Re: [PATCH 2/5] drm/core: Fix old_fb handling in drm_mode_atomic_ioctl.

Re: [PATCH 2/5] drm/core: Fix old_fb handling in drm_mode_atomic_ioctl.

[Daniel Vetter]

On Wed, Nov 11, 2015 at 11:29:08AM +0100, Maarten Lankhorst wrote:
> From: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> 
> plane_mask should be cleared inside the retry loop,
> because it gets reset on every retry.
> 
> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> Cc: stable@vger.kernel.org #v4.3

Nice catch, but a bit a terse commit message. We should add "Without this
fix the plane->fb refcounting might get out of sync on retries, resulting
in either leaked memory or use-after-free." With that:

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

> ---
>  drivers/gpu/drm/drm_atomic.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
> index 7bb3845d9974..0ac31b1ecb67 100644
> --- a/drivers/gpu/drm/drm_atomic.c
> +++ b/drivers/gpu/drm/drm_atomic.c
> @@ -1446,7 +1446,7 @@ int drm_mode_atomic_ioctl(struct drm_device *dev,
>  	struct drm_plane *plane;
>  	struct drm_crtc *crtc;
>  	struct drm_crtc_state *crtc_state;
> -	unsigned plane_mask = 0;
> +	unsigned plane_mask;
>  	int ret = 0;
>  	unsigned int i, j;
>  
> @@ -1486,6 +1486,7 @@ int drm_mode_atomic_ioctl(struct drm_device *dev,
>  	state->allow_modeset = !!(arg->flags & DRM_MODE_ATOMIC_ALLOW_MODESET);
>  
>  retry:
> +	plane_mask = 0;
>  	copied_objs = 0;
>  	copied_props = 0;
>  
> -- 
> 2.1.0
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch