AdGuardHome/internal/dhcpd/checkother.go

287 lines
7.6 KiB
Go

// +build aix darwin dragonfly freebsd linux netbsd openbsd solaris
package dhcpd
import (
"bytes"
"fmt"
"net"
"os"
"runtime"
"time"
"github.com/AdguardTeam/golibs/log"
"github.com/insomniacslk/dhcp/dhcpv4"
"github.com/insomniacslk/dhcp/dhcpv4/nclient4"
"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) (ok bool, err error) {
iface, err := net.InterfaceByName(ifaceName)
if err != nil {
return false, fmt.Errorf("couldn't find interface by name %s: %w", ifaceName, err)
}
ifaceIPNet, err := ifaceIPAddrs(iface, ipVersion4)
if err != nil {
return false, fmt.Errorf("getting ipv4 addrs for iface %s: %w", ifaceName, err)
}
if len(ifaceIPNet) == 0 {
return false, fmt.Errorf("interface %s has no ipv4 addresses", ifaceName)
}
// TODO(a.garipov): Find out what this is about. Perhaps this
// information is outdated or at least incomplete.
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: %w", 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, fmt.Errorf("couldn't resolve UDP address %s: %w", src, err)
}
if !udpAddr.IP.To4().Equal(srcIP) {
return false, fmt.Errorf("resolved UDP address is not %s: %w", src, err)
}
// resolve 255.255.255.255:67
dstAddr, err := net.ResolveUDPAddr("udp4", dst)
if err != nil {
return false, fmt.Errorf("couldn't resolve UDP address %s: %w", dst, err)
}
// 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, fmt.Errorf("couldn't listen on :68: %w", err)
}
if c != nil {
defer c.Close()
}
// send to 255.255.255.255:67
_, err = c.WriteTo(req.ToBytes(), dstAddr)
if err != nil {
return false, fmt.Errorf("couldn't send a packet to %s: %w", dst, err)
}
for {
var next bool
ok, next, err = tryConn4(req, c, iface)
if next {
if err != nil {
log.Debug("dhcpv4: trying a connection: %s", err)
}
continue
}
if err != nil {
return false, err
}
return ok, nil
}
}
// TODO(a.garipov): Refactor further. Inspect error handling, remove parameter
// next, address the TODO, merge with tryConn6, etc.
func tryConn4(req *dhcpv4.DHCPv4, c net.PacketConn, iface *net.Interface) (ok, next bool, err error) {
// TODO: replicate dhclient's behavior of retrying several times with
// progressively longer timeouts.
log.Tracef("dhcpv4: waiting %v for an answer", defaultDiscoverTime)
b := make([]byte, 1500)
err = c.SetDeadline(time.Now().Add(defaultDiscoverTime))
if err != nil {
return false, false, fmt.Errorf("setting deadline: %w", err)
}
n, _, err := c.ReadFrom(b)
if err != nil {
if isTimeout(err) {
log.Debug("dhcpv4: didn't receive dhcp response")
return false, false, nil
}
return false, false, fmt.Errorf("receiving packet: %w", err)
}
log.Tracef("dhcpv4: received packet, %d bytes", n)
response, err := dhcpv4.FromBytes(b[:n])
if err != nil {
log.Debug("dhcpv4: encoding: %s", err)
return false, true, err
}
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")
return false, true, nil
}
log.Tracef("dhcpv4: the packet is from an active dhcp server")
return true, false, 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) (ok bool, err error) {
iface, err := net.InterfaceByName(ifaceName)
if err != nil {
return false, fmt.Errorf("dhcpv6: net.InterfaceByName: %s: %w", ifaceName, err)
}
ifaceIPNet, err := ifaceIPAddrs(iface, ipVersion6)
if err != nil {
return false, fmt.Errorf("getting ipv6 addrs for iface %s: %w", ifaceName, err)
}
if len(ifaceIPNet) == 0 {
return false, fmt.Errorf("interface %s has no ipv6 addresses", ifaceName)
}
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: %w", err)
}
udpAddr, err := net.ResolveUDPAddr("udp6", src)
if err != nil {
return false, fmt.Errorf("dhcpv6: Couldn't resolve UDP address %s: %w", src, err)
}
if !udpAddr.IP.To16().Equal(srcIP) {
return false, fmt.Errorf("dhcpv6: Resolved UDP address is not %s: %w", src, err)
}
dstAddr, err := net.ResolveUDPAddr("udp6", dst)
if err != nil {
return false, fmt.Errorf("dhcpv6: Couldn't resolve UDP address %s: %w", 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: %w", 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: %w", dst, err)
}
for {
var next bool
ok, next, err = tryConn6(req, c)
if next {
if err != nil {
log.Debug("dhcpv6: trying a connection: %s", err)
}
continue
}
if err != nil {
return false, err
}
return ok, nil
}
}
// TODO(a.garipov): See the comment on tryConn4. Sigh…
func tryConn6(req *dhcpv6.Message, c net.PacketConn) (ok, next bool, err error) {
// TODO: replicate dhclient's behavior of retrying several times with
// progressively longer timeouts.
log.Tracef("dhcpv6: waiting %v for an answer", defaultDiscoverTime)
b := make([]byte, 4096)
err = c.SetDeadline(time.Now().Add(defaultDiscoverTime))
if err != nil {
return false, false, fmt.Errorf("setting deadline: %w", err)
}
n, _, err := c.ReadFrom(b)
if err != nil {
if isTimeout(err) {
log.Debug("dhcpv6: didn't receive dhcp response")
return false, false, nil
}
return false, false, fmt.Errorf("receiving packet: %w", err)
}
log.Tracef("dhcpv6: received packet, %d bytes", n)
response, err := dhcpv6.FromBytes(b[:n])
if err != nil {
log.Debug("dhcpv6: encoding: %s", err)
return false, true, err
}
log.Debug("dhcpv6: received message from server: %s", response.Summary())
cid := req.Options.ClientID()
msg, err := response.GetInnerMessage()
if err != nil {
log.Debug("dhcpv6: resp.GetInnerMessage(): %s", err)
return false, true, err
}
rcid := msg.Options.ClientID()
if !(response.Type() == dhcpv6.MessageTypeAdvertise &&
msg.TransactionID == req.TransactionID &&
rcid != nil &&
cid.Equal(*rcid)) {
log.Debug("dhcpv6: received message from server doesn't match our request")
return false, true, nil
}
log.Tracef("dhcpv6: the packet is from an active dhcp server")
return true, false, nil
}