Re: [PATCH v1] drm/shmem-helper: Remove another errant put in error path

[Rob Clark]

On Sun, Jan 8, 2023 at 1:13 PM Dmitry Osipenko
<dmitry.osipenko@xxxxxxxxxxxxx> wrote:
>
> 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@xxxxxxxxxxxxxxx
> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@xxxxxxxxxxxxx>

Reviewed-by: Rob Clark <robdclark@xxxxxxxxx>

> ---
>  drivers/gpu/drm/drm_gem_shmem_helper.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
> index f21f47737817..8b20b41497e8 100644
> --- a/drivers/gpu/drm/drm_gem_shmem_helper.c
> +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
> @@ -624,11 +624,14 @@ 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);
> --
> 2.38.1
>