117 lines
3.3 KiB
Go
117 lines
3.3 KiB
Go
// +build aix darwin dragonfly freebsd linux netbsd openbsd solaris
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package dhcpd
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import (
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"bytes"
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"fmt"
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"net"
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"os"
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"time"
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"github.com/AdguardTeam/golibs/log"
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"github.com/insomniacslk/dhcp/dhcpv4"
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"github.com/insomniacslk/dhcp/iana"
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"golang.org/x/net/ipv4"
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)
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// CheckIfOtherDHCPServersPresent sends a DHCP request to the specified network interface,
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// and waits for a response for a period defined by defaultDiscoverTime
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func CheckIfOtherDHCPServersPresent(ifaceName string) (bool, error) {
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iface, err := net.InterfaceByName(ifaceName)
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if err != nil {
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return false, wrapErrPrint(err, "Couldn't find interface by name %s", ifaceName)
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}
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// get ipv4 address of an interface
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ifaceIPNet := getIfaceIPv4(*iface)
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if len(ifaceIPNet) == 0 {
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return false, fmt.Errorf("couldn't find IPv4 address of interface %s %+v", ifaceName, iface)
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}
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srcIP := ifaceIPNet[0]
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src := net.JoinHostPort(srcIP.String(), "68")
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dst := "255.255.255.255:67"
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hostname, _ := os.Hostname()
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req, err := dhcpv4.NewDiscovery(iface.HardwareAddr)
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if err != nil {
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return false, fmt.Errorf("dhcpv4.NewDiscovery: %s", err)
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}
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req.Options.Update(dhcpv4.OptClientIdentifier(iface.HardwareAddr))
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req.Options.Update(dhcpv4.OptHostName(hostname))
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// resolve 0.0.0.0:68
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udpAddr, err := net.ResolveUDPAddr("udp4", src)
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if err != nil {
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return false, wrapErrPrint(err, "Couldn't resolve UDP address %s", src)
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}
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if !udpAddr.IP.To4().Equal(srcIP) {
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return false, wrapErrPrint(err, "Resolved UDP address is not %s", src)
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}
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// resolve 255.255.255.255:67
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dstAddr, err := net.ResolveUDPAddr("udp4", dst)
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if err != nil {
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return false, wrapErrPrint(err, "Couldn't resolve UDP address %s", dst)
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}
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// bind to 0.0.0.0:68
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log.Tracef("Listening to udp4 %+v", udpAddr)
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c, err := newBroadcastPacketConn(net.IPv4(0, 0, 0, 0), 68, ifaceName)
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if c != nil {
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defer c.Close()
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}
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if err != nil {
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return false, wrapErrPrint(err, "Couldn't listen on :68")
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}
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// send to 255.255.255.255:67
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cm := ipv4.ControlMessage{}
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_, err = c.WriteTo(req.ToBytes(), &cm, dstAddr)
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if err != nil {
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return false, wrapErrPrint(err, "Couldn't send a packet to %s", dst)
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}
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for {
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// wait for answer
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log.Tracef("Waiting %v for an answer", defaultDiscoverTime)
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// TODO: replicate dhclient's behaviour of retrying several times with progressively bigger timeouts
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b := make([]byte, 1500)
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_ = c.SetReadDeadline(time.Now().Add(defaultDiscoverTime))
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n, _, _, err := c.ReadFrom(b)
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if isTimeout(err) {
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// timed out -- no DHCP servers
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return false, nil
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}
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if err != nil {
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return false, wrapErrPrint(err, "Couldn't receive packet")
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}
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log.Tracef("Received packet (%v bytes)", n)
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response, err := dhcpv4.FromBytes(b[:n])
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if err != nil {
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log.Debug("DHCPv4: dhcpv4.FromBytes: %s", err)
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continue
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}
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log.Debug("DHCPv4: received message from server: %s", response.Summary())
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if !(response.OpCode == dhcpv4.OpcodeBootReply &&
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response.HWType == iana.HWTypeEthernet &&
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bytes.Equal(response.ClientHWAddr, iface.HardwareAddr) &&
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bytes.Equal(response.TransactionID[:], req.TransactionID[:]) &&
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response.Options.Has(dhcpv4.OptionDHCPMessageType)) {
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log.Debug("DHCPv4: received message from server doesn't match our request")
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continue
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}
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log.Tracef("The packet is from an active DHCP server")
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// that's a DHCP server there
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return true, nil
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}
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}
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