Re: [PATCH] [v2] drm/imx: imx-ldb: fix out of bounds array access warning

From: Arnd Bergmann <arnd@kernel.org>
To: Joe Perches <joe@perches.com>
Cc: Philipp Zabel <p.zabel@pengutronix.de>,
	David Airlie <airlied@linux.ie>, Daniel Vetter <daniel@ffwll.ch>,
	Shawn Guo <shawnguo@kernel.org>,
	Sascha Hauer <s.hauer@pengutronix.de>,
	Pengutronix Kernel Team <kernel@pengutronix.de>,
	Fabio Estevam <festevam@gmail.com>,
	NXP Linux Team <linux-imx@nxp.com>,
	Marco Felsch <m.felsch@pengutronix.de>,
	Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
	Liu Ying <victor.liu@nxp.com>,
	dri-devel <dri-devel@lists.freedesktop.org>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] [v2] drm/imx: imx-ldb: fix out of bounds array access warning
Date: Wed, 24 Mar 2021 17:42:34 +0100	[thread overview]
Message-ID: <CAK8P3a0JyoAtTYTi+M_mJ3_KtUJ6NeJB=FNWhzezqcXMac++mQ@mail.gmail.com> (raw)
In-Reply-To: <e1310273dcc577f3a772380ada7b6cc1906d680b.camel@perches.com>

On Wed, Mar 24, 2021 at 3:20 PM Joe Perches <joe@perches.com> wrote:
>
> On Wed, 2021-03-24 at 13:17 +0100, Arnd Bergmann wrote:
> > From: Arnd Bergmann <arnd@arndb.de>
> >
> > When CONFIG_OF is disabled, building with 'make W=1' produces warnings
> > about out of bounds array access:
> >
> > drivers/gpu/drm/imx/imx-ldb.c: In function 'imx_ldb_set_clock.constprop':
> > drivers/gpu/drm/imx/imx-ldb.c:186:8: error: array subscript -22 is below array bounds of 'struct clk *[4]' [-Werror=array-bounds]
> >
> > Add an error check before the index is used, which helps with the
> > warning, as well as any possible other error condition that may be
> > triggered at runtime.
> >
> > The warning could be fixed by adding a Kconfig depedency on CONFIG_OF,
> > but Liu Ying points out that the driver may hit the out-of-bounds
> > problem at runtime anyway.
> >
> > Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> > ---
> > v2: fix subject line
> >     expand patch description
> >     print mux number
> >     check upper bound as well
> []
> > diff --git a/drivers/gpu/drm/imx/imx-ldb.c b/drivers/gpu/drm/imx/imx-ldb.c
> []
> > @@ -197,6 +197,12 @@ static void imx_ldb_encoder_enable(struct drm_encoder *encoder)
> >       int dual = ldb->ldb_ctrl & LDB_SPLIT_MODE_EN;
> >       int mux = drm_of_encoder_active_port_id(imx_ldb_ch->child, encoder);
> >
> > +     if (mux < 0 || mux >= ARRAY_SIZE(ldb->clk_sel)) {
> > +             dev_warn(ldb->dev, "%s: invalid mux %d\n",
> > +                      __func__, ERR_PTR(mux));
>
> This does not compile without warnings.
>
> drivers/gpu/drm/imx/imx-ldb.c: In function ‘imx_ldb_encoder_enable’:
> drivers/gpu/drm/imx/imx-ldb.c:201:22: warning: format ‘%d’ expects argument of type ‘int’, but argument 4 has type ‘void *’ [-Wformat=]
>   201 |   dev_warn(ldb->dev, "%s: invalid mux %d\n",
>       |                      ^~~~~~~~~~~~~~~~~~~~~~
>
> If you want to use ERR_PTR, the %d should be %pe as ERR_PTR
> is converting an int a void * to decode the error type and
> emit it as a string.

Sorry about that.

I decided against using ERR_PTR() in order to also check for
positive array overflow, but the version I tested was different from
the version I sent.

v3 coming.

         Arnd