Re: [PATCH] drm/vmwgfx: Stop accessing buffer objects which failed init

["Maaz Mombasawala (VMware)]

On 2/8/23 10:00, Zack Rusin wrote:
> From: Zack Rusin <za...@vmware.com>
> 
> ttm_bo_init_reserved on failure puts the buffer object back which
> causes it to be deleted, but kfree was still being called on the same
> buffer in vmw_bo_create leading to a double free.
> 
> After the double free the vmw_gem_object_create_with_handle was
> setting the gem function objects before checking the return status
> of vmw_bo_create leading to null pointer access.
> 
> Fix the entire path by relaying on ttm_bo_init_reserved to delete the
> buffer objects on failure and making sure the return status is checked
> before setting the gem function objects on the buffer object.
> 
> Signed-off-by: Zack Rusin <za...@vmware.com>
> Fixes: 8afa13a0583f ("drm/vmwgfx: Implement DRIVER_GEM")
> Cc: <sta...@vger.kernel.org> # v5.17+
> ---
>  drivers/gpu/drm/vmwgfx/vmwgfx_bo.c  | 4 +++-
>  drivers/gpu/drm/vmwgfx/vmwgfx_gem.c | 4 ++--
>  2 files changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_bo.c 
> b/drivers/gpu/drm/vmwgfx/vmwgfx_bo.c
> index 63486802c8fd..43ffa5c7acbd 100644
> --- a/drivers/gpu/drm/vmwgfx/vmwgfx_bo.c
> +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_bo.c
> @@ -431,13 +431,15 @@ int vmw_bo_create(struct vmw_private *vmw,
>               return -ENOMEM;
>       }
>  
> +     /*
> +      * vmw_bo_init will delete the *p_bo object if it fails
> +      */
>       ret = vmw_bo_init(vmw, *p_bo, params, vmw_bo_free);
>       if (unlikely(ret != 0))
>               goto out_error;
>  
>       return ret;
>  out_error:
> -     kfree(*p_bo);
>       *p_bo = NULL;
>       return ret;
>  }
> diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_gem.c 
> b/drivers/gpu/drm/vmwgfx/vmwgfx_gem.c
> index f042e22b8b59..51bd1f8c5cc4 100644
> --- a/drivers/gpu/drm/vmwgfx/vmwgfx_gem.c
> +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_gem.c
> @@ -127,11 +127,11 @@ int vmw_gem_object_create_with_handle(struct 
> vmw_private *dev_priv,
>       };
>  
>       ret = vmw_bo_create(dev_priv, &params, p_vbo);
> -
> -     (*p_vbo)->tbo.base.funcs = &vmw_gem_object_funcs;
>       if (ret != 0)
>               goto out_no_bo;
>  
> +     (*p_vbo)->tbo.base.funcs = &vmw_gem_object_funcs;
> +
>       ret = drm_gem_handle_create(filp, &(*p_vbo)->tbo.base, handle);
>       /* drop reference from allocate - handle holds it now */
>       drm_gem_object_put(&(*p_vbo)->tbo.base);

LGTM!

Reviewed-by: Maaz Mombasawala <mombasawa...@vmware.com>

-- 
Maaz Mombasawala (VMware) <ma...@fastmail.com>