[PATCHv2 net-next] ipvs: strip gre tunnel headers from icmp errors

[Julian Anastasov <ja@xxxxxx>]

Recognize GRE tunnels in received ICMP errors and
properly strip the tunnel headers.

Signed-off-by: Julian Anastasov <ja@xxxxxx>
---
 net/netfilter/ipvs/ip_vs_core.c | 46 ++++++++++++++++++++++++++++++---
 1 file changed, 42 insertions(+), 4 deletions(-)

 Here is v2 in case it is needed, with net/gre.h included

diff --git a/net/netfilter/ipvs/ip_vs_core.c b/net/netfilter/ipvs/ip_vs_core.c
index e8651fd621ef..dd4727a5d6ec 100644
--- a/net/netfilter/ipvs/ip_vs_core.c
+++ b/net/netfilter/ipvs/ip_vs_core.c
@@ -35,6 +35,7 @@
 #include <net/udp.h>
 #include <net/icmp.h>                   /* for icmp_send */
 #include <net/gue.h>
+#include <net/gre.h>
 #include <net/route.h>
 #include <net/ip6_checksum.h>
 #include <net/netns/generic.h>         /* net_generic() */
@@ -1610,6 +1611,38 @@ static int ipvs_udp_decap(struct netns_ipvs *ipvs, 
struct sk_buff *skb,
        return 0;
 }
 
+/* Check the GRE tunnel and return its header length */
+static int ipvs_gre_decap(struct netns_ipvs *ipvs, struct sk_buff *skb,
+                         unsigned int offset, __u16 af,
+                         const union nf_inet_addr *daddr, __u8 *proto)
+{
+       struct gre_base_hdr _greh, *greh;
+       struct ip_vs_dest *dest;
+
+       greh = skb_header_pointer(skb, offset, sizeof(_greh), &_greh);
+       if (!greh)
+               goto unk;
+       dest = ip_vs_find_tunnel(ipvs, af, daddr, 0);
+       if (!dest)
+               goto unk;
+       if (dest->tun_type == IP_VS_CONN_F_TUNNEL_TYPE_GRE) {
+               __be16 type;
+
+               /* Only support version 0 and C (csum) */
+               if ((greh->flags & ~GRE_CSUM) != 0)
+                       goto unk;
+               type = greh->protocol;
+               /* Later we can support also IPPROTO_IPV6 */
+               if (type != htons(ETH_P_IP))
+                       goto unk;
+               *proto = IPPROTO_IPIP;
+               return gre_calc_hlen(gre_flags_to_tnl_flags(greh->flags));
+       }
+
+unk:
+       return 0;
+}
+
 /*
  *     Handle ICMP messages in the outside-to-inside direction (incoming).
  *     Find any that might be relevant, check against existing connections,
@@ -1689,7 +1722,8 @@ 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 */
+       } else if ((cih->protocol == IPPROTO_UDP ||     /* Can be UDP encap */
+                   cih->protocol == IPPROTO_GRE) &&    /* Can be GRE encap */
                   /* Error for our tunnel must arrive at LOCAL_IN */
                   (skb_rtable(skb)->rt_flags & RTCF_LOCAL)) {
                __u8 iproto;
@@ -1699,10 +1733,14 @@ ip_vs_in_icmp(struct netns_ipvs *ipvs, struct sk_buff 
*skb, int *related,
                if (unlikely(cih->frag_off & htons(IP_OFFSET)))
                        return NF_ACCEPT;
                offset2 = offset + cih->ihl * 4;
-               ulen = ipvs_udp_decap(ipvs, skb, offset2, AF_INET, raddr,
-                                     &iproto);
+               if (cih->protocol == IPPROTO_UDP)
+                       ulen = ipvs_udp_decap(ipvs, skb, offset2, AF_INET,
+                                             raddr, &iproto);
+               else
+                       ulen = ipvs_gre_decap(ipvs, skb, offset2, AF_INET,
+                                             raddr, &iproto);
                if (ulen > 0) {
-                       /* Skip IP and UDP tunnel headers */
+                       /* Skip IP and UDP/GRE tunnel headers */
                        offset = offset2 + ulen;
                        /* Now we should be at the original IP header */
                        cih = skb_header_pointer(skb, offset, sizeof(_ciph),
-- 
2.21.0