netdev - Re: [PATCH v5 0/2] Remove false-positive VLAs when using max()

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Message-ID: <CA+55aFx92dXg-qnrjGS2Rsna6TE5HSPBgGpSA3cv4n_n3RqBzA@mail.gmail.com>
Date:   Fri, 16 Mar 2018 10:29:16 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Florian Weimer <fweimer@...hat.com>
Cc:     Kees Cook <keescook@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Randy Dunlap <rdunlap@...radead.org>,
        Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        Ingo Molnar <mingo@...nel.org>,
        David Laight <David.Laight@...lab.com>,
        Ian Abbott <abbotti@....co.uk>,
        linux-input <linux-input@...r.kernel.org>,
        linux-btrfs <linux-btrfs@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH v5 0/2] Remove false-positive VLAs when using max()

On Fri, Mar 16, 2018 at 4:47 AM, Florian Weimer <fweimer@...hat.com> wrote:
>
> If you want to catch stack frames which have unbounded size,
> -Werror=stack-usage=1000 or -Werror=vla-larger-than=1000 (with the constant
> adjusted as needed) might be the better approach.

No, we want to catch *variable* stack sizes.

Does "-Werror=vla-larger-than=0" perhaps work for that? No, because
the stupid compiler says that is "meaningless".

And no, using "-Werror=vla-larger-than=1" doesn't work either, because
the moronic compiler continues to think that "vla" is about the
_type_, not the code:

   t.c: In function ‘test’:
   t.c:6:6: error: argument to variable-length array is too large
[-Werror=vla-larger-than=]
     int array[(1,100)];

Gcc people are crazy.

Is there really no way to just say "shut up about the stupid _syntax_
issue that is entirely irrelevant, and give us the _code_ issue".

                 Linus