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bbf1893cc0
In WaitForSomething(), the fd_set clientsWritable may be used unitialized when the boolean AnyClientsWriteBlocked is set in the WakeupHandler(). This leads to a crash in FlushAllOutput() after x11proto's commit 2c94cdb453bc641246cc8b9a876da9799bee1ce7. The problem did not manifest before because both the XFD_SIZE and the maximum number of clients were set to 256. As the connectionTranslation table was initalized for the 256 clients to 0, the test on the index not being 0 was aborting before dereferencing the client #0. As of commit 2c94cdb453bc641246cc8b9a876da9799bee1ce7 in x11proto, the XFD_SIZE got bumped to 512. This lead the OutputPending fd_set to have any fd above 256 to be uninitialized which in turns lead to reading an index after the end of the ConnectionTranslation table. This index would then be used to find the client corresponding to the fd marked as pending writes and would also result to an out-of-bound access which would usually be the fatal one. Fix this by zeroing the clientsWritable fd_set at the beginning of WaitForSomething(). In this case, the bottom part of the loop, which would indirectly call FlushAllOutput, will not do any work but the next call to select will result in the execution of the right codepath. This is exactly what we want because we need to know the writable clients before handling them. In the end, it also makes sure that the fds above MaxClient are initialized, preventing the crash in FlushAllOutput(). Thanks to everyone involved in tracking this one down! Reported-by: Karol Herbst <freedesktop@karolherbst.de> Reported-by: Tobias Klausmann <tobias.klausmann@mni.thm.de> Signed-off-by: Martin Peres <martin.peres@linux.intel.com> Tested-by: Tobias Klausmann <tobias.klausmann@mni.thm.de> Tested-by: Martin Peres <martin.peres@linux.intel.com> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=91316 Cc: Ilia Mirkin <imirkin@alum.mit.edu> Cc: Olivier Fourdan <ofourdan@redhat.com Cc: Adam Jackson <ajax@redhat.com> Cc: Alan Coopersmith <alan.coopersmith@oracle.com Cc: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Alan Coopersmith <alan.coopersmith@oracle.com> |
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X Server
The X server accepts requests from client applications to create windows,
which are (normally rectangular) "virtual screens" that the client program
can draw into.
Windows are then composed on the actual screen by the X server
(or by a separate composite manager) as directed by the window manager,
which usually communicates with the user via graphical controls such as buttons
and draggable titlebars and borders.
For a comprehensive overview of X Server and X Window System, consult the
following article:
http://en.wikipedia.org/wiki/X_server
All questions regarding this software should be directed at the
Xorg mailing list:
http://lists.freedesktop.org/mailman/listinfo/xorg
Please submit bug reports to the Xorg bugzilla:
https://bugs.freedesktop.org/enter_bug.cgi?product=xorg
The master development code repository can be found at:
git://anongit.freedesktop.org/git/xorg/xserver
http://cgit.freedesktop.org/xorg/xserver
For patch submission instructions, see:
http://www.x.org/wiki/Development/Documentation/SubmittingPatches
For more information on the git code manager, see:
http://wiki.x.org/wiki/GitPage