netdev - Re: [PATCH net v2] netfilter: nat: cope with negative port range

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Message-ID: <20180214123037.GD2810@breakpoint.cc>
Date:   Wed, 14 Feb 2018 13:30:37 +0100
From:   Florian Westphal <fw@...len.de>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Florian Westphal <fw@...len.de>,
        "David S. Miller" <davem@...emloft.net>,
        netfilter-devel@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Re: [PATCH net v2] netfilter: nat: cope with negative port range

Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Wed, 2018-02-14 at 12:13 +0100, Paolo Abeni wrote:
> > syzbot reported a division by 0 bug in the netfilter nat code:
> 
> > Adding the relevant check at parse time could break existing
> > setup, moreover we would need to read/write such values atomically
> > to avoid possible transient negative ranges at update time.
> 
> I do not quite follow why it is so hard to add a check at parse time.
> 
> Breaking buggy setups would not be a concern I think.

It would be possible for xtables but afaics in nft_nat.c case
(nft_nat_eval) range.{min,max}_proto.all values are loaded from nft
registers at runtime.