CVE-2026-31488

In the Linux kernel, the following vulnerability has been resolved:<br /> <br /> drm/amd/display: Do not skip unrelated mode changes in DSC validation<br /> <br /> Starting with commit 17ce8a6907f7 ("drm/amd/display: Add dsc pre-validation in<br /> atomic check"), amdgpu resets the CRTC state mode_changed flag to false when<br /> recomputing the DSC configuration results in no timing change for a particular<br /> stream.<br /> <br /> However, this is incorrect in scenarios where a change in MST/DSC configuration<br /> happens in the same KMS commit as another (unrelated) mode change. For example,<br /> the integrated panel of a laptop may be configured differently (e.g., HDR<br /> enabled/disabled) depending on whether external screens are attached. In this<br /> case, plugging in external DP-MST screens may result in the mode_changed flag<br /> being dropped incorrectly for the integrated panel if its DSC configuration<br /> did not change during precomputation in pre_validate_dsc().<br /> <br /> At this point, however, dm_update_crtc_state() has already created new streams<br /> for CRTCs with DSC-independent mode changes. In turn,<br /> amdgpu_dm_commit_streams() will never release the old stream, resulting in a<br /> memory leak. amdgpu_dm_atomic_commit_tail() will never acquire a reference to<br /> the new stream either, which manifests as a use-after-free when the stream gets<br /> disabled later on:<br /> <br /> BUG: KASAN: use-after-free in dc_stream_release+0x25/0x90 [amdgpu]<br /> Write of size 4 at addr ffff88813d836524 by task kworker/9:9/29977<br /> <br /> Workqueue: events drm_mode_rmfb_work_fn<br /> Call Trace:<br /> <br /> dump_stack_lvl+0x6e/0xa0<br /> print_address_description.constprop.0+0x88/0x320<br /> ? dc_stream_release+0x25/0x90 [amdgpu]<br /> print_report+0xfc/0x1ff<br /> ? srso_alias_return_thunk+0x5/0xfbef5<br /> ? __virt_addr_valid+0x225/0x4e0<br /> ? dc_stream_release+0x25/0x90 [amdgpu]<br /> kasan_report+0xe1/0x180<br /> ? dc_stream_release+0x25/0x90 [amdgpu]<br /> kasan_check_range+0x125/0x200<br /> dc_stream_release+0x25/0x90 [amdgpu]<br /> dc_state_destruct+0x14d/0x5c0 [amdgpu]<br /> dc_state_release.part.0+0x4e/0x130 [amdgpu]<br /> dm_atomic_destroy_state+0x3f/0x70 [amdgpu]<br /> drm_atomic_state_default_clear+0x8ee/0xf30<br /> ? drm_mode_object_put.part.0+0xb1/0x130<br /> __drm_atomic_state_free+0x15c/0x2d0<br /> atomic_remove_fb+0x67e/0x980<br /> <br /> Since there is no reliable way of figuring out whether a CRTC has unrelated<br /> mode changes pending at the time of DSC validation, remember the value of the<br /> mode_changed flag from before the point where a CRTC was marked as potentially<br /> affected by a change in DSC configuration. Reset the mode_changed flag to this<br /> earlier value instead in pre_validate_dsc().<br /> <br /> (cherry picked from commit cc7c7121ae082b7b82891baa7280f1ff2608f22b)