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List:       openssh-unix-dev
Subject:    "ServerAliveInterval" and "ServerAliveCountMax" doesnt work in
From:       leanne <njleanne () hotmail ! com>
Date:       2008-05-15 2:15:26
Message-ID: BAY123-W32E38712EF401634109F38C6C90 () phx ! gbl
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Hi OpenSSH team,

We found that openssh5.0 has a bug with the "ServerAliveInterval" and \
"ServerAliveCountMax" options. 

This function doesnt work at all, which means when the Maxtime reached, the ssh will \
not kill the connection and prompt the infomation "Connection Timedout" as it used to \
do.

 

We built the openssh5.0p1 code on the a Linux box,  and use the following \
configruation, and reproduced on it.

 

Following is the experiment i did on my Ubuntu Linux box. 

 

In Terminal 1:

root@sway-desktop:~# uname -aLinux sway-desktop 2.6.22-14-generic #1 SMP Sun Oct 14 \
23:05:12 GMT 2007 i686 GNU/Linux

root@sway-desktop:~# cat /ssh_config   Protocol 2   HashKnownHosts yes   \
ServerAliveInterval 5   ServerAliveCountMax 1      #This tells the ssh to close the \
connection after 5*1 = 5 seconds  if no data has been received from the server. 

 

root@sway-desktop:~# ps -ef|grep sshdroot      5415     1  0 14:21 ?        00:00:00 \
/home/sway/openssh-5.0p1/sshd -p 5555

root@sway-desktop:~# cd \
/home/sway/openssh-5.0p1root@sway-desktop:/home/sway/openssh-5.0p1# /ssh -F \
/ssh_config 192.168.37.131 -p 5555root@192.168.37.131's password:Last login: Sun May  \
4 14:22:20 2008 from qianbo-desktop.localroot@sway-desktop:

 

 

In termial 2:

root@sway-desktop:~# ps -ef|grep sshd

root      5415     1  0 14:21 ?        00:00:00 /home/sway/openssh-5.0p1/sshd -p 5555

root      5832  5415  0 14:34 ?        00:00:00 sshd: root@pts/0

root@sway-desktop:~# kill -19 5832                     // 19 means SIGSTOP

 

I waited more than 10 miniutes, the ssh still  hangs there without giving any \
information about "Connection timeout"...

 

So i sent a SIGCONT to the sshd server, and the ssh come back alive.

We debugged into the code, found out that everytime the ssh did check the variable \
"keep_alive_timeouts" with the ServerAliveCountMax value after ServerAliveInterval \
seconds to see if keep_alive_timeouts > ServerAliveCountMax, if so , ssh will close \
the connection and give the "connection timeout" information, else it will increment \
the keep_alive_timeouts by 1. 

After Checking, ssh will jump into the "packet_read_poll_seqnr(u_int32_t *seqnr_p)" \
function, and there it will reset the keep_alive_timeouts variable to "0" again which \
actually caused the problem. Can you check if it is a bug with openssh50's code or \
not?Thanks very much.  
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