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Commit 895162b1 authored by Florian Westphal's avatar Florian Westphal Committed by Pablo Neira Ayuso
Browse files

netfilter: ipv4: defrag: set local_df flag on defragmented skb 



else we may fail to forward skb even if original fragments do fit
outgoing link mtu:

1. remote sends 2k packets in two 1000 byte frags, DF set
2. we want to forward but only see '2k > mtu and DF set'
3. we then send icmp error saying that outgoing link is 1500

But original sender never sent a packet that would not fit
the outgoing link.

Setting local_df makes outgoing path test size vs.
IPCB(skb)->frag_max_size, so we will still send the correct
error in case the largest original size did not fit
outgoing link mtu.

Reported-by: default avatarMaxime Bizon <mbizon@freebox.fr>
Suggested-by: default avatarMaxime Bizon <mbizon@freebox.fr>
Fixes: 5f2d04f1 (ipv4: fix path MTU discovery with connection tracking)
Signed-off-by: default avatarFlorian Westphal <fw@strlen.de>
Signed-off-by: default avatarPablo Neira Ayuso <pablo@netfilter.org>
parent fe337ac2

net/ipv4/netfilter/nf_defrag_ipv4.c

+3 −2
Original line number Diff line number Diff line
@@ -22,7 +22,6 @@ 
#endif

#include <net/netfilter/nf_conntrack_zones.h>



/* Returns new sk_buff, or NULL */

static int nf_ct_ipv4_gather_frags(struct sk_buff *skb, u_int32_t user)

{

	int err;
@@ -33,8 +32,10 @@ static int nf_ct_ipv4_gather_frags(struct sk_buff *skb, u_int32_t user) 
	err = ip_defrag(skb, user);

	local_bh_enable();



	if (!err)

	if (!err) {

		ip_send_check(ip_hdr(skb));

		skb->local_df = 1;

	}



	return err;

}