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Commit cf826244 authored by Florian Westphal's avatar Florian Westphal Committed by David S. Miller
Browse files

ip: reject too-big defragmented DF-skb when forwarding 



Send icmp pmtu error if we find that the largest fragment of df-skb
exceeded the output path mtu.

The ip output path will still catch this later on but we can avoid the
forward/postrouting hook traversal by rejecting right away.

This is what ipv6 already does.

Acked-by: default avatarHannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: default avatarFlorian Westphal <fw@strlen.de>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent b10e3d6c

net/ipv4/ip_forward.c

+11 −7
Original line number Diff line number Diff line
@@ -39,17 +39,21 @@ 
#include <net/route.h>

#include <net/xfrm.h>



static bool ip_may_fragment(const struct sk_buff *skb)

{

	return unlikely((ip_hdr(skb)->frag_off & htons(IP_DF)) == 0) ||

		skb->ignore_df;

}



static bool ip_exceeds_mtu(const struct sk_buff *skb, unsigned int mtu)

{

	if (skb->len <= mtu)

		return false;



	if (unlikely((ip_hdr(skb)->frag_off & htons(IP_DF)) == 0))

		return false;



	/* original fragment exceeds mtu and DF is set */

	if (unlikely(IPCB(skb)->frag_max_size > mtu))

		return true;



	if (skb->ignore_df)

		return false;



	if (skb_is_gso(skb) && skb_gso_network_seglen(skb) <= mtu)

		return false;
@@ -114,7 +118,7 @@ int ip_forward(struct sk_buff *skb) 


	IPCB(skb)->flags |= IPSKB_FORWARDED;

	mtu = ip_dst_mtu_maybe_forward(&rt->dst, true);

	if (!ip_may_fragment(skb) && ip_exceeds_mtu(skb, mtu)) {

	if (ip_exceeds_mtu(skb, mtu)) {

		IP_INC_STATS(dev_net(rt->dst.dev), IPSTATS_MIB_FRAGFAILS);

		icmp_send(skb, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED,

			  htonl(mtu));