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

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Message-ID: <20191002183856.GA13866@breakpoint.cc>
Date:   Wed, 2 Oct 2019 20:38:56 +0200
From:   Florian Westphal <fw@...len.de>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Florian Westphal <fw@...len.de>,
        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:
> The dual stack API automatically forces the traffic to be IPv4
> if v4mapped addresses are used at bind() or connect(), so it makes
> no sense to allow IPv6 traffic to use the same v4mapped class.
> 
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: Florian Westphal <fw@...len.de>
> Cc: Hannes Frederic Sowa <hannes@...essinduktion.org>
> Reported-by: syzbot <syzkaller@...glegroups.com>
> ---
>  net/ipv6/ip6_input.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/net/ipv6/ip6_input.c b/net/ipv6/ip6_input.c
> index d432d0011c160f41aec09640e95179dd7b364cfc..2bb0b66181a741c7fb73cacbdf34c5160f52d186 100644
> --- a/net/ipv6/ip6_input.c
> +++ b/net/ipv6/ip6_input.c
> @@ -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?