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: Timo Teräs <timo.teras@iki.fi>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 15 insertions, 0 deletions

diff --git a/net/ipv4/xfrm4_policy.c b/net/ipv4/xfrm4_policy.c
index dd1fd8c473fc..4a8c5335770c 100644
--- a/net/ipv4/xfrm4_policy.c
+++ b/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;