Implements #36: Decapsulate MPLS in promisc mode.

./configure --promisc-mpls to enable.

It's OK to fully decapsualte them there because packets captured in
promisc mode (or 'otherhost' packets) are only visible into raw
PREROUTING chain and then dropped w/o routing.

Thanks to mzi77@github for feature request, discussion and help.

README

@@ -52,7 +52,8 @@ ipt_NETFLOW linux 2.6.x-3.x kernel module by <[email protected]> -- 2008-2015.
    * SNMP-index translation rules, let convert meaningless and unstable
      interface indexes (ifIndex) to more meaningful numbering scheme.
 
-   * Easy support for catching mirrored traffic with promisc option.
+   * Easy support for catching mirrored traffic with promisc option. Which is
+     also supporting optional MPLS decapsulation.
 
 
 ============================
@@ -228,13 +229,20 @@ ipt_NETFLOW linux 2.6.x-3.x kernel module by <[email protected]> -- 2008-2015.
          case you will want to install it manually.
 
      --enable-physdev
-
 	 Export ingressPhysicalInterface(252) and egressPhysicalInterface(253)
 	 (relevant for bridges) in V9 and IPFIX. If your collector does not
 	 support these Elements but you still need physdevs then use
 	 --enable-physdev-override, in that case physdevs will override normal
 	 interface numbers ingressInterface(10) and egressInterface(14).
 
+     --enable-promisc
+	 Enables capturing of promiscuous packets into raw/PREROUTING chain.
+	 See README.promisc Solution 1 for usage details and example.
+
+     --promisc-mpls
+	 Enables MPLS label stack decapsulation for promiscuous packets. (For
+	 IPv4 and IPv6 packets only).
+
 
 ===========
 = RUNNING =
@@ -538,7 +546,7 @@ ipt_NETFLOW linux 2.6.x-3.x kernel module by <[email protected]> -- 2008-2015.
        in kernel jiffies units (which is x/HZ seconds).
 
    promisc=1
-     - Enable promisc hack. See README.promisc Solution.1 for details.
+     - Enables promisc hack. See README.promisc Solution 1 for details.
 
    exportcpu=number
      - Lock exporter to single CPU. This may be useful to fine control CPU

compat.h

@@ -268,4 +268,19 @@ static void *__seq_open_private(struct file *f, struct seq_operations *ops,
 #define __get_cpu_var(var)	(*this_cpu_ptr(&(var)))
 #endif
 
+#ifndef MPLS_HLEN
+#define MPLS_HLEN 4
+static inline int eth_p_mpls(__be16 eth_type)
+{
+	return eth_type == htons(ETH_P_MPLS_UC) ||
+		eth_type == htons(ETH_P_MPLS_MC);
+}
+#endif
+#ifndef MPLS_LS_S_MASK
+struct mpls_label {
+	__be32 entry;
+};
+#define MPLS_LS_S_MASK          0x00000100
+#endif
+
 #endif /* COMPAT_NETFLOW_H */

configure

@@ -270,7 +270,8 @@ show_help() {
   echo "  --enable-sampler       enables Flow Sampling"
   echo "  --enable-sampler=hash  enables Hash sampler"
   echo "  --enable-aggregation   enables aggregation rules"
-  echo "  --enable-promisc       enables promisc hack"
+  echo "  --enable-promisc       enables promisc hack mode"
+  echo "  --promisc-mpls         decapsulate MPLS in promisc mode"
   echo "  --enable-physdev       enables physdev reporting"
   echo "  --enable-physdev-override      to override interfaces"
   echo "  --disable-snmp-agent   disables net-snmp agent"
@@ -302,7 +303,8 @@ do
     --enable-sampl*hash) KOPTS="$KOPTS -DENABLE_SAMPLER -DSAMPLING_HASH" ;;
     --enable-sampl*) KOPTS="$KOPTS -DENABLE_SAMPLER" ;;
     --enable-aggr*)  KOPTS="$KOPTS -DENABLE_AGGR" ;;
-    --enable-promi*) KOPTS="$KOPTS -DENABLE_PROMISC" ;;
+    --enable-promi*) ENABLE_PROMISC=1 ;;
+    --promisc-mpls)  ENABLE_PROMISC=1; PROMISC_MPLS=1 ;;
     --enable-snmp-r*)  KOPTS="$KOPTS -DENABLE_SNMP" ;;
     --enable-physdev)       KOPTS="$KOPTS -DENABLE_PHYSDEV" ;;
     --enable-physdev-over*) KOPTS="$KOPTS -DENABLE_PHYSDEV_OVER" ;;
@@ -318,6 +320,9 @@ do
   esac
 done
 
+if [ "$ENABLE_PROMISC" = 1 ]; then KOPTS="$KOPTS -DENABLE_PROMISC"; fi
+if [ "$PROMISC_MPLS" = 1 ]; then   KOPTS="$KOPTS -DPROMISC_MPLS"; fi
+
 kernel_find_version() {
   KHOW=requested
   test "$KVERSION" && return 0

ipt_NETFLOW.c

@@ -578,6 +578,9 @@ static int nf_seq_show(struct seq_file *seq, void *v)
 #endif
 #ifdef ENABLE_PROMISC
 	    " promisc"
+# ifdef PROMISC_MPLS
+	    "+mpls"
+# endif
 #endif
 #ifdef ENABLE_SAMPLER
 	    " samp"
@@ -1302,17 +1305,38 @@ static int promisc_rcv(struct sk_buff *skb, struct net_device *dev, struct packe
 		skb_pull(skb, vlan_depth);
 
 		skb_reset_network_header(skb);
-		skb_reset_transport_header(skb);
 		skb_reset_mac_len(skb);
 	}
+# ifdef PROMISC_MPLS
+	if (eth_p_mpls(skb->protocol)) {
+		size_t stack_len = 0;
+		const struct mpls_label *mpls;
+
+		do {
+			mpls = (struct mpls_label *)(skb->data + stack_len);
+			stack_len += MPLS_HLEN;
+			if (unlikely(!pskb_may_pull(skb, stack_len)))
+				goto drop;
+		} while (!(mpls->entry & htonl(MPLS_LS_S_MASK)));
+
+		skb_pull(skb, stack_len);
+		skb_reset_network_header(skb);
 
+		if (!pskb_may_pull(skb, 1))
+			goto drop;
+		switch (ip_hdr(skb)->version) {
+		case 4:  skb->protocol = htons(ETH_P_IP);   break;
+		case 6:  skb->protocol = htons(ETH_P_IPV6); break;
+		default: goto drop;
+		}
+	}
+# endif
 	switch (skb->protocol) {
 	case htons(ETH_P_IP):
 		return promisc4_rcv(skb, dev, pt, orig_dev);
 	case htons(ETH_P_IPV6):
 		return promisc6_rcv(skb, dev, pt, orig_dev);
 	}
-
 drop:
 	NETFLOW_STAT_INC(pkt_promisc_drop);
 out:

testing.sh

@@ -31,12 +31,12 @@ readarray -t opts <<EOF
   --enable-direction
   --enable-sampler
   --enable-sampler=hash
-  --enable-promisc
+  --enable-promisc --promisc-mpls
   --enable-physdev
   --enable-physdev-override
 EOF
 if [ "$SHORT" ]; then
-  opts=("")
+  opts=("$SHORT")
 fi
 
 colorecho() {