- djm@cvs.openbsd.org 2004/05/21 11:33:11

     [channels.c channels.h clientloop.c serverloop.c ssh.1]
     bz #756: add support for the cancel-tcpip-forward request for the server and
     the client (through the ~C commandline). reported by z3p AT twistedmatrix.com;
     ok markus@

6 files changed, 153 insertions, 35 deletions

diff --git a/ChangeLog b/ChangeLog
index 91c9ce5ec..0e8f4a556 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -10,6 +10,11 @@
    - markus@cvs.openbsd.org 2004/05/21 08:43:03
      [kex.h moduli.c tildexpand.c]
      add prototypes for -Wall; ok djm
+   - djm@cvs.openbsd.org 2004/05/21 11:33:11
+     [channels.c channels.h clientloop.c serverloop.c ssh.1]
+     bz #756: add support for the cancel-tcpip-forward request for the server and
+     the client (through the ~C commandline). reported by z3p AT twistedmatrix.com;
+     ok markus@
 
 20040523
  - (djm) [sshd_config] Explain consequences of UsePAM=yes a little better in 
@@ -1139,4 +1144,4 @@
    - (djm) Trim deprecated options from INSTALL. Mention UsePAM
    - (djm) Fix quote handling in sftp; Patch from admorten AT umich.edu
 
-$Id: ChangeLog,v 1.3361 2004/05/24 00:14:24 dtucker Exp $
+$Id: ChangeLog,v 1.3362 2004/05/24 00:18:05 dtucker Exp $
diff --git a/channels.c b/channels.c
index 55dc67342..2b1ce0e5c 100644
--- a/channels.c
+++ b/channels.c
@@ -39,7 +39,7 @@
  */
 
 #include "includes.h"
-RCSID("$OpenBSD: channels.c,v 1.201 2004/05/11 19:01:43 deraadt Exp $");
+RCSID("$OpenBSD: channels.c,v 1.202 2004/05/21 11:33:11 djm Exp $");
 
 #include "ssh.h"
 #include "ssh1.h"
@@ -2228,6 +2228,26 @@ channel_setup_fwd_listener(int type, const char *listen_addr, u_short listen_por
         return success;
 }
 
+int
+channel_cancel_rport_listener(const char *host, u_short port)
+{
+        int i, found = 0;
+
+        for(i = 0; i < channels_alloc; i++) {
+                Channel *c = channels[i];
+
+                if (c != NULL && c->type == SSH_CHANNEL_RPORT_LISTENER &&
+                    strncmp(c->path, host, sizeof(c->path)) == 0 &&
+                    c->listening_port == port) {
+                        debug2("%s: close clannel %d", __func__, i);
+                        channel_free(c);
+                        found = 1;
+                }
+        }
+
+        return (found);
+}
+
 /* protocol local port fwd, used by ssh (and sshd in v1) */
 int
 channel_setup_local_fwd_listener(u_short listen_port,
@@ -2305,6 +2325,42 @@ channel_request_remote_forwarding(u_short listen_port,
 }
 
 /*
+ * Request cancellation of remote forwarding of connection host:port from 
+ * local side.
+ */
+
+void
+channel_request_rforward_cancel(u_short port)
+{
+        int i;
+        const char *address_to_bind = "0.0.0.0";
+
+        if (!compat20)
+                return;
+
+        for (i = 0; i < num_permitted_opens; i++) {
+                if (permitted_opens[i].host_to_connect != NULL && 
+                    permitted_opens[i].listen_port == port)
+                        break;
+        }
+        if (i >= num_permitted_opens) {
+                debug("%s: requested forward not found", __func__);
+                return;
+        }
+        packet_start(SSH2_MSG_GLOBAL_REQUEST);
+        packet_put_cstring("cancel-tcpip-forward");
+        packet_put_char(0);
+        packet_put_cstring(address_to_bind);
+        packet_put_int(port);
+        packet_send();
+
+        permitted_opens[i].listen_port = 0;
+        permitted_opens[i].port_to_connect = 0;
+        free(permitted_opens[i].host_to_connect);
+        permitted_opens[i].host_to_connect = NULL;
+}
+
+/*
  * This is called after receiving CHANNEL_FORWARDING_REQUEST.  This initates
  * listening for the port, and sends back a success reply (or disconnect
  * message if there was an error).  This never returns if there was an error.
@@ -2373,7 +2429,8 @@ channel_clear_permitted_opens(void)
         int i;
 
         for (i = 0; i < num_permitted_opens; i++)
-                xfree(permitted_opens[i].host_to_connect);
+                if (permitted_opens[i].host_to_connect != NULL)
+                        xfree(permitted_opens[i].host_to_connect);
         num_permitted_opens = 0;
 
 }
@@ -2441,7 +2498,8 @@ channel_connect_by_listen_address(u_short listen_port)
         int i;
 
         for (i = 0; i < num_permitted_opens; i++)
-                if (permitted_opens[i].listen_port == listen_port)
+                if (permitted_opens[i].host_to_connect != NULL &&
+                    permitted_opens[i].listen_port == listen_port)
                         return connect_to(
                             permitted_opens[i].host_to_connect,
                             permitted_opens[i].port_to_connect);
@@ -2459,7 +2517,8 @@ channel_connect_to(const char *host, u_short port)
         permit = all_opens_permitted;
         if (!permit) {
                 for (i = 0; i < num_permitted_opens; i++)
-                        if (permitted_opens[i].port_to_connect == port &&
+                        if (permitted_opens[i].host_to_connect != NULL &&
+                            permitted_opens[i].port_to_connect == port &&
                             strcmp(permitted_opens[i].host_to_connect, host) == 0)
                                 permit = 1;
 
diff --git a/channels.h b/channels.h
index 7d981479b..0a49c55ea 100644
--- a/channels.h
+++ b/channels.h
@@ -1,4 +1,4 @@
-/*      $OpenBSD: channels.h,v 1.71 2003/09/23 20:41:11 markus Exp $    */
+/*      $OpenBSD: channels.h,v 1.72 2004/05/21 11:33:11 djm Exp $       */
 
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
@@ -200,8 +200,10 @@ void     channel_input_port_forward_request(int, int);
 int      channel_connect_to(const char *, u_short);
 int      channel_connect_by_listen_address(u_short);
 void     channel_request_remote_forwarding(u_short, const char *, u_short);
+void     channel_request_rforward_cancel(u_short port);
 int      channel_setup_local_fwd_listener(u_short, const char *, u_short, int);
 int      channel_setup_remote_fwd_listener(const char *, u_short, int);
+int      channel_cancel_rport_listener(const char *, u_short);
 
 /* x11 forwarding */
 
diff --git a/clientloop.c b/clientloop.c
index 9cbc1b0ce..ce627e8b8 100644
--- a/clientloop.c
+++ b/clientloop.c
@@ -59,7 +59,7 @@
  */
 
 #include "includes.h"
-RCSID("$OpenBSD: clientloop.c,v 1.120 2004/05/20 10:58:05 dtucker Exp $");
+RCSID("$OpenBSD: clientloop.c,v 1.121 2004/05/21 11:33:11 djm Exp $");
 
 #include "ssh.h"
 #include "ssh1.h"
@@ -506,6 +506,7 @@ process_cmdline(void)
         char *s, *cmd;
         u_short fwd_port, fwd_host_port;
         char buf[1024], sfwd_port[6], sfwd_host_port[6];
+        int delete = 0;
         int local = 0;
 
         leave_raw_mode();
@@ -515,44 +516,77 @@ process_cmdline(void)
                 goto out;
         while (*s && isspace(*s))
                 s++;
+        if (*s == '-')
+                s++;    /* Skip cmdline '-', if any */
         if (*s == '\0')
                 goto out;
-        if (strlen(s) < 2 || s[0] != '-' || !(s[1] == 'L' || s[1] == 'R')) {
+
+        if (*s == '?') {
+                logit("Commands:");
+                logit("      -Lport:host:hostport    Request local forward");
+                logit("      -Rport:host:hostport    Request remote forward");
+                logit("      -KRhostport             Cancel remote forward");
+                goto out;
+        }
+
+        if (*s == 'K') {
+                delete = 1;
+                s++;
+        }
+        if (*s != 'L' && *s != 'R') {
                 logit("Invalid command.");
                 goto out;
         }
-        if (s[1] == 'L')
+        if (*s == 'L')
                 local = 1;
-        if (!local && !compat20) {
+        if (local && delete) {
+                logit("Not supported.");
+                goto out;
+        }
+        if ((!local || delete) && !compat20) {
                 logit("Not supported for SSH protocol version 1.");
                 goto out;
         }
-        s += 2;
+
+        s++;
         while (*s && isspace(*s))
                 s++;
 
-        if (sscanf(s, "%5[0-9]:%255[^:]:%5[0-9]",
-            sfwd_port, buf, sfwd_host_port) != 3 &&
-            sscanf(s, "%5[0-9]/%255[^/]/%5[0-9]",
-            sfwd_port, buf, sfwd_host_port) != 3) {
-                logit("Bad forwarding specification.");
-                goto out;
-        }
-        if ((fwd_port = a2port(sfwd_port)) == 0 ||
-            (fwd_host_port = a2port(sfwd_host_port)) == 0) {
-                logit("Bad forwarding port(s).");
-                goto out;
-        }
-        if (local) {
-                if (channel_setup_local_fwd_listener(fwd_port, buf,
-                    fwd_host_port, options.gateway_ports) < 0) {
-                        logit("Port forwarding failed.");
+        if (delete) {
+                if (sscanf(s, "%5[0-9]", sfwd_host_port) != 1) {
+                        logit("Bad forwarding specification.");
+                        goto out;
+                }
+                if ((fwd_host_port = a2port(sfwd_host_port)) == 0) {
+                        logit("Bad forwarding port(s).");
+                        goto out;
+                }
+                channel_request_rforward_cancel(fwd_host_port);
+        } else {
+                if (sscanf(s, "%5[0-9]:%255[^:]:%5[0-9]",
+                    sfwd_port, buf, sfwd_host_port) != 3 &&
+                    sscanf(s, "%5[0-9]/%255[^/]/%5[0-9]",
+                    sfwd_port, buf, sfwd_host_port) != 3) {
+                        logit("Bad forwarding specification.");
                         goto out;
                 }
-        } else
-                channel_request_remote_forwarding(fwd_port, buf,
-                    fwd_host_port);
-        logit("Forwarding port.");
+                if ((fwd_port = a2port(sfwd_port)) == 0 ||
+                    (fwd_host_port = a2port(sfwd_host_port)) == 0) {
+                        logit("Bad forwarding port(s).");
+                        goto out;
+                }
+                if (local) {
+                        if (channel_setup_local_fwd_listener(fwd_port, buf,
+                            fwd_host_port, options.gateway_ports) < 0) {
+                                logit("Port forwarding failed.");
+                                goto out;
+                        }
+                } else
+                        channel_request_remote_forwarding(fwd_port, buf,
+                            fwd_host_port);
+                logit("Forwarding port.");
+        }
+
 out:
         signal(SIGINT, handler);
         enter_raw_mode();
diff --git a/serverloop.c b/serverloop.c
index a777a048d..8d2642d5b 100644
--- a/serverloop.c
+++ b/serverloop.c
@@ -35,7 +35,7 @@
  */
 
 #include "includes.h"
-RCSID("$OpenBSD: serverloop.c,v 1.115 2004/01/19 21:25:15 markus Exp $");
+RCSID("$OpenBSD: serverloop.c,v 1.116 2004/05/21 11:33:11 djm Exp $");
 
 #include "xmalloc.h"
 #include "packet.h"
@@ -991,6 +991,17 @@ server_input_global_request(int type, u_int32_t seq, void *ctxt)
                             listen_address, listen_port, options.gateway_ports);
                 }
                 xfree(listen_address);
+        } else if (strcmp(rtype, "cancel-tcpip-forward") == 0) {
+                char *cancel_address;
+                u_short cancel_port;
+
+                cancel_address = packet_get_string(NULL);
+                cancel_port = (u_short)packet_get_int();
+                debug("%s: cancel-tcpip-forward addr %s port %d", __func__,
+                    cancel_address, cancel_port);
+
+                success = channel_cancel_rport_listener(cancel_address,
+                    cancel_port);
         }
         if (want_reply) {
                 packet_start(success ?
diff --git a/ssh.1 b/ssh.1
index b7b126440..7da143b19 100644
--- a/ssh.1
+++ b/ssh.1
@@ -34,7 +34,7 @@
 .\" (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 1.185 2004/05/02 11:57:52 dtucker Exp $
+.\" $OpenBSD: ssh.1,v 1.186 2004/05/21 11:33:11 djm Exp $
 .Dd September 25, 1999
 .Dt SSH 1
 .Os
@@ -302,11 +302,18 @@ Display a list of escape characters.
 Send a BREAK to the remote system
 (only useful for SSH protocol version 2 and if the peer supports it).
 .It Cm ~C
-Open command line (only useful for adding port forwardings using the
+Open command line.
+Currently this allows the addition of port forwardings using the
 .Fl L
 and
 .Fl R
-options).
+options (see below).
+It also allows the cancellation of existing remote port-forwardings 
+using
+.Fl KR Ar hostport .
+Basic help is available, using the 
+.Fl ?
+option.
 .It Cm ~R
 Request rekeying of the connection
 (only useful for SSH protocol version 2 and if the peer supports it).