Fix TCP_LINGER2 behavior to match linux.

We still deviate a bit from linux in how long we will actually wait in
FIN-WAIT-2. Linux seems to cap it with TIME_WAIT_LEN and it's not completely
obvious as to why it's done that way. For now I think we can ignore that and
fix it if it really is an issue.

PiperOrigin-RevId: 328324922

pkg/sentry/socket/netstack/netstack.go

@@ -1409,8 +1409,12 @@ func getSockOptTCP(t *kernel.Task, ep commonEndpoint, name, outLen int) (marshal
 		if err := ep.GetSockOpt(&v); err != nil {
 			return nil, syserr.TranslateNetstackError(err)
 		}
-
-		lingerTimeout := primitive.Int32(time.Duration(v) / time.Second)
+		var lingerTimeout primitive.Int32
+		if v >= 0 {
+			lingerTimeout = primitive.Int32(time.Duration(v) / time.Second)
+		} else {
+			lingerTimeout = -1
+		}
 		return &lingerTimeout, nil
 
 	case linux.TCP_DEFER_ACCEPT:
@@ -1967,7 +1971,7 @@ func setSockOptTCP(t *kernel.Task, ep commonEndpoint, name int, optVal []byte) *
 			return syserr.ErrInvalidArgument
 		}
 
-		v := usermem.ByteOrder.Uint32(optVal)
+		v := int32(usermem.ByteOrder.Uint32(optVal))
 		return syserr.TranslateNetstackError(ep.SetSockOpt(tcpip.TCPLingerTimeoutOption(time.Second * time.Duration(v))))
 
 	case linux.TCP_DEFER_ACCEPT:

pkg/tcpip/transport/tcp/endpoint.go

@@ -1775,15 +1775,24 @@ func (e *endpoint) SetSockOpt(opt interface{}) *tcpip.Error {
 
 	case tcpip.TCPLingerTimeoutOption:
 		e.LockUser()
-		if v < 0 {
+
+		switch {
+		case v < 0:
 			// Same as effectively disabling TCPLinger timeout.
-			v = 0
-		}
-		// Cap it to MaxTCPLingerTimeout.
-		stkTCPLingerTimeout := tcpip.TCPLingerTimeoutOption(MaxTCPLingerTimeout)
-		if v > stkTCPLingerTimeout {
-			v = stkTCPLingerTimeout
+			v = -1
+		case v == 0:
+			// Same as the stack default.
+			var stackLingerTimeout tcpip.TCPLingerTimeoutOption
+			if err := e.stack.TransportProtocolOption(ProtocolNumber, &stackLingerTimeout); err != nil {
+				panic(fmt.Sprintf("e.stack.TransportProtocolOption(%d, %+v) = %v", ProtocolNumber, &stackLingerTimeout, err))
+			}
+			v = stackLingerTimeout
+		case v > tcpip.TCPLingerTimeoutOption(MaxTCPLingerTimeout):
+			// Cap it to Stack's default TCP_LINGER2 timeout.
+			v = tcpip.TCPLingerTimeoutOption(MaxTCPLingerTimeout)
+		default:
 		}
+
 		e.tcpLingerTimeout = time.Duration(v)
 		e.UnlockUser()
 

pkg/tcpip/transport/tcp/tcp_test.go

@@ -6206,12 +6206,13 @@ func TestTCPLingerTimeout(t *testing.T) {
 		tcpLingerTimeout time.Duration
 		want             time.Duration
 	}{
-		{"NegativeLingerTimeout", -123123, 0},
-		{"ZeroLingerTimeout", 0, 0},
+		{"NegativeLingerTimeout", -123123, -1},
+		// Zero is treated same as the stack's default TCP_LINGER2 timeout.
+		{"ZeroLingerTimeout", 0, tcp.DefaultTCPLingerTimeout},
 		{"InRangeLingerTimeout", 10 * time.Second, 10 * time.Second},
 		// Values > stack's TCPLingerTimeout are capped to the stack's
 		// value. Defaults to tcp.DefaultTCPLingerTimeout(60 seconds)
-		{"AboveMaxLingerTimeout", 125 * time.Second, 120 * time.Second},
+		{"AboveMaxLingerTimeout", tcp.MaxTCPLingerTimeout + 5*time.Second, tcp.MaxTCPLingerTimeout},
 	}
 	for _, tc := range testCases {
 		t.Run(tc.name, func(t *testing.T) {

test/syscalls/linux/socket_ip_tcp_generic.cc

@@ -819,18 +819,37 @@ TEST_P(TCPSocketPairTest, TCPLingerTimeoutDefault) {
   EXPECT_EQ(get, kDefaultTCPLingerTimeout);
 }
 
-TEST_P(TCPSocketPairTest, SetTCPLingerTimeoutZeroOrLess) {
+TEST_P(TCPSocketPairTest, SetTCPLingerTimeoutLessThanZero) {
+  auto sockets = ASSERT_NO_ERRNO_AND_VALUE(NewSocketPair());
+
+  constexpr int kNegative = -1234;
+  EXPECT_THAT(setsockopt(sockets->first_fd(), IPPROTO_TCP, TCP_LINGER2,
+                         &kNegative, sizeof(kNegative)),
+              SyscallSucceedsWithValue(0));
+  int get = INT_MAX;
+  socklen_t get_len = sizeof(get);
+  EXPECT_THAT(
+      getsockopt(sockets->first_fd(), IPPROTO_TCP, TCP_LINGER2, &get, &get_len),
+      SyscallSucceedsWithValue(0));
+  EXPECT_EQ(get_len, sizeof(get));
+  EXPECT_EQ(get, -1);
+}
+
+TEST_P(TCPSocketPairTest, SetTCPLingerTimeoutZero) {
   auto sockets = ASSERT_NO_ERRNO_AND_VALUE(NewSocketPair());
 
   constexpr int kZero = 0;
   EXPECT_THAT(setsockopt(sockets->first_fd(), IPPROTO_TCP, TCP_LINGER2, &kZero,
                          sizeof(kZero)),
               SyscallSucceedsWithValue(0));
-
-  constexpr int kNegative = -1234;
-  EXPECT_THAT(setsockopt(sockets->first_fd(), IPPROTO_TCP, TCP_LINGER2,
-                         &kNegative, sizeof(kNegative)),
-              SyscallSucceedsWithValue(0));
+  int get = -1;
+  socklen_t get_len = sizeof(get);
+  EXPECT_THAT(
+      getsockopt(sockets->first_fd(), IPPROTO_TCP, TCP_LINGER2, &get, &get_len),
+      SyscallSucceedsWithValue(0));
+  EXPECT_EQ(get_len, sizeof(get));
+  EXPECT_THAT(get,
+              AnyOf(Eq(kMaxTCPLingerTimeout), Eq(kOldMaxTCPLingerTimeout)));
 }
 
 TEST_P(TCPSocketPairTest, SetTCPLingerTimeoutAboveMax) {