openssh unix dev - Jan 2002 - [Bug 79] New: A race with select() in SIGCHLD handling causes hangs occasionally

http://bugzilla.mindrot.org/show_bug.cgi?id=79

           Summary: A race with select() in SIGCHLD handling causes hangs
                    occasionally
           Product: Portable OpenSSH
           Version: 3.0.2p1
          Platform: All
               URL: http://marc.theaimsgroup.com/?l=openssh-unix-
                    dev&m=100454673601558&w=2
        OS/Version: All
            Status: NEW
          Severity: major
          Priority: P2
         Component: sshd
        AssignedTo: openssh-unix-dev at mindrot.org
        ReportedBy: Nicolas.Williams at ubsw.com
                CC: openssh-unix-dev at mindrot.org


There's a race condition in OpenSSH (all versions - haven't checked
-current)
such that if SIGCHLD arrives after the check for child_terminated, but before
entering select() (with no timeout) AND if the session's pty/pipes have
received EOF before SIGCHLD is handled, then sshd will block in select()
forever, while the client hangs waiting for the session-exit message that
will never arrive (because sshd will never send it, because it's blocking
in select()).

Markus Friedl posted a fix for it (see URL associated with this bug report).
It works. It should be applied.

Thanks.



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