linux-kernel - Re: [PATCH] media: nxp: imx8-isi: Check whether pad is non-NULL before access

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Message-ID: <20250820141439.GA10547@pendragon.ideasonboard.com>
Date: Wed, 20 Aug 2025 17:14:39 +0300
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Maud Spierings <maudspierings@...ontroll.com>
Cc: Mauro Carvalho Chehab <mchehab@...nel.org>,
	Shawn Guo <shawnguo@...nel.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Pengutronix Kernel Team <kernel@...gutronix.de>,
	Fabio Estevam <festevam@...il.com>,
	Stefan Riedmueller <s.riedmueller@...tec.de>,
	Jacopo Mondi <jacopo@...ndi.org>, Christian Hemp <c.hemp@...tec.de>,
	Guoniu Zhou <guoniu.zhou@....com>,
	Dong Aisheng <aisheng.dong@....com>, linux-media@...r.kernel.org,
	imx@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: nxp: imx8-isi: Check whether pad is non-NULL
 before access

On Wed, Aug 20, 2025 at 04:07:55PM +0200, Maud Spierings wrote:
> On 8/20/25 16:01, Laurent Pinchart wrote:
> > On Mon, Aug 18, 2025 at 02:31:43PM +0200, Maud Spierings via B4 Relay wrote:
> >> From: Maud Spierings <maudspierings@...ontroll.com>
> >>
> >> media_pad_remote_pad_first() can return NULL if no valid link is found.
> >> Check for this possibility before dereferencing it in the next line.
> >>
> >> Reported/investigated in [1]:
> >>
> >> Link: https://lore.kernel.org/all/1536a61b-b405-4762-9fb4-7e257f95e49e@gocontroll.com/ [1]
> >> Fixes: cf21f328fcaf ("media: nxp: Add i.MX8 ISI driver")
> >> Signed-off-by: Maud Spierings <maudspierings@...ontroll.com>
> >> ---
> >> I'm not sure if this should be a dev_dbg(), just following the pattern
> >> around it for now, also not sure if EPIPE is the correct error.
> > 
> > I've submitted
> > https://lore.kernel.org/linux-media/20250820140021.8026-1-laurent.pinchart@ideasonboard.com,
> > which should fix this issue in a more generic way.
> 
> Saw it, but I think my patch technically is still correct as the 
> function documentation states it can potentially return NULL right? [1]

The function documentation states

"returns a pointer to the pad at the remote end of the first found
enabled link, or NULL if no enabled link has been found."

The MUST_CONNECT flag ensures that there is an enabled link, so the
function can't return NULL.

> Link: 
> https://www.kernel.org/doc/html/latest/driver-api/media/mc-core.html [1]
> 
> I will test you patches tomorrow.
> 
> >> ---
> >>   drivers/media/platform/nxp/imx8-isi/imx8-isi-crossbar.c | 7 +++++++
> >>   1 file changed, 7 insertions(+)
> >>
> >> diff --git a/drivers/media/platform/nxp/imx8-isi/imx8-isi-crossbar.c b/drivers/media/platform/nxp/imx8-isi/imx8-isi-crossbar.c
> >> index ede6cc74c0234049fa225ad82aaddaad64aa53d7..1ed8b031178b7d934b04a8752747f556bd1fc5a9 100644
> >> --- a/drivers/media/platform/nxp/imx8-isi/imx8-isi-crossbar.c
> >> +++ b/drivers/media/platform/nxp/imx8-isi/imx8-isi-crossbar.c
> >> @@ -160,6 +160,13 @@ mxc_isi_crossbar_xlate_streams(struct mxc_isi_crossbar *xbar,
> >>   	}
> >>   
> >>   	pad = media_pad_remote_pad_first(&xbar->pads[sink_pad]);
> >> +
> >> +	if (pad == NULL) {
> >> +		dev_dbg(xbar->isi->dev, "no valid link found to pad %u\n",
> >> +			sink_pad);
> >> +		return ERR_PTR(-EPIPE);
> >> +	}
> >> +
> >>   	sd = media_entity_to_v4l2_subdev(pad->entity);
> >>   	if (!sd) {
> >>   		dev_dbg(xbar->isi->dev,
> >>
> >> ---
> >> base-commit: 3ac864c2d9bb8608ee236e89bf561811613abfce
> >> change-id: 20250818-imx8_isi-954898628bb6

-- 
Regards,

Laurent Pinchart