netdev - Re: problem forwarding IP fragments with DF bit set (caused by ipv4: fix path MTU discovery with connection tracking)

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Date:	Mon, 28 Apr 2014 19:59:40 +0200
From:	Maxime Bizon <mbizon@...ebox.fr>
To:	Patrick McHardy <kaber@...sh.net>
Cc:	Eric Dumazet <edumazet@...gle.com>, davem@...emloft.net,
	netdev <netdev@...r.kernel.org>
Subject: Re: problem forwarding IP fragments with DF bit set (caused by
 ipv4: fix path MTU discovery with connection tracking)


On Mon, 2014-04-28 at 18:37 +0200, Maxime Bizon wrote:
> 
> conntrack causes the packets to be re-assembled, but since the
> resulting skb now has IP_DF set, it fails the (DF + MTU) test in
> ip_forward.c and causes ICMP frag_needed to be sent. 

hum isn't it just a matter of doing this ?

--- a/net/ipv4/ip_fragment.c
+++ b/net/ipv4/ip_fragment.c
@@ -493,6 +493,8 @@ found:
            skb->len + ihl > qp->q.max_size)
                qp->q.max_size = skb->len + ihl;
 
+       skb->local_df = 1;
+
        if (qp->q.last_in == (INET_FRAG_FIRST_IN | INET_FRAG_LAST_IN) &&
            qp->q.meat == qp->q.len) {
                unsigned long orefdst = skb->_skb_refdst;


-- 
Maxime


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