Add support for filtering VNTag frames

Add a "vntag" keyword similar to the existing "vlan" and "mpls" keywords to
filter on VNTag frames. VNTag was proposed as 802.1Qbh but has been replaced in
the standards by 802.1Qbr although some vendors are still using VNTag. Skips the
6 bytes of the VNTag header similar to the 4 byte skip of VLAN. They both inject
themselves between Ethernet dest addr and EtherType.

This resolves GitHub issue #770

Author: Stefan Baranoff

CHANGES

@@ -51,6 +51,7 @@ DayOfTheWeek, Month DD, YYYY / The Tcpdump Group
       Require a live capture for all Linux BPF extensions.
       Have "outbound" mean Tx only for DLT_SLIP.
       Filter Linux SocketCAN frames in userland if necessary.
+      Add support for filtering VNTag frames (pull request #1480)
     rpcap:
       Support user names and passwords in rpcap:// and rpcaps:// URLs.
       Add a -t flag to rpcapd to specify the data channel port; from

ethertype.h

@@ -115,6 +115,9 @@
 #ifndef ETHERTYPE_8021AD
 #define ETHERTYPE_8021AD	0x88a8
 #endif
+#ifndef ETHERTYPE_VNTAG
+#define ETHERTYPE_VNTAG		0x8926
+#endif
 #ifndef	ETHERTYPE_LOOPBACK
 #define ETHERTYPE_LOOPBACK	0x9000
 #endif

gencode.c

@@ -10710,3 +10710,76 @@ gen_atmmulti_abbrev(compiler_state_t *cstate, int type)
 	}
 	return b1;
 }
+
+/*
+ * support VNTag (proposed as IEEE 802.1Qbh but never accepted) over Ethernet
+ * VNTag headers look like this on their own:
+ *   0               1               2               3               4               5
+ *   0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+ *  |               |               |               |               |               |               |
+ *  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ *  |           EtherType           |D|P|    vif_list_id/dvif_id    |L|R|ver|        svif_id        |
+ *  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ *
+ *  In context that looks like this:
+ *   0               1               2               3               4               5
+ *   0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+ *  |               |               |               |               |               |               |
+ *  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ *  |                                      Destination Address                                      |
+ *  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ *  |                                         Source Address                                        |
+ *  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ *  |                                             VNTag                                             |
+ *  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ *  |           EtherType           |                           Payload...                          |
+ *  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ */
+struct block *
+gen_vntag(compiler_state_t *cstate)
+{
+	struct block *b0;
+
+	/*
+	 * Catch errors reported by us and routines below us, and return NULL
+	 * on an error.
+	 */
+	if (setjmp(cstate->top_ctx))
+		return (NULL);
+
+	/*
+	 * Check for a VNTag packet, and then change the offsets to point
+	 * to the type and data fields within the VLAN after the VNTag packet.
+	 * VNTag always requires VLAN afterwards, and that likely won't be
+	 * offloaded so handle it just like inline VLAN. Apply the same rules
+	 * and restrictions as VLAN, too.
+	 */
+	if (cstate->label_stack_depth > 0)
+		bpf_error(cstate, "no VNTag match after MPLS");
+
+	/* Assume any of the EtherTypes that can have VLAN can also have
+	 * VNTag as well. With VNTag not being accepted as 802.1Qbh but
+	 * being replaced in the standads by 802.1Qbr there's not much to go on
+	 * other than a few vendor proprietary implementations.
+	 */
+	switch (cstate->linktype) {
+	case DLT_EN10MB:
+	case DLT_NETANALYZER:
+	case DLT_NETANALYZER_TRANSPARENT:
+	case DLT_IEEE802_11:
+	case DLT_PRISM_HEADER:
+	case DLT_IEEE802_11_RADIO_AVS:
+	case DLT_IEEE802_11_RADIO:
+		/* Make sure we have a VNTag frame, then jump over it. */
+		b0 = gen_linktype(cstate, ETHERTYPE_VNTAG);
+		cstate->off_linkpl.constant_part += 6;
+		cstate->off_linktype.constant_part += 6;
+		break;
+	default:
+		bpf_error(cstate, "no VNTag support for %s",
+		      pcap_datalink_val_to_description_or_dlt(cstate->linktype));
+		/*NOTREACHED*/
+	}
+
+	return (b0);
+}

gencode.h

@@ -352,6 +352,7 @@ struct block *gen_llc_u_subtype(compiler_state_t *, bpf_u_int32);
 
 struct block *gen_vlan(compiler_state_t *, bpf_u_int32, int);
 struct block *gen_mpls(compiler_state_t *, bpf_u_int32, int);
+struct block *gen_vntag(compiler_state_t *);
 
 struct block *gen_pppoed(compiler_state_t *);
 struct block *gen_pppoes(compiler_state_t *, bpf_u_int32, int);

grammar.y.in

@@ -389,7 +389,7 @@ DIAG_OFF_BISON_BYACC
 %token	LSH RSH
 %token  LEN
 %token  IPV6 ICMPV6 AH ESP
-%token	VLAN MPLS
+%token	VLAN MPLS VNTAG
 %token	PPPOED PPPOES GENEVE VXLAN
 %token  ISO ESIS CLNP ISIS L1 L2 IIH LSP SNP CSNP PSNP
 %token  STP
@@ -682,6 +682,7 @@ other:	  pqual TK_BROADCAST	{ CHECK_PTR_VAL(($$ = gen_broadcast(cstate, $1))); }
 	| VLAN			{ CHECK_PTR_VAL(($$ = gen_vlan(cstate, 0, 0))); }
 	| MPLS pnum		{ CHECK_PTR_VAL(($$ = gen_mpls(cstate, $2, 1))); }
 	| MPLS			{ CHECK_PTR_VAL(($$ = gen_mpls(cstate, 0, 0))); }
+	| VNTAG			{ CHECK_PTR_VAL(($$ = gen_vntag(cstate))); }
 	| PPPOED		{ CHECK_PTR_VAL(($$ = gen_pppoed(cstate))); }
 	| PPPOES pnum		{ CHECK_PTR_VAL(($$ = gen_pppoes(cstate, $2, 1))); }
 	| PPPOES		{ CHECK_PTR_VAL(($$ = gen_pppoes(cstate, 0, 0))); }

pcap-filter.manmisc.in

@@ -1011,6 +1011,24 @@ filters packets with an outer label of 100000 and an inner label of
 .in -.5i
 filters packets to or from 192.9.200.1 with an inner label of 1024 and
 any outer label.
+.IP "\fBvntag\fR"
+True if the packet is a VNTag packet (identified by EtherType 0x8926).
+Each use of that keyword increments the filter link header and payload offsets by 6.
+.IP
+For example:
+.in +.5i
+.nf
+\fBvntag\fR
+.fi
+.in -.5i
+filters on VNTag as the next EtherType and skips the VNTag header
+.in +.5i
+.nf
+\fBvntag\fR and \fBvlan\fR and \fBip src host\fR 192.0.2.0
+.fi
+.in -.5i
+filters on VNTag followed by any VLAN followed by an IPv4 packet from 192.0.2.0
+skipping over the VNTag header, then VLAN header, to allow finding the IPv4
 .IP \fBpppoed\fP
 True if the packet is a PPP-over-Ethernet Discovery packet (Ethernet
 type 0x8863).
@@ -1636,8 +1654,10 @@ The
 keyword became available in libpcap 1.10.0.
 .PP
 The
-.B vxlan
-keyword became available in libpcap 1.11.0.
+.BR vxlan
+and
+.B vntag
+keywords became available in libpcap 1.11.0.
 .SH SEE ALSO
 .BR pcap (3PCAP)
 .SH BUGS

scanner.l

@@ -339,6 +339,7 @@ pppoed		return PPPOED;
 pppoes		return PPPOES;
 geneve		return GENEVE;
 vxlan		return VXLAN;
+vntag		return VNTAG;
 
 lane		return LANE;
 llc		return LLC;

testprogs/TESTrun

@@ -9657,6 +9657,34 @@ my %accept_blocks = (
 			(020) ret      #0
 			',
 	}, # dst_portrange_degenerate
+	vntag_eth => {
+		DLT => 'EN10MB',
+		aliases => ['vntag'],
+		opt => '
+			(000) ldh      [12]
+			(001) jeq      #0x8926          jt 2	jf 3
+			(002) ret      #262144
+			(003) ret      #0
+			',
+	}, # vntag_eth
+	vntag_eth_vlan_vntag_vlan => {
+		DLT => 'EN10MB',
+		aliases => ['vlan and vntag and vlan'],
+		opt => '
+			(000) ldh      [12]
+			(001) jeq      #0x8100          jt 4	jf 2
+			(002) jeq      #0x88a8          jt 4	jf 3
+			(003) jeq      #0x9100          jt 4	jf 11
+			(004) ldh      [16]
+			(005) jeq      #0x8926          jt 6	jf 11
+			(006) ldh      [22]
+			(007) jeq      #0x8100          jt 10	jf 8
+			(008) jeq      #0x88a8          jt 10	jf 9
+			(009) jeq      #0x9100          jt 10	jf 11
+			(010) ret      #262144
+			(011) ret      #0
+			',
+	}, # vntag_eth
 );
 
 # In apply_blocks the top-level keys are test block names.  Each test block
@@ -10067,6 +10095,21 @@ my %apply_blocks = (
 		expr => 'outbound',
 		results => [46],
 	},
+	vntag => {
+		savefile => 'vntag-novntag-mixed.pcap',
+		expr => 'vntag',
+		results => [262144, 262144, 262144, 262144, 262144, 262144, 262144, 262144, 262144, 262144, 262144, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
+	},
+	vntag_vlan_ip => {
+		savefile => 'vntag-novntag-mixed.pcap',
+		expr => 'vntag and vlan 100 and ip',
+		results => [262144, 262144, 262144, 262144, 262144, 262144, 262144, 262144, 262144, 262144, 262144, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
+	},
+	vntag_vlan_dest_ip => {
+		savefile => 'vntag-novntag-mixed.pcap',
+		expr => 'vntag and vlan 100 and ip dst 192.168.20.102',
+		results => [0, 262144, 0, 0, 262144, 262144, 0, 0, 262144, 262144, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
+	},
 );
 
 # * DLT, expr, netmask and skip: same as in accept_blocks above
@@ -10698,6 +10741,10 @@ my %reject_tests = (
 		DLT => 'EN10MB',
 		expr => 'gateway $af',
 		errstr => 'aid supported only on ARCnet',
+	vntag_not_supported => {
+		DLT => 'RAW',
+		expr => 'vntag',
+		errstr => 'no VNTag support',
 	},
 );