Bug 2219

Summary:	Can't use -Ocancel on forward of dynamically allocated remote port
Product:	Portable OpenSSH	Reporter:	Sean Patrick Santos <quantheory>
Component:	ssh	Assignee:	Assigned to nobody <unassigned-bugs>
Status:	NEW ---
Severity:	enhancement	CC:	norman
Priority:	P5
Version:	6.5p1
Hardware:	Other
OS:	Linux

Description Sean Patrick Santos 2014-04-01 14:18:20 AEDT

If you are using a multiplexed connection, you can request a dynamically allocated remote port forward, but then there is no way to cancel it afterward.

Example:

> ssh -Oforward -R 0:127.0.0.1:56789 user@remote
Allocated port 12345 for remote forward to 127.0.0.1:56789
12345
> ssh -Ocancel -R 0:127.0.0.1:56789 user@remote
mux_client_forward: forwarding request failed: port not in permitted opens
muxclient: master cancel forward request failed
> ssh -Ocancel -R 12345:127.0.0.1:56789 user@remote
mux_client_forward: forwarding request failed: port not forwarded
muxclient: master cancel forward request failed

At least the second one should work, but OpenSSH doesn't check the cancel request against the allocated port in this case.

Comment 1 Norman Rasmussen 2021-04-24 06:30:00 AEST

Works for me with 8.4p1, so I'm guessing it has been fixed since.

$ ssh -O forward -R 0:localhost:1234 remote
35077
$ ssh -O cancel -R 0:localhost:1234 remote
$

There was a fix "markus@cvs.openbsd.org 2011/09/23 07:45:05" that looks potentially relevant, except that it was committed way before 6.5p1.