Nouveau - Oct 2020 - [RFC] gem: fix "refcount_t: underflow; use-after-free"

we can't use nouveau_bo_ref here as no ttm object was allocated and
nouveau_bo_ref mainly deals with that. Simply deallocate the object.

Signed-off-by: Karol Herbst <kherbst at redhat.com>
---
 drm/nouveau/nouveau_gem.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drm/nouveau/nouveau_gem.c b/drm/nouveau/nouveau_gem.c
index e11303fbc..45582a8dc 100644
--- a/drm/nouveau/nouveau_gem.c
+++ b/drm/nouveau/nouveau_gem.c
@@ -198,7 +198,8 @@ nouveau_gem_new(struct nouveau_cli *cli, u64 size, int
align, uint32_t domain,
 	 * to the caller, instead of a normal nouveau_bo ttm reference. */
 	ret = drm_gem_object_init(drm->dev, &nvbo->bo.base, size);
 	if (ret) {
-		nouveau_bo_ref(NULL, &nvbo);
+		drm_gem_object_release(&nvbo->bo.base);
+		kfree(nvbo);
 		return ret;
 	}
 
-- 
2.26.2

On Wed, 7 Oct 2020 at 08:08, Karol Herbst <kherbst at redhat.com>
wrote:
>
> we can't use nouveau_bo_ref here as no ttm object was allocated and
> nouveau_bo_ref mainly deals with that. Simply deallocate the object.
I suspect this was fallout from when that whole process was split into
stages, seems reasonable to me, applied.

Ben.
>
> Signed-off-by: Karol Herbst <kherbst at redhat.com>
> ---
>  drm/nouveau/nouveau_gem.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drm/nouveau/nouveau_gem.c b/drm/nouveau/nouveau_gem.c
> index e11303fbc..45582a8dc 100644
> --- a/drm/nouveau/nouveau_gem.c
> +++ b/drm/nouveau/nouveau_gem.c
> @@ -198,7 +198,8 @@ nouveau_gem_new(struct nouveau_cli *cli, u64 size, int
align, uint32_t domain,
>          * to the caller, instead of a normal nouveau_bo ttm reference. */
>         ret = drm_gem_object_init(drm->dev, &nvbo->bo.base,
size);
>         if (ret) {
> -               nouveau_bo_ref(NULL, &nvbo);
> +               drm_gem_object_release(&nvbo->bo.base);
> +               kfree(nvbo);
>                 return ret;
>         }
>
> --
> 2.26.2
>
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