From: Dan Carpenter <dan.carpenter@oracle.com>
To: "Luis R. Rodriguez" <mcgrof@kernel.org>
Cc: linux-kernel@vger.kernel.org, kernel-janitors@vger.kernel.org,
cocci@systeme.lip6.fr
Subject: Re: [PATCH] lib/test_kmod: Fix an integer overflow test
Date: Sun, 25 Feb 2018 02:34:36 +0300 [thread overview]
Message-ID: <20180224233436.6sj4vgn7l4rnfti5@mwanda> (raw)
In-Reply-To: <20180224220601.GG14069@wotan.suse.de>
On Sat, Feb 24, 2018 at 10:06:01PM +0000, Luis R. Rodriguez wrote:
> On Sat, Feb 24, 2018 at 11:45:16AM +0300, Dan Carpenter wrote:
> > On Sat, Feb 24, 2018 at 02:59:41AM +0000, Luis R. Rodriguez wrote:
> > > On Mon, Jan 22, 2018 at 01:27:54PM +0300, Dan Carpenter wrote:
> > > > The main problem is that the parentheses are in the wrong place and the
> > > > unlikely() call returns either 0 or 1 so it's never less than zero.
> > >
> > > Doh, thanks, yes. Seems worth considering a grammar rule for it.
> > >
> > > > The other problem is that signed integer overflows like "INT_MAX + 1" are
> > > > undefined behavior.
> > >
> > > Likewise.
> > >
> > > This seems like another possible generic typo issue. But I would not resolve it
> > > the way you did, in this particular case below num_test_devs represents the
> > > number of already registered devs, before we increment. So the way to resolve
> > > this would be:
> > >
> > > if (num_test_devs + 1 == INT_MAX)
> > >
> > > I'll get this upstream, thanks!
> >
> > There is no issue if num_test_devs is INT_MAX. But capping it at
> > INT_MAX - 1 is also fine.
>
> If num_test_devs is INT_MAX, then doing num_test_devs + 1 overflows
> and as you noted that is undefined?
If it's INT_MAX we never do "num_test_devs + 1", we return a NULL.
regards,
dan carpenter
prev parent reply other threads:[~2018-02-24 23:34 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-22 10:27 [PATCH] lib/test_kmod: Fix an integer overflow test Dan Carpenter
2018-02-24 2:59 ` Luis R. Rodriguez
2018-02-24 8:45 ` Dan Carpenter
2018-02-24 22:06 ` Luis R. Rodriguez
2018-02-24 23:34 ` Dan Carpenter [this message]
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