dhcpd: use unicast to reply messages

go.mod

@@ -7,7 +7,7 @@ require (
 	github.com/dgryski/go-camellia v0.0.0-20191119043421-69a8a13fb23d
 	github.com/dgryski/go-idea v0.0.0-20170306091226-d2fb45a411fb
 	github.com/dgryski/go-rc2 v0.0.0-20150621095337-8a9021637152
-	github.com/insomniacslk/dhcp v0.0.0-20231206064809-8c70d406f6d2
+	github.com/insomniacslk/dhcp v0.0.0-20240129002554-15c9b8791914
 	github.com/nadoo/conflag v0.3.1
 	github.com/nadoo/ipset v0.5.0
 	github.com/xtaci/kcp-go/v5 v5.6.7
@@ -19,7 +19,7 @@ require (
 	github.com/ebfe/rc2 v0.0.0-20131011165748-24b9757f5521 // indirect
 	github.com/josharian/native v1.1.0 // indirect
 	github.com/klauspost/cpuid/v2 v2.2.6 // indirect
-	github.com/klauspost/reedsolomon v1.12.0 // indirect
+	github.com/klauspost/reedsolomon v1.12.1 // indirect
 	github.com/pierrec/lz4/v4 v4.1.21 // indirect
 	github.com/pkg/errors v0.9.1 // indirect
 	github.com/templexxx/cpu v0.1.0 // indirect

go.sum

@@ -33,8 +33,10 @@ github.com/google/go-cmp v0.2.0/go.mod h1:oXzfMopK8JAjlY9xF4vHSVASa0yLyX7SntLO5a
 github.com/google/go-cmp v0.3.0/go.mod h1:8QqcDgzrUqlUb/G2PQTWiueGozuR1884gddMywk6iLU=
 github.com/google/go-cmp v0.3.1/go.mod h1:8QqcDgzrUqlUb/G2PQTWiueGozuR1884gddMywk6iLU=
 github.com/google/go-cmp v0.4.0/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
-github.com/insomniacslk/dhcp v0.0.0-20231206064809-8c70d406f6d2 h1:9K06NfxkBh25x56yVhWWlKFE8YpicaSfHwoV8SFbueA=
+github.com/google/gopacket v1.1.19 h1:ves8RnFZPGiFnTS0uPQStjwru6uO6h+nlr9j6fL7kF8=
-github.com/insomniacslk/dhcp v0.0.0-20231206064809-8c70d406f6d2/go.mod h1:3A9PQ1cunSDF/1rbTq99Ts4pVnycWg+vlPkfeD2NLFI=
+github.com/google/gopacket v1.1.19/go.mod h1:iJ8V8n6KS+z2U1A8pUwu8bW5SyEMkXJB8Yo/Vo+TKTo=
+github.com/insomniacslk/dhcp v0.0.0-20240129002554-15c9b8791914 h1:kD8PseueGeYiid/Mmcv17Q0Qqicc4F46jcX22L/e/Hs=
+github.com/insomniacslk/dhcp v0.0.0-20240129002554-15c9b8791914/go.mod h1:3A9PQ1cunSDF/1rbTq99Ts4pVnycWg+vlPkfeD2NLFI=
 github.com/josharian/native v1.0.1-0.20221213033349-c1e37c09b531/go.mod h1:7X/raswPFr05uY3HiLlYeyQntB6OO7E/d2Cu7qoaN2w=
 github.com/josharian/native v1.1.0 h1:uuaP0hAbW7Y4l0ZRQ6C9zfb7Mg1mbFKry/xzDAfmtLA=
 github.com/josharian/native v1.1.0/go.mod h1:7X/raswPFr05uY3HiLlYeyQntB6OO7E/d2Cu7qoaN2w=
@@ -44,8 +46,8 @@ github.com/klauspost/cpuid v1.3.1/go.mod h1:bYW4mA6ZgKPob1/Dlai2LviZJO7KGI3uoWLd
 github.com/klauspost/cpuid/v2 v2.2.6 h1:ndNyv040zDGIDh8thGkXYjnFtiN02M1PVVF+JE/48xc=
 github.com/klauspost/cpuid/v2 v2.2.6/go.mod h1:Lcz8mBdAVJIBVzewtcLocK12l3Y+JytZYpaMropDUws=
 github.com/klauspost/reedsolomon v1.9.9/go.mod h1:O7yFFHiQwDR6b2t63KPUpccPtNdp5ADgh1gg4fd12wo=
-github.com/klauspost/reedsolomon v1.12.0 h1:I5FEp3xSwVCcEh3F5A7dofEfhXdF/bWhQWPH+XwBFno=
+github.com/klauspost/reedsolomon v1.12.1 h1:NhWgum1efX1x58daOBGCFWcxtEhOhXKKl1HAPQUp03Q=
-github.com/klauspost/reedsolomon v1.12.0/go.mod h1:EPLZJeh4l27pUGC3aXOjheaoh1I9yut7xTURiW3LQ9Y=
+github.com/klauspost/reedsolomon v1.12.1/go.mod h1:nEi5Kjb6QqtbofI6s+cbG/j1da11c96IBYBSnVGtuBs=
 github.com/mdlayher/packet v1.1.2 h1:3Up1NG6LZrsgDVn6X4L9Ge/iyRyxFEFD9o6Pr3Q1nQY=
 github.com/mdlayher/socket v0.4.1 h1:eM9y2/jlbs1M615oshPQOHZzj6R6wMT7bX5NPiQvn2U=
 github.com/mmcloughlin/avo v0.0.0-20200803215136-443f81d77104/go.mod h1:wqKykBG2QzQDJEzvRkcS8x6MiSJkF52hXZsXcjaB3ls=
@@ -95,6 +97,8 @@ golang.org/x/exp v0.0.0-20190121172915-509febef88a4/go.mod h1:CJ0aWSM057203Lf6IL
 golang.org/x/lint v0.0.0-20181026193005-c67002cb31c3/go.mod h1:UVdnD1Gm6xHRNCYTkRU2/jEulfH38KcIWyp/GAMgvoE=
 golang.org/x/lint v0.0.0-20190227174305-5b3e6a55c961/go.mod h1:wehouNa3lNwaWXcvxsM5YxQ5yQlVC4a0KAMCusXpPoU=
 golang.org/x/lint v0.0.0-20190313153728-d0100b6bd8b3/go.mod h1:6SW0HCj/g11FgYtHlgUYUwCkIfeOF89ocIRzGO/8vkc=
+golang.org/x/lint v0.0.0-20200302205851-738671d3881b/go.mod h1:3xt1FjdF8hUf6vQPIChWIBhFzV8gjjsPE/fR3IyQdNY=
+golang.org/x/mod v0.1.1-0.20191105210325-c90efee705ee/go.mod h1:QqPTAvyqsEbceGzBzNggFXnrqF1CaUcvgkdR5Ot7KZg=
 golang.org/x/mod v0.2.0/go.mod h1:s0Qsj1ACt9ePp/hMypM3fl4fZqREWJwdYDEqhRiZZUA=
 golang.org/x/mod v0.3.0/go.mod h1:s0Qsj1ACt9ePp/hMypM3fl4fZqREWJwdYDEqhRiZZUA=
 golang.org/x/net v0.0.0-20180724234803-3673e40ba225/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
@@ -135,6 +139,7 @@ golang.org/x/tools v0.0.0-20190226205152-f727befe758c/go.mod h1:9Yl7xja0Znq3iFh3
 golang.org/x/tools v0.0.0-20190311212946-11955173bddd/go.mod h1:LCzVGOaR6xXOjkQ3onu1FJEFr0SW1gC7cKk1uF8kGRs=
 golang.org/x/tools v0.0.0-20190524140312-2c0ae7006135/go.mod h1:RgjU9mgBXZiqYHBnxXauZ1Gv1EHHAz9KjViQ78xBX0Q=
 golang.org/x/tools v0.0.0-20191119224855-298f0cb1881e/go.mod h1:b+2E5dAYhXwXZwtnZ6UAqBI28+e2cm9otk0dWdXHAEo=
+golang.org/x/tools v0.0.0-20200130002326-2f3ba24bd6e7/go.mod h1:TB2adYChydJhpapKDTa4BR/hXlZSLoq2Wpct/0txZ28=
 golang.org/x/tools v0.0.0-20200425043458-8463f397d07c/go.mod h1:EkVYQZoAsY45+roYkvgYkIh4xh/qjgUK9TdY2XT94GE=
 golang.org/x/tools v0.0.0-20200808161706-5bf02b21f123/go.mod h1:njjCfa9FT2d7l9Bc6FUM5FLjQPp3cFF28FI3qnDFljA=
 golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=

service/dhcpd/dhcpd.go

@@ -163,12 +163,13 @@ func (d *dhcpd) handleDHCP(serverIP net.IP, mask net.IPMask, pool *Pool) server4
 			replyType = dhcpv4.MessageTypeNak
 		}
 
-		reply, err := dhcpv4.NewReplyFromRequest(m,
+		resp, err := dhcpv4.NewReplyFromRequest(m,
 			dhcpv4.WithMessageType(replyType),
 			dhcpv4.WithNetmask(mask),
 			dhcpv4.WithYourIP(replyIP.AsSlice()),
 			dhcpv4.WithRouter(serverIP),
 			dhcpv4.WithDNS(serverIP),
+			dhcpv4.WithServerIP(serverIP), //
 			// RFC 2131, Section 4.3.1. IP lease time: MUST
 			dhcpv4.WithOption(dhcpv4.OptIPAddressLeaseTime(d.lease)),
 			// RFC 2131, Section 4.3.1. Server Identifier: MUST
@@ -179,14 +180,14 @@ func (d *dhcpd) handleDHCP(serverIP net.IP, mask net.IPMask, pool *Pool) server4
 			return
 		}
 
-		if _, err := conn.WriteTo(reply.ToBytes(), peer); err != nil {
+		if err := reply(d.iface, resp); err != nil {
 			log.F("[dpcpd] %s: could not write to %v(%v): %s",
-				d.name, reply.ClientHWAddr, peer, err)
+				d.name, resp.ClientHWAddr, peer, err)
 			return
 		}
 
 		log.F("[dpcpd] %s: %s to %v for %v",
-			d.name, replyType, reply.ClientHWAddr, replyIP)
+			d.name, replyType, resp.ClientHWAddr, replyIP)
 
 	}
 }

service/dhcpd/reply.go

@@ -0,0 +1,84 @@
+package dhcpd
+
+import (
+	"encoding/binary"
+	"fmt"
+	"net"
+	"syscall"
+
+	"github.com/insomniacslk/dhcp/dhcpv4"
+
+	"github.com/nadoo/glider/pkg/log"
+)
+
+func reply(iface *net.Interface, resp *dhcpv4.DHCPv4) error {
+	p := [590]byte{12: 0x08, //ethernet layer: 14 bytes
+		14: 0x45, 16: 0x02, 17: 0x40, 22: 0x40, 23: 0x11, //ip layer: 20 bytes
+		35: 67, 37: 68, 38: 0x02, 39: 0x2c, //udp layer: 8 bytes
+	}
+
+	copy(p[0:], resp.ClientHWAddr[0:6])
+	copy(p[6:], iface.HardwareAddr[0:6])
+	copy(p[26:], resp.ServerIPAddr[0:4])
+	copy(p[30:], resp.YourIPAddr[0:4])
+
+	// ip layer checksum
+	checksum := checksum(p[14:34])
+	binary.BigEndian.PutUint16(p[24:], checksum)
+
+	// dhcp payload
+	copy(p[42:], resp.ToBytes())
+
+	// udp layer checksum, set to zero
+	// https://datatracker.ietf.org/doc/html/rfc768
+	// An all zero transmitted checksum  value means that the transmitter generated no
+	// checksum (for debugging or for higher level protocols that don't care).
+
+	fd, err := syscall.Socket(syscall.AF_PACKET, syscall.SOCK_RAW, 0)
+	if err != nil {
+		return fmt.Errorf("cannot open socket: %v", err)
+	}
+	defer func() {
+		err = syscall.Close(fd)
+		if err != nil {
+			log.F("dhcpd: cannot close socket: %v", err)
+		}
+	}()
+
+	err = syscall.SetsockoptInt(fd, syscall.SOL_SOCKET, syscall.SO_REUSEADDR, 1)
+	if err != nil {
+		log.F("dhcpd: cannot set option for socket: %v", err)
+	}
+
+	var hwAddr [8]byte
+	copy(hwAddr[0:6], resp.ClientHWAddr[0:6])
+	ethAddr := syscall.SockaddrLinklayer{
+		Protocol: 0,
+		Ifindex:  iface.Index,
+		Halen:    6,
+		Addr:     hwAddr,
+	}
+	err = syscall.Sendto(fd, p[:], 0, &ethAddr)
+	if err != nil {
+		return fmt.Errorf("cannot send frame via socket: %v", err)
+	}
+	return nil
+}
+
+func checksum(bytes []byte) uint16 {
+	var csum uint32
+	for i := 0; i < len(bytes); i += 2 {
+		csum += uint32(bytes[i]) << 8
+		csum += uint32(bytes[i+1])
+	}
+	for {
+		// Break when sum is less or equals to 0xFFFF
+		if csum <= 65535 {
+			break
+		}
+		// Add carry to the sum
+		csum = (csum >> 16) + uint32(uint16(csum))
+	}
+	// Flip all the bits
+	return ^uint16(csum)
+}