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net/stunserver: reply from the address at which STUN was received

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Updates #15014

Signed-off-by: James Tucker <james@tailscale.com>
This commit is contained in:
James Tucker 2025-02-13 13:35:28 -08:00
parent 7aef4fd44d
commit ea5f78ceca
No known key found for this signature in database
1 changed files with 43 additions and 8 deletions
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51
net/stunserver/stunserver.go
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@ -15,6 +15,8 @@ import (
"net/netip"
"time"
"golang.org/x/net/ipv4"
"golang.org/x/net/ipv6"
"tailscale.com/metrics"
"tailscale.com/net/stun"
)
@ -70,13 +72,17 @@ func (s *STUNServer) Listen(listenAddr string) error {
// Serve starts serving responses to STUN requests. Listen must be called before Serve.
func (s *STUNServer) Serve() error {
var buf [64 << 10]byte
var oob [4096]byte
var (
n int
ua *net.UDPAddr
err error
n, oobn int
remote netip.AddrPort
local net.IP
err error
cm4 ipv4.ControlMessage
cm6 ipv6.ControlMessage
)
for {
n, ua, err = s.pc.ReadFromUDP(buf[:])
n, oobn, _, remote, err = s.pc.ReadMsgUDPAddrPort(buf[:], oob[:])
if err != nil {
if errors.Is(err, io.EOF) || errors.Is(err, net.ErrClosed) {
return nil
@ -86,6 +92,22 @@ func (s *STUNServer) Serve() error {
stunReadError.Add(1)
continue
}
if remote.Addr().Is4() {
err = cm4.Parse(oob[:oobn])
} else {
err = cm6.Parse(oob[:oobn])
}
if err != nil {
log.Printf("parse control msg error: %v", err)
continue
}
if remote.Addr().Is4() {
local = cm4.Dst
} else {
local = cm6.Dst
}
pkt := buf[:n]
if !stun.Is(pkt) {
stunNotSTUN.Add(1)
@ -96,14 +118,27 @@ func (s *STUNServer) Serve() error {
stunNotSTUN.Add(1)
continue
}
if ua.IP.To4() != nil {
if remote.Addr().Is4() {
stunIPv4.Add(1)
} else {
stunIPv6.Add(1)
}
addr, _ := netip.AddrFromSlice(ua.IP)
res := stun.Response(txid, netip.AddrPortFrom(addr, uint16(ua.Port)))
_, err = s.pc.WriteTo(res, ua)
res := stun.Response(txid, remote)
// TODO(raggi): send upstream patch to provide a way to serialize a
// control message into an existng buffer.
if remote.Addr().Is4() {
cm4 = ipv4.ControlMessage{
Src: local,
}
oobn = copy(oob[:], cm4.Marshal())
} else {
cm6 = ipv6.ControlMessage{
Src: local,
}
oobn = copy(oob[:], cm6.Marshal())
}
_, _, err = s.pc.WriteMsgUDPAddrPort(res, oob[:oobn], remote)
if err != nil {
stunWriteError.Add(1)
} else {