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

[Christian König]

Am 13.08.21 um 05:28 schrieb 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>


Good catch.


---
  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;


Would be nice to have if you could reuse the "r" variable here instead 
of a new one.


Regards,
Christian.

  
  	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));

[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