Reset pending connections on listener shutdown.

When the listening socket is read shutdown, we need to reset all pending
and incoming connections. Ensure that the endpoint is not cleaned up
from the demuxer and subsequent bind to same port does not go through.

PiperOrigin-RevId: 306958038

6 files changed, 50 insertions, 33 deletions

diff --git a/pkg/tcpip/transport/tcp/accept.go b/pkg/tcpip/transport/tcp/accept.go
index b61c2a8c3..5bb243e3b 100644
--- a/pkg/tcpip/transport/tcp/accept.go
+++ b/pkg/tcpip/transport/tcp/accept.go
@@ -26,7 +26,6 @@ import (
 	"gvisor.dev/gvisor/pkg/sleep"
 	"gvisor.dev/gvisor/pkg/sync"
 	"gvisor.dev/gvisor/pkg/tcpip"
-	"gvisor.dev/gvisor/pkg/tcpip/buffer"
 	"gvisor.dev/gvisor/pkg/tcpip/header"
 	"gvisor.dev/gvisor/pkg/tcpip/seqnum"
 	"gvisor.dev/gvisor/pkg/tcpip/stack"
@@ -433,19 +432,16 @@ func (e *endpoint) acceptQueueIsFull() bool {
 // handleListenSegment is called when a listening endpoint receives a segment
 // and needs to handle it.
 func (e *endpoint) handleListenSegment(ctx *listenContext, s *segment) {
-	if s.flagsAreSet(header.TCPFlagSyn | header.TCPFlagAck) {
+	e.rcvListMu.Lock()
+	rcvClosed := e.rcvClosed
+	e.rcvListMu.Unlock()
+	if rcvClosed || s.flagsAreSet(header.TCPFlagSyn|header.TCPFlagAck) {
+		// If the endpoint is shutdown, reply with reset.
+		//
 		// RFC 793 section 3.4 page 35 (figure 12) outlines that a RST
 		// must be sent in response to a SYN-ACK while in the listen
 		// state to prevent completing a handshake from an old SYN.
-		e.sendTCP(&s.route, tcpFields{
-			id:     s.id,
-			ttl:    e.ttl,
-			tos:    e.sendTOS,
-			flags:  header.TCPFlagRst,
-			seq:    s.ackNumber,
-			ack:    0,
-			rcvWnd: 0,
-		}, buffer.VectorisedView{}, nil)
+		replyWithReset(s, e.sendTOS, e.ttl)
 		return
 	}
 
@@ -534,7 +530,7 @@ func (e *endpoint) handleListenSegment(ctx *listenContext, s *segment) {
 			// The only time we should reach here when a connection
 			// was opened and closed really quickly and a delayed
 			// ACK was received from the sender.
-			replyWithReset(s)
+			replyWithReset(s, e.sendTOS, e.ttl)
 			return
 		}
 
diff --git a/pkg/tcpip/transport/tcp/connect.go b/pkg/tcpip/transport/tcp/connect.go
index 994ac52a3..368865911 100644
--- a/pkg/tcpip/transport/tcp/connect.go
+++ b/pkg/tcpip/transport/tcp/connect.go
@@ -1053,10 +1053,15 @@ func (e *endpoint) tryDeliverSegmentFromClosedEndpoint(s *segment) {
 		ep = e.stack.FindTransportEndpoint(header.IPv4ProtocolNumber, e.TransProto, e.ID, &s.route)
 	}
 	if ep == nil {
-		replyWithReset(s)
+		replyWithReset(s, stack.DefaultTOS, s.route.DefaultTTL())
 		s.decRef()
 		return
 	}
+
+	if e == ep {
+		panic("current endpoint not removed from demuxer, enqueing segments to itself")
+	}
+
 	if ep.(*endpoint).enqueueSegment(s) {
 		ep.(*endpoint).newSegmentWaker.Assert()
 	}
diff --git a/pkg/tcpip/transport/tcp/endpoint.go b/pkg/tcpip/transport/tcp/endpoint.go
index bffc59e9f..5d0ea9e93 100644
--- a/pkg/tcpip/transport/tcp/endpoint.go
+++ b/pkg/tcpip/transport/tcp/endpoint.go
@@ -2101,7 +2101,7 @@ func (e *endpoint) shutdownLocked(flags tcpip.ShutdownFlags) *tcpip.Error {
 	switch {
 	case e.EndpointState().connected():
 		// Close for read.
-		if (e.shutdownFlags & tcpip.ShutdownRead) != 0 {
+		if e.shutdownFlags&tcpip.ShutdownRead != 0 {
 			// Mark read side as closed.
 			e.rcvListMu.Lock()
 			e.rcvClosed = true
@@ -2110,7 +2110,7 @@ func (e *endpoint) shutdownLocked(flags tcpip.ShutdownFlags) *tcpip.Error {
 
 			// If we're fully closed and we have unread data we need to abort
 			// the connection with a RST.
-			if (e.shutdownFlags&tcpip.ShutdownWrite) != 0 && rcvBufUsed > 0 {
+			if e.shutdownFlags&tcpip.ShutdownWrite != 0 && rcvBufUsed > 0 {
 				e.resetConnectionLocked(tcpip.ErrConnectionAborted)
 				// Wake up worker to terminate loop.
 				e.notifyProtocolGoroutine(notifyTickleWorker)
@@ -2119,7 +2119,7 @@ func (e *endpoint) shutdownLocked(flags tcpip.ShutdownFlags) *tcpip.Error {
 		}
 
 		// Close for write.
-		if (e.shutdownFlags & tcpip.ShutdownWrite) != 0 {
+		if e.shutdownFlags&tcpip.ShutdownWrite != 0 {
 			e.sndBufMu.Lock()
 			if e.sndClosed {
 				// Already closed.
@@ -2142,12 +2142,23 @@ func (e *endpoint) shutdownLocked(flags tcpip.ShutdownFlags) *tcpip.Error {
 
 		return nil
 	case e.EndpointState() == StateListen:
-		// Tell protocolListenLoop to stop.
-		if flags&tcpip.ShutdownRead != 0 {
-			e.notifyProtocolGoroutine(notifyClose)
+		if e.shutdownFlags&tcpip.ShutdownRead != 0 {
+			// Reset all connections from the accept queue and keep the
+			// worker running so that it can continue handling incoming
+			// segments by replying with RST.
+			//
+			// By not removing this endpoint from the demuxer mapping, we
+			// ensure that any other bind to the same port fails, as on Linux.
+			// TODO(gvisor.dev/issue/2468): We need to enable applications to
+			// start listening on this endpoint again similar to Linux.
+			e.rcvListMu.Lock()
+			e.rcvClosed = true
+			e.rcvListMu.Unlock()
+			e.closePendingAcceptableConnectionsLocked()
+			// Notify waiters that the endpoint is shutdown.
+			e.waiterQueue.Notify(waiter.EventIn | waiter.EventOut | waiter.EventHUp | waiter.EventErr)
 		}
 		return nil
-
 	default:
 		return tcpip.ErrNotConnected
 	}
@@ -2251,8 +2262,11 @@ func (e *endpoint) Accept() (tcpip.Endpoint, *waiter.Queue, *tcpip.Error) {
 	e.LockUser()
 	defer e.UnlockUser()
 
+	e.rcvListMu.Lock()
+	rcvClosed := e.rcvClosed
+	e.rcvListMu.Unlock()
 	// Endpoint must be in listen state before it can accept connections.
-	if e.EndpointState() != StateListen {
+	if rcvClosed || e.EndpointState() != StateListen {
 		return nil, nil, tcpip.ErrInvalidEndpointState
 	}
 
diff --git a/pkg/tcpip/transport/tcp/forwarder.go b/pkg/tcpip/transport/tcp/forwarder.go
index 808410c92..704d01c64 100644
--- a/pkg/tcpip/transport/tcp/forwarder.go
+++ b/pkg/tcpip/transport/tcp/forwarder.go
@@ -130,7 +130,7 @@ func (r *ForwarderRequest) Complete(sendReset bool) {
 
 	// If the caller requested, send a reset.
 	if sendReset {
-		replyWithReset(r.segment)
+		replyWithReset(r.segment, stack.DefaultTOS, r.segment.route.DefaultTTL())
 	}
 
 	// Release all resources.
diff --git a/pkg/tcpip/transport/tcp/protocol.go b/pkg/tcpip/transport/tcp/protocol.go
index effbf203f..cfd9a4e8e 100644
--- a/pkg/tcpip/transport/tcp/protocol.go
+++ b/pkg/tcpip/transport/tcp/protocol.go
@@ -223,12 +223,12 @@ func (*protocol) HandleUnknownDestinationPacket(r *stack.Route, id stack.Transpo
 		return true
 	}
 
-	replyWithReset(s)
+	replyWithReset(s, stack.DefaultTOS, s.route.DefaultTTL())
 	return true
 }
 
 // replyWithReset replies to the given segment with a reset segment.
-func replyWithReset(s *segment) {
+func replyWithReset(s *segment, tos, ttl uint8) {
 	// Get the seqnum from the packet if the ack flag is set.
 	seq := seqnum.Value(0)
 	ack := seqnum.Value(0)
@@ -252,8 +252,8 @@ func replyWithReset(s *segment) {
 	}
 	sendTCP(&s.route, tcpFields{
 		id:     s.id,
-		ttl:    s.route.DefaultTTL(),
-		tos:    stack.DefaultTOS,
+		ttl:    ttl,
+		tos:    tos,
 		flags:  flags,
 		seq:    seq,
 		ack:    ack,
diff --git a/pkg/tcpip/transport/tcp/tcp_test.go b/pkg/tcpip/transport/tcp/tcp_test.go
index 74fb6e064..ab1014c7f 100644
--- a/pkg/tcpip/transport/tcp/tcp_test.go
+++ b/pkg/tcpip/transport/tcp/tcp_test.go
@@ -1034,8 +1034,8 @@ func TestSendRstOnListenerRxAckV6(t *testing.T) {
 		checker.SeqNum(200)))
 }
 
-// TestListenShutdown tests for the listening endpoint not processing
-// any receive when it is on read shutdown.
+// TestListenShutdown tests for the listening endpoint replying with RST
+// on read shutdown.
 func TestListenShutdown(t *testing.T) {
 	c := context.New(t, defaultMTU)
 	defer c.Cleanup()
@@ -1046,7 +1046,7 @@ func TestListenShutdown(t *testing.T) {
 		t.Fatal("Bind failed:", err)
 	}
 
-	if err := c.EP.Listen(10 /* backlog */); err != nil {
+	if err := c.EP.Listen(1 /* backlog */); err != nil {
 		t.Fatal("Listen failed:", err)
 	}
 
@@ -1054,9 +1054,6 @@ func TestListenShutdown(t *testing.T) {
 		t.Fatal("Shutdown failed:", err)
 	}
 
-	// Wait for the endpoint state to be propagated.
-	time.Sleep(10 * time.Millisecond)
-
 	c.SendPacket(nil, &context.Headers{
 		SrcPort: context.TestPort,
 		DstPort: context.StackPort,
@@ -1065,7 +1062,12 @@ func TestListenShutdown(t *testing.T) {
 		AckNum:  200,
 	})
 
-	c.CheckNoPacket("Packet received when listening socket was shutdown")
+	// Expect the listening endpoint to reset the connection.
+	checker.IPv4(t, c.GetPacket(),
+		checker.TCP(
+			checker.DstPort(context.TestPort),
+			checker.TCPFlags(header.TCPFlagAck|header.TCPFlagRst),
+		))
 }
 
 // TestListenCloseWhileConnect tests for the listening endpoint to