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: Lorenzo Colitti <lorenzo@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index db1e0da871f40a2284d67bd48c0f21d772b923f3..50e1e0feddfcdfcc69d641f27a2bd3596bd56098 100644 (file)
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -993,6 +993,9 @@ void ipv4_update_pmtu(struct sk_buff *skb, struct net *net, u32 mtu,
        struct flowi4 fl4;
        struct rtable *rt;
 
+       if (!mark)
+               mark = IP4_REPLY_MARK(net, skb->mark);
+
        __build_flow_key(&fl4, NULL, iph, oif,
                         RT_TOS(iph->tos), protocol, mark, flow_flags);
        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;
 
        __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);
        if (!IS_ERR(rt)) {
                __ip_rt_update_pmtu(rt, &fl4, mtu);

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 004fffb6c2218a12a9619eb08f359a8f2b391297..f0a8ff9ed8910aeb6f8ff8c2578bd13ac2c395ea 100644 (file)
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -1176,7 +1176,7 @@ void ip6_update_pmtu(struct sk_buff *skb, struct net *net, __be32 mtu,
 
        memset(&fl6, 0, sizeof(fl6));
        fl6.flowi6_oif = oif;
-       fl6.flowi6_mark = mark;
+       fl6.flowi6_mark = mark ? mark : IP6_REPLY_MARK(net, skb->mark);
        fl6.daddr = iph->daddr;
        fl6.saddr = iph->saddr;
        fl6.flowlabel = ip6_flowinfo(iph);