Re: [PATCH v2] dma-buf: fix an error pointer vs NULL bug

[Christian König]

Am 06.07.23 um 14:37 schrieb Dan Carpenter:

Smatch detected potential error pointer dereference.

     drivers/gpu/drm/drm_syncobj.c:888 drm_syncobj_transfer_to_timeline()
     error: 'fence' dereferencing possible ERR_PTR()

The error pointer comes from dma_fence_allocate_private_stub().  One
caller expected error pointers and one expected NULL pointers.  Change
it to return NULL and update the caller which expected error pointers,
drm_syncobj_assign_null_handle(), to check for NULL instead.

Fixes: f781f661e8c9 ("dma-buf: keep the signaling time of merged fences v3")
Signed-off-by: Dan Carpenter <dan.carpen...@linaro.org>

Reviewed-by: Christian König <christian.koe...@amd.com>

Should I push that one to drm-misc-fixes?

Regards,
Christian.

---
v2: Fix it in dma_fence_allocate_private_stub() instead of
    __dma_fence_unwrap_merge().


  drivers/dma-buf/dma-fence.c   | 2 +-
  drivers/gpu/drm/drm_syncobj.c | 4 ++--
  2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c
index ad076f208760..8aa8f8cb7071 100644
--- a/drivers/dma-buf/dma-fence.c
+++ b/drivers/dma-buf/dma-fence.c
@@ -160,7 +160,7 @@ struct dma_fence *dma_fence_allocate_private_stub(ktime_t 
timestamp)

fence = kzalloc(sizeof(*fence), GFP_KERNEL);

        if (fence == NULL)
-               return ERR_PTR(-ENOMEM);
+               return NULL;

dma_fence_init(fence,

                       &dma_fence_stub_ops,
diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c
index 04589a35eb09..e592c5da70ce 100644
--- a/drivers/gpu/drm/drm_syncobj.c
+++ b/drivers/gpu/drm/drm_syncobj.c
@@ -355,8 +355,8 @@ static int drm_syncobj_assign_null_handle(struct 
drm_syncobj *syncobj)
  {
        struct dma_fence *fence = dma_fence_allocate_private_stub(ktime_get());

- if (IS_ERR(fence))

-               return PTR_ERR(fence);
+       if (!fence)
+               return -ENOMEM;

drm_syncobj_replace_fence(syncobj, fence);

        dma_fence_put(fence);