[PATCH v2] drm/vgem: fix use-after-free when drm_gem_handle_create() fails

[Rodrigo Siqueira]

On 02/26, Eric Biggers wrote:
> From: Eric Biggers <ebiggers at google.com>
> 
> If drm_gem_handle_create() fails in vgem_gem_create(), then the
> drm_vgem_gem_object is freed twice: once when the reference is dropped
> by drm_gem_object_put_unlocked(), and again by __vgem_gem_destroy().
> 
> This was hit by syzkaller using fault injection.
> 
> Fix it by skipping the second free.
> 
> Reported-by: syzbot+e73f2fb5ed5a5df36d33 at syzkaller.appspotmail.com
> Fixes: af33a9190d02 ("drm/vgem: Enable dmabuf import interfaces")
> Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Laura Abbott <labbott at redhat.com>
> Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
> Cc: stable at vger.kernel.org
> Signed-off-by: Eric Biggers <ebiggers at google.com>
> ---
>  drivers/gpu/drm/vgem/vgem_drv.c | 6 +-----
>  1 file changed, 1 insertion(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/vgem/vgem_drv.c b/drivers/gpu/drm/vgem/vgem_drv.c
> index 5930facd6d2d8..11a8f99ba18c5 100644
> --- a/drivers/gpu/drm/vgem/vgem_drv.c
> +++ b/drivers/gpu/drm/vgem/vgem_drv.c
> @@ -191,13 +191,9 @@ static struct drm_gem_object *vgem_gem_create(struct drm_device *dev,
>  	ret = drm_gem_handle_create(file, &obj->base, handle);
>  	drm_gem_object_put_unlocked(&obj->base);
>  	if (ret)
> -		goto err;
> +		return ERR_PTR(ret);
>  
>  	return &obj->base;
> -
> -err:
> -	__vgem_gem_destroy(obj);
> -	return ERR_PTR(ret);
>  }
>  
>  static int vgem_gem_dumb_create(struct drm_file *file, struct drm_device *dev,
> -- 
> 2.21.0.rc2.261.ga7da99ff1b-goog
> 
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Applied to drm-misc-fixes.

Thanks

-- 
Rodrigo Siqueira
https://siqueira.tech
Graduate Student
Department of Computer Science
University of São Paulo
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