drm/shmem-helper: Remove another errant put in error path

drm_gem_shmem_mmap() doesn't own reference in error code path, resulting
in the dma-buf shmem GEM object getting prematurely freed leading to a
later use-after-free.

Fixes: f49a51bfdc8e ("drm/shme-helpers: Fix dma_buf_mmap forwarding bug")
Cc: stable@vger.kernel.org
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Reviewed-by: Rob Clark <robdclark@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230108211311.3950107-1-dmitry.osipenko@collabora.com

diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
index b602cd72a12059f124640475f64eb0e271073dc5..1a681de9a6eab24220c5e785e221031db791a2a6 100644 (file)
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -622,11 +622,14 @@ int drm_gem_shmem_mmap(struct drm_gem_shmem_object *shmem, struct vm_area_struct
        int ret;
 
        if (obj->import_attach) {
-               /* Drop the reference drm_gem_mmap_obj() acquired.*/
-               drm_gem_object_put(obj);
                vma->vm_private_data = NULL;
+               ret = dma_buf_mmap(obj->dma_buf, vma, 0);
+
+               /* Drop the reference drm_gem_mmap_obj() acquired.*/
+               if (!ret)
+                       drm_gem_object_put(obj);
 
-               return dma_buf_mmap(obj->dma_buf, vma, 0);
+               return ret;
        }
 
        ret = drm_gem_shmem_get_pages(shmem);