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

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Message-ID: <1518614652.3715.195.camel@gmail.com>
Date:   Wed, 14 Feb 2018 05:24:12 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Florian Westphal <fw@...len.de>
Cc:     Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
        Pablo Neira Ayuso <pablo@...filter.org>,
        "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

On Wed, 2018-02-14 at 13:30 +0100, Florian Westphal wrote:
> 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.

I prefer this explanation much more, I suggest we update the changelog
to explain the real reason.

Thanks Florian.