UBUNTU-CVE-2026-68266: Use After Free
In the Linux kernel, the following vulnerability has been resolved: drm/xe: Hold a dma-buf reference for imported BOs An imported dma-buf BO is created as a ttmbotypesg BO whose reservation object is the exporter's dmabuf->resv. The importer, however, only takes a dma-buf reference after a successful dmabufdynamicattach(). Until then nothing keeps the exporter alive, so if the exporter is freed while the BO still references its resv, a later access to that resv is a use-after-free: Oops: general protection fault, probably for non-canonical address 0x6b6b6b6b6b6b6b9c Workqueue: ttm ttmbodelayeddelete [ttm] RIP: 0010:mutexcanspinonowner+0x3f/0xc0 This can be reached on two paths: - dmabufdynamicattach() fails, or - ttmboinitreserved() fails during BO creation. In both cases the BO already has bo->base.resv pointing at the exporter resv, and sg BOs are always torn down via ttmbodelayeddelete(), which locks bo->base.resv asynchronously - potentially after the exporter has been freed. Take the dma-buf reference in xeboinitlocked(), before ttmboinitreserved(), so it also covers a creation failure there, and release it in xettmbodestroy(). The reference is held for the whole BO lifetime, keeping the shared resv alive on every path. v2: - Reworked the fix to avoid creating the imported sg BO before dmabufdynamicattach() succeeds. - Attach with importerpriv == NULL and make invalidatemappings ignore incomplete imports. v3: - Dropped the xe-side reordering approach since importerpriv must be valid when dmabufdynamicattach() publishes the attachment. - Per Christian's suggestion on the v1 thread, keyed the check on importattach rather than removing the sg guard entirely. - Fixes both xe and amdgpu in a single TTM patch. v4: - Moved importattach check to after dmaresvcopyfences() so fences are copied before returning for successful imports (Thomas). - Removed exporter-alive claim from commit message (Thomas). v5: - Add drm/xe patch to keep imported sg BOs off the LRU before attach succeeds; the TTM fix alone is not sufficient for xe if the BO is already LRU-visible. (Thomas) v4 patch: https://patchwork.freedesktop.org/patch/736663/?series=169129&rev=2 - Patch 1 (drm/ttm) carries Christian's Reviewed-by from v4. v6: - Reworked the fix based on Thomas' suggestion. Instead of the TTM resv individualization (v1-v5) plus the xe off-LRU/placement handling (v5), just hold a dma-buf reference for the imported BO lifetime so the shared resv can never be freed while the BO still references it. Single xe patch, no TTM change. (Thomas) - Take the reference in xeboinitlocked() before ttmboinitreserved() so a TTM creation failure is covered too (Thomas). - Dropped the v5 series (drm/ttm + drm/xe off-LRU); the off-LRU approach also regressed in CI BAT via ttmbopipelinegutting() creating a ghost BO that outlived the exporter. Link to v5: https://patchwork.freedesktop.org/series/169984/ v7: - Move changelog above --- so it stays in the commit message. - Reorder changelog entries oldest-to-newest. (Thomas) (cherry picked from commit 3516f3fae6be35642f8f06f8a218da6425c0306a)
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
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Patch 3516f3fae6be35642f8f06f8a218da6425c0306a
Event History
Frequently Asked Questions
What conditions are required to trigger this issue?
An attacker needs local access and low privileges. The affected path involves an imported dma-buf buffer object where either dma_buf_dynamic_attach() or ttm_bo_init_reserved() fails during buffer-object creation.
Which systems are most likely exposed?
Systems using the listed Ubuntu Linux kernel packages are affected by the vulnerability data provided. Exposure specifically depends on use of the drm/xe driver and imported dma-buf buffer objects.
What is the impact if the flaw is triggered?
The stale reservation-object reference can be accessed after the dma-buf exporter has been freed, causing a use-after-free during asynchronous TTM buffer-object teardown. The reported severity vector indicates potential high impact to confidentiality, integrity, and availability.
How can I determine whether a system has encountered this issue?
A triggered failure may produce a kernel Oops or general protection fault in the ttm workqueue, including ttm_bo_delayed_delete and mutex_can_spin_on_owner in the stack context. The described failure occurs when delayed teardown later locks a reservation object belonging to an already-freed exporter.