This is the equivalent check to miSyncTriggerFence() from
commit f19ab94ba9 ("miext/sync: Fix use-after-free in miSyncTriggerFence()")
When a trigger fires via SyncAwaitTriggerFired, the resulting
FreeResource/FreeAwait call invokes SyncDeleteTriggerFromSyncObject for
every trigger in the same Await group. This unlinks and frees the
corresponding trigger list nodes - potentially including the node pnext
points to.
Fix by restarting iteration from the list head after a trigger fires, since
TriggerFired may have arbitrarily mutated the list. Triggers that have fired
are removed from the list by FreeAwait, so restarting cannot cause infinite
loops.
This vulnerability was discovered by:
Anonymous working with TrendAI Zero Day Initiative
ZDI-CAN-30164
Assisted-by: Claude:claude-opus-4-6
(cherry picked from commit bdd7bf57af)
Part-of: <https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/2229>
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.
As with other projects hosted on freedesktop.org, X.Org follows its
Code of Conduct, based on the Contributor Covenant. Please conduct
yourself in a respectful and civilized manner when using the above
mailing lists, bug trackers, etc:
92a167ab3f