From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Ahern <dsahern@gmail.com>
Subject: Re: net/ipv6: GPF in rt6_device_match
Date: Wed, 3 May 2017 16:09:14 -0600
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Cc: Andrey Konovalov <andreyknvl@google.com>,
        "David S. Miller" <davem@davemloft.net>,
        Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>,
        James Morris <jmorris@namei.org>,
        Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
        Patrick McHardy <kaber@trash.net>,
        netdev <netdev@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Dmitry Vyukov <dvyukov@google.com>,
        Kostya Serebryany <kcc@google.com>,
        Eric Dumazet <edumazet@google.com>,
        syzkaller <syzkaller@googlegroups.com>
To: Cong Wang <xiyou.wangcong@gmail.com>
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On 5/3/17 4:02 PM, Cong Wang wrote:
> On Wed, May 3, 2017 at 11:22 AM, David Ahern <dsahern@gmail.com> wrote:
>> On 5/3/17 11:02 AM, Cong Wang wrote:
>>> A quick glance shows we need to simply check local->rt6i_idev
>>> since we do the same check for sprt right above.
>>
>> As I recall, rt6i_idev is set for all routes except null_entry and it is
>> not set on null_entry only because of initialization order.
> 
> Are you sure?
> 
>         if (event == NETDEV_REGISTER && (dev->flags & IFF_LOOPBACK)) {
>                 net->ipv6.ip6_null_entry->dst.dev = dev;
>                 net->ipv6.ip6_null_entry->rt6i_idev = in6_dev_get(dev);
> #ifdef CONFIG_IPV6_MULTIPLE_TABLES
>                 net->ipv6.ip6_prohibit_entry->dst.dev = dev;
>                 net->ipv6.ip6_prohibit_entry->rt6i_idev = in6_dev_get(dev);
>                 net->ipv6.ip6_blk_hole_entry->dst.dev = dev;
>                 net->ipv6.ip6_blk_hole_entry->rt6i_idev = in6_dev_get(dev);
> #endif
>         }
> 
> Loopback is the first one to register, so null entry is set to
> loopback dev initially. Similar for init_net.
> 

Why don't you add a printk and see ;-)