linux-hardening - Re: [PATCH] find: Do not read beyond variable boundaries on small sizes

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Date:   Fri, 3 Dec 2021 14:43:21 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Yury Norov <yury.norov@...il.com>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Wolfram Sang <wsa+renesas@...g-engineering.com>,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] find: Do not read beyond variable boundaries on small
 sizes

On Fri, Dec 03, 2021 at 11:16:11AM -0800, Yury Norov wrote:
> On Fri, Dec 03, 2021 at 08:37:59AM -0800, Kees Cook wrote:
> > 
> > 
> > On December 3, 2021 4:30:35 AM PST, Andy Shevchenko <andriy.shevchenko@...ux.intel.com> wrote:
> > >On Fri, Dec 03, 2021 at 02:08:46AM -0800, Kees Cook wrote:
> > >> It's common practice to cast small variable arguments to the find_*_bit()
> > >
> > >It's a bad practice and should be fixed accordingly, no?
> > 
> > There's an argument to be made that the first arg should be void * but that's a pretty invasive change at this point (and orthogonal to this fix).
> 
> What for? To save at most 7 bytes of alignment overhead for bitmaps
> like char bitmap[sizeof(unsigned long) + 1]?

I just meant to simplify the calling conventions. Right now everyone has
to cast to unsigned long *, which doesn't seem right: alignment and
strides can be done in the routine. But, I have no strong opinion about
this; it's just something I noticed while looking at it.

-- 
Kees Cook