Add ability to override layer type, and fix DNS issue.

Author: gconnell

layers/dns.go

@@ -561,6 +561,9 @@ loop:
 			*/
 
 			offsetp := int(binary.BigEndian.Uint16(data[index:index+2]) & 0x3fff)
+			if offsetp > len(data) {
+				return nil, 0, errors.New("dns offset pointer too high")
+			}
 			// This looks a little tricky, but actually isn't.  Because of how
 			// decodeName is written, calling it appends the decoded name to the
 			// current buffer.  We already have the start of the buffer, then, so

layers/dns_test.go

@@ -365,3 +365,35 @@ func TestDNSMalformedPacket(t *testing.T) {
 		t.Errorf("unexpected error message: %v", err)
 	}
 }
+
+// testDNSMalformedPacket2 is the packet:
+//   15:14:42.056054 IP 10.77.0.245.53 > 10.1.0.45.38769: 12625 zoneInit YXRRSet- [49833q],[|domain]
+//   	0x0000:  0055 22af c637 0022 55ac deac 0800 4500  .U"..7."U.....E.
+//   	0x0010:  0079 3767 4000 3911 f49d 0a4d 00f5 0a01  [email protected]....
+//   	0x0020:  002d 0035 9771 0065 6377 3151 f057 c2a9  .-.5.q.ecw1Q.W..
+//   	0x0030:  fc6e e86a beb0 f7d4 8599 373e b5f8 9db2  .n.j......7>....
+//   	0x0040:  a399 21a1 9762 def1 def4 f5ab 5675 023e  ..!..b......Vu.>
+//   	0x0050:  c9ca 304f 178a c2ad f2fc 677a 0e4c b892  ..0O......gz.L..
+//   	0x0060:  ab71 09bb 1ea4 f7c4 fe47 7a39 868b 29a0  .q.......Gz9..).
+//   	0x0070:  62c4 d184 5b4e 8817 4cc0 d1d0 d430 11d3  b...[N..L....0..
+//   	0x0080:  d147 543f afc7 1a                        .GT?...
+var testDNSMalformedPacket2 = []byte{
+	0x00, 0x55, 0x22, 0xaf, 0xc6, 0x37, 0x00, 0x22, 0x55, 0xac, 0xde, 0xac, 0x08, 0x00, 0x45, 0x00,
+	0x00, 0x79, 0x37, 0x67, 0x40, 0x00, 0x39, 0x11, 0xf4, 0x9d, 0x0a, 0x4d, 0x00, 0xf5, 0x0a, 0x01,
+	0x00, 0x2d, 0x00, 0x35, 0x97, 0x71, 0x00, 0x65, 0x63, 0x77, 0x31, 0x51, 0xf0, 0x57, 0xc2, 0xa9,
+	0xfc, 0x6e, 0xe8, 0x6a, 0xbe, 0xb0, 0xf7, 0xd4, 0x85, 0x99, 0x37, 0x3e, 0xb5, 0xf8, 0x9d, 0xb2,
+	0xa3, 0x99, 0x21, 0xa1, 0x97, 0x62, 0xde, 0xf1, 0xde, 0xf4, 0xf5, 0xab, 0x56, 0x75, 0x02, 0x3e,
+	0xc9, 0xca, 0x30, 0x4f, 0x17, 0x8a, 0xc2, 0xad, 0xf2, 0xfc, 0x67, 0x7a, 0x0e, 0x4c, 0xb8, 0x92,
+	0xab, 0x71, 0x09, 0xbb, 0x1e, 0xa4, 0xf7, 0xc4, 0xfe, 0x47, 0x7a, 0x39, 0x86, 0x8b, 0x29, 0xa0,
+	0x62, 0xc4, 0xd1, 0x84, 0x5b, 0x4e, 0x88, 0x17, 0x4c, 0xc0, 0xd1, 0xd0, 0xd4, 0x30, 0x11, 0xd3,
+	0xd1, 0x47, 0x54, 0x3f, 0xaf, 0xc7, 0x1a,
+}
+
+func TestDNSMalformedPacket2(t *testing.T) {
+	p := gopacket.NewPacket(testDNSMalformedPacket2, LinkTypeEthernet, testDecodeOptions)
+	if errLayer := p.ErrorLayer(); errLayer == nil {
+		t.Error("No error layer on invalid DNS name")
+	} else if err := errLayer.Error(); !strings.Contains(err.Error(), "offset pointer too high") {
+		t.Errorf("unexpected error message: %v", err)
+	}
+}

layertype.go

@@ -55,14 +55,24 @@ func RegisterLayerType(num int, meta LayerTypeMetadata) LayerType {
 		if ltMeta[num].inUse {
 			panic("Layer type already exists")
 		}
+	} else {
+		if ltMetaMap[LayerType(num)].inUse {
+			panic("Layer type already exists")
+		}
+	}
+	return OverrideLayerType(num, meta)
+}
+
+// OverrideLayerType acts like RegisterLayerType, except that if the layer type
+// has already been registered, it overrides the metadata with the passed-in
+// metadata intead of panicing.
+func OverrideLayerType(num int, meta LayerTypeMetadata) LayerType {
+	if 0 <= num && num < maxLayerType {
 		ltMeta[num] = layerTypeMetadata{
 			inUse:             true,
 			LayerTypeMetadata: meta,
 		}
 	} else {
-		if ltMetaMap[LayerType(num)].inUse {
-			panic("Layer type already exists")
-		}
 		ltMetaMap[LayerType(num)] = layerTypeMetadata{
 			inUse:             true,
 			LayerTypeMetadata: meta,