Re: [Intel-gfx] [PATCH] drm/i915: check fence to avoid null pointer dereference

[Tvrtko Ursulin]

Hi,

On 17/05/2022 17:56, Yongzhi Liu wrote:
if drm_syncobj_fence_get return null, we will get a
null pointer. Fix this by adding the null pointer check
on fence.

Signed-off-by: Yongzhi Liu <lyz...@pku.edu.cn>
---
  drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c | 4 ++++
  1 file changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c 
b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
index fd0e15d..3a82a62 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
@@ -3184,6 +3184,10 @@ eb_fences_add(struct i915_execbuffer *eb, struct 
i915_request *rq,
                struct dma_fence *fence;
  
  		fence = drm_syncobj_fence_get(eb->gem_context->syncobj);
+               if (!fence) {
+                       DRM_DEBUG("Syncobj has no fence\n");
+                       return ERR_PTR(-EINVAL);

Lookup can't fail here since reference to context is held and syncobj 
can't get replaced during that time. You could make it a single 
GEM_BUG_ON(!fence) instead if you really wanted but I am not convinced 
it would be useful.

Regards,

Tvrtko

+               }
                err = i915_request_await_dma_fence(rq, fence);
                dma_fence_put(fence);
                if (err)