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* [PATCH] drm/ttm: Fix UAF on dma-buf attach failure for sg BOs
@ 2026-07-01  6:26 Nitin Gote
  2026-07-01  5:56 ` ✓ CI.KUnit: success for drm/ttm: Fix UAF on dma-buf attach failure for sg BOs (rev2) Patchwork
                   ` (4 more replies)
  0 siblings, 5 replies; 13+ messages in thread
From: Nitin Gote @ 2026-07-01  6:26 UTC (permalink / raw)
  To: intel-xe
  Cc: Nitin Gote, stable, Thomas Hellstrom, Christian Konig,
	Matthew Auld

When a dma-buf importer creates a ttm_bo_type_sg BO with bo->base.resv
pointing at the exporter's dma_buf->resv and dma_buf_dynamic_attach()
fails, no dma_buf reference is held. The exporter can be freed before
the delayed_delete worker calls dma_resv_lock(bo->base.resv), causing 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

ttm_bo_individualize_resv() skips the resv swap for all sg BOs to keep
the shared resv available for delayed_delete to release the dma-buf
mapping. A BO whose attach never succeeded has no mapping to release,
yet it keeps bo->base.resv pointing at the exporter resv that
delayed_delete later locks once the exporter is gone.

Fix this by checking bo->base.import_attach, which is set only after a
successful attach. The check is placed after dma_resv_copy_fences() so
successful imports still copy fences to _resv before returning, keeping
the shared resv for delayed_delete. Failed imports fall through to swap
resv to _resv, so delayed_delete never locks the stale exporter resv.

Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/work_items/8023
Fixes: d99fbd9aab62 ("drm/ttm: Always take the bo delayed cleanup path for imported bos")
Cc: stable@vger.kernel.org # v6.8+
Cc: Thomas Hellstrom <thomas.hellstrom@linux.intel.com>
Cc: Christian Konig <christian.koenig@amd.com>
Cc: Matthew Auld <matthew.auld@intel.com>
Assisted-by: GitHub_Copilot:claude-sonnet-4.6
Signed-off-by: Nitin Gote <nitin.r.gote@intel.com>
---
Hi Thomas/Christian,
Thank you for the review. Addressed the v3 review comments in this 
v4 version.

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).

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.

 drivers/gpu/drm/ttm/ttm_bo.c | 24 +++++++++++++++---------
 1 file changed, 15 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
index bcd76f6bb7f0..9b6341f69805 100644
--- a/drivers/gpu/drm/ttm/ttm_bo.c
+++ b/drivers/gpu/drm/ttm/ttm_bo.c
@@ -203,15 +203,21 @@ static int ttm_bo_individualize_resv(struct ttm_buffer_object *bo)
 	if (r)
 		return r;
 
-	if (bo->type != ttm_bo_type_sg) {
-		/* This works because the BO is about to be destroyed and nobody
-		 * reference it any more. The only tricky case is the trylock on
-		 * the resv object while holding the lru_lock.
-		 */
-		spin_lock(&bo->bdev->lru_lock);
-		bo->base.resv = &bo->base._resv;
-		spin_unlock(&bo->bdev->lru_lock);
-	}
+	/*
+	 * Successfully imported sg BOs need the shared resv for dma-buf
+	 * cleanup. Failed imports have no attachment or mapping and can
+	 * use the private _resv.
+	 */
+	if (bo->type == ttm_bo_type_sg && bo->base.import_attach)
+		return 0;
+
+	/* This works because the BO is about to be destroyed and nobody
+	 * references it any more. The only tricky case is the trylock on
+	 * the resv object while holding the lru_lock.
+	 */
+	spin_lock(&bo->bdev->lru_lock);
+	bo->base.resv = &bo->base._resv;
+	spin_unlock(&bo->bdev->lru_lock);
 
 	return r;
 }
-- 
2.50.1


^ permalink raw reply related	[flat|nested] 13+ messages in thread
* [PATCH] drm/ttm: Fix UAF on dma-buf attach failure for sg BOs
@ 2026-06-25  5:57 Nitin Gote
  2026-06-25 10:45 ` Christian König
  2026-06-29  9:18 ` Thomas Hellström
  0 siblings, 2 replies; 13+ messages in thread
From: Nitin Gote @ 2026-06-25  5:57 UTC (permalink / raw)
  To: intel-xe
  Cc: Nitin Gote, stable, Thomas Hellstrom, Christian Konig,
	Matthew Auld

When a dma-buf importer creates a ttm_bo_type_sg BO with bo->base.resv
pointing at the exporter's dma_buf->resv and dma_buf_dynamic_attach()
fails, no dma_buf reference is held. The exporter can be freed before
the delayed_delete worker calls dma_resv_lock(bo->base.resv), causing 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

ttm_bo_individualize_resv() skips the resv swap for all sg BOs to keep
the shared resv available for delayed_delete to release the dma-buf
mapping. A BO whose attach never succeeded has no mapping to release,
yet it keeps bo->base.resv pointing at the exporter resv that
delayed_delete later locks once the exporter is gone.

Fix this by checking bo->base.import_attach, which is only set after
successful dma_buf_dynamic_attach(). Failed imports now individualize
normally, so delayed_delete operates on the BO's private _resv. The
exporter remains alive during individualize as it runs synchronously
in ttm_bo_release(), while the gem_prime_import caller still holds
its dma_buf reference.

Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/work_items/8023
Fixes: d99fbd9aab62 ("drm/ttm: Always take the bo delayed cleanup path for imported bos")
Cc: stable@vger.kernel.org # v6.8+
Cc: Thomas Hellstrom <thomas.hellstrom@linux.intel.com>
Cc: Christian Konig <christian.koenig@amd.com>
Cc: Matthew Auld <matthew.auld@intel.com>
Assisted-by: GitHub_Copilot:claude-sonnet-4.6
Signed-off-by: Nitin Gote <nitin.r.gote@intel.com>
---
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.
- Exporter lifetime: individualize runs synchronously inside
  ttm_bo_release(), called from drm_gem_object_put() in the
  gem_prime_import error path while drm_gem_prime_fd_to_handle()
  still holds its dma_buf reference.
- Fixes both xe and amdgpu in a single TTM patch.

 drivers/gpu/drm/ttm/ttm_bo.c | 24 +++++++++++++++---------
 1 file changed, 15 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
index bcd76f6bb7f0..bf8eaec0e9ca 100644
--- a/drivers/gpu/drm/ttm/ttm_bo.c
+++ b/drivers/gpu/drm/ttm/ttm_bo.c
@@ -196,6 +196,14 @@ static int ttm_bo_individualize_resv(struct ttm_buffer_object *bo)
 	if (bo->base.resv == &bo->base._resv)
 		return 0;
 
+	/*
+	 * Successfully imported sg BOs need the shared resv for dma-buf
+	 * cleanup. Failed imports have no attachment or mapping and can
+	 * use the private _resv.
+	 */
+	if (bo->type == ttm_bo_type_sg && bo->base.import_attach)
+		return 0;
+
 	BUG_ON(!dma_resv_trylock(&bo->base._resv));
 
 	r = dma_resv_copy_fences(&bo->base._resv, bo->base.resv);
@@ -203,15 +211,13 @@ static int ttm_bo_individualize_resv(struct ttm_buffer_object *bo)
 	if (r)
 		return r;
 
-	if (bo->type != ttm_bo_type_sg) {
-		/* This works because the BO is about to be destroyed and nobody
-		 * reference it any more. The only tricky case is the trylock on
-		 * the resv object while holding the lru_lock.
-		 */
-		spin_lock(&bo->bdev->lru_lock);
-		bo->base.resv = &bo->base._resv;
-		spin_unlock(&bo->bdev->lru_lock);
-	}
+	/* This works because the BO is about to be destroyed and nobody
+	 * references it any more. The only tricky case is the trylock on
+	 * the resv object while holding the lru_lock.
+	 */
+	spin_lock(&bo->bdev->lru_lock);
+	bo->base.resv = &bo->base._resv;
+	spin_unlock(&bo->bdev->lru_lock);
 
 	return r;
 }
-- 
2.50.1


^ permalink raw reply related	[flat|nested] 13+ messages in thread
end of thread, other threads:[~2026-07-01 21:55 UTC | newest]

Thread overview: 13+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2026-07-01  6:26 [PATCH] drm/ttm: Fix UAF on dma-buf attach failure for sg BOs Nitin Gote
2026-07-01  5:56 ` ✓ CI.KUnit: success for drm/ttm: Fix UAF on dma-buf attach failure for sg BOs (rev2) Patchwork
2026-07-01  6:46 ` ✓ Xe.CI.BAT: " Patchwork
2026-07-01  8:48 ` [PATCH] drm/ttm: Fix UAF on dma-buf attach failure for sg BOs Christian König
2026-07-01 12:59 ` Thomas Hellström
2026-07-01 13:20   ` Christian König
2026-07-01 15:23     ` Thomas Hellström
2026-07-01 21:55 ` ✓ Xe.CI.FULL: success for drm/ttm: Fix UAF on dma-buf attach failure for sg BOs (rev2) Patchwork
  -- strict thread matches above, loose matches on Subject: below --
2026-06-25  5:57 [PATCH] drm/ttm: Fix UAF on dma-buf attach failure for sg BOs Nitin Gote
2026-06-25 10:45 ` Christian König
2026-06-25 17:10   ` Gote, Nitin R
2026-06-29 12:09     ` Christian König
2026-06-29  9:18 ` Thomas Hellström

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