linux-kernel - Re: [PATCH] gpio: mpc8xxx: resolve coverity warnings

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Date:   Thu, 3 Dec 2020 10:03:41 +0100
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     "Biwen Li (OSS)" <biwen.li@....nxp.com>
Cc:     Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Leo Li <leoyang.li@....com>,
        Aisheng Dong <aisheng.dong@....com>,
        LKML <linux-kernel@...r.kernel.org>,
        Jiafei Pan <jiafei.pan@....com>,
        linux-gpio <linux-gpio@...r.kernel.org>
Subject: Re: [PATCH] gpio: mpc8xxx: resolve coverity warnings

On Thu, Dec 3, 2020 at 9:51 AM Biwen Li (OSS) <biwen.li@....nxp.com> wrote:
>
> >
> > On Thu, Dec 3, 2020 at 9:07 AM Biwen Li (OSS) <biwen.li@....nxp.com> wrote:
> > >
> > > > On Thu, Dec 3, 2020 at 8:31 AM Biwen Li <biwen.li@....nxp.com> wrote:
> > > > >
> > > > > From: Biwen Li <biwen.li@....com>
> > > > >
> > > > > Resolve coverity warnings as follows,
> > > > >     cond_at_most: Checking gpio >= 28U implies that gpio may be up
> > > > >     to 27 on the false branch.
> > > > >     overrun-call: Overrunning callees array of size 3 by passing
> > > > >     argument gpio (which evaluates to 27)
> > > > >     in call to *mpc8xxx_gc->direction_output
> > > > >
> > > > >     cond_at_least: Checking gpio <= 3U implies that gpio is at least 4 on
> > > > >     the false branch.
> > > > >     overrun-call: Overrunning callee's array of size 3 by passing argument
> > > > >     gpio (which evaluates to 4) in call to
> > > > > *mpc8xxx_gc->direction_output
> > > > >
> > > > > Signed-off-by: Biwen Li <biwen.li@....com>
> > > > > ---
> > > > >  drivers/gpio/gpio-mpc8xxx.c | 5 +++--
> > > > >  1 file changed, 3 insertions(+), 2 deletions(-)
> > > > >
> > > > > diff --git a/drivers/gpio/gpio-mpc8xxx.c
> > > > > b/drivers/gpio/gpio-mpc8xxx.c index a6c2bbdcaa10..12c9a91d87b7
> > > > > 100644
> > > > > --- a/drivers/gpio/gpio-mpc8xxx.c
> > > > > +++ b/drivers/gpio/gpio-mpc8xxx.c
> > > > > @@ -3,6 +3,7 @@
> > > > >   *
> > > > >   * Copyright (C) 2008 Peter Korsgaard <jacmet@...site.dk>
> > > > >   * Copyright (C) 2016 Freescale Semiconductor Inc.
> > > > > + * Copyright 2020 NXP
> > > >
> > > > A copyright notice on a two-line change is a bit too much, don't you think?
> > > Okay, got it. Will remove it in v2.
> > > >
> > > > >   *
> > > > >   * This file is licensed under the terms of the GNU General Public License
> > > > >   * version 2.  This program is licensed "as is" without any
> > > > > warranty of any @@ -80,7 +81,7 @@ static int
> > > > > mpc5121_gpio_dir_out(struct gpio_chip *gc,  {
> > > > >         struct mpc8xxx_gpio_chip *mpc8xxx_gc =
> > gpiochip_get_data(gc);
> > > > >         /* GPIO 28..31 are input only on MPC5121 */
> > > > > -       if (gpio >= 28)
> > > > > +       if (gpio >= 28U)
> > > > >                 return -EINVAL;
> > > >
> > > > I don't really understand the commit message but looking at the code
> > > > is even more confusing. What are you fixing here actually?
> > > Try to fix code warning that generated by coverity scan tool(static
> > > code analysis tool)
> >
> > Please explain what benefit there is to using 28U over 28. No tool is perfect,
> > that's why you should try to understand what it is it's trying to fix. I don't see any
> > reason this code could fail.
> This code couldn't fail.
> The variable gpio is unsigned int type, prefer to append "U" for unsigned typed values, this makes is clearer also when comparing values and variables.
> >

This only makes sense if we're using large values that could
potentially overflow a signed int. This is a small constant value so
there's no reason for this churn. NAK

Bartosz

> > Bartosz
> >
> > > >
> > > > Bartosz
> > > >
> > > > >
> > > > >         return mpc8xxx_gc->direction_output(gc, gpio, val); @@
> > > > > -91,7
> > > > > +92,7 @@ static int mpc5125_gpio_dir_out(struct gpio_chip *gc,  {
> > > > >         struct mpc8xxx_gpio_chip *mpc8xxx_gc =
> > gpiochip_get_data(gc);
> > > > >         /* GPIO 0..3 are input only on MPC5125 */
> > > > > -       if (gpio <= 3)
> > > > > +       if (gpio <= 3U)
> > > > >                 return -EINVAL;
> > > > >
> > > > >         return mpc8xxx_gc->direction_output(gc, gpio, val);
> > > > > --
> > > > > 2.17.1
> > > > >