From 7743f313c3855fcc3d11f107843be56663203384 Mon Sep 17 00:00:00 2001
From: Zeling Feng <zeling@google.com>
Date: Tue, 16 May 2023 15:38:39 -0700
Subject: [PATCH] Add a syscall test to test address conflicts during `connect`

When SO_REUSEADDR is enabled, it is possible to create two connections with the
same 4-tuple, the error is only reported when `connect` instead of `bind`, also
the reported errno is `EADDRNOTAVAIL` instead of `EADDRINUSE`.

PiperOrigin-RevId: 532593923
---
 pkg/tcpip/transport/tcp/endpoint.go           |  3 +
 .../linux/socket_inet_loopback_isolated.cc    | 61 +++++++++++++++++++
 2 files changed, 64 insertions(+)

diff --git a/pkg/tcpip/transport/tcp/endpoint.go b/pkg/tcpip/transport/tcp/endpoint.go
index b9d1de679..ffd8eb415 100644
--- a/pkg/tcpip/transport/tcp/endpoint.go
+++ b/pkg/tcpip/transport/tcp/endpoint.go
@@ -2425,6 +2425,9 @@ func (e *endpoint) connect(addr tcpip.FullAddress, handshake bool) tcpip.Error {
 	e.setEndpointState(StateConnecting)
 	if err := e.registerEndpoint(addr, netProto, r.NICID()); err != nil {
 		e.setEndpointState(oldState)
+		if _, ok := err.(*tcpip.ErrPortInUse); ok {
+			return &tcpip.ErrBadLocalAddress{}
+		}
 		return err
 	}
 
diff --git a/test/syscalls/linux/socket_inet_loopback_isolated.cc b/test/syscalls/linux/socket_inet_loopback_isolated.cc
index 7c8f3d502..9f80c829e 100644
--- a/test/syscalls/linux/socket_inet_loopback_isolated.cc
+++ b/test/syscalls/linux/socket_inet_loopback_isolated.cc
@@ -13,7 +13,9 @@
 // limitations under the License.
 
 #include <netinet/tcp.h>
+#include <sys/socket.h>
 
+#include "gmock/gmock.h"
 #include "gtest/gtest.h"
 #include "absl/time/clock.h"
 #include "absl/time/time.h"
@@ -291,6 +293,65 @@ TEST_P(SocketInetLoopbackIsolatedTest, TCPLinger2TimeoutAfterClose) {
       SyscallSucceeds());
 }
 
+TEST_P(SocketInetLoopbackIsolatedTest, TCPConnectionReuseAddrConflicts) {
+  SocketInetTestParam const& param = GetParam();
+  TestAddress const& listener = param.listener;
+  TestAddress const& connector = param.connector;
+
+  const FileDescriptor listen_fd =
+      ASSERT_NO_ERRNO_AND_VALUE(Socket(listener.family(), SOCK_STREAM, 0));
+
+  sockaddr_storage listen_addr = listener.addr;
+  ASSERT_THAT(
+      bind(listen_fd.get(), AsSockAddr(&listen_addr), listener.addr_len),
+      SyscallSucceeds());
+  ASSERT_THAT(listen(listen_fd.get(), SOMAXCONN), SyscallSucceeds());
+
+  // Get the port bound by the listening socket.
+  socklen_t addrlen = listener.addr_len;
+  ASSERT_THAT(getsockname(listen_fd.get(), AsSockAddr(&listen_addr), &addrlen),
+              SyscallSucceeds());
+
+  const uint16_t port =
+      ASSERT_NO_ERRNO_AND_VALUE(AddrPort(listener.family(), listen_addr));
+
+  // Create a first connection.
+  FileDescriptor conn_fd1 = ASSERT_NO_ERRNO_AND_VALUE(
+      Socket(connector.family(), SOCK_STREAM, IPPROTO_TCP));
+  ASSERT_THAT(setsockopt(conn_fd1.get(), SOL_SOCKET, SO_REUSEADDR, &kSockOptOn,
+                         sizeof(kSockOptOn)),
+              SyscallSucceeds());
+
+  sockaddr_storage conn_addr = connector.addr;
+  ASSERT_NO_ERRNO(SetAddrPort(connector.family(), &conn_addr, port));
+  ASSERT_THAT(RetryEINTR(connect)(conn_fd1.get(), AsSockAddr(&conn_addr),
+                                  connector.addr_len),
+              SyscallSucceeds());
+  sockaddr_storage conn_bound_addr;
+  addrlen = sizeof(conn_bound_addr);
+  ASSERT_THAT(
+      getsockname(conn_fd1.get(), AsSockAddr(&conn_bound_addr), &addrlen),
+      SyscallSucceeds());
+  ASSERT_EQ(addrlen, connector.addr_len);
+
+  // Create the second connection that is bind to the same local address as the
+  // first.
+  FileDescriptor conn_fd2 = ASSERT_NO_ERRNO_AND_VALUE(
+      Socket(connector.family(), SOCK_STREAM, IPPROTO_TCP));
+  ASSERT_THAT(setsockopt(conn_fd2.get(), SOL_SOCKET, SO_REUSEADDR, &kSockOptOn,
+                         sizeof(kSockOptOn)),
+              SyscallSucceeds());
+  // Bind should succeed.
+  ASSERT_THAT(bind(conn_fd2.get(), AsSockAddr(&conn_bound_addr), addrlen),
+              SyscallSucceeds());
+
+  // Connect should fail.
+  ASSERT_NO_ERRNO(SetAddrPort(connector.family(), &conn_addr, port));
+  ASSERT_THAT(RetryEINTR(connect)(conn_fd2.get(), AsSockAddr(&conn_addr),
+                                  connector.addr_len),
+              SyscallFailsWithErrno(EADDRNOTAVAIL));
+}
+
 INSTANTIATE_TEST_SUITE_P(All, SocketInetLoopbackIsolatedTest,
                          SocketInetLoopbackTestValues(),
                          DescribeSocketInetTestParam);