In the Linux kernel, the following vulnerability has been resolved:
drm/amdgpu/userq: Fix fence reference leak on queue teardown v2
The user mode queue keeps a pointer to the most recent fence in
userq->last_fence. This pointer holds an extra dma_fence reference.
When the queue is destroyed, we free the fence driver and its xarray,
but we forgot to drop the last_fence reference.
Because of the missing dma_fence_put(), the last fence object can stay
alive when the driver unloads. This leaves an allocated object in the
amdgpu_userq_fence slab cache and triggers
This is visible during driver unload as:
BUG amdgpu_userq_fence: Objects remaining on __kmem_cache_shutdown()
kmem_cache_destroy amdgpu_userq_fence: Slab cache still has objects
Call Trace:
kmem_cache_destroy
amdgpu_userq_fence_slab_fini
amdgpu_exit
__do_sys_delete_module
Fix this by putting userq->last_fence and clearing the pointer during
amdgpu_userq_fence_driver_free().
This makes sure the fence reference is released and the slab cache is
empty when the module exits.
v2: Update to only release userq->last_fence with dma_fence_put()
(Christian)
(cherry picked from commit 8e051e38a8d45caf6a866d4ff842105b577953bb)
