CVE-2026-53145 — drm/gem: Try to fix change_handle ioctl, attempt 4

Affected: Linux, Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 7, Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9

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

drm/gem: Try to fix change_handle ioctl, attempt 4

[airlied: just added some comments on how to reenable] On-list because the cat is out of the bag and we're clearly not good enough to figure this out in private. The story thus far:

5e28b7b94408 ("drm: Set old handle to NULL before prime swap in change_handle") tried to fix a race condition between the gem_close and gem_change_handle ioctls, but got a few things wrong:

- There's a confusion with the local variable handle, which is actually the new handle, and so the two-stage trick was actually applied to the wrong idr slot. 7164d78559b0 ("drm/gem: fix race between change_handle and handle_delete") tried to fix that by adding yet another code block, but forgot to add the error handling. Which meant we now have two paths, both kinda wrong.

- dc366607c41c ("drm: Replace old pointer to new idr") tried to apply another fix, but inconsistently, again because of the handle confusion - this would be the right fix (kinda, somewhat, it's a mess) if we'd do the two-stage approach for the new handle. Except that wasn't the intent of the original fix.

We also didn't have an igt merged for the original ioctl, which is a big no-go. This was attempted to address off-list in the original bugfix, and amd QA people claimed the bug was fixed now. Very clearly that's not the case. Here's my attempt to sort this out:

- Rename the local variable to new_ha…

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CVE-2026-53145 — drm/gem: Try to fix change_handle ioctl, attempt 4