netdev - Re: net/icmp: null-ptr-deref in icmp6

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Date:   Tue, 22 Nov 2016 10:11:00 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Andrey Konovalov <andreyknvl@...gle.com>
Cc:     David Ahern <dsa@...ulusnetworks.com>,
        "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>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Alexander Potapenko <glider@...gle.com>,
        Kostya Serebryany <kcc@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        syzkaller <syzkaller@...glegroups.com>
Subject: Re: net/icmp: null-ptr-deref in icmp6_send

On Tue, Nov 22, 2016 at 2:23 AM, Andrey Konovalov <andreyknvl@...gle.com> wrote:
> Hi,
>
> I've got the following error report while fuzzing the kernel with syzkaller.
>
> It seems that skb_dst(skb) may end up being NULL.
>
> As far as I can see the bug was introduced in commit 5d41ce29e ("net:
> icmp6_send should use dst dev to determine L3 domain").
> ICMP v4 probaly has similar issue due to 9d1a6c4ea ("net:
> icmp_route_lookup should use rt dev to determine L3 domain").


ipv6_parse_hopopts() is called before NF_INET_PRE_ROUTING,
so the skb_dst could be NULL.

I have no idea what commit 5d41ce29e tried to fix, but we already
use skb->dev a few lines before l3mdev_master_ifindex(), so I don't
understand why skb->dev could be NULL, maybe just for vrf dev?