linux-kernel - Re: netlink: NULL timer crash

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Date:   Thu, 23 Mar 2017 12:00:35 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     eric.dumazet@...il.com
Cc:     edumazet@...gle.com, dvyukov@...gle.com, xiyou.wangcong@...il.com,
        herbert@...dor.apana.org.au, ast@...nel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        syzkaller@...glegroups.com
Subject: Re: netlink: NULL timer crash

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Thu, 23 Mar 2017 09:00:58 -0700

> On Thu, 2017-03-23 at 07:53 -0700, Eric Dumazet wrote:
> 
>> Nice !
>> 
>> Looks like neigh->ops->solicit is NULL
> 
> Apparently we allow admins to do really stupid things with neighbours
> on tunnels.
> 
> Following patch should avoid the crash.
> 
> Anyone has better ideas ?

This is probably good enough for now, but you need to also handle
dn_neigh_ops.

Another way to solve this is to add a NULL method check to the
one spot where we invoke this method.  That clearly shows that
the method is optional.