On Sun, 27 Aug 2023 20:54:27 +0300
Dmitry Osipenko <dmitry.osipe...@collabora.com> wrote:
> Freeing drm-shmem GEM right after creating it using
> drm_gem_shmem_prime_import_sg_table() frees SGT of the imported dma-buf
> and then dma-buf frees this SGT second time.
>
> The v3d_prime_import_sg_table() is example of a error code path where
> dma-buf's SGT is freed by drm-shmem and then it's freed second time by
> dma_buf_unmap_attachment() in drm_gem_prime_import_dev().
>
> Add drm-shmem GEM flag telling that this is imported SGT shall not be
> treated as own SGT, fixing the use-after-free bug.
>
> Cc: sta...@vger.kernel.org
> Fixes: 2194a63a818d ("drm: Add library for shmem backed GEM objects")
> Signed-off-by: Dmitry Osipenko <dmitry.osipe...@collabora.com>
> ---
> drivers/gpu/drm/drm_gem_shmem_helper.c | 3 ++-
> include/drm/drm_gem_shmem_helper.h | 7 +++++++
> 2 files changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c
> b/drivers/gpu/drm/drm_gem_shmem_helper.c
> index a783d2245599..78d9cf2355a5 100644
> --- a/drivers/gpu/drm/drm_gem_shmem_helper.c
> +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
> @@ -141,7 +141,7 @@ void drm_gem_shmem_free(struct drm_gem_shmem_object
> *shmem)
>
> if (obj->import_attach) {
> drm_prime_gem_destroy(obj, shmem->sgt);
> - } else {
> + } else if (!shmem->imported_sgt) {
> dma_resv_lock(shmem->base.resv, NULL);
>
> drm_WARN_ON(obj->dev, shmem->vmap_use_count);
> @@ -758,6 +758,7 @@ drm_gem_shmem_prime_import_sg_table(struct drm_device
> *dev,
> return ERR_CAST(shmem);
>
> shmem->sgt = sgt;
> + shmem->imported_sgt = true;
I feel like adding more fields that can be used to do the is_imported()
check is going to be even more confusing. Can we instead have
/* drm_gem_shmem_prime_import_sg_table() can be called from a
* driver specific ->import_sg_table() implementations that
* have extra failable initialization steps. Assign
* drm_gem_object::import_attach here (even though it's
* assigned in drm_gem_prime_import_dev()), so we don't end up
* with driver error paths calling drm_gem_shmem_free() with an
* imported sg_table assigned to drm_gem_shmem_object::sgt and
* drm_gem_object::import_attach left uninitialized.
*/
shmem->base.import_attach = attach;
here?
>
> drm_dbg_prime(dev, "size = %zu\n", size);
>
> diff --git a/include/drm/drm_gem_shmem_helper.h
> b/include/drm/drm_gem_shmem_helper.h
> index bf0c31aa8fbe..ec70a98a8fe1 100644
> --- a/include/drm/drm_gem_shmem_helper.h
> +++ b/include/drm/drm_gem_shmem_helper.h
> @@ -73,6 +73,13 @@ struct drm_gem_shmem_object {
> */
> unsigned int vmap_use_count;
>
> + /**
> + * @imported_sgt:
> + *
> + * True if SG table belongs to imported dma-buf.
> + */
> + bool imported_sgt : 1;
> +
> /**
> * @pages_mark_dirty_on_put:
> *
