CVE-2026-46215

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

drm: Set old handle to NULL before prime swap in change_handle

There was a potential race condition in changehandle. The ioctl briefly had a single object with two idr entries; a concurrent gemclose could delete the object and remove one of the handles while leaving the other one dangling, which could subsequently be dereferenced for a use-after-free.

To fix this, do the same dance that gemclose itself does. (f6cd7daecff5 drm: Release driver references to handle before making it available again) First idrreplace the old handle to NULL. Later, if the prime operations are successful, actually close it.

createtail required a similar dance to avoid a similar problem. (bd46cece51a3 drm/gem: Fix race in drmgemhandlecreatetail()) It idrallocs the new handle with NULL, then swaps in the correct object later to avoid races. We don't need to do that here, since the only operations that could race are drmprime, and changehandle holds the prime lock for the entire duration.

v2: cleanups of error paths