Re: [PATCH] drm/bridge: imx: fix potential NULL pointer dereference in imx8qxp_ldb_parse_dt_companion()

From: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To: Zhang Shurong <zhang_shurong@foxmail.com>
Cc: victor.liu@nxp.com, andrzej.hajda@intel.com,
	neil.armstrong@linaro.org, rfoss@kernel.org, jonas@kwiboo.se,
	jernej.skrabec@gmail.com, airlied@gmail.com, daniel@ffwll.ch,
	shawnguo@kernel.org, s.hauer@pengutronix.de,
	kernel@pengutronix.de, festevam@gmail.com, linux-imx@nxp.com,
	dri-devel@lists.freedesktop.org,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] drm/bridge: imx: fix potential NULL pointer dereference in imx8qxp_ldb_parse_dt_companion()
Date: Mon, 28 Aug 2023 21:37:48 +0300	[thread overview]
Message-ID: <20230828183748.GK14596@pendragon.ideasonboard.com> (raw)
In-Reply-To: <tencent_2E893742B5115B5260081E410A34A89E1208@qq.com>

On Tue, Aug 29, 2023 at 02:01:25AM +0800, Zhang Shurong wrote:
> 在 2023年8月29日星期二 CST 上午1:28:22，Laurent Pinchart 写道：
> > Hi Zhang,
> > 
> > Thank you for the patch.
> > 
> > On Tue, Aug 29, 2023 at 12:55:01AM +0800, Zhang Shurong wrote:
> > > of_match_device() may fail and returns a NULL pointer.
> > 
> > How can it return a NULL pointer here ?
> > 
> > > Fix this by checking the return value of of_match_device().
> > > 
> > > Fixes: 3818715f62b4 ("drm/bridge: imx: Add LDB support for i.MX8qxp")
> > > Signed-off-by: Zhang Shurong <zhang_shurong@foxmail.com>
> > > ---
> > > 
> > >  drivers/gpu/drm/bridge/imx/imx8qxp-ldb.c | 2 ++
> > >  1 file changed, 2 insertions(+)
> > > 
> > > diff --git a/drivers/gpu/drm/bridge/imx/imx8qxp-ldb.c
> > > b/drivers/gpu/drm/bridge/imx/imx8qxp-ldb.c index
> > > 7984da9c0a35..d272f35c8eac 100644
> > > --- a/drivers/gpu/drm/bridge/imx/imx8qxp-ldb.c
> > > +++ b/drivers/gpu/drm/bridge/imx/imx8qxp-ldb.c
> > > @@ -488,6 +488,8 @@ static int imx8qxp_ldb_parse_dt_companion(struct imx8qxp_ldb *imx8qxp_ldb)
> > >  	 * string.
> > >  	 */
> > >  	match = of_match_device(dev->driver->of_match_table, dev);
> > > +	if (!match)
> > > +		return -ENODEV;
> > >  	if (!of_device_is_compatible(companion, match->compatible)) {
> > >  		DRM_DEV_ERROR(dev, "companion LDB is incompatible\n");
> > >  		ret = -ENXIO;
>
> I think we can make it happen by designing the platform device in a way that 
> its name aligns with that of the driver. In such a scenario, when the driver 
> is probed, the of_match_device function will return null. You can verify this 
> functionality by reviewing the following function:
> 
> static int platform_match(struct device *dev, struct device_driver *drv)

This particular device is found in OF-based systems only, and only
instantiated through DT. You can create a platform_device manually that
may match this driver, but that would be a made-up situation, not
something that can happen in practice.

-- 
Regards,

Laurent Pinchart

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