Re: [PATCH] drm/ttm: fix potential null ptr deref in when mem space alloc fails

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Am 18.03.22 um 20:50 schrieb Robert Beckett:
when allocating a resource in place it is common to free the buffer's
resource, then allocate a new resource in a different placement.

e.g. amdgpu_bo_create_kernel_at calls ttm_resource_free, then calls
ttm_bo_mem_space.

Well yes I'm working the drivers towards this, but NAK at the moment. Currently bo->resource is never expected to be NULL.

And yes I'm searching for this bug in amdgpu for quite a while. Where exactly does that happen?

Amdgpu is supposed to allocate a new resource first, then do a swap and the free the old one.

Thanks,
Christian.


In this situation, bo->resource will be null as it is cleared during
the initial freeing of the previous resource.
This leads to a null deref.

Fixes: d3116756a710 (drm/ttm: rename bo->mem and make it a pointer)

Signed-off-by: Robert Beckett <bob.beckett@xxxxxxxxxxxxx>
---
  drivers/gpu/drm/ttm/ttm_bo.c | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
index db3dc7ef5382..62b29ee7d040 100644
--- a/drivers/gpu/drm/ttm/ttm_bo.c
+++ b/drivers/gpu/drm/ttm/ttm_bo.c
@@ -875,7 +875,7 @@ int ttm_bo_mem_space(struct ttm_buffer_object *bo,
  	}
error:
-	if (bo->resource->mem_type == TTM_PL_SYSTEM && !bo->pin_count)
+	if (bo->resource && bo->resource->mem_type == TTM_PL_SYSTEM && !bo->pin_count)
  		ttm_bo_move_to_lru_tail_unlocked(bo);
return ret;




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