[Bug 1254] Race condition in ssh-agent AUTH_CONNECTION

[bugzilla-daemon at mindrot.org]

http://bugzilla.mindrot.org/show_bug.cgi?id=1254

           Summary: Race condition in ssh-agent AUTH_CONNECTION
           Product: Portable OpenSSH
           Version: 4.4p1
          Platform: ix86
        OS/Version: FreeBSD
            Status: NEW
          Keywords: patch
          Severity: normal
          Priority: P2
         Component: ssh-agent
        AssignedTo: bitbucket at mindrot.org
        ReportedBy: ohannet at allez-oop.net


In function after_select(), case AUTH_CONNECTION, the do-loop which
handles socket reads will peg my CPU at close to 100% when errno is
EAGAIN.

I'm running FreeBSD 6.2 pre-release, with OpenSSH built from the ports
collection (security/openssh-portable).

The problem only occurs for me while running an automation script that
sends commands through ssh to about a hundred servers at at time, and I
have not been successful in identifying which server causes the
problem.  But the bottom line is that the read fails with errno EAGAIN,
and continues to fail in a very tight loop until a timeout occurs at
some point.

My work-around was to introduce a tiny sleep before the continue
statement in that loop, which is apparently enough to allow some data
to become available for reading, and makes the problem go away.

I will attach my work-around as a patch, realizing that usleep() is
probably not available on all platforms.




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