[PATCH net-next 3/3] ipvs: strip udp tunnel headers from icmp errors

[Julian Anastasov <ja@xxxxxx>]

Recognize UDP tunnels in received ICMP errors and
properly strip the tunnel headers. GUE is what we
have for now.

Signed-off-by: Julian Anastasov <ja@xxxxxx>
---
 net/netfilter/ipvs/ip_vs_core.c | 58 +++++++++++++++++++++++++++++++++
 1 file changed, 58 insertions(+)

diff --git a/net/netfilter/ipvs/ip_vs_core.c b/net/netfilter/ipvs/ip_vs_core.c
index 4447ee512b88..0b624e8e7982 100644
--- a/net/netfilter/ipvs/ip_vs_core.c
+++ b/net/netfilter/ipvs/ip_vs_core.c
@@ -39,6 +39,7 @@
 #include <net/tcp.h>
 #include <net/udp.h>
 #include <net/icmp.h>                   /* for icmp_send */
+#include <net/gue.h>
 #include <net/route.h>
 #include <net/ip6_checksum.h>
 #include <net/netns/generic.h>         /* net_generic() */
@@ -1579,6 +1580,34 @@ ip_vs_try_to_schedule(struct netns_ipvs *ipvs, int af, 
struct sk_buff *skb,
        return 1;
 }
 
+/* Check the UDP tunnel and return its header length */
+static int ipvs_udp_decap(struct netns_ipvs *ipvs, struct sk_buff *skb,
+                         unsigned int offset, __u16 af, __be16 dport,
+                         const union nf_inet_addr *daddr, __u8 *proto)
+{
+       struct ip_vs_dest *dest = ip_vs_find_tunnel(ipvs, af, daddr, dport);
+
+       if (!dest)
+               goto unk;
+       if (dest->tun_type == IP_VS_CONN_F_TUNNEL_TYPE_GUE) {
+               struct guehdr _gueh, *gueh;
+
+               gueh = skb_header_pointer(skb, offset, sizeof(_gueh), &_gueh);
+               if (!gueh)
+                       goto unk;
+               if (gueh->control != 0 || gueh->version != 0)
+                       goto unk;
+               /* Later we can support also IPPROTO_IPV6 */
+               if (gueh->proto_ctype != IPPROTO_IPIP)
+                       goto unk;
+               *proto = gueh->proto_ctype;
+               return sizeof(struct guehdr) + (gueh->hlen << 2);
+       }
+
+unk:
+       return -1;
+}
+
 /*
  *     Handle ICMP messages in the outside-to-inside direction (incoming).
  *     Find any that might be relevant, check against existing connections,
@@ -1658,8 +1687,37 @@ ip_vs_in_icmp(struct netns_ipvs *ipvs, struct sk_buff 
*skb, int *related,
                if (cih == NULL)
                        return NF_ACCEPT; /* The packet looks wrong, ignore */
                ipip = true;
+       } else if (cih->protocol == IPPROTO_UDP) {      /* Can be UDP encap */
+               struct udphdr _udph, *udph;
+               __u8 iproto;
+               int ulen;
+
+               if (unlikely(cih->frag_off & htons(IP_OFFSET)))
+                       return NF_ACCEPT;
+               /* Error for our tunnel must arrive at LOCAL_IN */
+               if (!(skb_rtable(skb)->rt_flags & RTCF_LOCAL))
+                       return NF_ACCEPT;
+               offset2 = offset + cih->ihl * 4;
+               udph = skb_header_pointer(skb, offset2, sizeof(_udph), &_udph);
+               if (!udph)
+                       goto check;
+               offset2 += sizeof(struct udphdr);
+               ulen = ipvs_udp_decap(ipvs, skb, offset2, AF_INET, udph->dest,
+                                     raddr, &iproto);
+               if (ulen < 0)
+                       goto check;
+               /* Skip IP + UDP + ulen */
+               offset = offset2 + ulen;
+               /* Now we should be at the original IP header */
+               cih = skb_header_pointer(skb, offset, sizeof(_ciph), &_ciph);
+               if (cih && cih->version == 4 && cih->ihl >= 5 &&
+                   iproto == IPPROTO_IPIP)
+                       ipip = true;
+               else
+                       return NF_ACCEPT;
        }
 
+check:
        pd = ip_vs_proto_data_get(ipvs, cih->protocol);
        if (!pd)
                return NF_ACCEPT;
-- 
2.17.1