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Re: [Libvir] PATCH: Prevent zombie ssh tunnels



On Fri, Sep 14, 2007 at 03:14:02AM +0100, Daniel P. Berrange wrote:
> On Tue, Sep 11, 2007 at 04:56:13AM -0400, Daniel Veillard wrote:
> > On Tue, Sep 11, 2007 at 12:59:59AM +0100, Daniel P. Berrange wrote:
> > > I noticed that when using the SSH tunnel for the remote driver I ended up
> > > with alot of zombie SSH processes. We simply forgot to waitpid() on the
> > > child when a connection attempt failed, or when shutting down an open remote
> > > connection. Attached is a possible patch
> > 
> >   Looks fine, like Rich maybe a bit of refactoring might be good. The
> > only worries I have is the following scenario:
> >    - the ssh process dies
> >    - libvirt based application takes some time to notice it
> >    - the OS span a new process with the same PID after a PID rollabck
> >      (not completely unlikely since the ssh may have been started a long
> >      time ago)
> >    - we end-up killing a random process in the system
> > 
> > I think this is mostly avoidable by resetting priv->pid to -1 or 0 on 
> > any child communication error, and before doing the kill in the patch.
> > Even better would be to be able to check that the process corresponding
> > to priv->pid is still a child of the current process, I wonder if this
> > can be achieved without blocking with an initial waitpid()
> 
> After some testing I believe we can safely do away with kill() completely.
> If we simply close(priv->sock) which is our end of the socketpair used
> to talk to SSH, then SSH detects the end-of-file condition and exits of
> its on accord. So there's no need to kill() - just close the socket and
> waitpid() seems to do the trickm, unless I'm missing something bad.

  Looks fine and safe to me, I like it +1 !

Daniel

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Daniel Veillard      | virtualization library  http://libvirt.org/
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