drm/amdgpu: fix potential double drop fence reference

BugLink: https://bugs.launchpad.net/bugs/1859712
[ Upstream commit 946ab8db6953535a3a88c957db8328beacdfed9d ]

The object fence is not set to NULL after its reference is dropped. As a
result, its reference may be dropped again if error occurs after that,
which may lead to a use after free bug. To avoid the issue, fence is
explicitly set to NULL after dropping its reference.

Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Pan Bian <bianpan2016@163.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_test.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_test.c
index ed8c3739015be481cfd7072b712b3c8ee562d2e4..b35b0741fd97e6f1e4cc836df61bcf081c77dabb 100644 (file)
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_test.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_test.c
@@ -125,6 +125,7 @@ static void amdgpu_do_test_moves(struct amdgpu_device *adev)
                }
 
                dma_fence_put(fence);
+               fence = NULL;
 
                r = amdgpu_bo_kmap(vram_obj, &vram_map);
                if (r) {
@@ -170,6 +171,7 @@ static void amdgpu_do_test_moves(struct amdgpu_device *adev)
                }
 
                dma_fence_put(fence);
+               fence = NULL;
 
                r = amdgpu_bo_kmap(gtt_obj[i], &gtt_map);
                if (r) {