https://bugzilla.mindrot.org/show_bug.cgi?id=2572
Bug ID: 2572
Summary: dead sessions aren't closed despite ClientAlive
enabled
Product: Portable OpenSSH
Version: 3.7.1p2
Hardware: All
OS: Linux
Status: NEW
Severity: major
Priority: P5
Component: sshd
Assignee: [email protected]
Reporter: [email protected]
Hi.
I'm experiencing the following every now and then:
A ssh session somehow gets stuck and never gets closed despite
ClientAlive messages being enabled.
Unfortunately I do not know how to reproduce it, nor did I found any
other indicative log messages or so.
It happens with the Debian sid version of ssh, but I think I experience
it since 6.9 (I think it wasn't happening in 6.8) - but maybe I mix
things up here.
systemd is used sshd run in daemon mode.
I have amongst other the following set in sshd_config:
ClientAliveInterval 15
ClientAliveCountMax 8
TCPKeepAlive no
AFAIU, ClientAlive messages should do more or less the same just not on
the TCP level but within the encrypted SSH connection. So if that is
gone and the client doesn't reply anymore, I'd expect sshd to kill the
connection.
A current example shows me:
# w
05:08:19 up 2 days, 5:19, 3 users, load average: 0,00, 0,05, 0,05
USER TTY FROM LOGIN@ IDLE JCPU PCPU WHAT
root pts/0 141.[snipsnap] Tue14 39:08m 0.23s 0.23s -bash
root pts/1 142.[snipsnap] Tue14 38:04m 0.23s 0.23s -bash
root pts/2 2001:[snipsnap] 01:36 1.00s 0.34s 0.00s w
The ones on pts 0 and 1 are dead (they were made from the same laptop
that makes the connection to 2, just from another network, and the
laptop has been rebooted several times since then.
# netstat --inet --inet6 -pn | grep ssh
tcp 0 0 85.[snipsnap]:22 141.[snipsnap]:34016
ESTABLISHED 15847/sshd: root@pt
tcp 0 0 85.[snipsnap]:22 142.[snipsnap]:51726
ESTABLISHED 17000/sshd: root@pt
tcp6 0 276 2a01:[snipsnap]:46538 ESTABLISHED 29362/sshd:
root@pt
interestingly, the kernel doesn't kill of the connections either,
despite them being definitely gone
Any ideas how to further debug that?
Thanks,
Chris.
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