xfrm: use gre key as flow upper protocol info

The GRE Key field is intended to be used for identifying an individual
traffic flow within a tunnel. It is useful to be able to have XFRM
policy selector matches to have different policies for different
GRE tunnels.
Signed-off-by: NTimo Teräs <timo.teras@iki.fi>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/net/flow.h

@@ -67,6 +67,7 @@ struct flowi {
 		} dnports;
 
 		__be32		spi;
+		__be32		gre_key;
 
 		struct {
 			__u8	type;
@@ -78,6 +79,7 @@ struct flowi {
 #define fl_icmp_code	uli_u.icmpt.code
 #define fl_ipsec_spi	uli_u.spi
 #define fl_mh_type	uli_u.mht.type
+#define fl_gre_key	uli_u.gre_key
 	__u32           secid;	/* used by xfrm; see secid.txt */
 } __attribute__((__aligned__(BITS_PER_LONG/8)));
 

include/net/xfrm.h

@@ -805,6 +805,9 @@ __be16 xfrm_flowi_sport(struct flowi *fl)
 	case IPPROTO_MH:
 		port = htons(fl->fl_mh_type);
 		break;
+	case IPPROTO_GRE:
+		port = htonl(fl->fl_gre_key) >> 16;
+		break;
 	default:
 		port = 0;	/*XXX*/
 	}
@@ -826,6 +829,9 @@ __be16 xfrm_flowi_dport(struct flowi *fl)
 	case IPPROTO_ICMPV6:
 		port = htons(fl->fl_icmp_code);
 		break;
+	case IPPROTO_GRE:
+		port = htonl(fl->fl_gre_key) & 0xffff;
+		break;
 	default:
 		port = 0;	/*XXX*/
 	}

net/ipv4/ip_gre.c

@@ -779,9 +779,9 @@ static netdev_tx_t ipgre_tunnel_xmit(struct sk_buff *skb, struct net_device *dev
 					.tos = RT_TOS(tos)
 				}
 			},
-			.proto = IPPROTO_GRE
-		}
-;
+			.proto = IPPROTO_GRE,
+			.fl_gre_key = tunnel->parms.o_key
+		};
 		if (ip_route_output_key(dev_net(dev), &rt, &fl)) {
 			dev->stats.tx_carrier_errors++;
 			goto tx_error;
@@ -958,7 +958,8 @@ static int ipgre_tunnel_bind_dev(struct net_device *dev)
 					.tos = RT_TOS(iph->tos)
 				}
 			},
-			.proto = IPPROTO_GRE
+			.proto = IPPROTO_GRE,
+			.fl_gre_key = tunnel->parms.o_key
 		};
 		struct rtable *rt;
 
@@ -1223,7 +1224,8 @@ static int ipgre_open(struct net_device *dev)
 					.tos = RT_TOS(t->parms.iph.tos)
 				}
 			},
-			.proto = IPPROTO_GRE
+			.proto = IPPROTO_GRE,
+			.fl_gre_key = t->parms.o_key
 		};
 		struct rtable *rt;
 

net/ipv4/xfrm4_policy.c

@@ -11,6 +11,7 @@
 #include <linux/err.h>
 #include <linux/kernel.h>
 #include <linux/inetdevice.h>
+#include <linux/if_tunnel.h>
 #include <net/dst.h>
 #include <net/xfrm.h>
 #include <net/ip.h>
@@ -154,6 +155,20 @@ _decode_session4(struct sk_buff *skb, struct flowi *fl, int reverse)
 				fl->fl_ipsec_spi = htonl(ntohs(ipcomp_hdr[1]));
 			}
 			break;
+
+		case IPPROTO_GRE:
+			if (pskb_may_pull(skb, xprth + 12 - skb->data)) {
+				__be16 *greflags = (__be16 *)xprth;
+				__be32 *gre_hdr = (__be32 *)xprth;
+
+				if (greflags[0] & GRE_KEY) {
+					if (greflags[0] & GRE_CSUM)
+						gre_hdr++;
+					fl->fl_gre_key = gre_hdr[1];
+				}
+			}
+			break;
+
 		default:
 			fl->fl_ipsec_spi = 0;
 			break;