[PATCH] accel/amdxdna: Fix double drm_gem_object_put() in dma-buf mmap error path

[PATCH] accel/amdxdna: Fix double drm_gem_object_put() in dma-buf mmap error path

[Jhonraushan]

amdxdna_gem_dmabuf_mmap() takes a reference with drm_gem_object_get()
and, on the vm_insert_pages() failure path, jumps to close_vma which
calls vma->vm_ops->close(). For a shmem GEM object vm_ops is
drm_gem_shmem_vm_ops, whose .close (drm_gem_shmem_vm_close ->
drm_gem_vm_close) already drops that reference. Execution then falls
through to put_obj and drops it a second time.

This underflows the GEM object refcount and frees it prematurely while
the dma-buf still references it, leading to a use-after-free.

Return directly after vm_ops->close() instead of falling through to the
extra drm_gem_object_put(), matching the sibling amdxdna_insert_pages()
error path.

Fixes: e486147c912f ("accel/amdxdna: Add BO import and export")
Cc: stable@vger.kernel.org
Signed-off-by: Jhonraushan <raushan.jhon@gmail.com>
---
 drivers/accel/amdxdna/amdxdna_gem.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/accel/amdxdna/amdxdna_gem.c b/drivers/accel/amdxdna/amdxdna_gem.c
index 891112c2cddf..3ac8c345b25b 100644
--- a/drivers/accel/amdxdna/amdxdna_gem.c
+++ b/drivers/accel/amdxdna/amdxdna_gem.c
@@ -526,7 +526,12 @@ static int amdxdna_gem_dmabuf_mmap(struct dma_buf *dma_buf, struct vm_area_struc
 	return 0;
 
 close_vma:
+	/* vm_ops->close() drops the reference taken by drm_gem_object_get()
+	 * above, so return directly instead of falling through to put_obj
+	 * and dropping it a second time.
+	 */
 	vma->vm_ops->close(vma);
+	return ret;
 put_obj:
 	drm_gem_object_put(gobj);
 	return ret;
-- 
2.43.0

Re: [PATCH] accel/amdxdna: Fix double drm_gem_object_put() in dma-buf mmap error path

[Lizhi Hou]

Thanks for providing the patch. There was a same patch posted: 
https://lore.kernel.org/all/20260625113239.49764-1-vulab@iscas.ac.cn/

Lizhi

On 7/2/26 00:25, Jhonraushan wrote:
> amdxdna_gem_dmabuf_mmap() takes a reference with drm_gem_object_get()
> and, on the vm_insert_pages() failure path, jumps to close_vma which
> calls vma->vm_ops->close(). For a shmem GEM object vm_ops is
> drm_gem_shmem_vm_ops, whose .close (drm_gem_shmem_vm_close ->
> drm_gem_vm_close) already drops that reference. Execution then falls
> through to put_obj and drops it a second time.
>
> This underflows the GEM object refcount and frees it prematurely while
> the dma-buf still references it, leading to a use-after-free.
>
> Return directly after vm_ops->close() instead of falling through to the
> extra drm_gem_object_put(), matching the sibling amdxdna_insert_pages()
> error path.
>
> Fixes: e486147c912f ("accel/amdxdna: Add BO import and export")
> Cc: stable@vger.kernel.org
> Signed-off-by: Jhonraushan <raushan.jhon@gmail.com>
> ---
>   drivers/accel/amdxdna/amdxdna_gem.c | 5 +++++
>   1 file changed, 5 insertions(+)
>
> diff --git a/drivers/accel/amdxdna/amdxdna_gem.c b/drivers/accel/amdxdna/amdxdna_gem.c
> index 891112c2cddf..3ac8c345b25b 100644
> --- a/drivers/accel/amdxdna/amdxdna_gem.c
> +++ b/drivers/accel/amdxdna/amdxdna_gem.c
> @@ -526,7 +526,12 @@ static int amdxdna_gem_dmabuf_mmap(struct dma_buf *dma_buf, struct vm_area_struc
>   	return 0;
>   
>   close_vma:
> +	/* vm_ops->close() drops the reference taken by drm_gem_object_get()
> +	 * above, so return directly instead of falling through to put_obj
> +	 * and dropping it a second time.
> +	 */
>   	vma->vm_ops->close(vma);
> +	return ret;
>   put_obj:
>   	drm_gem_object_put(gobj);
>   	return ret;