fix(socks5): select only offered authentication methods

proxy/socks5/server.go

@@ -4,6 +4,7 @@ import (
 	"errors"
 	"io"
 	"net"
+	"slices"
 	"strings"
 	"sync"
 	"time"
@@ -208,8 +209,19 @@ func (s *Socks5) handshake(c net.Conn) (socks.Addr, error) {
 		return nil, err
 	}
 
-	// write VER METHOD
+	method := byte(socks.AuthNone)
 	if s.user != "" && s.password != "" {
+		method = socks.AuthPassword
+	}
+	if !slices.Contains(buf[:nmethods], method) {
+		if _, err := c.Write([]byte{Version, 0xff}); err != nil {
+			return nil, err
+		}
+		return nil, errors.New("no acceptable authentication method")
+	}
+
+	// write VER METHOD
+	if method == socks.AuthPassword {
 		_, err := c.Write([]byte{Version, socks.AuthPassword})
 		if err != nil {
 			return nil, err

proxy/socks5/server_test.go

@@ -0,0 +1,56 @@
+package socks5
+
+import (
+	"io"
+	"net"
+	"testing"
+	"time"
+
+	"github.com/nadoo/glider/pkg/socks"
+)
+
+func TestHandshakeSelectsOfferedMethod(t *testing.T) {
+	for _, tt := range []struct {
+		name     string
+		user     string
+		password string
+		methods  []byte
+		want     byte
+	}{
+		{name: "no authentication", methods: []byte{socks.AuthNone}, want: socks.AuthNone},
+		{name: "password authentication", user: "user", password: "pass", methods: []byte{socks.AuthPassword}, want: socks.AuthPassword},
+		{name: "password offered second", user: "user", password: "pass", methods: []byte{socks.AuthNone, socks.AuthPassword}, want: socks.AuthPassword},
+		{name: "no supported method", methods: []byte{0x80}, want: 0xff},
+		{name: "no methods", want: 0xff},
+		{name: "password not offered", user: "user", password: "pass", methods: []byte{socks.AuthNone}, want: 0xff},
+		{name: "no-auth not offered", methods: []byte{socks.AuthPassword}, want: 0xff},
+	} {
+		t.Run(tt.name, func(t *testing.T) {
+			client, server := net.Pipe()
+			t.Cleanup(func() { client.Close(); server.Close() })
+			client.SetDeadline(time.Now().Add(3 * time.Second))
+			done := make(chan error, 1)
+			go func() {
+				s := &Socks5{user: tt.user, password: tt.password}
+				_, err := s.handshake(server)
+				server.Close()
+				done <- err
+			}()
+			greeting := append([]byte{Version, byte(len(tt.methods))}, tt.methods...)
+			if _, err := client.Write(greeting); err != nil {
+				t.Fatal(err)
+			}
+			var reply [2]byte
+			if _, err := io.ReadFull(client, reply[:]); err != nil {
+				t.Fatal(err)
+			}
+			if reply != [2]byte{Version, tt.want} {
+				t.Errorf("method reply = %v, want [%d %d]", reply, Version, tt.want)
+			}
+			client.Close()
+			if err := <-done; err == nil {
+				t.Error("incomplete handshake unexpectedly succeeded")
+			}
+		})
+	}
+}