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Description of problem:
When both a RekeyLimit timeout is specified and ClientAliveCountMax is set to zero, sshd disconnects sessions even when input has been detected from the client within the specified ClientAliveInterval.
Version-Release number of selected component (if applicable):
8.0p1
How reproducible:
Always
Steps to Reproduce:
1. Edit /etc/ssh/sshd_config, set RekeyLimit to "512M 120", ClientAliveCountMax to 0 and ClientAliveInterval to 60
2. Restart sshd
3. Create a connection to the server via ssh, and type "date" every 10 seconds
Actual results:
The server disconnects the client session even though input was received from the client within the last ClientAliveInterval seconds. In the example below, the client produced input at 8:39:25 UTC and the server disconnected the session 15 seconds later at 8:39:40 UTC even though ClientAliveInterval is set to 60.
Client side:
...
$ date
Thu Apr 22 08:39:02 UTC 2021
$ date
Thu Apr 22 08:39:19 UTC 2021
$ date
Thu Apr 22 08:39:25 UTC 2021
$ Connection to SERVERNAME closed by remote host.
Connection to SERVERNAME closed.
Server side:
Apr 22 08:39:40 SERVERNAME sshd[1428458]: Timeout, client not responding from user USERNAME CLIENT-IP port 37998
Expected results:
It is expected that the server allows the connection to remain open as long as input is received from the client every ClientAliveInterval seconds.
Additional info:
This is a re-open of Bug #1686065 because the fix for that bug appears to be incomplete.
Comment 3Dmitry Belyavskiy
2021-04-23 12:35:19 UTC
Would you mind to test the proposed patch?
Comment 6Alexander Sosedkin
2021-04-27 09:20:18 UTC
Note: the meaning of setting ClientAliveCountMax to 0 used to be undefined.
In newer openssh versions it disables connection termination [1] altogether.
The documentation suggests that the disconnect timeout on inactivity
is a product of ClientAliveCountMax and ClientAliveInterval.
[1] https://github.com/openssh/openssh-portable/commit/69334996ae203c51c70bf01d414c918a44618f8e