linux-kernel - Re: [PATCH] skbuff: Switch structure bounds to struct

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Message-ID: <202111191015.509A0BD@keescook>
Date:   Fri, 19 Nov 2021 10:26:19 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     "Jason A. Donenfeld" <Jason@...c4.com>,
        "Gustavo A . R . Silva" <gustavoars@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        Alexander Lobakin <alobakin@...me>,
        Jakub Sitnicki <jakub@...udflare.com>,
        Marco Elver <elver@...gle.com>,
        Willem de Bruijn <willemb@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Cong Wang <cong.wang@...edance.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Talal Ahmad <talalahmad@...gle.com>,
        Kevin Hao <haokexin@...il.com>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        Kumar Kartikeya Dwivedi <memxor@...il.com>,
        Vasily Averin <vvs@...tuozzo.com>,
        linux-kernel@...r.kernel.org, wireguard@...ts.zx2c4.com,
        netdev@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] skbuff: Switch structure bounds to struct_group()

On Thu, Nov 18, 2021 at 11:13:55PM -0800, Jakub Kicinski wrote:
> On Thu, 18 Nov 2021 10:36:15 -0800 Kees Cook wrote:
> > In preparation for FORTIFY_SOURCE performing compile-time and run-time
> > field bounds checking for memcpy(), memmove(), and memset(), avoid
> > intentionally writing across neighboring fields.
> > 
> > Replace the existing empty member position markers "headers_start" and
> > "headers_end" with a struct_group(). This will allow memcpy() and sizeof()
> > to more easily reason about sizes, and improve readability.
> > 
> > "pahole" shows no size nor member offset changes to struct sk_buff.
> > "objdump -d" shows no object code changes (outside of WARNs affected by
> > source line number changes).
> 
> This adds ~27k of these warnings to W=1 gcc builds:
> 
> include/linux/skbuff.h:851:1: warning: directive in macro's argument list

Hrm, I can't reproduce this, using several GCC versions and net-next. What
compiler version[1] and base commit[2] were used here?

-Kees

[1] https://github.com/kuba-moo/nipa/pull/10
[2] https://github.com/kuba-moo/nipa/pull/11

-- 
Kees Cook