ping: Fix unprivileged response on linux

ping/socket_linux_unprivileged.go

@@ -0,0 +1,173 @@
+package ping
+
+import (
+	"context"
+	"net"
+	"net/netip"
+	"os"
+	"time"
+
+	"github.com/sagernet/sing-tun/internal/gtcpip/checksum"
+	"github.com/sagernet/sing-tun/internal/gtcpip/header"
+	"github.com/sagernet/sing/common/atomic"
+	"github.com/sagernet/sing/common/buf"
+	"github.com/sagernet/sing/common/control"
+	M "github.com/sagernet/sing/common/metadata"
+)
+
+type UnprivilegedConn struct {
+	ctx           context.Context
+	cancel        context.CancelFunc
+	controlFunc   control.Func
+	destination   netip.Addr
+	receiveChan   chan *unprivilegedResponse
+	readDeadline  atomic.TypedValue[time.Time]
+	writeDeadline atomic.TypedValue[time.Time]
+}
+
+type unprivilegedResponse struct {
+	Buffer *buf.Buffer
+	Cmsg   *buf.Buffer
+	Addr   netip.Addr
+}
+
+func newUnprivilegedConn(ctx context.Context, controlFunc control.Func, destination netip.Addr) (net.Conn, error) {
+	conn, err := connect(false, controlFunc, destination)
+	if err != nil {
+		return nil, err
+	}
+	conn.Close()
+	ctx, cancel := context.WithCancel(ctx)
+	return &UnprivilegedConn{
+		ctx:         ctx,
+		cancel:      cancel,
+		controlFunc: controlFunc,
+		destination: destination,
+		receiveChan: make(chan *unprivilegedResponse),
+	}, nil
+}
+
+func (c *UnprivilegedConn) Read(b []byte) (n int, err error) {
+	select {
+	case packet := <-c.receiveChan:
+		n = copy(b, packet.Buffer.Bytes())
+		packet.Buffer.Release()
+		packet.Cmsg.Release()
+		return
+	case <-c.ctx.Done():
+		return 0, os.ErrClosed
+	}
+}
+
+func (c *UnprivilegedConn) ReadMsg(b []byte, oob []byte) (n, oobn int, addr netip.Addr, err error) {
+	select {
+	case packet := <-c.receiveChan:
+		n = copy(b, packet.Buffer.Bytes())
+		oobn = copy(oob, packet.Cmsg.Bytes())
+		addr = packet.Addr
+		packet.Buffer.Release()
+		packet.Cmsg.Release()
+		return
+	case <-c.ctx.Done():
+		return 0, 0, netip.Addr{}, os.ErrClosed
+	}
+}
+
+func (c *UnprivilegedConn) Write(b []byte) (n int, err error) {
+	conn, err := connect(false, c.controlFunc, c.destination)
+	if err != nil {
+		return
+	}
+	var identifier uint16
+	if !c.destination.Is6() {
+		icmpHdr := header.ICMPv4(b)
+		identifier = icmpHdr.Ident()
+	} else {
+		icmpHdr := header.ICMPv6(b)
+		identifier = icmpHdr.Ident()
+	}
+	if readDeadline := c.readDeadline.Load(); !readDeadline.IsZero() {
+		conn.SetReadDeadline(readDeadline)
+	}
+	if writeDeadline := c.writeDeadline.Load(); !writeDeadline.IsZero() {
+		conn.SetWriteDeadline(writeDeadline)
+	}
+	n, err = conn.Write(b)
+	if err != nil {
+		conn.Close()
+		return
+	}
+	go c.fetchResponse(conn, identifier)
+	return
+}
+
+func (c *UnprivilegedConn) fetchResponse(conn net.Conn, identifier uint16) {
+	done := make(chan struct{})
+	defer close(done)
+	go func() {
+		select {
+		case <-c.ctx.Done():
+		case <-done:
+		}
+		conn.Close()
+	}()
+	buffer := buf.NewPacket()
+	cmsgBuffer := buf.NewSize(1024)
+	n, oobN, _, addr, err := conn.(*net.UDPConn).ReadMsgUDPAddrPort(buffer.FreeBytes(), cmsgBuffer.FreeBytes())
+	if err != nil {
+		buffer.Release()
+		cmsgBuffer.Release()
+		return
+	}
+	buffer.Truncate(n)
+	cmsgBuffer.Truncate(oobN)
+	if !c.destination.Is6() {
+		icmpHdr := header.ICMPv4(buffer.Bytes())
+		icmpHdr.SetIdent(identifier)
+		icmpHdr.SetChecksum(0)
+		icmpHdr.SetChecksum(header.ICMPv4Checksum(icmpHdr[:header.ICMPv4MinimumSize], checksum.Checksum(icmpHdr.Payload(), 0)))
+	} else {
+		icmpHdr := header.ICMPv6(buffer.Bytes())
+		icmpHdr.SetIdent(identifier)
+		// offload checksum here since we don't have source address here
+	}
+	select {
+	case c.receiveChan <- &unprivilegedResponse{
+		Buffer: buffer,
+		Cmsg:   cmsgBuffer,
+		Addr:   addr.Addr(),
+	}:
+	case <-c.ctx.Done():
+		buffer.Release()
+		cmsgBuffer.Release()
+	}
+}
+
+func (c *UnprivilegedConn) Close() error {
+	c.cancel()
+	return nil
+}
+
+func (c *UnprivilegedConn) LocalAddr() net.Addr {
+	return M.Socksaddr{}
+}
+
+func (c *UnprivilegedConn) RemoteAddr() net.Addr {
+	return M.SocksaddrFrom(c.destination, 0).UDPAddr()
+}
+
+func (c *UnprivilegedConn) SetDeadline(t time.Time) error {
+	c.readDeadline.Store(t)
+	c.writeDeadline.Store(t)
+	return nil
+}
+
+func (c *UnprivilegedConn) SetReadDeadline(t time.Time) error {
+	c.readDeadline.Store(t)
+	return nil
+}
+
+func (c *UnprivilegedConn) SetWriteDeadline(t time.Time) error {
+	c.writeDeadline.Store(t)
+	return nil
+}