core/dnsserver: preserve UDP packet destination addresses (#8644)

* core/dnsserver: preserve UDP packet destination addresses Signed-off-by: houyuwushang <180804215+houyuwushang@users.noreply.github.com> * test: modernize reverse UDP reply traversal Signed-off-by: houyuwushang <180804215+houyuwushang@users.noreply.github.com> * test: account for Unix IPv4 source-control capabilities Signed-off-by: houyuwushang <180804215+houyuwushang@users.noreply.github.com> --------- Signed-off-by: houyuwushang <180804215+houyuwushang@users.noreply.github.com>
2026-10-24 11:15:43 -04:00 · 2026-10-21 11:34:18 +08:00
parent e7f823b261
commit 0fe7b08fbb
12 changed files with 1026 additions and 3 deletions
--- a/core/dnsserver/udp_windows.go
+++ b/core/dnsserver/udp_windows.go
@@ -0,0 +1,107 @@
+package dnsserver
+
+import (
+	"encoding/binary"
+	"math"
+	"net"
+	"strconv"
+
+	"golang.org/x/sys/windows"
+)
+
+// WSACMSGHDR contains a native-size length followed by two 32-bit integers.
+// Each control message is aligned to SIZE_T; its length excludes tail padding.
+const udpCmsgWord = strconv.IntSize / 8
+const udpCmsgHeader = udpCmsgWord + 8
+
+var udpOOBSize = udpCmsgAlign(udpCmsgHeader+8) + udpCmsgAlign(udpCmsgHeader+20)
+
+func udpCmsgAlign(n int) int { return (n + udpCmsgWord - 1) & ^(udpCmsgWord - 1) }
+
+func enableUDPPacketInfo(conn *net.UDPConn) bool {
+	raw, err := conn.SyscallConn()
+	if err != nil {
+		return false
+	}
+	var err4, err6 error
+	err = raw.Control(func(fd uintptr) {
+		// Dual-stack sockets need both options to receive both families.
+		err4 = windows.SetsockoptInt(windows.Handle(fd), windows.IPPROTO_IP, windows.IP_PKTINFO, 1)
+		err6 = windows.SetsockoptInt(windows.Handle(fd), windows.IPPROTO_IPV6, windows.IPV6_PKTINFO, 1)
+	})
+	return err == nil && (err4 == nil || err6 == nil)
+}
+
+func parseUDPPacketInfo(oob []byte, flags int) udpPacketInfo {
+	if flags&windows.MSG_CTRUNC != 0 {
+		return udpPacketInfo{}
+	}
+	for len(oob) >= udpCmsgHeader {
+		var length uint64
+		if udpCmsgWord == 8 {
+			length = binary.NativeEndian.Uint64(oob)
+		} else {
+			length = uint64(binary.NativeEndian.Uint32(oob))
+		}
+		if length < udpCmsgHeader || length > uint64(len(oob)) || length > math.MaxInt32 {
+			return udpPacketInfo{}
+		}
+		level := binary.NativeEndian.Uint32(oob[udpCmsgWord:])
+		kind := binary.NativeEndian.Uint32(oob[udpCmsgWord+4:])
+		data := oob[udpCmsgHeader:length]
+		ipLen := 0
+		switch {
+		case level == windows.IPPROTO_IP && kind == windows.IP_PKTINFO:
+			ipLen = net.IPv4len
+		case level == windows.IPPROTO_IPV6 && kind == windows.IPV6_PKTINFO:
+			ipLen = net.IPv6len
+		}
+		if ipLen != 0 {
+			if len(data) < ipLen+4 {
+				return udpPacketInfo{}
+			}
+			ifIndex := binary.NativeEndian.Uint32(data[ipLen:])
+			if ifIndex > math.MaxInt32 {
+				return udpPacketInfo{}
+			}
+			return udpPacketInfo{dst: net.IP(data[:ipLen]), ifIndex: int(ifIndex)}
+		}
+		next := udpCmsgAlign(int(length))
+		if next < int(length) || next > len(oob) {
+			break
+		}
+		oob = oob[next:]
+	}
+	return udpPacketInfo{}
+}
+
+func udpSourceControl(info udpPacketInfo) []byte {
+	if info.dst == nil || info.dst.IsUnspecified() || info.dst.IsMulticast() {
+		return nil
+	}
+	ifIndex := info.replyInterface()
+	if ifIndex < 0 || ifIndex > math.MaxInt32 {
+		return nil
+	}
+	ip := info.dst.To4()
+	level, kind := uint32(windows.IPPROTO_IP), uint32(windows.IP_PKTINFO)
+	if ip == nil {
+		ip = info.dst.To16()
+		level, kind = windows.IPPROTO_IPV6, windows.IPV6_PKTINFO
+	}
+	if ip == nil {
+		return nil
+	}
+	length := udpCmsgHeader + len(ip) + 4
+	oob := make([]byte, udpCmsgAlign(length))
+	if udpCmsgWord == 8 {
+		binary.NativeEndian.PutUint64(oob, uint64(length))
+	} else {
+		binary.NativeEndian.PutUint32(oob, uint32(length)) //nolint:gosec // Header plus a 4- or 16-byte IP and a 4-byte interface.
+	}
+	binary.NativeEndian.PutUint32(oob[udpCmsgWord:], level)
+	binary.NativeEndian.PutUint32(oob[udpCmsgWord+4:], kind)
+	copy(oob[udpCmsgHeader:], ip)
+	binary.NativeEndian.PutUint32(oob[udpCmsgHeader+len(ip):], uint32(ifIndex))
+	return oob
+}