[PATCH] Expose remote forwarding ports as environment variable

[Nico Schottelius]

Good evening gentlemen,

the attached patch against openssh 6.2p1 exposes remote
forwarding ports to the remote shell:

    targethost % ssh -R 1234:localhost:22 controlhost
    controlhost % echo $SSH_REMOTE_FORWARDING_PORTS
    1234
    
    targethost % ssh -R 0:localhost:22 controlhost
    controlhost % echo $SSH_REMOTE_FORWARDING_PORTS
    54294
    
    targethost % ssh -R 0:localhost:22 -R 1234:localhost:22 controlhost
    controlhost % echo $SSH_REMOTE_FORWARDING_PORTS
    59056 1234

Detailled motivation can be found at

    http://www.nico.schottelius.org/blog/openssh-6.2-add-callback-functionality-using-dynamic-remote-port-forwarding/

The patch is attached.

Please let me know what you think about it and whether you'd
consider it for inclusion (with or without changes).

Cheers,

Nico

-- 
PGP key: 7ED9 F7D3 6B10 81D7 0EC5  5C09 D7DC C8E4 3187 7DF0
-------------- next part --------------
diff -ru openssh-6.2p1/channels.c openssh-6.2p1.patched/channels.c
--- openssh-6.2p1/channels.c	2012-12-02 23:50:55.000000000 +0100
+++ openssh-6.2p1.patched/channels.c	2013-05-15 23:26:17.119989982 +0200
@@ -2865,6 +2865,52 @@
 	return success;
 }
 
+/*
+ * Write list of remote forwarding ports into an existing buffer 
+ */
+void
+channel_list_rport_listener(char *buf, size_t size)
+{
+	u_int i, j, num_ports = 0;
+	int offset = 0;
+	int *ports;
+	int skip;
+
+	ports = xcalloc(channels_alloc, sizeof(int));
+
+	for (i = 0; i < channels_alloc; i++) {
+		skip = 0;
+		Channel *c = channels[i];
+		if (c == NULL || c->type != SSH_CHANNEL_RPORT_LISTENER)
+			continue;
+
+		/* Skip already added ports - IPv4 + IPv6 == same port twice */
+		for(j = 0; j < num_ports; j++) {
+			if (ports[j] == c->listening_port) {
+				skip = 1;
+				break;
+			}
+		}
+
+		if(skip) continue;
+
+		ports[num_ports] = c->listening_port;
+		num_ports++;
+
+		if(!offset) {
+			offset += snprintf(&buf[offset], size - offset, "%d", c->listening_port);
+		} else
+			offset += snprintf(&buf[offset], size - offset, " %d", c->listening_port);
+
+		if(offset >= size) {
+			error("Exceeded buffer space for remote forwarding ports listing");
+			break;
+		}
+	}
+
+	xfree(ports);
+}
+
 int
 channel_cancel_rport_listener(const char *host, u_short port)
 {
Only in openssh-6.2p1.patched/: .channels.c.swp
diff -ru openssh-6.2p1/channels.h openssh-6.2p1.patched/channels.h
--- openssh-6.2p1/channels.h	2012-04-22 03:21:10.000000000 +0200
+++ openssh-6.2p1.patched/channels.h	2013-05-09 23:21:37.385423623 +0200
@@ -222,6 +222,7 @@
 void	 channel_cancel_cleanup(int);
 int	 channel_close_fd(int *);
 void	 channel_send_window_changes(void);
+void	 channel_list_rport_listener(char *buf, size_t size);
 
 /* protocol handler */
 
diff -ru openssh-6.2p1/session.c openssh-6.2p1.patched/session.c
--- openssh-6.2p1/session.c	2013-03-15 01:22:37.000000000 +0100
+++ openssh-6.2p1.patched/session.c	2013-05-15 23:27:12.459989713 +0200
@@ -1235,6 +1235,9 @@
 	xfree(laddr);
 	child_set_env(&env, &envsize, "SSH_CONNECTION", buf);
 
+	channel_list_rport_listener(buf, sizeof buf);
+	child_set_env(&env, &envsize, "SSH_REMOTE_FORWARDING_PORTS", buf);
+
 	if (s->ttyfd != -1)
 		child_set_env(&env, &envsize, "SSH_TTY", s->tty);
 	if (s->term)
Only in openssh-6.2p1.patched/: .session.c.swp