linux-kernel - Re: [PATCH 1/2] netlink: Bounds-check nlmsg

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Message-ID: <20220901124915.24ebc067@kernel.org>
Date:   Thu, 1 Sep 2022 12:49:15 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Jozsef Kadlecsik <kadlec@...filter.org>,
        Florian Westphal <fw@...len.de>,
        syzbot <syzkaller@...glegroups.com>,
        Yajun Deng <yajun.deng@...ux.dev>, netdev@...r.kernel.org,
        netfilter-devel@...r.kernel.org, coreteam@...filter.org,
        Oliver Hartkopp <socketcan@...tkopp.net>,
        Harshit Mogalapalli <harshit.m.mogalapalli@...cle.com>,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH 1/2] netlink: Bounds-check nlmsg_len()

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?