linux-kernel - Re: [PATCH][next] drm: fix null pointer dereference on null state pointer

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Date:   Mon, 24 Dec 2018 11:53:18 +0100
From:   Daniel Vetter <daniel@...ll.ch>
To:     Colin King <colin.king@...onical.com>
Cc:     Rob Clark <robdclark@...il.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        dri-devel@...ts.freedesktop.org, kernel-janitors@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH][next] drm: fix null pointer dereference on null state
 pointer

On Sat, Dec 22, 2018 at 01:00:46PM +0000, Colin King wrote:
> From: Colin Ian King <colin.king@...onical.com>
> 
> In the case where state cannot be allocated, the current exit path via
> label 'out' will dereference the null state pointer when calling
> drm_atomic_state_put. Fix this by adding a new error exit label and
> jumping to this to avoid the drm_atomic_state_put.
> 
> Detected by CoverityScan, CID#1476034 ("Dereference after null check")
> 
> Fixes: b9fc5e01d1ce ("drm: Add helper to implement legacy dirtyfb")
> Signed-off-by: Colin Ian King <colin.king@...onical.com>

Looks correct to me, merged into drm-misc-next-fixes for 4.21.

Thanks, Daniel

> ---
>  drivers/gpu/drm/drm_damage_helper.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_damage_helper.c b/drivers/gpu/drm/drm_damage_helper.c
> index d2a1c7372f36..31032407254d 100644
> --- a/drivers/gpu/drm/drm_damage_helper.c
> +++ b/drivers/gpu/drm/drm_damage_helper.c
> @@ -178,7 +178,7 @@ int drm_atomic_helper_dirtyfb(struct drm_framebuffer *fb,
>  	state = drm_atomic_state_alloc(fb->dev);
>  	if (!state) {
>  		ret = -ENOMEM;
> -		goto out;
> +		goto out_drop_locks;
>  	}
>  	state->acquire_ctx = &ctx;
>  
> @@ -238,6 +238,7 @@ int drm_atomic_helper_dirtyfb(struct drm_framebuffer *fb,
>  	kfree(rects);
>  	drm_atomic_state_put(state);
>  
> +out_drop_locks:
>  	drm_modeset_drop_locks(&ctx);
>  	drm_modeset_acquire_fini(&ctx);
>  
> -- 
> 2.19.1
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch