Fix data-race when reading/writing e.amss.

PiperOrigin-RevId: 298451319

3 files changed, 42 insertions, 13 deletions

diff --git a/pkg/tcpip/transport/tcp/connect.go b/pkg/tcpip/transport/tcp/connect.go
index cd247f3e1..ae4f3f3a9 100644
--- a/pkg/tcpip/transport/tcp/connect.go
+++ b/pkg/tcpip/transport/tcp/connect.go
@@ -295,6 +295,7 @@ func (h *handshake) synSentState(s *segment) *tcpip.Error {
 	h.state = handshakeSynRcvd
 	h.ep.mu.Lock()
 	ttl := h.ep.ttl
+	amss := h.ep.amss
 	h.ep.setEndpointState(StateSynRecv)
 	h.ep.mu.Unlock()
 	synOpts := header.TCPSynOptions{
@@ -307,7 +308,7 @@ func (h *handshake) synSentState(s *segment) *tcpip.Error {
 		// permits SACK. This is not explicitly defined in the RFC but
 		// this is the behaviour implemented by Linux.
 		SACKPermitted: rcvSynOpts.SACKPermitted,
-		MSS:           h.ep.amss,
+		MSS:           amss,
 	}
 	if ttl == 0 {
 		ttl = s.route.DefaultTTL()
@@ -356,6 +357,10 @@ func (h *handshake) synRcvdState(s *segment) *tcpip.Error {
 			return tcpip.ErrInvalidEndpointState
 		}
 
+		h.ep.mu.RLock()
+		amss := h.ep.amss
+		h.ep.mu.RUnlock()
+
 		h.resetState()
 		synOpts := header.TCPSynOptions{
 			WS:            h.rcvWndScale,
@@ -363,7 +368,7 @@ func (h *handshake) synRcvdState(s *segment) *tcpip.Error {
 			TSVal:         h.ep.timestamp(),
 			TSEcr:         h.ep.recentTimestamp(),
 			SACKPermitted: h.ep.sackPermitted,
-			MSS:           h.ep.amss,
+			MSS:           amss,
 		}
 		h.ep.sendSynTCP(&s.route, h.ep.ID, h.ep.ttl, h.ep.sendTOS, h.flags, h.iss, h.ackNum, h.rcvWnd, synOpts)
 		return nil
@@ -530,6 +535,7 @@ func (h *handshake) execute() *tcpip.Error {
 
 	// Send the initial SYN segment and loop until the handshake is
 	// completed.
+	h.ep.mu.Lock()
 	h.ep.amss = calculateAdvertisedMSS(h.ep.userMSS, h.ep.route)
 
 	synOpts := header.TCPSynOptions{
@@ -540,6 +546,7 @@ func (h *handshake) execute() *tcpip.Error {
 		SACKPermitted: bool(sackEnabled),
 		MSS:           h.ep.amss,
 	}
+	h.ep.mu.Unlock()
 
 	// Execute is also called in a listen context so we want to make sure we
 	// only send the TS/SACK option when we received the TS/SACK in the
diff --git a/pkg/tcpip/transport/tcp/endpoint.go b/pkg/tcpip/transport/tcp/endpoint.go
index 9e72730bd..8b9154e69 100644
--- a/pkg/tcpip/transport/tcp/endpoint.go
+++ b/pkg/tcpip/transport/tcp/endpoint.go
@@ -959,15 +959,18 @@ func (e *endpoint) initialReceiveWindow() int {
 // ModerateRecvBuf adjusts the receive buffer and the advertised window
 // based on the number of bytes copied to user space.
 func (e *endpoint) ModerateRecvBuf(copied int) {
+	e.mu.RLock()
 	e.rcvListMu.Lock()
 	if e.rcvAutoParams.disabled {
 		e.rcvListMu.Unlock()
+		e.mu.RUnlock()
 		return
 	}
 	now := time.Now()
 	if rtt := e.rcvAutoParams.rtt; rtt == 0 || now.Sub(e.rcvAutoParams.measureTime) < rtt {
 		e.rcvAutoParams.copied += copied
 		e.rcvListMu.Unlock()
+		e.mu.RUnlock()
 		return
 	}
 	prevRTTCopied := e.rcvAutoParams.copied + copied
@@ -1008,7 +1011,7 @@ func (e *endpoint) ModerateRecvBuf(copied int) {
 			e.rcvBufSize = rcvWnd
 			availAfter := e.receiveBufferAvailableLocked()
 			mask := uint32(notifyReceiveWindowChanged)
-			if crossed, above := e.windowCrossedACKThreshold(availAfter - availBefore); crossed && above {
+			if crossed, above := e.windowCrossedACKThresholdLocked(availAfter - availBefore); crossed && above {
 				mask |= notifyNonZeroReceiveWindow
 			}
 			e.notifyProtocolGoroutine(mask)
@@ -1023,6 +1026,7 @@ func (e *endpoint) ModerateRecvBuf(copied int) {
 	e.rcvAutoParams.measureTime = now
 	e.rcvAutoParams.copied = 0
 	e.rcvListMu.Unlock()
+	e.mu.RUnlock()
 }
 
 // IPTables implements tcpip.Endpoint.IPTables.
@@ -1052,7 +1056,6 @@ func (e *endpoint) Read(*tcpip.FullAddress) (buffer.View, tcpip.ControlMessages,
 
 	v, err := e.readLocked()
 	e.rcvListMu.Unlock()
-
 	e.mu.RUnlock()
 
 	if err == tcpip.ErrClosedForReceive {
@@ -1085,7 +1088,7 @@ func (e *endpoint) readLocked() (buffer.View, *tcpip.Error) {
 	// enough buffer space, to either fit an aMSS or half a receive buffer
 	// (whichever smaller), then notify the protocol goroutine to send a
 	// window update.
-	if crossed, above := e.windowCrossedACKThreshold(len(v)); crossed && above {
+	if crossed, above := e.windowCrossedACKThresholdLocked(len(v)); crossed && above {
 		e.notifyProtocolGoroutine(notifyNonZeroReceiveWindow)
 	}
 
@@ -1303,9 +1306,9 @@ func (e *endpoint) Peek(vec [][]byte) (int64, tcpip.ControlMessages, *tcpip.Erro
 	return num, tcpip.ControlMessages{}, nil
 }
 
-// windowCrossedACKThreshold checks if the receive window to be announced now
-// would be under aMSS or under half receive buffer, whichever smaller. This is
-// useful as a receive side silly window syndrome prevention mechanism. If
+// windowCrossedACKThresholdLocked checks if the receive window to be announced
+// now would be under aMSS or under half receive buffer, whichever smaller. This
+// is useful as a receive side silly window syndrome prevention mechanism. If
 // window grows to reasonable value, we should send ACK to the sender to inform
 // the rx space is now large. We also want ensure a series of small read()'s
 // won't trigger a flood of spurious tiny ACK's.
@@ -1316,7 +1319,9 @@ func (e *endpoint) Peek(vec [][]byte) (int64, tcpip.ControlMessages, *tcpip.Erro
 // crossed will be true if the window size crossed the ACK threshold.
 // above will be true if the new window is >= ACK threshold and false
 // otherwise.
-func (e *endpoint) windowCrossedACKThreshold(deltaBefore int) (crossed bool, above bool) {
+//
+// Precondition: e.mu and e.rcvListMu must be held.
+func (e *endpoint) windowCrossedACKThresholdLocked(deltaBefore int) (crossed bool, above bool) {
 	newAvail := e.receiveBufferAvailableLocked()
 	oldAvail := newAvail - deltaBefore
 	if oldAvail < 0 {
@@ -1379,6 +1384,7 @@ func (e *endpoint) SetSockOptInt(opt tcpip.SockOptInt, v int) *tcpip.Error {
 
 		mask := uint32(notifyReceiveWindowChanged)
 
+		e.mu.RLock()
 		e.rcvListMu.Lock()
 
 		// Make sure the receive buffer size allows us to send a
@@ -1405,11 +1411,11 @@ func (e *endpoint) SetSockOptInt(opt tcpip.SockOptInt, v int) *tcpip.Error {
 		// Immediately send an ACK to uncork the sender silly window
 		// syndrome prevetion, when our available space grows above aMSS
 		// or half receive buffer, whichever smaller.
-		if crossed, above := e.windowCrossedACKThreshold(availAfter - availBefore); crossed && above {
+		if crossed, above := e.windowCrossedACKThresholdLocked(availAfter - availBefore); crossed && above {
 			mask |= notifyNonZeroReceiveWindow
 		}
 		e.rcvListMu.Unlock()
-
+		e.mu.RUnlock()
 		e.notifyProtocolGoroutine(mask)
 		return nil
 
@@ -2414,13 +2420,14 @@ func (e *endpoint) updateSndBufferUsage(v int) {
 // to be read, or when the connection is closed for receiving (in which case
 // s will be nil).
 func (e *endpoint) readyToRead(s *segment) {
+	e.mu.RLock()
 	e.rcvListMu.Lock()
 	if s != nil {
 		s.incRef()
 		e.rcvBufUsed += s.data.Size()
 		// Increase counter if the receive window falls down below MSS
 		// or half receive buffer size, whichever smaller.
-		if crossed, above := e.windowCrossedACKThreshold(-s.data.Size()); crossed && !above {
+		if crossed, above := e.windowCrossedACKThresholdLocked(-s.data.Size()); crossed && !above {
 			e.stats.ReceiveErrors.ZeroRcvWindowState.Increment()
 		}
 		e.rcvList.PushBack(s)
@@ -2428,7 +2435,7 @@ func (e *endpoint) readyToRead(s *segment) {
 		e.rcvClosed = true
 	}
 	e.rcvListMu.Unlock()
-
+	e.mu.RUnlock()
 	e.waiterQueue.Notify(waiter.EventIn)
 }
 
diff --git a/test/syscalls/linux/tcp_socket.cc b/test/syscalls/linux/tcp_socket.cc
index c4591a3b9..579463384 100644
--- a/test/syscalls/linux/tcp_socket.cc
+++ b/test/syscalls/linux/tcp_socket.cc
@@ -1349,6 +1349,21 @@ TEST_P(SimpleTcpSocketTest, RecvOnClosedSocket) {
               SyscallFailsWithErrno(ENOTCONN));
 }
 
+TEST_P(SimpleTcpSocketTest, TCPConnectSoRcvBufRace) {
+  auto s = ASSERT_NO_ERRNO_AND_VALUE(
+      Socket(GetParam(), SOCK_STREAM | SOCK_NONBLOCK, IPPROTO_TCP));
+  sockaddr_storage addr =
+      ASSERT_NO_ERRNO_AND_VALUE(InetLoopbackAddr(GetParam()));
+  socklen_t addrlen = sizeof(addr);
+
+  RetryEINTR(connect)(s.get(), reinterpret_cast<struct sockaddr*>(&addr),
+                      addrlen);
+  int buf_sz = 1 << 18;
+  EXPECT_THAT(
+      setsockopt(s.get(), SOL_SOCKET, SO_RCVBUF, &buf_sz, sizeof(buf_sz)),
+      SyscallSucceedsWithValue(0));
+}
+
 INSTANTIATE_TEST_SUITE_P(AllInetTests, SimpleTcpSocketTest,
                          ::testing::Values(AF_INET, AF_INET6));