server may reply with a MUX_S_OK, a MUX_S_REMOTE_PORT, a
-MUX_S_FAILURE.
+MUX_S_PERMISSION_DENIED or a MUX_S_FAILURE.
+
+For dynamically allocated listen port the server replies with
+
+	uint32	MUX_S_REMOTE_PORT
+	uint32	client request id
+	uint32	allocated remote listen port
 
 5. Requesting closure of port forwards
 
@@ -178,6 +184,7 @@ The MUX_S_PERMISSION_DENIED and MUX_S_FAILURE include a reason:
 #define MUX_S_EXIT_MESSAGE	0x80000004
 #define MUX_S_ALIVE		0x80000005
 #define MUX_S_SESSION_OPENED	0x80000006
+#define MUX_S_REMOTE_PORT	0x80000007
 
 #define MUX_FWD_LOCAL	1
 #define MUX_FWD_REMOTE	2
@@ -193,4 +200,4 @@ XXX server->client error/warning notifications
 XXX port0 rfwd (need custom response message)
 XXX send signals via mux
 
-$OpenBSD: PROTOCOL.mux,v 1.1 2010/01/26 01:28:35 djm Exp $
+$OpenBSD: PROTOCOL.mux,v 1.2 2010/05/16 12:55:51 markus Exp $

clientloop.h

@@ -1,4 +1,4 @@
-/* $OpenBSD: clientloop.h,v 1.23 2010/01/26 01:28:35 djm Exp $ */
+/* $OpenBSD: clientloop.h,v 1.24 2010/05/16 12:55:51 markus Exp $ */
 
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
@@ -63,6 +63,7 @@ void	 client_register_global_confirm(global_confirm_cb *, void *);
 #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_COMMAND_FORWARD		5	/* Forward only, no command */
 
 void	muxserver_listen(void);
 void	muxclient(const char *);

mux.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: mux.c,v 1.17 2010/05/14 23:29:23 djm Exp $ */
+/* $OpenBSD: mux.c,v 1.18 2010/05/16 12:55:51 markus Exp $ */
 /*
  * Copyright (c) 2002-2008 Damien Miller <djm@openbsd.org>
  *
@@ -71,6 +71,7 @@
 #include "xmalloc.h"
 #include "log.h"
 #include "ssh.h"
+#include "ssh2.h"
 #include "pathnames.h"
 #include "misc.h"
 #include "match.h"
@@ -109,6 +110,13 @@ struct mux_session_confirm_ctx {
 	u_int rid;
 };
 
+/* Context for global channel callback */
+struct mux_channel_confirm_ctx {
+	u_int cid;	/* channel id */
+	u_int rid;	/* request id */
+	int fid;	/* forward id */
+};
+
 /* fd to control socket */
 int muxserver_sock = -1;
 
@@ -144,6 +152,7 @@ struct mux_master_state {
 #define MUX_S_EXIT_MESSAGE	0x80000004
 #define MUX_S_ALIVE		0x80000005
 #define MUX_S_SESSION_OPENED	0x80000006
+#define MUX_S_REMOTE_PORT	0x80000007
 
 /* type codes for MUX_C_OPEN_FWD and MUX_C_CLOSE_FWD */
 #define MUX_FWD_LOCAL   1
@@ -557,6 +566,61 @@ compare_forward(Forward *a, Forward *b)
 	return 1;
 }
 
+static void
+mux_confirm_remote_forward(int type, u_int32_t seq, void *ctxt)
+{
+	struct mux_channel_confirm_ctx *fctx = ctxt;
+	char *failmsg = NULL;
+	Forward *rfwd;
+	Channel *c;
+	Buffer out;
+
+	if ((c = channel_by_id(fctx->cid)) == NULL) {
+		/* no channel for reply */
+		error("%s: unknown channel", __func__);
+		return;
+	}
+	buffer_init(&out);
+	if (fctx->fid >= options.num_remote_forwards) {
+		xasprintf(&failmsg, "unknown forwarding id %d", fctx->fid);
+		goto fail;
+	}
+	rfwd = &options.remote_forwards[fctx->fid];
+	debug("%s: %s for: listen %d, connect %s:%d", __func__,
+	    type == SSH2_MSG_REQUEST_SUCCESS ? "success" : "failure",
+	    rfwd->listen_port, rfwd->connect_host, rfwd->connect_port);
+	if (type == SSH2_MSG_REQUEST_SUCCESS) {
+		if (rfwd->listen_port == 0) {
+			rfwd->allocated_port = packet_get_int();
+			logit("Allocated port %u for mux remote forward"
+			    " to %s:%d", rfwd->allocated_port,
+			    rfwd->connect_host, rfwd->connect_port);
+			buffer_put_int(&out, MUX_S_REMOTE_PORT);
+			buffer_put_int(&out, fctx->rid);
+			buffer_put_int(&out, rfwd->allocated_port);
+		} else {
+			buffer_put_int(&out, MUX_S_OK);
+			buffer_put_int(&out, fctx->rid);
+		}
+		goto out;
+	} else {
+		xasprintf(&failmsg, "remote port forwarding failed for "
+		    "listen port %d", rfwd->listen_port);
+	}
+ fail:
+	error("%s: %s", __func__, failmsg);
+	buffer_put_int(&out, MUX_S_FAILURE);
+	buffer_put_int(&out, fctx->rid);
+	buffer_put_cstring(&out, failmsg);
+	xfree(failmsg);
+ out:
+	buffer_put_string(&c->output, buffer_ptr(&out), buffer_len(&out));
+	buffer_free(&out);
+	if (c->mux_pause <= 0)
+		fatal("%s: mux_pause %d", __func__, c->mux_pause);
+	c->mux_pause = 0; /* start processing messages again */
+}
+
 static int
 process_mux_open_fwd(u_int rid, Channel *c, Buffer *m, Buffer *r)
 {
@@ -592,15 +656,16 @@ process_mux_open_fwd(u_int rid, Channel *c, Buffer *m, Buffer *r)
 	    ftype != MUX_FWD_DYNAMIC) {
 		logit("%s: invalid forwarding type %u", __func__, ftype);
  invalid:
-		xfree(fwd.listen_host);
+		if (fwd.listen_host)
-		xfree(fwd.connect_host);
+			xfree(fwd.listen_host);
+		if (fwd.connect_host)
+			xfree(fwd.connect_host);
 		buffer_put_int(r, MUX_S_FAILURE);
 		buffer_put_int(r, rid);
 		buffer_put_cstring(r, "Invalid forwarding request");
 		return 0;
 	}
-	/* XXX support rport0 forwarding with reply of port assigned */
+	if (fwd.listen_port >= 65536) {
-	if (fwd.listen_port == 0 || fwd.listen_port >= 65536) {
 		logit("%s: invalid listen port %u", __func__,
 		    fwd.listen_port);
 		goto invalid;
@@ -635,8 +700,17 @@ process_mux_open_fwd(u_int rid, Channel *c, Buffer *m, Buffer *r)
 	case MUX_FWD_REMOTE:
 		for (i = 0; i < options.num_remote_forwards; i++) {
 			if (compare_forward(&fwd,
-			    options.remote_forwards + i))
+			    options.remote_forwards + i)) {
-				goto exists;
+				if (fwd.listen_port != 0)
+					goto exists;
+				debug2("%s: found allocated port",
+				    __func__);
+				buffer_put_int(r, MUX_S_REMOTE_PORT);
+				buffer_put_int(r, rid);
+				buffer_put_int(r,
+				    options.remote_forwards[i].allocated_port);
+				goto out;
+			}
 		}
 		break;
 	}
@@ -668,14 +742,24 @@ process_mux_open_fwd(u_int rid, Channel *c, Buffer *m, Buffer *r)
 		add_local_forward(&options, &fwd);
 		freefwd = 0;
 	} else {
-		/* XXX wait for remote to confirm */
+		struct mux_channel_confirm_ctx *fctx;
+
 		if (options.num_remote_forwards + 1 >=
 		    SSH_MAX_FORWARDS_PER_DIRECTION ||
 		    channel_request_remote_forwarding(fwd.listen_host,
 		    fwd.listen_port, fwd.connect_host, fwd.connect_port) < 0)
 			goto fail;
 		add_remote_forward(&options, &fwd);
+		fctx = xcalloc(1, sizeof(*fctx));
+		fctx->cid = c->self;
+		fctx->rid = rid;
+		fctx->fid = options.num_remote_forwards-1;
+		client_register_global_confirm(mux_confirm_remote_forward,
+		    fctx);
 		freefwd = 0;
+		c->mux_pause = 1; /* wait for mux_confirm_remote_forward */
+		/* delayed reply in mux_confirm_remote_forward */
+		goto out;
 	}
 	buffer_put_int(r, MUX_S_OK);
 	buffer_put_int(r, rid);
@@ -1392,6 +1476,15 @@ mux_client_request_forward(int fd, u_int ftype, Forward *fwd)
 	switch (type) {
 	case MUX_S_OK:
 		break;
+	case MUX_S_REMOTE_PORT:
+		fwd->allocated_port = buffer_get_int(&m);
+		logit("Allocated port %u for remote forward to %s:%d",
+		    fwd->allocated_port,
+		    fwd->connect_host ? fwd->connect_host : "",
+		    fwd->connect_port);
+		if (muxclient_command == SSHMUX_COMMAND_FORWARD)
+			fprintf(stdout, "%u\n", fwd->allocated_port);
+		break;
 	case MUX_S_PERMISSION_DENIED:
 		e = buffer_get_string(&m, NULL);
 		buffer_free(&m);
@@ -1758,6 +1851,10 @@ muxclient(const char *path)
 		mux_client_request_terminate(sock);
 		fprintf(stderr, "Exit request sent.\r\n");
 		exit(0);
+	case SSHMUX_COMMAND_FORWARD:
+		if (mux_client_request_forwards(sock) != 0)
+			fatal("%s: master forward request failed", __func__);
+		exit(0);
 	case SSHMUX_COMMAND_OPEN:
 		if (mux_client_request_forwards(sock) != 0) {
 			error("%s: master forward request failed", __func__);

readconf.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: readconf.c,v 1.183 2010/02/08 10:50:20 markus Exp $ */
+/* $OpenBSD: readconf.c,v 1.184 2010/05/16 12:55:51 markus Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -283,6 +283,7 @@ add_remote_forward(Options *options, const Forward *newfwd)
 	fwd->listen_port = newfwd->listen_port;
 	fwd->connect_host = newfwd->connect_host;
 	fwd->connect_port = newfwd->connect_port;
+	fwd->allocated_port = 0;
 }
 
 static void

readconf.h

@@ -1,4 +1,4 @@
-/* $OpenBSD: readconf.h,v 1.82 2010/02/08 10:50:20 markus Exp $ */
+/* $OpenBSD: readconf.h,v 1.83 2010/05/16 12:55:51 markus Exp $ */
 
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
@@ -23,6 +23,7 @@ typedef struct {
 	int	  listen_port;		/* Port to forward. */
 	char	 *connect_host;		/* Host to connect. */
 	int	  connect_port;		/* Port to connect on connect_host. */
+	int	  allocated_port;	/* Dynamically allocated listen port */
 }       Forward;
 /* Data structure for representing option data. */
 

ssh.1

@@ -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.1,v 1.304 2010/03/26 06:54:36 jmc Exp $
+.\" $OpenBSD: ssh.1,v 1.305 2010/05/16 12:55:51 markus Exp $
-.Dd $Mdocdate: March 26 2010 $
+.Dd $Mdocdate: May 16 2010 $
 .Dt SSH 1
 .Os
 .Sh NAME
@@ -421,7 +421,9 @@ option is specified, the
 argument is interpreted and passed to the master process.
 Valid commands are:
 .Dq check
-(check that the master process is running) and
+(check that the master process is running),
+.Dq forward
+(request forwardings without command execution) and
 .Dq exit
 (request the master to exit).
 .It Fl o Ar option
@@ -557,6 +559,9 @@ argument is
 .Ql 0 ,
 the listen port will be dynamically allocated on the server and reported
 to the client at run time.
+When used together with
+.Ic -O forward
+the allocated port will be printed to the standard output.
 .It Fl S Ar ctl_path
 Specifies the location of a control socket for connection sharing,
 or the string

ssh.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: ssh.c,v 1.337 2010/05/14 23:29:23 djm Exp $ */
+/* $OpenBSD: ssh.c,v 1.338 2010/05/16 12:55:51 markus Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -327,6 +327,8 @@ main(int ac, char **av)
 				fatal("Multiplexing command already specified");
 			if (strcmp(optarg, "check") == 0)
 				muxclient_command = SSHMUX_COMMAND_ALIVE_CHECK;
+			else if (strcmp(optarg, "forward") == 0)
+				muxclient_command = SSHMUX_COMMAND_FORWARD;
 			else if (strcmp(optarg, "exit") == 0)
 				muxclient_command = SSHMUX_COMMAND_TERMINATE;
 			else
@@ -877,9 +879,10 @@ ssh_confirm_remote_forward(int type, u_int32_t seq, void *ctxt)
 	    type == SSH2_MSG_REQUEST_SUCCESS ? "success" : "failure",
 	    rfwd->listen_port, rfwd->connect_host, rfwd->connect_port);
 	if (type == SSH2_MSG_REQUEST_SUCCESS && rfwd->listen_port == 0) {
+		rfwd->allocated_port = packet_get_int();
 		logit("Allocated port %u for remote forward to %s:%d",
-			packet_get_int(),
+		    rfwd->allocated_port,
-			rfwd->connect_host, rfwd->connect_port);
+		    rfwd->connect_host, rfwd->connect_port);
 	}
 	
 	if (type == SSH2_MSG_REQUEST_FAILURE) {