netdev - Re: [PATCH/RFC net] ipv6: fix fragmentation bug

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Date:	Mon, 04 Nov 2013 06:25:42 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Alexander Aring <alex.aring@...il.com>
Cc:	davem@...emloft.net, kuznet@....inr.ac.ru, jmorris@...ei.org,
	yoshfuji@...ux-ipv6.org, kaber@...sh.net, netdev@...r.kernel.org
Subject: Re: [PATCH/RFC net] ipv6: fix fragmentation bug

On Mon, 2013-11-04 at 10:26 +0100, Alexander Aring wrote:
> In a very poor 6lowpan wireless connection I got this:

> 
> I think we need to drop skb_dst_drop(skb) in ip6_frag_queue because we
> send a icmp6_send in the expire function "ip6_expire_frag_queue":
> 
> icmpv6_send(fq->q.fragments, ICMPV6_TIME_EXCEED, ICMPV6_EXC_FRAGTIME,
> 0);
> 
> and it can be that the skb is already freed. This null pointer
> dereference occurs when the timer expires.
> 
> Signed-off-by: Alexander Aring <alex.aring@...il.com>
> ---
>  net/ipv6/reassembly.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/net/ipv6/reassembly.c b/net/ipv6/reassembly.c
> index cc85a9b..6463ae0 100644
> --- a/net/ipv6/reassembly.c
> +++ b/net/ipv6/reassembly.c
> @@ -352,7 +352,6 @@ found:
>  		return res;
>  	}
>  
> -	skb_dst_drop(skb);
>  	inet_frag_lru_move(&fq->q);
>  	return -1;
>  

Well, no, this call is needed, please check commit
97599dc792b45b1669c3cdb9a4b365aad0232f65
(" net: drop dst before queueing fragments")

for details.


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