Improve TCPFinWait2Test syscall test

This test was under specified in that it does not try to bind to same
local address before the second connect. This is problematic as we
may see unexpected passes because the second connect can just use any
other port to succeed, while the true intention for this test is to
reuse the exact same port as the first connect.

PiperOrigin-RevId: 612666475

test/syscalls/linux/BUILD

@@ -3212,6 +3212,7 @@ cc_binary(
         ":socket_inet_loopback_test_params",
         ":socket_netlink_util",
         "//test/util:capability_util",
+        "//test/util:save_util",
         "//test/util:socket_util",
         "//test/util:test_main",
         "//test/util:test_util",

test/syscalls/linux/socket_inet_loopback_isolated.cc

@@ -21,6 +21,7 @@
 #include "absl/time/time.h"
 #include "test/syscalls/linux/socket_inet_loopback_test_params.h"
 #include "test/util/capability_util.h"
+#include "test/util/save_util.h"
 #include "test/util/socket_util.h"
 #include "test/util/test_util.h"
 
@@ -134,7 +135,7 @@ TEST_P(SocketInetLoopbackIsolatedTest, TCPPassiveCloseNoTimeWaitReuseTest) {
 // trigger FIN_WAIT2 state for the closed endpoint. Then it binds the same local
 // IP/port on a new socket and tries to connect. The connect should fail w/
 // an EADDRINUSE. Then we wait till the FIN_WAIT2 timeout is over and try the
-// connect again with a new socket and this time it should succeed.
+// bind/connect again with a new socket and this time it should succeed.
 //
 // TCP timers are not S/R today, this can cause this test to be flaky when run
 // under random S/R due to timer being reset on a restore.
@@ -143,6 +144,11 @@ TEST_P(SocketInetLoopbackIsolatedTest, TCPFinWait2Test) {
   TestAddress const& listener = param.listener;
   TestAddress const& connector = param.connector;
 
+  // Disable cooperative saves after this point. As a save between the first
+  // bind/connect and the second one can cause the linger timeout timer to
+  // be restarted causing the final bind/connect to fail.
+  DisableSave ds;
+
   // Create the listening socket.
   const FileDescriptor listen_fd = ASSERT_NO_ERRNO_AND_VALUE(
       Socket(listener.family(), SOCK_STREAM, IPPROTO_TCP));
@@ -194,11 +200,6 @@ TEST_P(SocketInetLoopbackIsolatedTest, TCPFinWait2Test) {
   const FileDescriptor conn_fd2 = ASSERT_NO_ERRNO_AND_VALUE(
       Socket(connector.family(), SOCK_STREAM, IPPROTO_TCP));
 
-  // Disable cooperative saves after this point. As a save between the first
-  // bind/connect and the second one can cause the linger timeout timer to
-  // be restarted causing the final bind/connect to fail.
-  DisableSave ds;
-
   ASSERT_THAT(bind(conn_fd2.get(), AsSockAddr(&conn_bound_addr), conn_addrlen),
               SyscallFailsWithErrno(EADDRINUSE));
 
@@ -206,7 +207,8 @@ TEST_P(SocketInetLoopbackIsolatedTest, TCPFinWait2Test) {
   // save/restore tests.
   absl::SleepFor(absl::Seconds(kTCPLingerTimeout + 2));
 
-  ds.reset();
+  ASSERT_THAT(bind(conn_fd2.get(), AsSockAddr(&conn_bound_addr), conn_addrlen),
+              SyscallSucceeds());
 
   ASSERT_THAT(
       RetryEINTR(connect)(conn_fd2.get(), AsSockAddr(&conn_addr), conn_addrlen),