[Xcb] [Bug 29412] [regression] unexpected libX11 IOError

bugzilla-daemon at freedesktop.org bugzilla-daemon at freedesktop.org
Thu Aug 5 11:24:09 PDT 2010


--- Comment #4 from Matthieu Herrb <matthieu.herrb at laas.fr> 2010-08-05 11:24:08 PDT ---
I strongly believe that this is the use-after-free problem I reported here:


> After updating to libX11 1.3.4, I started seeing window managers or
> toolbar programs exit without reasons when closing windows or pop-ups.

> After a bit of debugging, I figured out that this is caused by
> a use after free bug in _XReply. Most people running Linux won't see it 
> because the data in the just free()'d memory is still there. But
> Using OpenBSD's malloc which fills free()'d memory with a specific 
> pattern, you get a different code path. 

> The proplem arises in xcb_io.c:582. the 'current' pointer can have
> been free()'d already (by dequeue_pending_request() called at line 562)
> when getting there.

> A simple test program to reproduce the issue is appended below: just
> call XGetWindowProperty on a non-existent window.

> Using his favourite malloc debugger one should be able to see the problem
> on Linux too...

> Unfortunatly I'm not sure of what the fix is...

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