AdGuardHome/dhcpd/check_other_dhcp.go

216 lines
6.2 KiB
Go

// +build aix darwin dragonfly freebsd linux netbsd openbsd solaris
package dhcpd
import (
"bytes"
"fmt"
"net"
"os"
"runtime"
"time"
"github.com/AdguardTeam/AdGuardHome/dhcpd/nclient4"
"github.com/AdguardTeam/golibs/log"
"github.com/insomniacslk/dhcp/dhcpv4"
"github.com/insomniacslk/dhcp/dhcpv6"
"github.com/insomniacslk/dhcp/dhcpv6/nclient6"
"github.com/insomniacslk/dhcp/iana"
)
// CheckIfOtherDHCPServersPresentV4 sends a DHCP request to the specified network interface,
// and waits for a response for a period defined by defaultDiscoverTime
func CheckIfOtherDHCPServersPresentV4(ifaceName string) (bool, error) {
iface, err := net.InterfaceByName(ifaceName)
if err != nil {
return false, wrapErrPrint(err, "Couldn't find interface by name %s", ifaceName)
}
// get ipv4 address of an interface
ifaceIPNet := getIfaceIPv4(*iface)
if len(ifaceIPNet) == 0 {
return false, fmt.Errorf("couldn't find IPv4 address of interface %s %+v", ifaceName, iface)
}
if runtime.GOOS == "darwin" {
return false, fmt.Errorf("can't find DHCP server: not supported on macOS")
}
srcIP := ifaceIPNet[0]
src := net.JoinHostPort(srcIP.String(), "68")
dst := "255.255.255.255:67"
hostname, _ := os.Hostname()
req, err := dhcpv4.NewDiscovery(iface.HardwareAddr)
if err != nil {
return false, fmt.Errorf("dhcpv4.NewDiscovery: %s", err)
}
req.Options.Update(dhcpv4.OptClientIdentifier(iface.HardwareAddr))
req.Options.Update(dhcpv4.OptHostName(hostname))
// resolve 0.0.0.0:68
udpAddr, err := net.ResolveUDPAddr("udp4", src)
if err != nil {
return false, wrapErrPrint(err, "Couldn't resolve UDP address %s", src)
}
if !udpAddr.IP.To4().Equal(srcIP) {
return false, wrapErrPrint(err, "Resolved UDP address is not %s", src)
}
// resolve 255.255.255.255:67
dstAddr, err := net.ResolveUDPAddr("udp4", dst)
if err != nil {
return false, wrapErrPrint(err, "Couldn't resolve UDP address %s", dst)
}
// bind to 0.0.0.0:68
log.Tracef("Listening to udp4 %+v", udpAddr)
c, err := nclient4.NewRawUDPConn(ifaceName, 68)
if err != nil {
return false, wrapErrPrint(err, "Couldn't listen on :68")
}
if c != nil {
defer c.Close()
}
// send to 255.255.255.255:67
_, err = c.WriteTo(req.ToBytes(), dstAddr)
if err != nil {
return false, wrapErrPrint(err, "Couldn't send a packet to %s", dst)
}
for {
// wait for answer
log.Tracef("Waiting %v for an answer", defaultDiscoverTime)
// TODO: replicate dhclient's behaviour of retrying several times with progressively bigger timeouts
b := make([]byte, 1500)
_ = c.SetReadDeadline(time.Now().Add(defaultDiscoverTime))
n, _, err := c.ReadFrom(b)
if isTimeout(err) {
// timed out -- no DHCP servers
log.Debug("DHCPv4: didn't receive DHCP response")
return false, nil
}
if err != nil {
return false, wrapErrPrint(err, "Couldn't receive packet")
}
log.Tracef("Received packet (%v bytes)", n)
response, err := dhcpv4.FromBytes(b[:n])
if err != nil {
log.Debug("DHCPv4: dhcpv4.FromBytes: %s", err)
continue
}
log.Debug("DHCPv4: received message from server: %s", response.Summary())
if !(response.OpCode == dhcpv4.OpcodeBootReply &&
response.HWType == iana.HWTypeEthernet &&
bytes.Equal(response.ClientHWAddr, iface.HardwareAddr) &&
bytes.Equal(response.TransactionID[:], req.TransactionID[:]) &&
response.Options.Has(dhcpv4.OptionDHCPMessageType)) {
log.Debug("DHCPv4: received message from server doesn't match our request")
continue
}
log.Tracef("The packet is from an active DHCP server")
// that's a DHCP server there
return true, nil
}
}
// CheckIfOtherDHCPServersPresentV6 sends a DHCP request to the specified network interface,
// and waits for a response for a period defined by defaultDiscoverTime
func CheckIfOtherDHCPServersPresentV6(ifaceName string) (bool, error) {
iface, err := net.InterfaceByName(ifaceName)
if err != nil {
return false, fmt.Errorf("DHCPv6: net.InterfaceByName: %s: %s", ifaceName, err)
}
ifaceIPNet := getIfaceIPv6(*iface)
if len(ifaceIPNet) == 0 {
return false, fmt.Errorf("DHCPv6: couldn't find IPv6 address of interface %s %+v", ifaceName, iface)
}
srcIP := ifaceIPNet[0]
src := net.JoinHostPort(srcIP.String(), "546")
dst := "[ff02::1:2]:547"
req, err := dhcpv6.NewSolicit(iface.HardwareAddr)
if err != nil {
return false, fmt.Errorf("DHCPv6: dhcpv6.NewSolicit: %s", err)
}
udpAddr, err := net.ResolveUDPAddr("udp6", src)
if err != nil {
return false, wrapErrPrint(err, "DHCPv6: Couldn't resolve UDP address %s", src)
}
if !udpAddr.IP.To16().Equal(srcIP) {
return false, wrapErrPrint(err, "DHCPv6: Resolved UDP address is not %s", src)
}
dstAddr, err := net.ResolveUDPAddr("udp6", dst)
if err != nil {
return false, fmt.Errorf("DHCPv6: Couldn't resolve UDP address %s: %s", dst, err)
}
log.Debug("DHCPv6: Listening to udp6 %+v", udpAddr)
c, err := nclient6.NewIPv6UDPConn(ifaceName, dhcpv6.DefaultClientPort)
if err != nil {
return false, fmt.Errorf("DHCPv6: Couldn't listen on :546: %s", err)
}
if c != nil {
defer c.Close()
}
_, err = c.WriteTo(req.ToBytes(), dstAddr)
if err != nil {
return false, fmt.Errorf("DHCPv6: Couldn't send a packet to %s: %s", dst, err)
}
for {
log.Debug("DHCPv6: Waiting %v for an answer", defaultDiscoverTime)
b := make([]byte, 4096)
_ = c.SetReadDeadline(time.Now().Add(defaultDiscoverTime))
n, _, err := c.ReadFrom(b)
if isTimeout(err) {
log.Debug("DHCPv6: didn't receive DHCP response")
return false, nil
}
if err != nil {
return false, wrapErrPrint(err, "Couldn't receive packet")
}
log.Debug("DHCPv6: Received packet (%v bytes)", n)
resp, err := dhcpv6.FromBytes(b[:n])
if err != nil {
log.Debug("DHCPv6: dhcpv6.FromBytes: %s", err)
continue
}
log.Debug("DHCPv6: received message from server: %s", resp.Summary())
cid := req.Options.ClientID()
msg, err := resp.GetInnerMessage()
if err != nil {
log.Debug("DHCPv6: resp.GetInnerMessage: %s", err)
continue
}
rcid := msg.Options.ClientID()
if resp.Type() == dhcpv6.MessageTypeAdvertise &&
msg.TransactionID == req.TransactionID &&
rcid != nil &&
cid.Equal(*rcid) {
log.Debug("DHCPv6: The packet is from an active DHCP server")
return true, nil
}
log.Debug("DHCPv6: received message from server doesn't match our request")
}
}