tcpip/transport/tcp: read side only shutdown of an endpoint

Support shutdown on only the read side of an endpoint. Reads performed
after a call to Shutdown with only the ShutdownRead flag will return
ErrClosedForReceive without data.

Break out the shutdown(2) with SHUT_RD syscall test into to two tests.
The first tests that no packets are sent when shutting down the read
side of a socket. The second tests that, after shutting down the read
side of a socket, unread data can still be read, or an EOF if there is
no more data to read.

Change-Id: I9d7c0a06937909cbb466b7591544a4bcaebb11ce
PiperOrigin-RevId: 244459430

2 files changed, 35 insertions, 13 deletions

diff --git a/pkg/tcpip/transport/tcp/endpoint.go b/pkg/tcpip/transport/tcp/endpoint.go
index c0b785431..09eff5be1 100644
--- a/pkg/tcpip/transport/tcp/endpoint.go
+++ b/pkg/tcpip/transport/tcp/endpoint.go
@@ -1199,21 +1199,24 @@ func (e *endpoint) Shutdown(flags tcpip.ShutdownFlags) *tcpip.Error {
 
 	switch e.state {
 	case stateConnected:
-		// Close for write.
-		if (e.shutdownFlags & tcpip.ShutdownWrite) != 0 {
-			if (e.shutdownFlags & tcpip.ShutdownRead) != 0 {
-				// We're fully closed, if we have unread data we need to abort
-				// the connection with a RST.
-				e.rcvListMu.Lock()
-				rcvBufUsed := e.rcvBufUsed
-				e.rcvListMu.Unlock()
-
-				if rcvBufUsed > 0 {
-					e.notifyProtocolGoroutine(notifyReset)
-					return nil
-				}
+		// Close for read.
+		if (e.shutdownFlags & tcpip.ShutdownRead) != 0 {
+			// Mark read side as closed.
+			e.rcvListMu.Lock()
+			e.rcvClosed = true
+			rcvBufUsed := e.rcvBufUsed
+			e.rcvListMu.Unlock()
+
+			// 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 {
+				e.notifyProtocolGoroutine(notifyReset)
+				return nil
 			}
+		}
 
+		// Close for write.
+		if (e.shutdownFlags & tcpip.ShutdownWrite) != 0 {
 			e.sndBufMu.Lock()
 
 			if e.sndClosed {
diff --git a/pkg/tcpip/transport/tcp/tcp_test.go b/pkg/tcpip/transport/tcp/tcp_test.go
index af50ac8af..c5732ad1c 100644
--- a/pkg/tcpip/transport/tcp/tcp_test.go
+++ b/pkg/tcpip/transport/tcp/tcp_test.go
@@ -687,6 +687,25 @@ func TestRstOnCloseWithUnreadDataFinConvertRst(t *testing.T) {
 	})
 }
 
+func TestShutdownRead(t *testing.T) {
+	c := context.New(t, defaultMTU)
+	defer c.Cleanup()
+
+	c.CreateConnected(789, 30000, nil)
+
+	if _, _, err := c.EP.Read(nil); err != tcpip.ErrWouldBlock {
+		t.Fatalf("got c.EP.Read(nil) = %v, want = %v", err, tcpip.ErrWouldBlock)
+	}
+
+	if err := c.EP.Shutdown(tcpip.ShutdownRead); err != nil {
+		t.Fatalf("Shutdown failed: %v", err)
+	}
+
+	if _, _, err := c.EP.Read(nil); err != tcpip.ErrClosedForReceive {
+		t.Fatalf("got c.EP.Read(nil) = %v, want = %v", err, tcpip.ErrClosedForReceive)
+	}
+}
+
 func TestFullWindowReceive(t *testing.T) {
 	c := context.New(t, defaultMTU)
 	defer c.Cleanup()