[Bug 1517] New: ssh ControlMaster process is crashing frequently when multiplexing ssh and scp connections with error 'select: Invalid argument'

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https://bugzilla.mindrot.org/show_bug.cgi?id=1517

           Summary: ssh ControlMaster process is crashing frequently when
                    multiplexing ssh and scp connections with error
                    'select: Invalid argument'
           Product: Portable OpenSSH
           Version: 5.1p1
          Platform: Sparc
        OS/Version: Solaris
            Status: NEW
          Severity: normal
          Priority: P2
         Component: ssh
        AssignedTo: unassigned-bugs at mindrot.org
        ReportedBy: james at bluecat.demon.co.uk


ssh ControlMaster process is crashing frequently when multiplexing ssh
and scp connections with error 'select: Invalid argument'.

We have an application which is constantly making two to three hundred
concurrent multiplexed scp and ssh connections between two Solaris
platforms.  The scripts are transferring 3KB files and then performing
checkum and mv commands.  We are using ssh multiplexing to reduce CPU
and network load.  We have a script in cron to restart the
ControlMaster process; it is restarting approx 280 times per day. 

The ssh ControlMaster syntax:
/usr/local/bin/ssh -oControlMaster=yes
-oControlPath="/cdrc/.ssh/mp_sock-scholzite" -fnN -c blowfish-cbc
transfer at scholzite-be

We are using Openssh-5.1p1 compiled from source (and Openssl-0.9.8h). 
This OpenSSH version is used on the client and server, both servers are
Solaris 9 Sparc platforms.  The max file descriptors kernel parameter
on both systems is 8192.

The following parameters are set in the sshd_config (these values are
overkill, but we were clutching at straws!), if we set values below 300
for MaxSessions we get 'Administratively Prohibited' authentication
failures on the server side. 
MaxSessions 8192
MaxStartups 8192

I have attached level 9 debug.  The debug always ends with 'select:
Invalid argument' when the process fails.

Last few lines of debug:
debug3: channel 296: close_fds r 1023 w 1024 e 1025 c 1022
debug3: fd 0 is not O_NONBLOCK
debug3: fd 1 is not O_NONBLOCK
debug3: fd 2 is not O_NONBLOCK
select: Invalid argument
Transferred: sent 12310448, received 106560 bytes, in 88.1 seconds
Bytes per second: sent 139799.0, received 1210.1
debug1: Exit status -1

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