bugzilla-daemon at bugzilla.mindrot.org
2018-Oct-11 19:35 UTC
[Bug 2917] New: keepalive packets are sent twice each interval if connection is interrupted
https://bugzilla.mindrot.org/show_bug.cgi?id=2917
Bug ID: 2917
Summary: keepalive packets are sent twice each interval if
connection is interrupted
Product: Portable OpenSSH
Version: -current
Hardware: amd64
OS: Linux
Status: NEW
Severity: normal
Priority: P5
Component: sshd
Assignee: unassigned-bugs at mindrot.org
Reporter: dev at sapalski.de
Created attachment 3193
--> https://bugzilla.mindrot.org/attachment.cgi?id=3193&action=edit
Update last_client_time on timeout
I've discovered a bug in
serverloop.c(function=wait_until_can_do_something)!
With latest openssh (7.8p1 as well as current master) sshd disconnects
a non-responding client after approximately: ((ClientAliveCountMax / 2)
* ClientAliveInterval) seconds
I did a bisect which showed that the fix introduced for bz#2756 causes
this behavior: https://bugzilla.mindrot.org/show_bug.cgi?id=2756
How to reproduce:
1. server #> /sbin/sshd -p 2020 -ddd -f ${sshd_config} 2>&1 | ts
2. client $> ssh $IP -p2020
3. close e.g. notebook of the client connection and wait for the
timeout to happen (maybe killing the client process is already enough,
didn't test it).
${sshd_config}
----
TCPKeepAlive no
ClientAliveInterval 15
ClientAliveCountMax 8
----
The debug log of sshd shows:
----
...
[2018-04-26 11:59:35] debug3: /tmp/sshd_config:94 setting TCPKeepAlive
no
[2018-04-26 11:59:35] debug3: /tmp/sshd_config:98 setting
ClientAliveInterval 15
[2018-04-26 11:59:35] debug3: /tmp/sshd_config:99 setting
ClientAliveCountMax 8
...
[2018-04-26 12:00:16] debug2: channel 0: request keepalive at openssh.com
confirm 1
[2018-04-26 12:00:16] debug2: channel 0: request keepalive at openssh.com
confirm 1
[2018-04-26 12:00:31] debug2: channel 0: request keepalive at openssh.com
confirm 1
[2018-04-26 12:00:31] debug2: channel 0: request keepalive at openssh.com
confirm 1
[2018-04-26 12:00:46] debug2: channel 0: request keepalive at openssh.com
confirm 1
[2018-04-26 12:00:46] debug2: channel 0: request keepalive at openssh.com
confirm 1
[2018-04-26 12:01:01] debug2: channel 0: request keepalive at openssh.com
confirm 1
[2018-04-26 12:01:01] debug2: channel 0: request keepalive at openssh.com
confirm 1
[2018-04-26 12:01:16] Timeout, client not responding from user $USER
x.x.x.x port xxxxx
----
keepalive packets are sent twice on every interval. I think the problem
is that if a timeout of the select call in
function=wait_until_can_do_something happens the next select call will
return immediately with data contained in 'writesetp' which causes to
send another keepalive packet since variable=last_client_time wasn't
updated.
A very naive patch which solves the problem for me is attached.
However, there might a better solution for this problem!
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bugzilla-daemon at bugzilla.mindrot.org
2018-Oct-11 19:35 UTC
[Bug 2917] keepalive packets are sent twice each interval if connection is interrupted
https://bugzilla.mindrot.org/show_bug.cgi?id=2917
Samuel Sapalski <dev at sapalski.de> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |dev at sapalski.de
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bugzilla-daemon at mindrot.org
2023-Oct-11 05:29 UTC
[Bug 2917] keepalive packets are sent twice each interval if connection is interrupted
https://bugzilla.mindrot.org/show_bug.cgi?id=2917
Damien Miller <djm at mindrot.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Resolution|--- |FIXED
Status|NEW |RESOLVED
CC| |djm at mindrot.org
--- Comment #1 from Damien Miller <djm at mindrot.org> ---
I think this got fixed in 9d7193a835963 if it wasn't already fixed
during refactoring.
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