1 files changed, 173 insertions, 0 deletions
diff --git a/dhcpv4/nclient4/conn_linux.go b/dhcpv4/nclient4/conn_linux.go
new file mode 100644
index 0000000..00c8a32
--- /dev/null
+++ b/dhcpv4/nclient4/conn_linux.go
@@ -0,0 +1,173 @@
+// Copyright 2018 the u-root Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build go1.12
+
+package nclient4
+
+import (
+	"fmt"
+	"io"
+	"net"
+	"os"
+
+	"github.com/insomniacslk/dhcp/dhcpv4"
+	"github.com/mdlayher/ethernet"
+	"github.com/mdlayher/raw"
+	"github.com/u-root/u-root/pkg/uio"
+	"golang.org/x/sys/unix"
+)
+
+var (
+	// BroadcastMac is the broadcast MAC address.
+	//
+	// Any UDP packet sent to this address is broadcast on the subnet.
+	BroadcastMac = net.HardwareAddr([]byte{255, 255, 255, 255, 255, 255})
+)
+
+// NewIPv4UDPConn returns a UDP connection bound to both the interface and port
+// given based on a IPv4 DGRAM socket. The UDP connection allows broadcasting.
+//
+// The interface must already be configured.
+func NewIPv4UDPConn(iface string, port int) (net.PacketConn, error) {
+	fd, err := unix.Socket(unix.AF_INET, unix.SOCK_DGRAM, unix.IPPROTO_UDP)
+	if err != nil {
+		return nil, fmt.Errorf("cannot get a UDP socket: %v", err)
+	}
+	f := os.NewFile(uintptr(fd), "")
+	// net.FilePacketConn dups the FD, so we have to close this in any case.
+	defer f.Close()
+
+	// Allow broadcasting.
+	if err := unix.SetsockoptInt(fd, unix.SOL_SOCKET, unix.SO_BROADCAST, 1); err != nil {
+		return nil, fmt.Errorf("cannot set broadcasting on socket: %v", err)
+	}
+	// Allow reusing the addr to aid debugging.
+	if err := unix.SetsockoptInt(fd, unix.SOL_SOCKET, unix.SO_REUSEADDR, 1); err != nil {
+		return nil, fmt.Errorf("cannot set reuseaddr on socket: %v", err)
+	}
+	if len(iface) != 0 {
+		// Bind directly to the interface.
+		if err := dhcpv4.BindToInterface(fd, iface); err != nil {
+			return nil, fmt.Errorf("cannot bind to interface %s: %v", iface, err)
+		}
+	}
+	// Bind to the port.
+	if err := unix.Bind(fd, &unix.SockaddrInet4{Port: port}); err != nil {
+		return nil, fmt.Errorf("cannot bind to port %d: %v", port, err)
+	}
+
+	return net.FilePacketConn(f)
+}
+
+// NewRawUDPConn returns a UDP connection bound to the interface and port
+// given based on a raw packet socket. All packets are broadcasted.
+//
+// The interface can be completely unconfigured.
+func NewRawUDPConn(iface string, port int) (net.PacketConn, error) {
+	ifc, err := net.InterfaceByName(iface)
+	if err != nil {
+		return nil, err
+	}
+	rawConn, err := raw.ListenPacket(ifc, uint16(ethernet.EtherTypeIPv4), &raw.Config{LinuxSockDGRAM: true})
+	if err != nil {
+		return nil, err
+	}
+	return NewBroadcastUDPConn(rawConn, &net.UDPAddr{Port: port}), nil
+}
+
+// BroadcastRawUDPConn uses a raw socket to send UDP packets to the broadcast
+// MAC address.
+type BroadcastRawUDPConn struct {
+	// PacketConn is a raw DGRAM socket.
+	net.PacketConn
+
+	// boundAddr is the address this RawUDPConn is "bound" to.
+	//
+	// Calls to ReadFrom will only return packets destined to this address.
+	boundAddr *net.UDPAddr
+}
+
+// NewBroadcastUDPConn returns a PacketConn that marshals and unmarshals UDP
+// packets, sending them to the broadcast MAC at on rawPacketConn.
+//
+// Calls to ReadFrom will only return packets destined to boundAddr.
+func NewBroadcastUDPConn(rawPacketConn net.PacketConn, boundAddr *net.UDPAddr) net.PacketConn {
+	return &BroadcastRawUDPConn{
+		PacketConn: rawPacketConn,
+		boundAddr:  boundAddr,
+	}
+}
+
+func udpMatch(addr *net.UDPAddr, bound *net.UDPAddr) bool {
+	if bound == nil {
+		return true
+	}
+	if bound.IP != nil && !bound.IP.Equal(addr.IP) {
+		return false
+	}
+	return bound.Port == addr.Port
+}
+
+// ReadFrom implements net.PacketConn.ReadFrom.
+//
+// ReadFrom reads raw IP packets and will try to match them against
+// upc.boundAddr. Any matching packets are returned via the given buffer.
+func (upc *BroadcastRawUDPConn) ReadFrom(b []byte) (int, net.Addr, error) {
+	ipLen := IPv4MaximumHeaderSize
+	udpLen := UDPMinimumSize
+
+	for {
+		pkt := make([]byte, ipLen+udpLen+len(b))
+		n, _, err := upc.PacketConn.ReadFrom(pkt)
+		if err != nil {
+			return 0, nil, err
+		}
+		if n == 0 {
+			return 0, nil, io.EOF
+		}
+		pkt = pkt[:n]
+		buf := uio.NewBigEndianBuffer(pkt)
+
+		// To read the header length, access data directly.
+		ipHdr := IPv4(buf.Data())
+		ipHdr = IPv4(buf.Consume(int(ipHdr.HeaderLength())))
+
+		if ipHdr.TransportProtocol() != UDPProtocolNumber {
+			continue
+		}
+		udpHdr := UDP(buf.Consume(udpLen))
+
+		addr := &net.UDPAddr{
+			IP:   net.IP(ipHdr.DestinationAddress()),
+			Port: int(udpHdr.DestinationPort()),
+		}
+		if !udpMatch(addr, upc.boundAddr) {
+			continue
+		}
+		srcAddr := &net.UDPAddr{
+			IP:   net.IP(ipHdr.SourceAddress()),
+			Port: int(udpHdr.SourcePort()),
+		}
+		return copy(b, buf.ReadAll()), srcAddr, nil
+	}
+}
+
+// WriteTo implements net.PacketConn.WriteTo and broadcasts all packets at the
+// raw socket level.
+//
+// WriteTo wraps the given packet in the appropriate UDP and IP header before
+// sending it on the packet conn.
+func (upc *BroadcastRawUDPConn) WriteTo(b []byte, addr net.Addr) (int, error) {
+	udpAddr, ok := addr.(*net.UDPAddr)
+	if !ok {
+		return 0, fmt.Errorf("must supply UDPAddr")
+	}
+
+	// Using the boundAddr is not quite right here, but it works.
+	packet := udp4pkt(b, udpAddr, upc.boundAddr)
+
+	// Broadcasting is not always right, but hell, what the ARP do I know.
+	return upc.PacketConn.WriteTo(packet, &raw.Addr{HardwareAddr: BroadcastMac})
+}