linux-kernel - Re: net/ipv6: slab-out-of-bounds in ip6_tnl

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Date:   Tue, 25 Apr 2017 14:32:47 +0200
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        James Morris <jmorris@...ei.org>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Patrick McHardy <kaber@...sh.net>,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Kostya Serebryany <kcc@...gle.com>,
        syzkaller <syzkaller@...glegroups.com>
Subject: Re: net/ipv6: slab-out-of-bounds in ip6_tnl_xmit

On Tue, Apr 25, 2017 at 7:04 AM, Cong Wang <xiyou.wangcong@...il.com> wrote:
> On Mon, Apr 24, 2017 at 9:47 AM, Cong Wang <xiyou.wangcong@...il.com> wrote:
>>
>> We use ipv4 dst in ip6_tunnel and cast an IPv4 neigh key as an
>> IPv6 address...
>>
>>
>>                 neigh = dst_neigh_lookup(skb_dst(skb),
>>                                          &ipv6_hdr(skb)->daddr);
>>                 if (!neigh)
>>                         goto tx_err_link_failure;
>>
>>                 addr6 = (struct in6_addr *)&neigh->primary_key; // <=== HERE
>>                 addr_type = ipv6_addr_type(addr6);
>>
>>                 if (addr_type == IPV6_ADDR_ANY)
>>                         addr6 = &ipv6_hdr(skb)->daddr;
>>
>>                 memcpy(&fl6->daddr, addr6, sizeof(fl6->daddr));
>>
>> Also the network header of the skb at this point should be still IPv4?
>
> Please try the attached patch.

I don't see these crashes with your patch.

Thanks!

Tested-by: Andrey Konovalov <andreyknvl@...gle.com>

>
> I am not sure how we could handle 4in6 case better than just relying on
> the config of ip6 tunnel.