ipvs: make rerouting optional with snat_reroute

	Add new sysctl flag "snat_reroute". Recent kernels use
ip_route_me_harder() to route LVS-NAT responses properly by
VIP when there are multiple paths to client. But setups
that do not have alternative default routes can skip this
routing lookup by using snat_reroute=0.

Signed-off-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: Patrick McHardy <kaber@trash.net>

3 files changed, 38 insertions, 8 deletions

diff --git a/include/net/ip_vs.h b/include/net/ip_vs.h
index e8ec5231eae9..3915a4f4cd30 100644
--- a/include/net/ip_vs.h
+++ b/include/net/ip_vs.h
@@ -801,6 +801,7 @@ extern int sysctl_ip_vs_expire_quiescent_template;
 extern int sysctl_ip_vs_sync_threshold[2];
 extern int sysctl_ip_vs_nat_icmp_send;
 extern int sysctl_ip_vs_conntrack;
+extern int sysctl_ip_vs_snat_reroute;
 extern struct ip_vs_stats ip_vs_stats;
 extern const struct ctl_path net_vs_ctl_path[];
 
diff --git a/net/netfilter/ipvs/ip_vs_core.c b/net/netfilter/ipvs/ip_vs_core.c
index 7fbc80d81fe8..06c388bf4e33 100644
--- a/net/netfilter/ipvs/ip_vs_core.c
+++ b/net/netfilter/ipvs/ip_vs_core.c
@@ -929,20 +929,31 @@ handle_response(int af, struct sk_buff *skb, struct ip_vs_protocol *pp,
                 ip_send_check(ip_hdr(skb));
         }
 
+        /*
+         * nf_iterate does not expect change in the skb->dst->dev.
+         * It looks like it is not fatal to enable this code for hooks
+         * where our handlers are at the end of the chain list and
+         * when all next handlers use skb->dst->dev and not outdev.
+         * It will definitely route properly the inout NAT traffic
+         * when multiple paths are used.
+         */
+
         /* For policy routing, packets originating from this
          * machine itself may be routed differently to packets
          * passing through.  We want this packet to be routed as
          * if it came from this machine itself.  So re-compute
          * the routing information.
          */
+        if (sysctl_ip_vs_snat_reroute) {
 #ifdef CONFIG_IP_VS_IPV6
-        if (af == AF_INET6) {
-                if (ip6_route_me_harder(skb) != 0)
-                        goto drop;
-        } else
+                if (af == AF_INET6) {
+                        if (ip6_route_me_harder(skb) != 0)
+                                goto drop;
+                } else
 #endif
-                if (ip_route_me_harder(skb, RTN_LOCAL) != 0)
-                        goto drop;
+                        if (ip_route_me_harder(skb, RTN_LOCAL) != 0)
+                                goto drop;
+        }
 
         IP_VS_DBG_PKT(10, pp, skb, 0, "After SNAT");
 
@@ -991,8 +1002,13 @@ ip_vs_out(unsigned int hooknum, struct sk_buff *skb,
                 if (unlikely(iph.protocol == IPPROTO_ICMPV6)) {
                         int related, verdict = ip_vs_out_icmp_v6(skb, &related);
 
-                        if (related)
+                        if (related) {
+                                if (sysctl_ip_vs_snat_reroute &&
+                                        NF_ACCEPT == verdict &&
+                                        ip6_route_me_harder(skb))
+                                        verdict = NF_DROP;
                                 return verdict;
+                        }
                         ip_vs_fill_iphdr(af, skb_network_header(skb), &iph);
                 }
         } else
@@ -1000,8 +1016,13 @@ ip_vs_out(unsigned int hooknum, struct sk_buff *skb,
                 if (unlikely(iph.protocol == IPPROTO_ICMP)) {
                         int related, verdict = ip_vs_out_icmp(skb, &related);
 
-                        if (related)
+                        if (related) {
+                                if (sysctl_ip_vs_snat_reroute &&
+                                        NF_ACCEPT == verdict &&
+                                        ip_route_me_harder(skb, RTN_LOCAL))
+                                        verdict = NF_DROP;
                                 return verdict;
+                        }
                         ip_vs_fill_iphdr(af, skb_network_header(skb), &iph);
                 }
 
diff --git a/net/netfilter/ipvs/ip_vs_ctl.c b/net/netfilter/ipvs/ip_vs_ctl.c
index d2d842f292c6..e637cd0384b1 100644
--- a/net/netfilter/ipvs/ip_vs_ctl.c
+++ b/net/netfilter/ipvs/ip_vs_ctl.c
@@ -91,6 +91,7 @@ int sysctl_ip_vs_nat_icmp_send = 0;
 #ifdef CONFIG_IP_VS_NFCT
 int sysctl_ip_vs_conntrack;
 #endif
+int sysctl_ip_vs_snat_reroute = 1;
 
 
 #ifdef CONFIG_IP_VS_DEBUG
@@ -1599,6 +1600,13 @@ static struct ctl_table vs_vars[] = {
                 .mode           = 0644,
                 .proc_handler   = proc_do_defense_mode,
         },
+        {
+                .procname       = "snat_reroute",
+                .data           = &sysctl_ip_vs_snat_reroute,
+                .maxlen         = sizeof(int),
+                .mode           = 0644,
+                .proc_handler   = &proc_dointvec,
+        },
 #if 0
         {
                 .procname       = "timeout_established",