linux-kernel - Re: [PATCH v6 2/2] drm: Prevent release fb after cleanup mode config

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Message-ID: <20170410203126.bfufxn3yijqq7f7y@art_vandelay>
Date:   Mon, 10 Apr 2017 16:31:26 -0400
From:   Sean Paul <seanpaul@...omium.org>
To:     Jeffy Chen <jeffy.chen@...k-chips.com>
Cc:     linux-kernel@...r.kernel.org, briannorris@...omium.org,
        dianders@...omium.org, tfiga@...omium.org, seanpaul@...omium.org,
        zyw@...k-chips.com, marcheu@...omium.org, mark.yao@...k-chips.com,
        hshi@...omium.org, Daniel Vetter <daniel.vetter@...el.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        dri-devel@...ts.freedesktop.org, David Airlie <airlied@...ux.ie>
Subject: Re: [PATCH v6 2/2] drm: Prevent release fb after cleanup mode config

On Mon, Apr 10, 2017 at 06:00:45PM +0800, Jeffy Chen wrote:
> After unbinding drm, the user space may still owns the drm dev fd,
> and may trigger fb release after cleanup mode config.
> 
> Add a sanity check to prevent that.
> 
> Signed-off-by: Jeffy Chen <jeffy.chen@...k-chips.com>
> ---
> 
> Changes in v6: None
> Changes in v5: None
> Changes in v2: None
> 
>  drivers/gpu/drm/drm_framebuffer.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_framebuffer.c b/drivers/gpu/drm/drm_framebuffer.c
> index e8f9c13..03c1632 100644
> --- a/drivers/gpu/drm/drm_framebuffer.c
> +++ b/drivers/gpu/drm/drm_framebuffer.c
> @@ -583,6 +583,11 @@ void drm_fb_release(struct drm_file *priv)
>  {
>  	struct drm_framebuffer *fb, *tfb;
>  	struct drm_mode_rmfb_work arg;
> +	struct drm_minor *minor = priv->minor;
> +	struct drm_device *dev = minor->dev;
> +
> +	if (WARN_ON(!dev->mode_config.num_fb && !list_empty(&priv->fbs)))

Have you actually seen this happen? num_fb should be tightly couple to
priv->fbs, so it seems like this could only result from a driver bug (or I'm not
reading the code correctly).

Sean

> +		return;
>  
>  	INIT_LIST_HEAD(&arg.fbs);
>  
> -- 
> 2.1.4
> 

-- 
Sean Paul, Software Engineer, Google / Chromium OS