net/tcp: allow to call listen without bind

When listen(2) is called on an unbound socket, the socket is
automatically bound to a random free port with the local address
set to INADDR_ANY.

PiperOrigin-RevId: 286305906

2 files changed, 37 insertions, 9 deletions

diff --git a/pkg/tcpip/transport/tcp/endpoint.go b/pkg/tcpip/transport/tcp/endpoint.go
index dd8b47cbe..fe629aa40 100644
--- a/pkg/tcpip/transport/tcp/endpoint.go
+++ b/pkg/tcpip/transport/tcp/endpoint.go
@@ -1974,6 +1974,15 @@ func (e *endpoint) listen(backlog int) *tcpip.Error {
 		return nil
 	}
 
+	if e.state == StateInitial {
+		// The listen is called on an unbound socket, the socket is
+		// automatically bound to a random free port with the local
+		// address set to INADDR_ANY.
+		if err := e.bindLocked(tcpip.FullAddress{}); err != nil {
+			return err
+		}
+	}
+
 	// Endpoint must be bound before it can transition to listen mode.
 	if e.state != StateBound {
 		e.stats.ReadErrors.InvalidEndpointState.Increment()
@@ -2033,6 +2042,10 @@ func (e *endpoint) Bind(addr tcpip.FullAddress) (err *tcpip.Error) {
 	e.mu.Lock()
 	defer e.mu.Unlock()
 
+	return e.bindLocked(addr)
+}
+
+func (e *endpoint) bindLocked(addr tcpip.FullAddress) (err *tcpip.Error) {
 	// Don't allow binding once endpoint is not in the initial state
 	// anymore. This is because once the endpoint goes into a connected or
 	// listen state, it is already bound.
diff --git a/test/syscalls/linux/socket_inet_loopback.cc b/test/syscalls/linux/socket_inet_loopback.cc
index 5bb9d2e99..619d41901 100644
--- a/test/syscalls/linux/socket_inet_loopback.cc
+++ b/test/syscalls/linux/socket_inet_loopback.cc
@@ -102,19 +102,17 @@ TEST(BadSocketPairArgs, ValidateErrForBadCallsToSocketPair) {
               SyscallFailsWithErrno(EAFNOSUPPORT));
 }
 
-TEST_P(SocketInetLoopbackTest, TCP) {
-  auto const& param = GetParam();
-
-  TestAddress const& listener = param.listener;
-  TestAddress const& connector = param.connector;
-
+void tcpSimpleConnectTest(TestAddress const& listener,
+                          TestAddress const& connector, bool unbound) {
   // Create the listening socket.
   const FileDescriptor listen_fd = ASSERT_NO_ERRNO_AND_VALUE(
       Socket(listener.family(), SOCK_STREAM, IPPROTO_TCP));
   sockaddr_storage listen_addr = listener.addr;
-  ASSERT_THAT(bind(listen_fd.get(), reinterpret_cast<sockaddr*>(&listen_addr),
-                   listener.addr_len),
-              SyscallSucceeds());
+  if (!unbound) {
+    ASSERT_THAT(bind(listen_fd.get(), reinterpret_cast<sockaddr*>(&listen_addr),
+                     listener.addr_len),
+                SyscallSucceeds());
+  }
   ASSERT_THAT(listen(listen_fd.get(), SOMAXCONN), SyscallSucceeds());
 
   // Get the port bound by the listening socket.
@@ -148,6 +146,23 @@ TEST_P(SocketInetLoopbackTest, TCP) {
   ASSERT_THAT(shutdown(conn_fd.get(), SHUT_RDWR), SyscallSucceeds());
 }
 
+TEST_P(SocketInetLoopbackTest, TCP) {
+  auto const& param = GetParam();
+  TestAddress const& listener = param.listener;
+  TestAddress const& connector = param.connector;
+
+  tcpSimpleConnectTest(listener, connector, true);
+}
+
+TEST_P(SocketInetLoopbackTest, TCPListenUnbound) {
+  auto const& param = GetParam();
+
+  TestAddress const& listener = param.listener;
+  TestAddress const& connector = param.connector;
+
+  tcpSimpleConnectTest(listener, connector, false);
+}
+
 TEST_P(SocketInetLoopbackTest, TCPListenClose) {
   auto const& param = GetParam();