dns/udp_linux.go

221 lines
5.9 KiB
Go

// +build linux,!appengine
package dns
// See:
// * http://stackoverflow.com/questions/3062205/setting-the-source-ip-for-a-udp-socket and
// * http://blog.powerdns.com/2012/10/08/on-binding-datagram-udp-sockets-to-the-any-addresses/
//
// Why do we need this: When listening on 0.0.0.0 with UDP so kernel decides what is the outgoing
// interface, this might not always be the correct one. This code will make sure the egress
// packet's interface matched the ingress' one.
import (
"net"
"syscall"
"unsafe"
"github.com/miekg/dns/internal/socket"
)
const (
sizeofInet6Pktinfo = 0x14
sizeofInetPktinfo = 0xc
protocolIP = 0
protocolIPv6 = 41
)
type inetPktinfo struct {
Ifindex int32
Spec_dst [4]byte /* in_addr */
Addr [4]byte /* in_addr */
}
type inet6Pktinfo struct {
Addr [16]byte /* in6_addr */
Ifindex int32
}
type inetControlMessage struct {
Src net.IP // source address, specifying only
Dst net.IP // destination address, receiving only
}
// setUDPSocketOptions sets the UDP socket options.
// This function is implemented on a per platform basis. See udp_*.go for more details
func setUDPSocketOptions(conn *net.UDPConn) error {
sa, err := getUDPSocketName(conn)
if err != nil {
return err
}
switch sa.(type) {
case *syscall.SockaddrInet6:
v6only, err := getUDPSocketOptions6Only(conn)
if err != nil {
return err
}
setUDPSocketOptions6(conn)
if !v6only {
setUDPSocketOptions4(conn)
}
case *syscall.SockaddrInet4:
setUDPSocketOptions4(conn)
}
return nil
}
// setUDPSocketOptions4 prepares the v4 socket for sessions.
func setUDPSocketOptions4(conn *net.UDPConn) error {
file, err := conn.File()
if err != nil {
return err
}
if err := syscall.SetsockoptInt(int(file.Fd()), syscall.IPPROTO_IP, syscall.IP_PKTINFO, 1); err != nil {
file.Close()
return err
}
// Calling File() above results in the connection becoming blocking, we must fix that.
// See https://github.com/miekg/dns/issues/279
err = syscall.SetNonblock(int(file.Fd()), true)
if err != nil {
file.Close()
return err
}
file.Close()
return nil
}
// setUDPSocketOptions6 prepares the v6 socket for sessions.
func setUDPSocketOptions6(conn *net.UDPConn) error {
file, err := conn.File()
if err != nil {
return err
}
if err := syscall.SetsockoptInt(int(file.Fd()), syscall.IPPROTO_IPV6, syscall.IPV6_RECVPKTINFO, 1); err != nil {
file.Close()
return err
}
err = syscall.SetNonblock(int(file.Fd()), true)
if err != nil {
file.Close()
return err
}
file.Close()
return nil
}
// getUDPSocketOption6Only return true if the socket is v6 only and false when it is v4/v6 combined
// (dualstack).
func getUDPSocketOptions6Only(conn *net.UDPConn) (bool, error) {
file, err := conn.File()
if err != nil {
return false, err
}
// dual stack. See http://stackoverflow.com/questions/1618240/how-to-support-both-ipv4-and-ipv6-connections
v6only, err := syscall.GetsockoptInt(int(file.Fd()), syscall.IPPROTO_IPV6, syscall.IPV6_V6ONLY)
if err != nil {
file.Close()
return false, err
}
file.Close()
return v6only == 1, nil
}
func getUDPSocketName(conn *net.UDPConn) (syscall.Sockaddr, error) {
file, err := conn.File()
if err != nil {
return nil, err
}
defer file.Close()
return syscall.Getsockname(int(file.Fd()))
}
// marshalInetPacketInfo marshals a ipv4 control message, returning
// the byte slice for the next marshal, if any
func marshalInetPacketInfo(b []byte, cm *inetControlMessage) []byte {
m := socket.ControlMessage(b)
m.MarshalHeader(protocolIP, syscall.IP_PKTINFO, sizeofInetPktinfo)
if cm != nil {
pi := (*inetPktinfo)(unsafe.Pointer(&m.Data(sizeofInetPktinfo)[0]))
if ip := cm.Src.To4(); ip != nil {
copy(pi.Spec_dst[:], ip)
}
}
return m.Next(sizeofInetPktinfo)
}
// marshalInet6PacketInfo marshals a ipv6 control message, returning
// the byte slice for the next marshal, if any
func marshalInet6PacketInfo(b []byte, cm *inetControlMessage) []byte {
m := socket.ControlMessage(b)
m.MarshalHeader(protocolIPv6, syscall.IPV6_PKTINFO, sizeofInet6Pktinfo)
if cm != nil {
pi := (*inet6Pktinfo)(unsafe.Pointer(&m.Data(sizeofInet6Pktinfo)[0]))
if ip := cm.Src.To16(); ip != nil && ip.To4() == nil {
copy(pi.Addr[:], ip)
}
}
return m.Next(sizeofInet6Pktinfo)
}
func parseInetPacketInfo(cm *inetControlMessage, b []byte) {
pi := (*inetPktinfo)(unsafe.Pointer(&b[0]))
if len(cm.Dst) < net.IPv4len {
cm.Dst = make(net.IP, net.IPv4len)
}
copy(cm.Dst, pi.Addr[:])
}
func parseInet6PacketInfo(cm *inetControlMessage, b []byte) {
pi := (*inet6Pktinfo)(unsafe.Pointer(&b[0]))
if len(cm.Dst) < net.IPv6len {
cm.Dst = make(net.IP, net.IPv6len)
}
copy(cm.Dst, pi.Addr[:])
}
// parseUDPSocketDst takes out-of-band data from ReadMsgUDP and parses it for
// the Dst address
func parseUDPSocketDst(oob []byte) (net.IP, error) {
cm := new(inetControlMessage)
ms, err := socket.ControlMessage(oob).Parse()
if err != nil {
return nil, err
}
for _, m := range ms {
lvl, typ, l, err := m.ParseHeader()
if err != nil {
return nil, err
}
if lvl == protocolIPv6 { // IPv6
if typ == syscall.IPV6_PKTINFO && l >= sizeofInet6Pktinfo {
parseInet6PacketInfo(cm, m.Data(l))
}
} else if lvl == protocolIP { // IPv4
if typ == syscall.IP_PKTINFO && l >= sizeofInetPktinfo {
parseInetPacketInfo(cm, m.Data(l))
}
}
}
return cm.Dst, nil
}
// marshalUDPSocketSrc takes the given src address and returns out-of-band data
// to give to WriteMsgUDP
func marshalUDPSocketSrc(src net.IP) []byte {
var oob []byte
// If the dst is definitely an ipv6, then use ipv6 control to respond
// otherwise use ipv4 because the ipv6 marshal ignores ipv4 messages.
// See marshalInet6PacketInfo
cm := new(inetControlMessage)
cm.Src = src
if src.To4() == nil {
oob = make([]byte, socket.ControlMessageSpace(sizeofInet6Pktinfo))
marshalInet6PacketInfo(oob, cm)
} else {
oob = make([]byte, socket.ControlMessageSpace(sizeofInetPktinfo))
marshalInetPacketInfo(oob, cm)
}
return oob
}