Date:   Fri, 3 Dec 2021 14:43:21 -0800
From:   Kees Cook <keescook@chromium.org>
To:     Yury Norov <yury.norov@gmail.com>
Cc:     Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        Wolfram Sang <wsa+renesas@sang-engineering.com>,
        linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org
Subject: Re: [PATCH] find: Do not read beyond variable boundaries on small
 sizes
Message-ID: <202112031441.200FE4975@keescook>
References: <20211203100846.3977195-1-keescook@chromium.org>
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 <E1A4953A-8801-48FA-A744-63DA548C5924@chromium.org>
 <20211203191611.GB450223@lapt>
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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@linux.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