AdGuardHome/internal/dhcpd/routeradv.go

288 lines
6.8 KiB
Go

package dhcpd
import (
"encoding/binary"
"fmt"
"net"
"sync/atomic"
"time"
"github.com/AdguardTeam/golibs/log"
"github.com/AdguardTeam/golibs/netutil"
"golang.org/x/net/icmp"
"golang.org/x/net/ipv6"
)
type raCtx struct {
raAllowSLAAC bool // send RA packets without MO flags
raSLAACOnly bool // send RA packets with MO flags
ipAddr net.IP // source IP address (link-local-unicast)
dnsIPAddr net.IP // IP address for DNS Server option
prefixIPAddr net.IP // IP address for Prefix option
ifaceName string
iface *net.Interface
packetSendPeriod time.Duration // how often RA packets are sent
conn *icmp.PacketConn // ICMPv6 socket
stop atomic.Value // stop the packet sending loop
}
type icmpv6RA struct {
managedAddressConfiguration bool
otherConfiguration bool
prefix net.IP
prefixLen int
sourceLinkLayerAddress net.HardwareAddr
recursiveDNSServer net.IP
mtu uint32
}
// hwAddrToLinkLayerAddr converts a hardware address into a form required by
// RFC4861. That is, a byte slice of length divisible by 8.
//
// See https://tools.ietf.org/html/rfc4861#section-4.6.1.
func hwAddrToLinkLayerAddr(hwa net.HardwareAddr) (lla []byte, err error) {
err = netutil.ValidateMAC(hwa)
if err != nil {
// Don't wrap the error, because it already contains enough
// context.
return nil, err
}
if len(hwa) == 6 || len(hwa) == 8 {
lla = make([]byte, 8)
copy(lla, hwa)
return lla, nil
}
// Assume that netutil.ValidateMAC prevents lengths other than 20 by
// now.
lla = make([]byte, 24)
copy(lla, hwa)
return lla, nil
}
// Create an ICMPv6.RouterAdvertisement packet with all necessary options.
// Data scheme:
//
// ICMPv6:
// - type[1]
// - code[1]
// - chksum[2]
// - body (RouterAdvertisement):
// - Cur Hop Limit[1]
// - Flags[1]: MO......
// - Router Lifetime[2]
// - Reachable Time[4]
// - Retrans Timer[4]
// - Option=Prefix Information(3):
// - Type[1]
// - Length * 8bytes[1]
// - Prefix Length[1]
// - Flags[1]: LA......
// - Valid Lifetime[4]
// - Preferred Lifetime[4]
// - Reserved[4]
// - Prefix[16]
// - Option=MTU(5):
// - Type[1]
// - Length * 8bytes[1]
// - Reserved[2]
// - MTU[4]
// - Option=Source link-layer address(1):
// - Link-Layer Address[8/24]
// - Option=Recursive DNS Server(25):
// - Type[1]
// - Length * 8bytes[1]
// - Reserved[2]
// - Lifetime[4]
// - Addresses of IPv6 Recursive DNS Servers[16]
//
// TODO(a.garipov): Replace with an existing implementation from a dependency.
func createICMPv6RAPacket(params icmpv6RA) (data []byte, err error) {
var lla []byte
lla, err = hwAddrToLinkLayerAddr(params.sourceLinkLayerAddress)
if err != nil {
return nil, fmt.Errorf("converting source link layer address: %w", err)
}
// TODO(a.garipov): Don't use a magic constant here. Refactor the code
// and make all constants named instead of all those comments..
data = make([]byte, 82+len(lla))
i := 0
// ICMPv6:
data[i] = 134 // type
data[i+1] = 0 // code
data[i+2] = 0 // chksum
data[i+3] = 0
i += 4
// RouterAdvertisement:
data[i] = 64 // Cur Hop Limit[1]
i++
data[i] = 0 // Flags[1]: MO......
if params.managedAddressConfiguration {
data[i] |= 0x80
}
if params.otherConfiguration {
data[i] |= 0x40
}
i++
binary.BigEndian.PutUint16(data[i:], 1800) // Router Lifetime[2]
i += 2
binary.BigEndian.PutUint32(data[i:], 0) // Reachable Time[4]
i += 4
binary.BigEndian.PutUint32(data[i:], 0) // Retrans Timer[4]
i += 4
// Option=Prefix Information:
data[i] = 3 // Type
data[i+1] = 4 // Length
i += 2
data[i] = byte(params.prefixLen) // Prefix Length[1]
i++
data[i] = 0xc0 // Flags[1]
i++
binary.BigEndian.PutUint32(data[i:], 3600) // Valid Lifetime[4]
i += 4
binary.BigEndian.PutUint32(data[i:], 3600) // Preferred Lifetime[4]
i += 4
binary.BigEndian.PutUint32(data[i:], 0) // Reserved[4]
i += 4
copy(data[i:], params.prefix[:8]) // Prefix[16]
binary.BigEndian.PutUint32(data[i+8:], 0)
binary.BigEndian.PutUint32(data[i+12:], 0)
i += 16
// Option=MTU:
data[i] = 5 // Type
data[i+1] = 1 // Length
i += 2
binary.BigEndian.PutUint16(data[i:], 0) // Reserved[2]
i += 2
binary.BigEndian.PutUint32(data[i:], params.mtu) // MTU[4]
i += 4
// Option=Source link-layer address:
data[i] = 1 // Type
data[i+1] = 1 // Length
i += 2
copy(data[i:], lla) // Link-Layer Address[8/24]
i += len(lla)
// Option=Recursive DNS Server:
data[i] = 25 // Type
data[i+1] = 3 // Length
i += 2
binary.BigEndian.PutUint16(data[i:], 0) // Reserved[2]
i += 2
binary.BigEndian.PutUint32(data[i:], 3600) // Lifetime[4]
i += 4
copy(data[i:], params.recursiveDNSServer) // Addresses of IPv6 Recursive DNS Servers[16]
return data, nil
}
// Init - initialize RA module
func (ra *raCtx) Init() (err error) {
ra.stop.Store(0)
ra.conn = nil
if !(ra.raAllowSLAAC || ra.raSLAACOnly) {
return nil
}
log.Debug("dhcpv6 ra: source IP address: %s DNS IP address: %s",
ra.ipAddr, ra.dnsIPAddr)
params := icmpv6RA{
managedAddressConfiguration: !ra.raSLAACOnly,
otherConfiguration: !ra.raSLAACOnly,
mtu: uint32(ra.iface.MTU),
prefixLen: 64,
recursiveDNSServer: ra.dnsIPAddr,
sourceLinkLayerAddress: ra.iface.HardwareAddr,
}
params.prefix = make([]byte, 16)
copy(params.prefix, ra.prefixIPAddr[:8]) // /64
var data []byte
data, err = createICMPv6RAPacket(params)
if err != nil {
return fmt.Errorf("creating packet: %w", err)
}
success := false
ipAndScope := ra.ipAddr.String() + "%" + ra.ifaceName
ra.conn, err = icmp.ListenPacket("ip6:ipv6-icmp", ipAndScope)
if err != nil {
return fmt.Errorf("dhcpv6 ra: icmp.ListenPacket: %w", err)
}
defer func() {
if !success {
derr := ra.Close()
if derr != nil {
log.Error("closing context: %s", derr)
}
}
}()
con6 := ra.conn.IPv6PacketConn()
if err = con6.SetHopLimit(255); err != nil {
return fmt.Errorf("dhcpv6 ra: SetHopLimit: %w", err)
}
if err = con6.SetMulticastHopLimit(255); err != nil {
return fmt.Errorf("dhcpv6 ra: SetMulticastHopLimit: %w", err)
}
msg := &ipv6.ControlMessage{
HopLimit: 255,
Src: ra.ipAddr,
IfIndex: ra.iface.Index,
}
addr := &net.UDPAddr{
IP: net.ParseIP("ff02::1"),
}
go func() {
log.Debug("dhcpv6 ra: starting to send periodic RouterAdvertisement packets")
for ra.stop.Load() == 0 {
_, err = con6.WriteTo(data, msg, addr)
if err != nil {
log.Error("dhcpv6 ra: WriteTo: %s", err)
}
time.Sleep(ra.packetSendPeriod)
}
log.Debug("dhcpv6 ra: loop exit")
}()
success = true
return nil
}
// Close closes the module.
func (ra *raCtx) Close() (err error) {
log.Debug("dhcpv6 ra: closing")
ra.stop.Store(1)
if ra.conn != nil {
return ra.conn.Close()
}
return nil
}