CVE-2026-68266

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 ttm_bo_type_sg BO whose reservation object is the exporters dma_buf->resv. The importer, however, only takes a dma-buf reference after a successful dma_buf_dynamic_attach(). 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 ttm_bo_delayed_delete [ttm] RIP: 0010:mutex_can_spin_on_owner+0x3f/0xc0

This can be reached on two paths:

• dma_buf_dynamic_attach() fails, or
• ttm_bo_init_reserved() 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 ttm_bo_delayed_delete(), which locks bo->base.resv asynchronously - potentially after the exporter has been freed.

Take the dma-buf reference in xe_bo_init_locked(), before ttm_bo_init_reserved(), so it also covers a creation failure there, and release it in xe_ttm_bo_destroy(). 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 dma_buf_dynamic_attach() succeeds.
• Attach with importer_priv == NULL and make invalidate_mappings ignore incomplete imports.

v3:

• Dropped the xe-side reordering approach since importer_priv must be valid when dma_buf_dynamic_attach() publishes the attachment.
• Per Christians suggestion on the v1 thread, keyed the check on import_attach rather than removing the sg guard entirely.
• Fixes both xe and amdgpu in a single TTM patch.

v4:

• Moved import_attach check to after dma_resv_copy_fences() 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 Christians 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 xe_bo_init_locked() before ttm_bo_init_reserved() 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 ttm_bo_pipeline_gutting() 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)

Weakness

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory “belongs” to the code that operates on the new pointer.

Affected Software

Potential Mitigations

References

• https://git.kernel.org/stable/c/62775525a27c3b0d56382e08ba81ee2d322058b6
• https://git.kernel.org/stable/c/ba8c4cbb31c6f81fa5b12d6e28f1f706040aff48
• https://git.kernel.org/stable/c/c1954c66662de477a8f4309335b775f7b07bd28b
• https://git.kernel.org/stable/c/c22d65d62b3318e237c0e5b1177d90ab83d9fe06