linux-kernel - RE: [PATCH] drm/bridge: imx: fix potential NULL pointer dereference in imx8qxp_ldb_parse_dt

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Date:   Tue, 29 Aug 2023 02:28:18 +0000
From:   Ying Liu <victor.liu@....com>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Zhang Shurong <zhang_shurong@...mail.com>
CC:     "andrzej.hajda@...el.com" <andrzej.hajda@...el.com>,
        "neil.armstrong@...aro.org" <neil.armstrong@...aro.org>,
        "rfoss@...nel.org" <rfoss@...nel.org>,
        "jonas@...boo.se" <jonas@...boo.se>,
        "jernej.skrabec@...il.com" <jernej.skrabec@...il.com>,
        "airlied@...il.com" <airlied@...il.com>,
        "daniel@...ll.ch" <daniel@...ll.ch>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "festevam@...il.com" <festevam@...il.com>,
        dl-linux-imx <linux-imx@....com>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] drm/bridge: imx: fix potential NULL pointer dereference
 in imx8qxp_ldb_parse_dt_companion()

On Tuesday, August 29, 2023 2:38 AM Laurent Pinchart <laurent.pinchart@...asonboard.com> wrote:
> 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@...mail.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.
> 

I agree with Laurent.

Regards,
Liu Ying