[PATCH] drm/i915: Check drm_syncobj_fence_get return value in eb_fences_add

[Wentao Liang]

The function drm_syncobj_fence_get() may return NULL if the syncobj
has no fence. In eb_fences_add(), this return value is not checked,
leading to a potential NULL pointer dereference in
i915_request_await_dma_fence().

This patch adds a check for the return value of drm_syncobj_fence_get
and returns an error if it is NULL, preventing the NULL pointer
dereference.

Fixes: 544460c33821 ("drm/i915: Multi-BB execbuf")
Cc: stable at vger.kernel.org # 5.16+
Signed-off-by: Wentao Liang <vulab at iscas.ac.cn>
---
 drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
index f151640c1d13..7da65535feb9 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
@@ -3252,6 +3252,12 @@ 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_dbg(&eb->i915->drm,
+				"Syncobj handle has no fence\n");
+			return ERR_PTR(-EINVAL);
+		}
+
 		err = i915_request_await_dma_fence(rq, fence);
 		dma_fence_put(fence);
 		if (err)
-- 
2.42.0.windows.2