[PATCH] drivers:gpu:drm:amd:amdgpu:fix a potential use-after-free

[lwt105]

in line 1503, "dma_fence_put(fence);" drop the reference to fence and may
cause fence to be released. However, fence is used subsequently in line
1510 "fence->error". This may result in an use-after-free bug.

It can be fixed by recording fence->error in an variable before dropping
the reference to fence and referencing it after dropping.

Signed-off-by: lwt105 <3061522...@qq.com>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c 
b/drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c
index 30fa1f61e0e5..99d03180e113 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c
@@ -1486,7 +1486,7 @@ static int amdgpu_cs_wait_all_fences(struct amdgpu_device 
*adev,
                                     struct drm_amdgpu_fence *fences)
 {
        uint32_t fence_count = wait->in.fence_count;
-       unsigned int i;
+       unsigned int i, error;
        long r = 1;
 
        for (i = 0; i < fence_count; i++) {
@@ -1500,6 +1500,7 @@ static int amdgpu_cs_wait_all_fences(struct amdgpu_device 
*adev,
                        continue;
 
                r = dma_fence_wait_timeout(fence, true, timeout);
+               error = fence->error;
                dma_fence_put(fence);
                if (r < 0)
                        return r;
@@ -1507,8 +1508,8 @@ static int amdgpu_cs_wait_all_fences(struct amdgpu_device 
*adev,
                if (r == 0)
                        break;
 
-               if (fence->error)
-                       return fence->error;
+               if (error)
+                       return error;
        }
 
        memset(wait, 0, sizeof(*wait));
-- 
2.25.1