CVE-2024-43863

In the Linux kernel, the following vulnerability has been resolved:

drm/vmwgfx: Fix a deadlock in dma buf fence polling

Introduce a version of the fence ops that on release doesnt remove the fence from the pending list, and thus doesnt require a lock to fix poll->fence wait->fence unref deadlocks.

vmwgfx overwrites the wait callback to iterate over the list of all fences and update their status, to do that it holds a lock to prevent the list modifcations from other threads. The fence destroy callback both deletes the fence and removes it from the list of pending fences, for which it holds a lock.

dma buf polling cb unrefs a fence after its been signaled: so the poll calls the wait, which signals the fences, which are being destroyed. The destruction tries to acquire the lock on the pending fences list which it can never get because its held by the wait from which it was called.

Old bug, but not a lot of userspace apps were using dma-buf polling interfaces. Fix those, in particular this fixes KDE stalls/deadlock.

Weakness

The product does not properly acquire or release a lock on a resource, leading to unexpected resource state changes and behaviors.

Affected Software

Extended Description

Locking is a type of synchronization behavior that ensures that multiple independently-operating processes or threads do not interfere with each other when accessing the same resource. All processes/threads are expected to follow the same steps for locking. If these steps are not followed precisely - or if no locking is done at all - then another process/thread could modify the shared resource in a way that is not visible or predictable to the original process. This can lead to data or memory corruption, denial of service, etc.

Potential Mitigations

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/25.html
• https://cwe.mitre.org/data/definitions/26.html
• https://cwe.mitre.org/data/definitions/27.html

References

• https://git.kernel.org/stable/c/3b933b16c996af8adb6bc1b5748a63dfb41a82bc
• https://git.kernel.org/stable/c/9908dc0d2ef0e4aec8a242c098455729c0e2f017
• https://git.kernel.org/stable/c/9e20d028d8d1deb1e7fed18f22ffc01669cf3237
• https://git.kernel.org/stable/c/a8943969f9ead2fd3044fc826140a21622ef830e
• https://git.kernel.org/stable/c/c98ab18b9f315ff977c2c65d7c71298ef98be8e3
• https://git.kernel.org/stable/c/e58337100721f3cc0c7424a18730e4f39844934f
• https://lists.debian.org/debian-lts-announce/2025/01/msg00001.html
• https://lists.debian.org/debian-lts-announce/2025/10/msg00007.html