Honor client bootp flags in response.

Signed-off-by: s3rj1k <[email protected]>

Author: s3rj1k

README.md

@@ -42,6 +42,7 @@ This repository contains a DHCPv4 Relay agent written in Go (Golang). This relay
 - [RFC3046: DHCP Relay Agent Information Option](https://www.rfc-editor.org/rfc/rfc3046.html)
 - [RFC3396: Encoding Long Options in the DHCPv4](https://www.rfc-editor.org/rfc/rfc3396.html)
 - [RFC3527: Link Selection sub-option for the Relay Agent Information Option for DHCPv4](https://www.rfc-editor.org/rfc/rfc3527.html)
+- [RFC5010: Relay Agent Flags Suboption](https://www.rfc-editor.org/rfc/rfc5010.html)
 - [RFC5107: DHCP Server Identifier Override Suboption](https://www.rfc-editor.org/rfc/rfc5107.html)
 
 ### Contribution

dhcpv4-reply-raw.go dhcpv4-reply.go

@@ -14,10 +14,16 @@ import (
 	"code.local/dhcp-relay/specs"
 )
 
-func HandleDHCPv4GenericReplyRaw(
+const (
+	UnicastReply   uint8 = 0
+	BroadcastReply uint8 = 1
+)
+
+func HandleDHCPv4GenericReply(
 	cfg *HandleOptions,
 	dhcpMessageType string,
 	layerDHCPv4 *layers.DHCPv4,
+	replyType uint8,
 ) error {
 	srcIP := layerDHCPv4.RelayAgentIP.To4()
 	if srcIP == nil || srcIP.IsLoopback() || srcIP.Equal(net.IPv4zero) || srcIP.Equal(net.IPv4bcast) {
@@ -61,8 +67,6 @@ func HandleDHCPv4GenericReplyRaw(
 		Flags:    layers.IPv4DontFragment,
 		TTL:      cfg.ReplyTTL,
 		Protocol: layers.IPProtocolUDP,
-		SrcIP:    srcIP.To4(),
-		DstIP:    layerDHCPv4.YourClientIP.To4(),
 	}
 
 	layerUDP := &layers.UDP{
@@ -84,7 +88,17 @@ func HandleDHCPv4GenericReplyRaw(
 		layerDHCPv4.RelayAgentIP = nil
 	}
 
-	dhcp.SetUnicast(layerDHCPv4)
+	if replyType == UnicastReply {
+		layerIPv4.SrcIP = srcIP.To4()
+		layerIPv4.DstIP = layerDHCPv4.YourClientIP.To4()
+
+		dhcp.SetUnicast(layerDHCPv4)
+	} else if replyType == BroadcastReply {
+		layerIPv4.SrcIP = net.IPv4zero
+		layerIPv4.DstIP = net.IPv4bcast
+
+		dhcp.SetBroadcast(layerDHCPv4)
+	}
 
 	buffer := gopacket.NewSerializeBuffer()
 
@@ -124,10 +138,10 @@ func HandleDHCPv4GenericReplyRaw(
 	cl.Infof("%s 0x%x: DHCP-%s [%d], IfIndex=%d, Src=%s, Dst=%s\n",
 		logDataOutPrefix, layerDHCPv4.Xid, dhcpMessageType, layerDHCPv4.Len(), ifIndex,
 		net.JoinHostPort(
-			srcIP.To4().String(), strconv.Itoa(specs.DHCPv4ServerPort),
+			layerIPv4.SrcIP.String(), strconv.Itoa(specs.DHCPv4ServerPort),
 		),
 		net.JoinHostPort(
-			layerDHCPv4.YourClientIP.To4().String(), strconv.Itoa(specs.DHCPv4ClientPort),
+			layerIPv4.DstIP.String(), strconv.Itoa(specs.DHCPv4ClientPort),
 		),
 	)
 

dhcpv4-request.go

@@ -71,7 +71,6 @@ func HandleDHCPv4GenericRequest(
 
 	dhcp.SetRelayAgentInformationOption(layerDHCPv4, subOpt1)
 
-	dhcp.SetUnicast(layerDHCPv4)
 	layerDHCPv4.RelayHops++
 
 	for _, addr := range addrs {
@@ -106,8 +105,6 @@ func ForwardDHCPv4RelayedRequest(
 	dhcpMessageType string,
 	layerDHCPv4 *layers.DHCPv4,
 ) error {
-	dhcp.SetUnicast(layerDHCPv4)
-
 	buffer := gopacket.NewSerializeBuffer()
 
 	err := gopacket.SerializeLayers(

dhcpv4.go

@@ -72,9 +72,21 @@ func HandleDHCPv4(
 
 		funcDataInLog()
 
-		if err := HandleDHCPv4GenericReplyRaw(cfg, dhcpMessageType, layerDHCPv4); err != nil {
-			cl.Errorf("Error handling DHCPv4-%s relayed message: %v\n",
-				dhcpMessageType, err)
+		bootFileName := dhcp.GetBootFileName(layerDHCPv4)
+		if bootFileName != "" {
+			cl.Debugf("Boot File Name: %s\n", bootFileName)
+		}
+
+		if dhcp.IsUnicast(layerDHCPv4) {
+			if err := HandleDHCPv4GenericReply(cfg, dhcpMessageType, layerDHCPv4, UnicastReply); err != nil {
+				cl.Errorf("Error handling DHCPv4-%s unicast relayed message: %v\n",
+					dhcpMessageType, err)
+			}
+		} else if dhcp.IsBroadcast(layerDHCPv4) {
+			if err := HandleDHCPv4GenericReply(cfg, dhcpMessageType, layerDHCPv4, BroadcastReply); err != nil {
+				cl.Errorf("Error handling DHCPv4-%s broadcast relayed message: %v\n",
+					dhcpMessageType, err)
+			}
 		}
 	}
 }

gpckt/dhcp/utils.go

@@ -0,0 +1,15 @@
+package dhcp
+
+import (
+	"bytes"
+
+	"github.com/gopacket/gopacket/layers"
+)
+
+func GetBootFileName(layerDHCPv4 *layers.DHCPv4) string {
+	if len(layerDHCPv4.File) == 0 {
+		return ""
+	}
+
+	return string(bytes.TrimSpace(layerDHCPv4.File))
+}

gpckt/layer.go

@@ -1,6 +1,8 @@
 package gpckt
 
 import (
+	"fmt"
+
 	"github.com/gopacket/gopacket"
 	"github.com/gopacket/gopacket/layers"
 )
@@ -60,3 +62,13 @@ func GetDHCPv4(packet gopacket.Packet) *layers.DHCPv4 {
 
 	return layerDHCPv4
 }
+
+func CopyDHCPv4(layerDHCPv4 *layers.DHCPv4) (*layers.DHCPv4, error) {
+	out := new(layers.DHCPv4)
+
+	if err := out.DecodeFromBytes(layerDHCPv4.Contents, gopacket.NilDecodeFeedback); err != nil {
+		return nil, fmt.Errorf("copy error: %w", err)
+	}
+
+	return out, nil
+}