CVE-2026-68266: drm/xe: Hold a dma-buf reference for imported BOs

From: Greg Kroah-Hartman <[email protected]>

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

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 exporter's 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 Christian's 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 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 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)

The Linux kernel CVE team has assigned CVE-2026-68266 to this issue.


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

	Issue introduced in 6.8 with commit dd08ebf6c3525a7ea2186e636df064ea47281987 and fixed in 6.12.103 with commit c22d65d62b3318e237c0e5b1177d90ab83d9fe06
	Issue introduced in 6.8 with commit dd08ebf6c3525a7ea2186e636df064ea47281987 and fixed in 6.18.42 with commit c1954c66662de477a8f4309335b775f7b07bd28b
	Issue introduced in 6.8 with commit dd08ebf6c3525a7ea2186e636df064ea47281987 and fixed in 7.1.6 with commit ba8c4cbb31c6f81fa5b12d6e28f1f706040aff48
	Issue introduced in 6.8 with commit dd08ebf6c3525a7ea2186e636df064ea47281987 and fixed in 7.2-rc4 with commit 62775525a27c3b0d56382e08ba81ee2d322058b6

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-2026-68266
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/xe/xe_bo.c
	drivers/gpu/drm/xe/xe_bo.h
	drivers/gpu/drm/xe/xe_bo_types.h
	drivers/gpu/drm/xe/xe_dma_buf.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/c22d65d62b3318e237c0e5b1177d90ab83d9fe06
	https://git.kernel.org/stable/c/c1954c66662de477a8f4309335b775f7b07bd28b
	https://git.kernel.org/stable/c/ba8c4cbb31c6f81fa5b12d6e28f1f706040aff48
	https://git.kernel.org/stable/c/62775525a27c3b0d56382e08ba81ee2d322058b6