Fix SO_ERROR behavior for TCP in gVisor.

Fixes the behaviour of SO_ERROR for tcp sockets where in linux it returns
sk->sk_err and if sk->sk_err is 0 then it returns sk->sk_soft_err. In gVisor TCP
we endpoint.HardError is the equivalent of sk->sk_err and endpoint.LastError
holds soft errors. This change brings this into alignment with Linux such that
both hard/soft errors are cleared when retrieved using getsockopt(.. SO_ERROR)
is called on a socket.

Fixes #3812

PiperOrigin-RevId: 342868552

4 files changed, 51 insertions, 33 deletions

diff --git a/pkg/tcpip/transport/tcp/connect.go b/pkg/tcpip/transport/tcp/connect.go
index ac6d879a7..6661e8915 100644
--- a/pkg/tcpip/transport/tcp/connect.go
+++ b/pkg/tcpip/transport/tcp/connect.go
@@ -496,7 +496,7 @@ func (h *handshake) resolveRoute() *tcpip.Error {
 				h.ep.mu.Lock()
 			}
 			if n&notifyError != 0 {
-				return h.ep.LastError()
+				return h.ep.lastErrorLocked()
 			}
 		}
 
@@ -575,7 +575,6 @@ func (h *handshake) complete() *tcpip.Error {
 		return err
 	}
 	defer timer.stop()
-
 	for h.state != handshakeCompleted {
 		// Unlock before blocking, and reacquire again afterwards (h.ep.mu is held
 		// throughout handshake processing).
@@ -631,9 +630,8 @@ func (h *handshake) complete() *tcpip.Error {
 				h.ep.mu.Lock()
 			}
 			if n&notifyError != 0 {
-				return h.ep.LastError()
+				return h.ep.lastErrorLocked()
 			}
-
 		case wakerForNewSegment:
 			if err := h.processSegments(); err != nil {
 				return err
@@ -1002,7 +1000,7 @@ func (e *endpoint) resetConnectionLocked(err *tcpip.Error) {
 	// Only send a reset if the connection is being aborted for a reason
 	// other than receiving a reset.
 	e.setEndpointState(StateError)
-	e.HardError = err
+	e.hardError = err
 	if err != tcpip.ErrConnectionReset && err != tcpip.ErrTimeout {
 		// The exact sequence number to be used for the RST is the same as the
 		// one used by Linux. We need to handle the case of window being shrunk
@@ -1141,7 +1139,7 @@ func (e *endpoint) handleReset(s *segment) (ok bool, err *tcpip.Error) {
 		//  delete the TCB, and return.
 		case StateCloseWait:
 			e.transitionToStateCloseLocked()
-			e.HardError = tcpip.ErrAborted
+			e.hardError = tcpip.ErrAborted
 			e.notifyProtocolGoroutine(notifyTickleWorker)
 			return false, nil
 		default:
@@ -1353,7 +1351,6 @@ func (e *endpoint) protocolMainLoop(handshake bool, wakerInitDone chan<- struct{
 
 	epilogue := func() {
 		// e.mu is expected to be hold upon entering this section.
-
 		if e.snd != nil {
 			e.snd.resendTimer.cleanup()
 		}
@@ -1383,7 +1380,7 @@ func (e *endpoint) protocolMainLoop(handshake bool, wakerInitDone chan<- struct{
 			e.lastErrorMu.Unlock()
 
 			e.setEndpointState(StateError)
-			e.HardError = err
+			e.hardError = err
 
 			e.workerCleanup = true
 			// Lock released below.
diff --git a/pkg/tcpip/transport/tcp/endpoint.go b/pkg/tcpip/transport/tcp/endpoint.go
index 4f4f4c65e..a2161e49d 100644
--- a/pkg/tcpip/transport/tcp/endpoint.go
+++ b/pkg/tcpip/transport/tcp/endpoint.go
@@ -315,11 +315,6 @@ func (*Stats) IsEndpointStats() {}
 // +stateify savable
 type EndpointInfo struct {
 	stack.TransportEndpointInfo
-
-	// HardError is meaningful only when state is stateError. It stores the
-	// error to be returned when read/write syscalls are called and the
-	// endpoint is in this state. HardError is protected by endpoint mu.
-	HardError *tcpip.Error `state:".(string)"`
 }
 
 // IsEndpointInfo is an empty method to implement the tcpip.EndpointInfo
@@ -386,6 +381,11 @@ type endpoint struct {
 	waiterQueue *waiter.Queue `state:"wait"`
 	uniqueID    uint64
 
+	// hardError is meaningful only when state is stateError. It stores the
+	// error to be returned when read/write syscalls are called and the
+	// endpoint is in this state. hardError is protected by endpoint mu.
+	hardError *tcpip.Error `state:".(string)"`
+
 	// lastError represents the last error that the endpoint reported;
 	// access to it is protected by the following mutex.
 	lastErrorMu sync.Mutex   `state:"nosave"`
@@ -1283,7 +1283,15 @@ func (e *endpoint) SetOwner(owner tcpip.PacketOwner) {
 	e.owner = owner
 }
 
-func (e *endpoint) LastError() *tcpip.Error {
+// Preconditions: e.mu must be held to call this function.
+func (e *endpoint) hardErrorLocked() *tcpip.Error {
+	err := e.hardError
+	e.hardError = nil
+	return err
+}
+
+// Preconditions: e.mu must be held to call this function.
+func (e *endpoint) lastErrorLocked() *tcpip.Error {
 	e.lastErrorMu.Lock()
 	defer e.lastErrorMu.Unlock()
 	err := e.lastError
@@ -1291,6 +1299,15 @@ func (e *endpoint) LastError() *tcpip.Error {
 	return err
 }
 
+func (e *endpoint) LastError() *tcpip.Error {
+	e.LockUser()
+	defer e.UnlockUser()
+	if err := e.hardErrorLocked(); err != nil {
+		return err
+	}
+	return e.lastErrorLocked()
+}
+
 // Read reads data from the endpoint.
 func (e *endpoint) Read(*tcpip.FullAddress) (buffer.View, tcpip.ControlMessages, *tcpip.Error) {
 	e.LockUser()
@@ -1312,9 +1329,8 @@ func (e *endpoint) Read(*tcpip.FullAddress) (buffer.View, tcpip.ControlMessages,
 	bufUsed := e.rcvBufUsed
 	if s := e.EndpointState(); !s.connected() && s != StateClose && bufUsed == 0 {
 		e.rcvListMu.Unlock()
-		he := e.HardError
 		if s == StateError {
-			return buffer.View{}, tcpip.ControlMessages{}, he
+			return buffer.View{}, tcpip.ControlMessages{}, e.hardErrorLocked()
 		}
 		e.stats.ReadErrors.NotConnected.Increment()
 		return buffer.View{}, tcpip.ControlMessages{}, tcpip.ErrNotConnected
@@ -1370,9 +1386,13 @@ func (e *endpoint) readLocked() (buffer.View, *tcpip.Error) {
 // indicating the reason why it's not writable.
 // Caller must hold e.mu and e.sndBufMu
 func (e *endpoint) isEndpointWritableLocked() (int, *tcpip.Error) {
+	// The endpoint cannot be written to if it's not connected.
 	switch s := e.EndpointState(); {
 	case s == StateError:
-		return 0, e.HardError
+		if err := e.hardErrorLocked(); err != nil {
+			return 0, err
+		}
+		return 0, tcpip.ErrClosedForSend
 	case !s.connecting() && !s.connected():
 		return 0, tcpip.ErrClosedForSend
 	case s.connecting():
@@ -1486,7 +1506,7 @@ func (e *endpoint) Peek(vec [][]byte) (int64, tcpip.ControlMessages, *tcpip.Erro
 	// but has some pending unread data.
 	if s := e.EndpointState(); !s.connected() && s != StateClose {
 		if s == StateError {
-			return 0, tcpip.ControlMessages{}, e.HardError
+			return 0, tcpip.ControlMessages{}, e.hardErrorLocked()
 		}
 		e.stats.ReadErrors.InvalidEndpointState.Increment()
 		return 0, tcpip.ControlMessages{}, tcpip.ErrInvalidEndpointState
@@ -2243,7 +2263,10 @@ func (e *endpoint) connect(addr tcpip.FullAddress, handshake bool, run bool) *tc
 		return tcpip.ErrAlreadyConnecting
 
 	case StateError:
-		return e.HardError
+		if err := e.hardErrorLocked(); err != nil {
+			return err
+		}
+		return tcpip.ErrConnectionAborted
 
 	default:
 		return tcpip.ErrInvalidEndpointState
@@ -2417,7 +2440,7 @@ func (e *endpoint) startMainLoop(handshake bool) *tcpip.Error {
 				e.lastErrorMu.Unlock()
 
 				e.setEndpointState(StateError)
-				e.HardError = err
+				e.hardError = err
 
 				// Call cleanupLocked to free up any reservations.
 				e.cleanupLocked()
diff --git a/pkg/tcpip/transport/tcp/endpoint_state.go b/pkg/tcpip/transport/tcp/endpoint_state.go
index bb901c0f8..ba67176b5 100644
--- a/pkg/tcpip/transport/tcp/endpoint_state.go
+++ b/pkg/tcpip/transport/tcp/endpoint_state.go
@@ -321,21 +321,21 @@ func (e *endpoint) loadRecentTSTime(unix unixTime) {
 }
 
 // saveHardError is invoked by stateify.
-func (e *EndpointInfo) saveHardError() string {
-	if e.HardError == nil {
+func (e *endpoint) saveHardError() string {
+	if e.hardError == nil {
 		return ""
 	}
 
-	return e.HardError.String()
+	return e.hardError.String()
 }
 
 // loadHardError is invoked by stateify.
-func (e *EndpointInfo) loadHardError(s string) {
+func (e *endpoint) loadHardError(s string) {
 	if s == "" {
 		return
 	}
 
-	e.HardError = tcpip.StringToError(s)
+	e.hardError = tcpip.StringToError(s)
 }
 
 // saveMeasureTime is invoked by stateify.
diff --git a/pkg/tcpip/transport/tcp/tcp_test.go b/pkg/tcpip/transport/tcp/tcp_test.go
index 9f0fb41e3..c366a4cbc 100644
--- a/pkg/tcpip/transport/tcp/tcp_test.go
+++ b/pkg/tcpip/transport/tcp/tcp_test.go
@@ -75,9 +75,6 @@ func TestGiveUpConnect(t *testing.T) {
 
 	// Wait for ep to become writable.
 	<-notifyCh
-	if err := ep.LastError(); err != tcpip.ErrAborted {
-		t.Fatalf("got ep.LastError() = %s, want = %s", err, tcpip.ErrAborted)
-	}
 
 	// Call Connect again to retreive the handshake failure status
 	// and stats updates.
@@ -3198,6 +3195,11 @@ loop:
 		case tcpip.ErrWouldBlock:
 			select {
 			case <-ch:
+				// Expect the state to be StateError and subsequent Reads to fail with HardError.
+				if _, _, err := c.EP.Read(nil); err != tcpip.ErrConnectionReset {
+					t.Fatalf("got c.EP.Read(nil) = %s, want = %s", err, tcpip.ErrConnectionReset)
+				}
+				break loop
 			case <-time.After(1 * time.Second):
 				t.Fatalf("Timed out waiting for reset to arrive")
 			}
@@ -3207,14 +3209,10 @@ loop:
 			t.Fatalf("got c.EP.Read(nil) = %s, want = %s", err, tcpip.ErrConnectionReset)
 		}
 	}
-	// Expect the state to be StateError and subsequent Reads to fail with HardError.
-	if _, _, err := c.EP.Read(nil); err != tcpip.ErrConnectionReset {
-		t.Fatalf("got c.EP.Read(nil) = %s, want = %s", err, tcpip.ErrConnectionReset)
-	}
+
 	if tcp.EndpointState(c.EP.State()) != tcp.StateError {
 		t.Fatalf("got EP state is not StateError")
 	}
-
 	if got := c.Stack().Stats().TCP.EstablishedResets.Value(); got != 1 {
 		t.Errorf("got stats.TCP.EstablishedResets.Value() = %d, want = 1", got)
 	}