f5abfb6199
Both FreeCounter() and miSyncDestroyFence() iterate over the trigger list and invoke the CounterDestroyed callback on each trigger. The CounterDestroyed callback (e.g. SyncAwaitTriggerFired) may call FreeResource/FreeAwait, which frees the SyncAwaitUnion containing all SyncAwait structs in the same Await group. When multiple conditions in a single Await reference the same sync object (counter or fence), the first callback frees all SyncAwait structs while subsequent trigger list nodes still reference them. On the next iteration, reading ptl->next or ptl->pTrigger dereferences freed memory, leading to a use-after-free. We need separate fixes for separate issues here to fix this in one go - use our null-terminated list macro to make sure our next pointer stays valid (the code accessed ptl->next after freeing it) - update the list head before deleting the trigger, eventually this ends up being NULL anyway but meanwhile the list head is a valid list during CounterDestroyed - check if we actually do have a trigger before dereferencing the callback - Set all triggers to NULL if they are shared so we don't dereference potentially freed memory This vulnerability was discovered by: Anonymous working with TrendAI Zero Day Initiative ZDI-CAN-30159 (miSyncDestroyFence), ZDI-CAN-30163 (FreeCounter) Assisted-by: Claude:claude-opus-4-6 Part-of: <https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/2228> |
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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: https://en.wikipedia.org/wiki/X_server
All questions regarding this software should be directed at the Xorg mailing list:
https://lists.freedesktop.org/mailman/listinfo/xorg
The primary development code repository can be found at:
https://gitlab.freedesktop.org/xorg/xserver
For patch submission instructions, see:
https://www.x.org/wiki/Development/Documentation/SubmittingPatches
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: