linux-kernel - Re: net/ipv6: GPF in rt6_device

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Date:   Wed, 3 May 2017 12:22:35 -0600
From:   David Ahern <dsahern@...il.com>
To:     Cong Wang <xiyou.wangcong@...il.com>,
        Andrey Konovalov <andreyknvl@...gle.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>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Kostya Serebryany <kcc@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        syzkaller <syzkaller@...glegroups.com>
Subject: Re: net/ipv6: GPF in rt6_device_match

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.

> 
> diff --git a/net/ipv6/route.c b/net/ipv6/route.c
> index a1bf426..61ec3c8 100644
> --- a/net/ipv6/route.c
> +++ b/net/ipv6/route.c
> @@ -511,7 +511,7 @@ static inline struct rt6_info
> *rt6_device_match(struct net *net,
>                                     sprt->rt6i_idev->dev->ifindex != oif) {
>                                         if (flags & RT6_LOOKUP_F_IFACE)
>                                                 continue;
> -                                       if (local &&
> +                                       if (local && local->rt6i_idev &&
> 
> local->rt6i_idev->dev->ifindex == oif)
>                                                 continue;
>                                 }
> 

Or don't consider null_entry at all:


@@ -515,7 +528,8 @@ static inline struct rt6_info
*rt6_device_match(struct net *net,

local->rt6i_idev->dev->ifindex == oif)
                                                continue;
                                }
-                               local = sprt;
+                               if (sprt != net->ipv6.ip6_null_entry)
+                                       local = sprt;
                        }