[Vortex] [BUG] Race condition in vortex_tls_start_negotiation_sync

Francis Brosnan Blazquez francis at aspl.es
Thu Sep 9 19:45:00 CEST 2010

Hi Benoit,

> Forgot the actual patch...

Thanks for the patch. I've being checking the issue and I see your race

Checking your patch I see it implements something that already provides
vortex_tls_start_negotation (which always returns a coherent connection,
no matter the termination status), and at the same time I think the
patch hides a bug in vortex_tls_start_negotation_sync which should
return NULL in the case of timeout for the reasons you have pointed.

In this context I find that the root issue is indeed located at the
incoherent behavior of vortex_tls_start_negotation_sync, so I've updated
its internal implementation to ensure that, if the user receives a
connection reference at the function termination it is because it is
safe and no background TLS process will shutdown/dealloc it, but in the
case a new NULL internal connection is received, due to a timeout in the
middle of TLS, the function returns NULL, and internally the connection
created is finished (if any).

I've added a regression test (test_05-d) to reproduce your bug
description and to check the fix introduced.

This change only applies to Vortex 1.1 series. I didn't apply your
patch. Thanks for reporting Benoit. Cheers!

> > -----Original Message-----
> > From: AMIAUX Benoît
> > Sent: Friday, August 20, 2010 10:27 AM
> > To: 'Vortex'
> > Subject: RE: [BUG] Race condition in vortex_tls_start_negotiation_sync
> >
> > Hello,
> >
> > Attached patch fixes the issue for me.
> >
> > The main point is that we have to ref the connection we're using inside
> > vortex_tls_start_negotiation_sync because it can be closed and un-
> > referred if a timeout happens.
> >
> > Moreover, my version returns NULL in case of timeouts because it seems
> > to be impossible without too many changes to ensure the input
> > vortex_connection* pointer is valid on errors. This is due to the
> > vortex_connection_unref in
> >
> > vortex_tls.c:895
> > vortex_connection_unref (connection_aux, "(vortex tls process)");
> >
> > which is not thread-safe in our case. We cannot guarantee not too many
> > unref happens if we return the old connection pointer.
> >
> > This patch works for me when I start 64 threads at once which tries to
> > create TLS connections and fail repeatedly.
> >
> > Thanks you,
> > Benoît Amiaux
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Francis Brosnan Blazquez <francis at aspl.es>

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