CVE-2026-72094

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

dma-buf: dma-fence: Fix potential NULL pointer dereference

The commit mentioned in the fixes tag below introduced a mechanism

through which fence producers can fully decouple from fence consumers.

This, desirable, mechanism is based on the fence's signaled-bit as the

"decoupling point".

A sophisticated interaction between RCU and atomic instructions attempts

to ensure that fence consumers can still interact with fence producers

through the dma_fence_ops (callback pointers into the producer).

This is the desired behavior: to check for decoupling, the signaled-bit

is first checked. If it's not yet signaled, RCU ensures that the ops

pointer cannot yet be NULL.

Hereby, dma_fence_signal_timestamp_locked() first sets the signaled-bit,

and then sets the ops pointer to NULL. Readers first load the ops

pointer, and then check through the signaled-bit whether the pointer can

legally be accessed.

These set and load operations could occur out of order on weakly ordered

platforms. This problem can be solved very elegantly by using the ops

pointer itself as the synchronization point. The pointer is either NULL,

or cannot become NULL while it is being used thanks to RCU.

Replace the signaled-bit check in dma_fence_timeline_name() and

dma_fence_driver_name().