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

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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: Maxime Bizon <mbizon@freebox.fr>
Suggested-by: Maxime Bizon <mbizon@freebox.fr>
Fixes: 5f2d04f1f9 (ipv4: fix path MTU discovery with connection tracking)
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
This commit is contained in:
Florian Westphal
2014-05-02 15:32:16 +02:00
committed by Pablo Neira Ayuso
parent fe337ac283
commit 895162b110
1 changed files with 3 additions and 2 deletions
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5
net/ipv4/netfilter/nf_defrag_ipv4.c
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@ -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;
}