CVE-2026-98166: drm/ttm: fix swapped-out resources never leaving their bulk_move range

CVE-2026-98166: drm/ttm: fix swapped-out resources never leaving their bulk_move range

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

Description
===========

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.

The Linux kernel CVE team has assigned CVE-2026-98166 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 7.1 with commit b2ed01e7ad3de80333e9b962a44024b094bc0b2b and fixed in 7.2.8 with commit 1169fe8c11ca45e3f91d59a73eb271d0ca8a7fb0
	Issue introduced in 7.1 with commit b2ed01e7ad3de80333e9b962a44024b094bc0b2b and fixed in 7.3-rc4 with commit 3db7d7d583419f7b1f2e141e36418802dbb25cf8
	Issue introduced in 7.0.10 with commit 0124a09e3e5f5f6080efe9663b27af27933f8382

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-98166
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	drivers/gpu/drm/ttm/ttm_bo.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/1169fe8c11ca45e3f91d59a73eb271d0ca8a7fb0
	https://git.kernel.org/stable/c/3db7d7d583419f7b1f2e141e36418802dbb25cf8