netdev - Re: [PATCH net] ipv6: drop incoming packets having a v4mapped source address

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Date:   Wed, 2 Oct 2019 23:54:17 +0200
From:   Florian Westphal <fw@...len.de>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     Florian Westphal <fw@...len.de>,
        "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Hannes Frederic Sowa <hannes@...essinduktion.org>,
        syzbot <syzkaller@...glegroups.com>
Subject: Re: [PATCH net] ipv6: drop incoming packets having a v4mapped source
 address

Eric Dumazet <edumazet@...gle.com> wrote:
> > > @@ -223,6 +223,16 @@ static struct sk_buff *ip6_rcv_core(struct sk_buff *skb, struct net_device *dev,
> > >       if (ipv6_addr_is_multicast(&hdr->saddr))
> > >               goto err;
> > >
> > > +     /* While RFC4291 is not explicit about v4mapped addresses
> > > +      * in IPv6 headers, it seems clear linux dual-stack
> > > +      * model can not deal properly with these.
> > > +      * Security models could be fooled by ::ffff:127.0.0.1 for example.
> > > +      *
> > > +      * https://tools.ietf.org/html/draft-itojun-v6ops-v4mapped-harmful-02
> > > +      */
> > > +     if (ipv6_addr_v4mapped(&hdr->saddr))
> > > +             goto err;
> > > +
> >
> > Any reason to only consider ->saddr instead of checking daddr as well?
> 
> I do not see reasons the packet should be accepted for sane configurations ?

Fair enough, thanks for explaining.