linux-kernel - Re: [PATCH next v3 0/5] minmax: Relax type checks in min() and max().

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAHk-=wh1SFzTM1nWwC30t55jzZradQmJ4942CDD1pM_umhU_Vw@mail.gmail.com>
Date:   Wed, 23 Aug 2023 08:32:05 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     David Laight <David.Laight@...lab.com>
Cc:     Kees Cook <keescook@...omium.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Christoph Hellwig <hch@...radead.org>,
        "Jason A. Donenfeld" <Jason@...c4.com>
Subject: Re: [PATCH next v3 0/5] minmax: Relax type checks in min() and max().

On Wed, 23 Aug 2023 at 01:52, David Laight <David.Laight@...lab.com> wrote:
>
> Linus doesn't like me silently converting unsigned constants
> to signed.

Note that my dislike is more about changing the sign of the
*comparison*, and not warning about it.

It's not the constant conversion itself that ends up being the
problem, but the downstream issues it causes.

Having grepped for those annoying "min_t(size_t..)" uses, lots of them
seem to have perfectly fine signedness, and the 'size_t' is literally
just due to different sizes of unsigned values. In fact, several of
them seem to be due to the unfortunate fact that 'size_t' can be
'unsigned int' on 32-bit architectures, so mixing 'size_t' and
'unsigned long' will sadly warn without it.

So we literally have the issue that 'min(a,b)' will warn even if 'a'
and 'b' have the same signedness *and* the same size, because 'size_t'
and 'unsigned long' are different types.

Your patch 2/5 will fix that. And then I'd certainly be ok with a
"comparing an unsigned value to a signed positive constant" thing
(just not the other way around: "comparing a signed value to an
unsigned positive constant" is wrong)

That might get rid of a number of the more annoying cases.

            Linus