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

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Message-ID: <810d36184b9fa2880d3ba7738a8f182e27f5107b.camel@perches.com>
Date:   Wed, 24 Mar 2021 09:52:11 -0700
From:   Joe Perches <joe@...ches.com>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     Philipp Zabel <p.zabel@...gutronix.de>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        Marco Felsch <m.felsch@...gutronix.de>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Liu Ying <victor.liu@....com>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] [v2] drm/imx: imx-ldb: fix out of bounds array access
 warning

On Wed, 2021-03-24 at 17:42 +0100, Arnd Bergmann wrote:
> On Wed, Mar 24, 2021 at 3:20 PM Joe Perches <joe@...ches.com> wrote:
[]
> > > 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.

Thanks.  No worries.

Up to you, vsprintf would emit the positive mux as a funky hashed
hex value by default if you use ERR_PTR with mux > ARRAY_SIZE so
perhaps %d without the ERR_PTR use makes the most sense.