[PATCH] drm/i915: check fence to avoid null pointer dereference

[Yongzhi Liu]

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);
+               }
                err = i915_request_await_dma_fence(rq, fence);
                dma_fence_put(fence);
                if (err)
-- 
2.7.4