Linux Kernel drm/ttm Swapout Path Omits bulk_move List Removal, Opening a Local Use-After-Free

Status: UPDATED  |  Advisory ID: CVE-2026-98166

Key Details

Affected Products, Subsystems & Sectors

What to Know

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

drm/ttm: fix swapped-out resources never leaving their bulk_move range

ttm_tt_swapout() returns the number of pages swapped out on success and

a negative error code on failure; for a populated ttm it never returns

zero. Commit b2ed01e7ad3d ("drm/ttm: Fix ttm_bo_swapout() infinite LRU

walk on swapout failure") moved the bulk_move bookkeeping in

ttm_bo_swapout_cb() under "if (!ret)", so the

ttm_resource_del_bulk_move_unevictable() / ttm_resource_move_to_lru_tail()

pair is now skipped on every successful swapout. The equivalent change

for the shrinker in commit 1d59f36e95f7 ("drm/ttm: Fix ttm_bo_shrink()

infinite LRU walk on backup failure") tests "lret > 0", which is what

was intended here as well.

Before b2ed01e7ad3d the resource was taken off the bulk_move before the

swapout; since then a swapped-out resource stays inside its BO's

bulk_move range (and on the manager LRU) although it is unevictable.

When it is later freed or the BO leaves the bulk_move

(ttm_resource_free(), ttm_bo_set_bulk_move() via amdgpu_vm_bo_del()),

ttm_resource_del_bulk_move() skips it because of its

!ttm_resource_unevictable() guard, so a range endpoint in pos->first /

pos->last is left pointing at freed memory. The next

ttm_lru_bulk_move_tail() or ttm_resource_add_bulk_move() on that cursor

is a use-after-free, seen as the resv WARN in ttm_lru_bulk_move_add(),

"list_del corruption" in ttm_resource_move_to_lru_tail() or a NULL

dereference in ttm_resource_manager_next() -- minutes to hours after a

hibernation, or at process exit / reboot following one. Samuel

Ainsworth's analysis of drm/amd issue 5387 (see Link) identified the

dangling cursor; the missing removal at swapout time is the reason it

dangles.

Testing the condition for success restores the removal. On an AMD

Phoenix APU (ASUS UM3406GA, gfx1103) running suspend-then-hibernate on

a 7.0.y stable kernel carrying the backport (Ubuntu 7.0.0-31) the bug

crashed 5 of 18 hibernation cycles; a function profile of one

hibernation showed 336 ttm_tt_swapout() calls and zero

ttm_resource_del_bulk_move_unevictable() calls. With this change the

removal happens for every swapped-out resource and 12 further cycles

were clean. (NVD)

What to Do

Monitor Linux's web page for any future patch releases.

References