iputils: add ExtractMAC

2 files changed, 80 insertions, 0 deletions

diff --git a/dhcpv6/iputils.go b/dhcpv6/iputils.go
index 2b9788c..3ad157e 100644
--- a/dhcpv6/iputils.go
+++ b/dhcpv6/iputils.go
@@ -42,3 +42,54 @@ func GetGlobalAddr(ifname string) (net.IP, error) {
 		return ip.To4() == nil && ip.IsGlobalUnicast()
 	})
 }
+
+// GetMacAddressFromEUI64 will return a valid MAC address ONLY if it's a EUI-48
+func GetMacAddressFromEUI64(ip net.IP) (net.HardwareAddr, error) {
+	if ip.To16() == nil {
+		return nil, fmt.Errorf("IP address shorter than 16 bytes")
+	}
+
+	if isEUI48 := ip[11] == 0xff && ip[12] == 0xfe; !isEUI48 {
+		return nil, fmt.Errorf("IP address is not an EUI48 address")
+	}
+
+	mac := make(net.HardwareAddr, 6)
+	copy(mac[0:3], ip[8:11])
+	copy(mac[3:6], ip[13:16])
+	mac[0] ^= 0x02
+
+	return mac, nil
+}
+
+// ExtractMAC looks into the inner most PeerAddr field in the RelayInfo header
+// which contains the EUI-64 address of the client making the request, populated
+// by the dhcp relay, it is possible to extract the mac address from that IP.
+// If that fails, it looks for the MAC addressed embededded in the DUID.
+// Note that this only works with type DuidLL and DuidLLT.
+// If a mac address cannot be found an error will be returned.
+func ExtractMAC(packet DHCPv6) (net.HardwareAddr, error) {
+	msg := packet
+	if packet.IsRelay() {
+		inner, err := DecapsulateRelayIndex(packet, -1)
+		if err != nil {
+			return nil, err
+		}
+		ip := inner.(*DHCPv6Relay).PeerAddr()
+		if mac, err := GetMacAddressFromEUI64(ip); err == nil {
+			return mac, nil
+		}
+		msg, err = msg.(*DHCPv6Relay).GetInnerMessage()
+		if err != nil {
+			return nil, err
+		}
+	}
+	optclientid := msg.GetOneOption(OptionClientID)
+	if optclientid == nil {
+		return nil, fmt.Errorf("client ID not found in packet")
+	}
+	duid := optclientid.(*OptClientId).Cid
+	if duid.LinkLayerAddr == nil {
+		return nil, fmt.Errorf("failed to extract MAC")
+	}
+	return duid.LinkLayerAddr, nil
+}
diff --git a/dhcpv6/iputils_test.go b/dhcpv6/iputils_test.go
index 765792e..1da249d 100644
--- a/dhcpv6/iputils_test.go
+++ b/dhcpv6/iputils_test.go
@@ -7,6 +7,7 @@ import (
 	"testing"
 
 	"github.com/stretchr/testify/mock"
+	"github.com/stretchr/testify/require"
 	"github.com/stretchr/testify/suite"
 )
 
@@ -101,3 +102,31 @@ func (s *MatchingAddressTestSuite) TestGetGlobalAddr() {
 func TestMatchingAddressTestSuite(t *testing.T) {
 	suite.Run(t, new(MatchingAddressTestSuite))
 }
+
+func Test_ExtractMAC(t *testing.T) {
+	//SOLICIT message wrapped in Relay-Forw
+	var relayForwBytesDuidUUID = []byte{
+		0x0c, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+		0x00, 0x00, 0xfe, 0x80, 0x00, 0x00, 0x00, 0x00,
+		0x00, 0x00, 0x26, 0x8a, 0x07, 0xff, 0xfe, 0x56,
+		0xdc, 0xa4, 0x00, 0x12, 0x00, 0x06, 0x24, 0x8a,
+		0x07, 0x56, 0xdc, 0xa4, 0x00, 0x09, 0x00, 0x5a,
+		0x06, 0x7d, 0x9b, 0xca, 0x00, 0x01, 0x00, 0x12,
+		0x00, 0x04, 0xb7, 0xfd, 0x0a, 0x8c, 0x1b, 0x14,
+		0x10, 0xaa, 0xeb, 0x0a, 0x5b, 0x3f, 0xe8, 0x9d,
+		0x0f, 0x56, 0x00, 0x06, 0x00, 0x0a, 0x00, 0x17,
+		0x00, 0x18, 0x00, 0x17, 0x00, 0x18, 0x00, 0x01,
+		0x00, 0x08, 0x00, 0x02, 0xff, 0xff, 0x00, 0x03,
+		0x00, 0x28, 0x07, 0x56, 0xdc, 0xa4, 0x00, 0x00,
+		0x0e, 0x10, 0x00, 0x00, 0x15, 0x18, 0x00, 0x05,
+		0x00, 0x18, 0x26, 0x20, 0x01, 0x0d, 0xc0, 0x82,
+		0x90, 0x63, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+		0xaf, 0xa0, 0x00, 0x00, 0x1c, 0x20, 0x00, 0x00,
+		0x1d, 0x4c}
+	packet, err := FromBytes(relayForwBytesDuidUUID)
+	require.NoError(t, err)
+	mac, err := ExtractMAC(packet)
+	require.NoError(t, err)
+	require.Equal(t, mac.String(), "24:8a:07:56:dc:a4")
+}