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

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Date:   Fri, 18 Mar 2022 19:50:04 +0000
From:   Robert Beckett <bob.beckett@...labora.com>
To:     dri-devel@...ts.freedesktop.org,
        Christian Koenig <christian.koenig@....com>,
        Huang Rui <ray.huang@....com>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Matthew Auld <matthew.auld@...el.com>
Cc:     Robert Beckett <bob.beckett@...labora.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] drm/ttm: fix potential null ptr deref in when mem space alloc fails

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.

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@...labora.com>
---
 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;
-- 
2.25.1