netdev - Re: NEIGH: BUG, double timer add, state is 8

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Date:   Fri, 5 Jul 2019 08:28:15 -0600
From:   David Ahern <dsahern@...il.com>
To:     Marek Majkowski <marek@...udflare.com>,
        David Miller <davem@...emloft.net>
Cc:     netdev@...r.kernel.org, kernel-team <kernel-team@...udflare.com>
Subject: Re: NEIGH: BUG, double timer add, state is 8

On 7/4/19 3:59 PM, Marek Majkowski wrote:
> I found a way to hit an obscure BUG in the
> net/core/neighbour.c:neigh_add_timer(), by piping two carefully
> crafted messages into AF_NETLINK socket.
> 
> https://github.com/torvalds/linux/blob/v5.2-rc7/net/core/neighbour.c#L259
> 
>     if (unlikely(mod_timer(&n->timer, when))) {
>         printk("NEIGH: BUG, double timer add, state is %x\n", n->nud_state);
>         dump_stack();
>      }
> 
> The repro is here:
> https://gist.github.com/majek/d70297b9d72bc2e2b82145e122722a0c
> 
> wget https://gist.githubusercontent.com/majek/d70297b9d72bc2e2b82145e122722a0c/raw/9e140bcedecc28d722022f1da142a379a9b7a7b0/double_timer_add_bug.c

Thanks for the report - and the reproducer. I am on PTO through Monday;
I will take a look next week if no one else does.