Commit 1b3c61dc authored by Lorenzo Colitti's avatar Lorenzo Colitti Committed by David S. Miller
Browse files

net: Use fwmark reflection in PMTU discovery. 



Currently, routing lookups used for Path PMTU Discovery in
absence of a socket or on unmarked sockets use a mark of 0.
This causes PMTUD not to work when using routing based on
netfilter fwmark mangling and fwmark ip rules, such as:

  iptables -j MARK --set-mark 17
  ip rule add fwmark 17 lookup 100

This patch causes these route lookups to use the fwmark from the
received ICMP error when the fwmark_reflect sysctl is enabled.
This allows the administrator to make PMTUD work by configuring
appropriate fwmark rules to mark the inbound ICMP packets.

Black-box tested using user-mode linux by pointing different
fwmarks at routing tables egressing on different interfaces, and
using iptables mangling to mark packets inbound on each interface
with the interface's fwmark. ICMPv4 and ICMPv6 PMTU discovery
work as expected when mark reflection is enabled and fail when
it is disabled.

Signed-off-by: default avatarLorenzo Colitti <lorenzo@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent e110861f

net/ipv4/route.c

+7 −0
Original line number Original line Diff line number Diff line
@@ -993,6 +993,9 @@ void ipv4_update_pmtu(struct sk_buff *skb, struct net *net, u32 mtu, 
	struct flowi4 fl4;

	struct flowi4 fl4;

	struct rtable *rt;

	struct rtable *rt;





	if (!mark)

		mark = IP4_REPLY_MARK(net, skb->mark);



	__build_flow_key(&fl4, NULL, iph, oif,

	__build_flow_key(&fl4, NULL, iph, oif,

			 RT_TOS(iph->tos), protocol, mark, flow_flags);

			 RT_TOS(iph->tos), protocol, mark, flow_flags);

	rt = __ip_route_output_key(net, &fl4);

	rt = __ip_route_output_key(net, &fl4);
@@ -1010,6 +1013,10 @@ static void __ipv4_sk_update_pmtu(struct sk_buff *skb, struct sock *sk, u32 mtu) 
	struct rtable *rt;

	struct rtable *rt;





	__build_flow_key(&fl4, sk, iph, 0, 0, 0, 0, 0);

	__build_flow_key(&fl4, sk, iph, 0, 0, 0, 0, 0);



	if (!fl4.flowi4_mark)

		fl4.flowi4_mark = IP4_REPLY_MARK(sock_net(sk), skb->mark);



	rt = __ip_route_output_key(sock_net(sk), &fl4);

	rt = __ip_route_output_key(sock_net(sk), &fl4);

	if (!IS_ERR(rt)) {

	if (!IS_ERR(rt)) {

		__ip_rt_update_pmtu(rt, &fl4, mtu);

		__ip_rt_update_pmtu(rt, &fl4, mtu);

net/ipv6/route.c

+1 −1
Original line number Original line Diff line number Diff line
@@ -1176,7 +1176,7 @@ void ip6_update_pmtu(struct sk_buff *skb, struct net *net, __be32 mtu, 




	memset(&fl6, 0, sizeof(fl6));

	memset(&fl6, 0, sizeof(fl6));

	fl6.flowi6_oif = oif;

	fl6.flowi6_oif = oif;

	fl6.flowi6_mark = mark;

	fl6.flowi6_mark = mark ? mark : IP6_REPLY_MARK(net, skb->mark);

	fl6.daddr = iph->daddr;

	fl6.daddr = iph->daddr;

	fl6.saddr = iph->saddr;

	fl6.saddr = iph->saddr;

	fl6.flowlabel = ip6_flowinfo(iph);

	fl6.flowlabel = ip6_flowinfo(iph);

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