CVE-2026-31488

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

drm/amd/display: Do not skip unrelated mode changes in DSC validation

Starting with commit 17ce8a6907f7 ("drm/amd/display: Add dsc pre-validation in

atomic check"), amdgpu resets the CRTC state mode_changed flag to false when

recomputing the DSC configuration results in no timing change for a particular

stream.

However, this is incorrect in scenarios where a change in MST/DSC configuration

happens in the same KMS commit as another (unrelated) mode change. For example,

the integrated panel of a laptop may be configured differently (e.g., HDR

enabled/disabled) depending on whether external screens are attached. In this

case, plugging in external DP-MST screens may result in the mode_changed flag

being dropped incorrectly for the integrated panel if its DSC configuration

did not change during precomputation in pre_validate_dsc().

At this point, however, dm_update_crtc_state() has already created new streams

for CRTCs with DSC-independent mode changes. In turn,

amdgpu_dm_commit_streams() will never release the old stream, resulting in a

memory leak. amdgpu_dm_atomic_commit_tail() will never acquire a reference to

the new stream either, which manifests as a use-after-free when the stream gets

disabled later on:

BUG: KASAN: use-after-free in dc_stream_release+0x25/0x90 [amdgpu]

Write of size 4 at addr ffff88813d836524 by task kworker/9:9/29977

Workqueue: events drm_mode_rmfb_work_fn

Call Trace:

<TASK>

dump_stack_lvl+0x6e/0xa0

print_address_description.constprop.0+0x88/0x320

? dc_stream_release+0x25/0x90 [amdgpu]

print_report+0xfc/0x1ff

? srso_alias_return_thunk+0x5/0xfbef5

? __virt_addr_valid+0x225/0x4e0

? dc_stream_release+0x25/0x90 [amdgpu]

kasan_report+0xe1/0x180

? dc_stream_release+0x25/0x90 [amdgpu]

kasan_check_range+0x125/0x200

dc_stream_release+0x25/0x90 [amdgpu]

dc_state_destruct+0x14d/0x5c0 [amdgpu]

dc_state_release.part.0+0x4e/0x130 [amdgpu]

dm_atomic_destroy_state+0x3f/0x70 [amdgpu]

drm_atomic_state_default_clear+0x8ee/0xf30

? drm_mode_object_put.part.0+0xb1/0x130

__drm_atomic_state_free+0x15c/0x2d0

atomic_remove_fb+0x67e/0x980

Since there is no reliable way of figuring out whether a CRTC has unrelated

mode changes pending at the time of DSC validation, remember the value of the

mode_changed flag from before the point where a CRTC was marked as potentially

affected by a change in DSC configuration. Reset the mode_changed flag to this

earlier value instead in pre_validate_dsc().

(cherry picked from commit cc7c7121ae082b7b82891baa7280f1ff2608f22b)