- 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@

6 files changed, 206 insertions, 80 deletions

diff --git a/ChangeLog b/ChangeLog
index dfce82822..b31ee81cd 100644
--- a/ChangeLog
+++ b/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
diff --git a/channels.c b/channels.c
index 24d4a9f42..0f7e1a872 100644
--- a/channels.c
+++ b/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 whether or not a port forward listens to loopback,
-         * 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
-         */
-        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;
-        }
-
+        /* Determine the bind address, cf. channel_fwd_bind_addr() comment */
+        addr = channel_fwd_bind_addr(listen_addr, &wildcard,
+            is_client, gateway_ports);
         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;
+                }
+        }
+
+        return (found);
+}
+
+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);
 
-                if (c != NULL && c->type == SSH_CHANNEL_RPORT_LISTENER &&
-                    strcmp(c->path, host) == 0 && c->listening_port == port) {
+        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;
@@ -2843,10 +2890,30 @@ channel_setup_remote_fwd_listener(const char *listen_address,
 }
 
 /*
+ * 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_cstring(address_to_bind);
+                packet_put_char(1);             /* boolean: want reply */
+                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;
 }
 
 /*
diff --git a/channels.h b/channels.h
index e2941c85a..37af32289 100644
--- a/channels.h
+++ b/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 */
 
diff --git a/clientloop.h b/clientloop.h
index a259b5e14..3bb794879 100644
--- a/clientloop.h
+++ b/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 *);
diff --git a/mux.c b/mux.c
index add0e26b1..6b63d813b 100644
--- a/mux.c
+++ b/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 */
-        buffer_put_int(r, MUX_S_FAILURE);
-        buffer_put_int(r, rid);
-        buffer_put_cstring(r, "unimplemented");
+        /* make sure this has been requested */
+        found_fwd = NULL;
+        switch (ftype) {
+        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);
         }
diff --git a/ssh.c b/ssh.c
index c717dcf1d..f437dec1c 100644
--- a/ssh.c
+++ b/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;