Re: [PATCH] kernel/sysctl.c: fix out of bounds access in fs.file-max

From: Matteo Croce <mcroce@redhat.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: Christian Brauner <christian@brauner.io>,
	linux-fsdevel@vger.kernel.org,
	LKML <linux-kernel@vger.kernel.org>,
	Luis Chamberlain <mcgrof@kernel.org>,
	Kees Cook <keescook@chromium.org>,
	Zev Weiss <zev@bewilderbeest.net>,
	Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH] kernel/sysctl.c: fix out of bounds access in fs.file-max
Date: Wed, 3 Apr 2019 18:40:04 +0200	[thread overview]
Message-ID: <CAGnkfhxBafq4KeR8Jp5XBd7yWrMiofmEwqsCpb_7eL+ddgWagw@mail.gmail.com> (raw)
In-Reply-To: <20190403155108.GI22763@bombadil.infradead.org>

On Wed, Apr 3, 2019 at 5:51 PM Matthew Wilcox <willy@infradead.org> wrote:
>
> On Wed, Apr 03, 2019 at 05:24:26PM +0200, Matteo Croce wrote:
> > On Wed, Apr 3, 2019 at 4:02 PM Christian Brauner <christian@brauner.io> wrote:
> > > Yeah, maybe but it still feels cleaner and more obvious to just add:
> > >
> > > static long long_zero;
> > >
> > > given that most callers actually seem to want an (unsigned) int.
> > >
> > > I don't have a strong opinion though so if others feel that it's just a
> > > waste of space consider it acked.
> > >
> >
> > Well, given that the value is zero, in this expectional case we could
> > avoid duplicating the symbol and save 4 bytes.
> > What the maintainers think?
>
> If we care about saving four bytes, we could just pass the address of
> ZERO_PAGE(0).

That would work, work too, maybe it's a bit overkill.
int zero is always there and it's static, so enlarging it to long
should be a straightforward fix.
Obviously we can't do it for other numbers, but we can alias it just
for the zero case..

Regards,

--
Matteo Croce
per aspera ad upstream