- djm@cvs.openbsd.org 2011/09/09 22:46:44

[channels.c channels.h clientloop.h mux.c ssh.c]
     support for cancelling local and remote port forwards via the multiplex
     socket. Use ssh -O cancel -L xx:xx:xx -R yy:yy:yy user@host" to request
     the cancellation of the specified forwardings; ok markus@

ChangeLog

@@ -51,6 +51,11 @@
      [sshd.c]
      kill the preauth privsep child on fatal errors in the monitor;
      ok markus@
+   - djm@cvs.openbsd.org 2011/09/09 22:46:44
+     [channels.c channels.h clientloop.h mux.c ssh.c]
+     support for cancelling local and remote port forwards via the multiplex
+     socket. Use ssh -O cancel -L xx:xx:xx -R yy:yy:yy user@host" to request
+     the cancellation of the specified forwardings; ok markus@
 
 20110909
  - (dtucker) [entropy.h] Bug #1932: remove old definition of init_rng.  From

channels.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: channels.c,v 1.311 2011/06/22 22:08:42 djm Exp $ */
+/* $OpenBSD: channels.c,v 1.312 2011/09/09 22:46:44 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -302,6 +302,8 @@ channel_new(char *ctype, int type, int rfd, int wfd, int efd,
 	buffer_init(&c->output);
 	buffer_init(&c->extended);
 	c->path = NULL;
+	c->listening_addr = NULL;
+	c->listening_port = 0;
 	c->ostate = CHAN_OUTPUT_OPEN;
 	c->istate = CHAN_INPUT_OPEN;
 	c->flags = 0;
@@ -411,6 +413,10 @@ channel_free(Channel *c)
 		xfree(c->path);
 		c->path = NULL;
 	}
+	if (c->listening_addr) {
+		xfree(c->listening_addr);
+		c->listening_addr = NULL;
+	}
 	while ((cc = TAILQ_FIRST(&c->status_confirms)) != NULL) {
 		if (cc->abandon_cb != NULL)
 			cc->abandon_cb(c, cc->ctx);
@@ -2634,6 +2640,46 @@ channel_set_af(int af)
 	IPv4or6 = af;
 }
 
+
+/*
+ * Determine whether or not a port forward listens to loopback, the
+ * specified address or wildcard. On the client, a specified bind
+ * address will always override gateway_ports. On the server, a
+ * gateway_ports of 1 (``yes'') will override the client's specification
+ * and force a wildcard bind, whereas a value of 2 (``clientspecified'')
+ * will bind to whatever address the client asked for.
+ *
+ * Special-case listen_addrs are:
+ *
+ * "0.0.0.0"               -> wildcard v4/v6 if SSH_OLD_FORWARD_ADDR
+ * "" (empty string), "*"  -> wildcard v4/v6
+ * "localhost"             -> loopback v4/v6
+ */
+static const char *
+channel_fwd_bind_addr(const char *listen_addr, int *wildcardp,
+    int is_client, int gateway_ports)
+{
+	const char *addr = NULL;
+	int wildcard = 0;
+
+	if (listen_addr == NULL) {
+		/* No address specified: default to gateway_ports setting */
+		if (gateway_ports)
+			wildcard = 1;
+	} else if (gateway_ports || is_client) {
+		if (((datafellows & SSH_OLD_FORWARD_ADDR) &&
+		    strcmp(listen_addr, "0.0.0.0") == 0 && is_client == 0) ||
+		    *listen_addr == '\0' || strcmp(listen_addr, "*") == 0 ||
+		    (!is_client && gateway_ports == 1))
+			wildcard = 1;
+		else if (strcmp(listen_addr, "localhost") != 0)
+			addr = listen_addr;
+	}
+	if (wildcardp != NULL)
+		*wildcardp = wildcard;
+	return addr;
+}
+
 static int
 channel_setup_fwd_listener(int type, const char *listen_addr,
     u_short listen_port, int *allocated_listen_port,
@@ -2659,36 +2705,9 @@ channel_setup_fwd_listener(int type, const char *listen_addr,
 		return 0;
 	}
 
-	/*
+	/* Determine the bind address, cf. channel_fwd_bind_addr() comment */
-	 * Determine whether or not a port forward listens to loopback,
+	addr = channel_fwd_bind_addr(listen_addr, &wildcard,
-	 * specified address or wildcard. On the client, a specified bind
+	    is_client, gateway_ports);
-	 * address will always override gateway_ports. On the server, a
-	 * gateway_ports of 1 (``yes'') will override the client's
-	 * specification and force a wildcard bind, whereas a value of 2
-	 * (``clientspecified'') will bind to whatever address the client
-	 * asked for.
-	 *
-	 * Special-case listen_addrs are:
-	 *
-	 * "0.0.0.0"               -> wildcard v4/v6 if SSH_OLD_FORWARD_ADDR
-	 * "" (empty string), "*"  -> wildcard v4/v6
-	 * "localhost"             -> loopback v4/v6
-	 */
-	addr = NULL;
-	if (listen_addr == NULL) {
-		/* No address specified: default to gateway_ports setting */
-		if (gateway_ports)
-			wildcard = 1;
-	} else if (gateway_ports || is_client) {
-		if (((datafellows & SSH_OLD_FORWARD_ADDR) &&
-		    strcmp(listen_addr, "0.0.0.0") == 0 && is_client == 0) ||
-		    *listen_addr == '\0' || strcmp(listen_addr, "*") == 0 ||
-		    (!is_client && gateway_ports == 1))
-			wildcard = 1;
-		else if (strcmp(listen_addr, "localhost") != 0)
-			addr = listen_addr;
-	}
-
 	debug3("channel_setup_fwd_listener: type %d wildcard %d addr %s",
 	    type, wildcard, (addr == NULL) ? "NULL" : addr);
 
@@ -2793,6 +2812,7 @@ channel_setup_fwd_listener(int type, const char *listen_addr,
 		c->path = xstrdup(host);
 		c->host_port = port_to_connect;
 		c->listening_port = listen_port;
+		c->listening_addr = addr == NULL ? NULL : xstrdup(addr);
 		success = 1;
 	}
 	if (success == 0)
@@ -2810,9 +2830,36 @@ channel_cancel_rport_listener(const char *host, u_short port)
 
 	for (i = 0; i < channels_alloc; i++) {
 		Channel *c = channels[i];
+		if (c == NULL || c->type != SSH_CHANNEL_RPORT_LISTENER)
+			continue;
+		if (strcmp(c->path, host) == 0 && c->listening_port == port) {
+			debug2("%s: close channel %d", __func__, i);
+			channel_free(c);
+			found = 1;
+		}
+	}
 
-		if (c != NULL && c->type == SSH_CHANNEL_RPORT_LISTENER &&
+	return (found);
-		    strcmp(c->path, host) == 0 && c->listening_port == port) {
+}
+
+int
+channel_cancel_lport_listener(const char *lhost, u_short lport,
+    u_short cport, int gateway_ports)
+{
+	u_int i;
+	int found = 0;
+	const char *addr = channel_fwd_bind_addr(lhost, NULL, 1, gateway_ports);
+
+	for (i = 0; i < channels_alloc; i++) {
+		Channel *c = channels[i];
+		if (c == NULL || c->type != SSH_CHANNEL_PORT_LISTENER)
+			continue;
+		if (c->listening_port != lport || c->host_port != cport)
+			continue;
+		if ((c->listening_addr == NULL && addr != NULL) ||
+		    (c->listening_addr != NULL && addr == NULL))
+			continue;
+		if (addr == NULL || strcmp(c->listening_addr, addr) == 0) {
 			debug2("%s: close channel %d", __func__, i);
 			channel_free(c);
 			found = 1;
@@ -2842,11 +2889,31 @@ channel_setup_remote_fwd_listener(const char *listen_address,
 	    NULL, 0, gateway_ports);
 }
 
+/*
+ * Translate the requested rfwd listen host to something usable for
+ * this server.
+ */
+static const char *
+channel_rfwd_bind_host(const char *listen_host)
+{
+	if (listen_host == NULL) {
+		if (datafellows & SSH_BUG_RFWD_ADDR)
+			return "127.0.0.1";
+		else
+			return "localhost";
+	} else if (*listen_host == '\0' || strcmp(listen_host, "*") == 0) {
+		if (datafellows & SSH_BUG_RFWD_ADDR)
+			return "0.0.0.0";
+		else
+			return "";
+	} else
+		return listen_host;
+}
+
 /*
  * Initiate forwarding of connections to port "port" on remote host through
  * the secure channel to host:port from local side.
  */
-
 int
 channel_request_remote_forwarding(const char *listen_host, u_short listen_port,
     const char *host_to_connect, u_short port_to_connect)
@@ -2855,25 +2922,10 @@ channel_request_remote_forwarding(const char *listen_host, u_short listen_port,
 
 	/* Send the forward request to the remote side. */
 	if (compat20) {
-		const char *address_to_bind;
-		if (listen_host == NULL) {
-			if (datafellows & SSH_BUG_RFWD_ADDR)
-				address_to_bind = "127.0.0.1";
-			else
-				address_to_bind = "localhost";
-		} else if (*listen_host == '\0' ||
-			   strcmp(listen_host, "*") == 0) {
-			if (datafellows & SSH_BUG_RFWD_ADDR)
-				address_to_bind = "0.0.0.0";
-			else
-				address_to_bind = "";
-		} else
-			address_to_bind = listen_host;
-
 		packet_start(SSH2_MSG_GLOBAL_REQUEST);
 		packet_put_cstring("tcpip-forward");
-		packet_put_char(1);			/* boolean: want reply */
+		packet_put_char(1);		/* boolean: want reply */
-		packet_put_cstring(address_to_bind);
+		packet_put_cstring(channel_rfwd_bind_host(listen_host));
 		packet_put_int(listen_port);
 		packet_send();
 		packet_write_wait();
@@ -2917,13 +2969,13 @@ channel_request_remote_forwarding(const char *listen_host, u_short listen_port,
  * Request cancellation of remote forwarding of connection host:port from
  * local side.
  */
-void
+int
 channel_request_rforward_cancel(const char *host, u_short port)
 {
 	int i;
 
 	if (!compat20)
-		return;
+		return -1;
 
 	for (i = 0; i < num_permitted_opens; i++) {
 		if (permitted_opens[i].host_to_connect != NULL &&
@@ -2932,12 +2984,12 @@ channel_request_rforward_cancel(const char *host, u_short port)
 	}
 	if (i >= num_permitted_opens) {
 		debug("%s: requested forward not found", __func__);
-		return;
+		return -1;
 	}
 	packet_start(SSH2_MSG_GLOBAL_REQUEST);
 	packet_put_cstring("cancel-tcpip-forward");
 	packet_put_char(0);
-	packet_put_cstring(host == NULL ? "" : host);
+	packet_put_cstring(channel_rfwd_bind_host(host));
 	packet_put_int(port);
 	packet_send();
 
@@ -2945,6 +2997,8 @@ channel_request_rforward_cancel(const char *host, u_short port)
 	permitted_opens[i].port_to_connect = 0;
 	xfree(permitted_opens[i].host_to_connect);
 	permitted_opens[i].host_to_connect = NULL;
+
+	return 0;
 }
 
 /*

channels.h

@@ -1,4 +1,4 @@
-/* $OpenBSD: channels.h,v 1.105 2011/06/22 22:08:42 djm Exp $ */
+/* $OpenBSD: channels.h,v 1.106 2011/09/09 22:46:44 djm Exp $ */
 
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
@@ -116,6 +116,7 @@ struct Channel {
 	char    *path;
 		/* path for unix domain sockets, or host name for forwards */
 	int     listening_port;	/* port being listened for forwards */
+	char   *listening_addr;	/* addr being listened for forwards */
 	int     host_port;	/* remote port to connect for forwards */
 	char   *remote_name;	/* remote hostname */
 
@@ -261,9 +262,10 @@ int	 channel_request_remote_forwarding(const char *, u_short,
 	     const char *, u_short);
 int	 channel_setup_local_fwd_listener(const char *, u_short,
 	     const char *, u_short, int);
-void	 channel_request_rforward_cancel(const char *host, u_short port);
+int	 channel_request_rforward_cancel(const char *host, u_short port);
 int	 channel_setup_remote_fwd_listener(const char *, u_short, int *, int);
 int	 channel_cancel_rport_listener(const char *, u_short);
+int	 channel_cancel_lport_listener(const char *, u_short, u_short, int);
 
 /* x11 forwarding */
 

clientloop.h

@@ -1,4 +1,4 @@
-/* $OpenBSD: clientloop.h,v 1.28 2011/06/22 22:08:42 djm Exp $ */
+/* $OpenBSD: clientloop.h,v 1.29 2011/09/09 22:46:44 djm Exp $ */
 
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
@@ -70,6 +70,7 @@ void client_expect_confirm(int, const char *, enum confirm_action);
 #define SSHMUX_COMMAND_STDIO_FWD	4	/* Open stdio fwd (ssh -W) */
 #define SSHMUX_COMMAND_FORWARD		5	/* Forward only, no command */
 #define SSHMUX_COMMAND_STOP		6	/* Disable mux but not conn */
+#define SSHMUX_COMMAND_CANCEL_FWD	7	/* Cancel forwarding(s) */
 
 void	muxserver_listen(void);
 void	muxclient(const char *);

mux.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: mux.c,v 1.29 2011/06/22 22:08:42 djm Exp $ */
+/* $OpenBSD: mux.c,v 1.30 2011/09/09 22:46:44 djm Exp $ */
 /*
  * Copyright (c) 2002-2008 Damien Miller <djm@openbsd.org>
  *
@@ -777,10 +777,11 @@ process_mux_open_fwd(u_int rid, Channel *c, Buffer *m, Buffer *r)
 static int
 process_mux_close_fwd(u_int rid, Channel *c, Buffer *m, Buffer *r)
 {
-	Forward fwd;
+	Forward fwd, *found_fwd;
 	char *fwd_desc = NULL;
+	const char *error_reason = NULL;
 	u_int ftype;
-	int ret = 0;
+	int i, ret = 0;
 
 	fwd.listen_host = fwd.connect_host = NULL;
 	if (buffer_get_int_ret(&ftype, m) != 0 ||
@@ -802,14 +803,66 @@ process_mux_close_fwd(u_int rid, Channel *c, Buffer *m, Buffer *r)
 		fwd.connect_host = NULL;
 	}
 
-	debug2("%s: channel %d: request %s", __func__, c->self,
+	debug2("%s: channel %d: request cancel %s", __func__, c->self,
 	    (fwd_desc = format_forward(ftype, &fwd)));
 
-	/* XXX implement this */
+	/* make sure this has been requested */
-	buffer_put_int(r, MUX_S_FAILURE);
+	found_fwd = NULL;
-	buffer_put_int(r, rid);
+	switch (ftype) {
-	buffer_put_cstring(r, "unimplemented");
+	case MUX_FWD_LOCAL:
+	case MUX_FWD_DYNAMIC:
+		for (i = 0; i < options.num_local_forwards; i++) {
+			if (compare_forward(&fwd,
+			    options.local_forwards + i)) {
+				found_fwd = options.local_forwards + i;
+				break;
+			}
+		}
+		break;
+	case MUX_FWD_REMOTE:
+		for (i = 0; i < options.num_remote_forwards; i++) {
+			if (compare_forward(&fwd,
+			    options.remote_forwards + i)) {
+				found_fwd = options.remote_forwards + i;
+				break;
+			}
+		}
+		break;
+	}
 
+	if (found_fwd == NULL)
+		error_reason = "port not forwarded";
+	else if (ftype == MUX_FWD_REMOTE) {
+		/*
+		 * This shouldn't fail unless we confused the host/port
+		 * between options.remote_forwards and permitted_opens.
+		 */
+		if (channel_request_rforward_cancel(fwd.listen_host,
+		    fwd.listen_port) == -1)
+			error_reason = "port not in permitted opens";
+	} else {	/* local and dynamic forwards */
+		/* Ditto */
+		if (channel_cancel_lport_listener(fwd.listen_host,
+		    fwd.listen_port, fwd.connect_port,
+		    options.gateway_ports) == -1)
+			error_reason = "port not found";
+	}
+
+	if (error_reason == NULL) {
+		buffer_put_int(r, MUX_S_OK);
+		buffer_put_int(r, rid);
+
+		if (found_fwd->listen_host != NULL)
+			xfree(found_fwd->listen_host);
+		if (found_fwd->connect_host != NULL)
+			xfree(found_fwd->connect_host);
+		found_fwd->listen_host = found_fwd->connect_host = NULL;
+		found_fwd->listen_port = found_fwd->connect_port = 0;
+	} else {
+		buffer_put_int(r, MUX_S_FAILURE);
+		buffer_put_int(r, rid);
+		buffer_put_cstring(r, error_reason);
+	}
  out:
 	if (fwd_desc != NULL)
 		xfree(fwd_desc);
@@ -1537,18 +1590,19 @@ mux_client_request_terminate(int fd)
 }
 
 static int
-mux_client_request_forward(int fd, u_int ftype, Forward *fwd)
+mux_client_forward(int fd, int cancel_flag, u_int ftype, Forward *fwd)
 {
 	Buffer m;
 	char *e, *fwd_desc;
 	u_int type, rid;
 
 	fwd_desc = format_forward(ftype, fwd);
-	debug("Requesting %s", fwd_desc);
+	debug("Requesting %s %s",
+	    cancel_flag ? "cancellation of" : "forwarding of", fwd_desc);
 	xfree(fwd_desc);
 
 	buffer_init(&m);
-	buffer_put_int(&m, MUX_C_OPEN_FWD);
+	buffer_put_int(&m, cancel_flag ? MUX_C_CLOSE_FWD : MUX_C_OPEN_FWD);
 	buffer_put_int(&m, muxclient_request_id);
 	buffer_put_int(&m, ftype);
 	buffer_put_cstring(&m,
@@ -1577,6 +1631,8 @@ mux_client_request_forward(int fd, u_int ftype, Forward *fwd)
 	case MUX_S_OK:
 		break;
 	case MUX_S_REMOTE_PORT:
+		if (cancel_flag)
+			fatal("%s: got MUX_S_REMOTE_PORT for cancel", __func__);
 		fwd->allocated_port = buffer_get_int(&m);
 		logit("Allocated port %u for remote forward to %s:%d",
 		    fwd->allocated_port,
@@ -1606,27 +1662,28 @@ mux_client_request_forward(int fd, u_int ftype, Forward *fwd)
 }
 
 static int
-mux_client_request_forwards(int fd)
+mux_client_forwards(int fd, int cancel_flag)
 {
-	int i;
+	int i, ret = 0;
 
-	debug3("%s: requesting forwardings: %d local, %d remote", __func__,
+	debug3("%s: %s forwardings: %d local, %d remote", __func__,
+	    cancel_flag ? "cancel" : "request",
 	    options.num_local_forwards, options.num_remote_forwards);
 
 	/* XXX ExitOnForwardingFailure */
 	for (i = 0; i < options.num_local_forwards; i++) {
-		if (mux_client_request_forward(fd,
+		if (mux_client_forward(fd, cancel_flag,
 		    options.local_forwards[i].connect_port == 0 ?
 		    MUX_FWD_DYNAMIC : MUX_FWD_LOCAL,
 		    options.local_forwards + i) != 0)
-			return -1;
+			ret = -1;
 	}
 	for (i = 0; i < options.num_remote_forwards; i++) {
-		if (mux_client_request_forward(fd, MUX_FWD_REMOTE,
+		if (mux_client_forward(fd, cancel_flag, MUX_FWD_REMOTE,
 		    options.remote_forwards + i) != 0)
-			return -1;
+			ret = -1;
 	}
-	return 0;
+	return ret;
 }
 
 static int
@@ -2014,11 +2071,11 @@ muxclient(const char *path)
 		fprintf(stderr, "Exit request sent.\r\n");
 		exit(0);
 	case SSHMUX_COMMAND_FORWARD:
-		if (mux_client_request_forwards(sock) != 0)
+		if (mux_client_forwards(sock, 0) != 0)
 			fatal("%s: master forward request failed", __func__);
 		exit(0);
 	case SSHMUX_COMMAND_OPEN:
-		if (mux_client_request_forwards(sock) != 0) {
+		if (mux_client_forwards(sock, 0) != 0) {
 			error("%s: master forward request failed", __func__);
 			return;
 		}
@@ -2031,6 +2088,11 @@ muxclient(const char *path)
 		mux_client_request_stop_listening(sock);
 		fprintf(stderr, "Stop listening request sent.\r\n");
 		exit(0);
+	case SSHMUX_COMMAND_CANCEL_FWD:
+		if (mux_client_forwards(sock, 1) != 0)
+			error("%s: master cancel forward request failed",
+			    __func__);
+		exit(0);
 	default:
 		fatal("unrecognised muxclient_command %d", muxclient_command);
 	}

ssh.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: ssh.c,v 1.364 2011/08/02 23:15:03 djm Exp $ */
+/* $OpenBSD: ssh.c,v 1.365 2011/09/09 22:46:44 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -377,6 +377,8 @@ main(int ac, char **av)
 				muxclient_command = SSHMUX_COMMAND_TERMINATE;
 			else if (strcmp(optarg, "stop") == 0)
 				muxclient_command = SSHMUX_COMMAND_STOP;
+			else if (strcmp(optarg, "cancel") == 0)
+				muxclient_command = SSHMUX_COMMAND_CANCEL_FWD;
 			else
 				fatal("Invalid multiplex command.");
 			break;