linux-kernel - Re: [PATCH] iio: imu: adis16480: clean up a condition

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Message-ID: <20191007102107.000067b6@huawei.com>
Date:   Mon, 7 Oct 2019 10:21:07 +0100
From:   Jonathan Cameron <jonathan.cameron@...wei.com>
To:     Dan Carpenter <dan.carpenter@...cle.com>
CC:     Jonathan Cameron <jic23@...nel.org>,
        "Ardelean, Alexandru" <alexandru.Ardelean@...log.com>,
        "lars@...afoo.de" <lars@...afoo.de>,
        "kernel-janitors@...r.kernel.org" <kernel-janitors@...r.kernel.org>,
        "Popa, Stefan Serban" <StefanSerban.Popa@...log.com>,
        "linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Hennerich, Michael" <Michael.Hennerich@...log.com>,
        "pmeerw@...erw.net" <pmeerw@...erw.net>,
        "knaack.h@....de" <knaack.h@....de>
Subject: Re: [PATCH] iio: imu: adis16480: clean up a condition

On Sun, 6 Oct 2019 21:14:40 +0300
Dan Carpenter <dan.carpenter@...cle.com> wrote:

> On Sun, Oct 06, 2019 at 09:51:33AM +0100, Jonathan Cameron wrote:
> > On Thu, 26 Sep 2019 14:36:30 +0300
> > Dan Carpenter <dan.carpenter@...cle.com> wrote:
> >   
> > > On Thu, Sep 26, 2019 at 11:06:39AM +0000, Ardelean, Alexandru wrote:  
> > > > On Thu, 2019-09-26 at 11:10 +0300, Dan Carpenter wrote:    
> > > > > [External]
> > > > > 
> > > > > The "t" variable is unsigned so it can't be less than zero.  We really
> > > > > are just trying to prevent divide by zero bugs so just checking against
> > > > > zero is sufficient.  
> > 
> > I'm not sure that true.  It if were signed we'd be detecting that the
> > input from userspace was negative.  
> 
> It does a really bad job of that though so it raises more questions than
> answers.  Maybe just one of the parameters is negative or maybe the
> multiply or the addition overflowed?  Should scenarios those be checked?
> 
> It turns out none of those situations matter, only divide by zero needs
> to be checked.

It isn't being nearly paranoid enough. Either val or val2 being
negative is a reason to fault out.  Divide by zero needs handling after
that.  Obviously divide by zero is the only one that causes a crash but
negatives are going to cause rather 'unexpected' results.

What fun.

Jonathan