6.15-stable review patch. If anyone has any objections, please let me know.
------------------
From: Thomas Zimmermann tzimmermann@suse.de
commit fb4ef4a52b79a22ad382bfe77332642d02aef773 upstream.
This reverts commit f83a9b8c7fd0557b0c50784bfdc1bbe9140c9bf8.
The dma_buf field in struct drm_gem_object is not stable over the object instance's lifetime. The field becomes NULL when user space releases the final GEM handle on the buffer object. This resulted in a NULL-pointer deref.
Workarounds in commit 5307dce878d4 ("drm/gem: Acquire references on GEM handles for framebuffers") and commit f6bfc9afc751 ("drm/framebuffer: Acquire internal references on GEM handles") only solved the problem partially. They especially don't work for buffer objects without a DRM framebuffer associated.
Hence, this revert to going back to using .import_attach->dmabuf.
v3: - cc stable
Signed-off-by: Thomas Zimmermann tzimmermann@suse.de Reviewed-by: Simona Vetter simona.vetter@ffwll.ch Acked-by: Christian König christian.koenig@amd.com Acked-by: Zack Rusin zack.rusin@broadcom.com Cc: stable@vger.kernel.org # v6.15+ Link: https://lore.kernel.org/r/20250715155934.150656-5-tzimmermann@suse.de Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/gpu/drm/drm_prime.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c index d828502268b8..a0a5d725eab0 100644 --- a/drivers/gpu/drm/drm_prime.c +++ b/drivers/gpu/drm/drm_prime.c @@ -453,7 +453,13 @@ struct dma_buf *drm_gem_prime_handle_to_dmabuf(struct drm_device *dev, }
mutex_lock(&dev->object_name_lock); - /* re-export the original imported/exported object */ + /* re-export the original imported object */ + if (obj->import_attach) { + dmabuf = obj->import_attach->dmabuf; + get_dma_buf(dmabuf); + goto out_have_obj; + } + if (obj->dma_buf) { get_dma_buf(obj->dma_buf); dmabuf = obj->dma_buf;