openssh unix dev - Sep 2017 - 'No more sessions available' / channels not closing issue

Hi all,



We've run into a curious issue.



We run CentOS 6.5 with openssh installed (OpenSSH_5.3p1, OpenSSL 1.0.1e-fips 11
Feb 2013 by default). We connect to this server through sftp (Subsystem sftp
internal-sftp) using the java JSch library. When opening many sftp channels on a
single ssh session OpenSsh does not seem to release the sftp channels closed
from the client side when there are still sftp channels open that are opened
later than the channel that is closed..  Eventually resulting in "No more
sessions available".



Here is what happens:



1) We open sftp connection (1) to server

2) We open another sftp connection (2) to server (before connection 1 is closed)

3) We close connection 1 before connection 2 is closed

4) Connection 1 will not be released because connection 2 is still open

5) We open connection 3.

6) We close connection 2, but will not be released because connection 3 is still
open. Connection 1 will also not be released because 2 is not released etc..



When the connections are closed "lifo" (last in first out) all works
as expected.



Is this a bug or by design? Is there a way to prevent this "leak"? Is
there a way to timeout unused channels (not sessions)? We have MaxSessions
raised but those will eventually max out too.


Thanks in advance,


Mickel Daelmans
Developer


Goeman Borgesiuslaan 77
3515 ET Utrecht
T. 030-7551560
W. www.addtofavorites.nl<http://www.addtofavorites.nl/>

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On Mon, 11 Sep 2017, Mickel Daelmans | Add to Favorites wrote:
> Hi all,
> 
> We've run into a curious issue.
> 
> We run CentOS 6.5 with openssh installed (OpenSSH_5.3p1,
http://www.openssh.com/releasenotes.html#5.3p1

That was released almost 8 years ago. We've fixed a lot of bugs since
then. Can you reproduce with a current version?

-d