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

2 files changed, 20 insertions, 10 deletions

diff --git a/pkg/tcpip/transport/tcp/endpoint.go b/pkg/tcpip/transport/tcp/endpoint.go
index 4ba0ea1c0..9c0f4c9f4 100644
--- a/pkg/tcpip/transport/tcp/endpoint.go
+++ b/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()
 
diff --git a/pkg/tcpip/transport/tcp/tcp_test.go b/pkg/tcpip/transport/tcp/tcp_test.go
index 55ae09a2f..9650bb06c 100644
--- a/pkg/tcpip/transport/tcp/tcp_test.go
+++ b/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) {