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

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Message-ID: <CALC8CXf2RTYz2YjbFHsbdjDSSAt3Jdv1NBbBQs4jRPmwkuUuXA@mail.gmail.com>
Date: Thu, 2 Oct 2025 12:30:12 -0400
From: ChaosEsque Team <chaosesqueteam@...il.com>
To: Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc: Maud Spierings <maudspierings@...ontroll.com>, 
	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

Maud... Laurent
Yea you a Mad Lad.

On Wed, Aug 20, 2025 at 10:19 AM Laurent Pinchart
<laurent.pinchart@...asonboard.com> wrote:
>
> 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
>