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Date:   Thu, 1 Sep 2022 12:49:15 -0700
From:   Jakub Kicinski <kuba@kernel.org>
To:     Kees Cook <keescook@chromium.org>
Cc:     "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Paolo Abeni <pabeni@redhat.com>,
        Pablo Neira Ayuso <pablo@netfilter.org>,
        Jozsef Kadlecsik <kadlec@netfilter.org>,
        Florian Westphal <fw@strlen.de>,
        syzbot <syzkaller@googlegroups.com>,
        Yajun Deng <yajun.deng@linux.dev>, netdev@vger.kernel.org,
        netfilter-devel@vger.kernel.org, coreteam@netfilter.org,
        Oliver Hartkopp <socketcan@hartkopp.net>,
        Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com>,
        linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org
Subject: Re: [PATCH 1/2] netlink: Bounds-check nlmsg_len()
Message-ID: <20220901124915.24ebc067@kernel.org>
In-Reply-To: <202208312324.F2F8B28CA@keescook>
References: <20220901030610.1121299-1-keescook@chromium.org>
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        <20220831201825.378d748d@kernel.org>
        <202208312324.F2F8B28CA@keescook>
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On Wed, 31 Aug 2022 23:27:08 -0700 Kees Cook wrote:
> This would catch corrupted values...
> 
> Is the concern the growth in image size? The check_sub_overflow() isn't
> large at all -- it's just adding a single overflow bit test. The WARNs
> are heavier, but they're all out-of-line.

It turns the most obvious function into a noodle bar :(

Looking at this function in particular is quite useful, because 
it clearly indicates that the nlmsg_len includes the header.

How about we throw in a

	WARN_ON_ONCE(nlh->nlmsg_len < NLMSG_HDRLEN ||
		     nlh->nlmsg_len > INT_MAX);

but leave the actual calculation human readable C?