fix: fix open AF_INET sockets in s2n_self_talk_ktls_test.c

[boquan-fang]

Resolved issues:

Partially solve #4005. Detected opened AF_INET sockets in s2n_self_talk_ktls_test.c.

Description of changes:

• Remove fork in s2n_new_inet_socket_pair, and do connect and accept in the same process.
• Close a file fd, that was left opened.

Call-outs:

• This problem is detected while running the open fds check.
  • The result shows such leak in Ubuntu 22 and 24 (test results for awslc, openssl-3.0, and openssl-1.0.2).
  • Previous check on open fds were ran on Ubuntu 18. KTLS is not support on our Ubuntu 18 platform, so the test is skipped. Hence, such problem was not detected previously.

Removing fork doesn't change the test behavior.

Logical Explanations: Given that our sockets are initialized as blocking sockets, accept will be blocked and wait for its first connection request if no connection is previously requested. This behavior is specified in the man page for accept. With fork, if accept is called before connect, the parent process will be blocked and switch to child process where connect will be called. We can move the connect function call into the main process before accept to make sure the test will not be blocked. connect function doesn't expect accept to be called before it, so it won't block the process.

The purpose of s2n_new_inet_socket_pair is to set up io_pair's client and server with AF_INET sockets, so that io_pair can be used in the test for KTLS communications. The test behaviors won't be changed, as long as s2n_new_inet_socket_pair fulfills that purpose.

Concerns if the function failed: If such change makes s2n_new_inet_socket_pair failed, then unit tests running in CI will fail the test. Local test might still passes, since I didn't set the S2N_KTLS_TESTING_EXPECTED environment variable locally. Because of the check, the test might just ends if the s2n_new_inet_socket_pair fails.

s2n-tls/tests/unit/s2n_self_talk_ktls_test.c

Lines 168 to 175 in c58f23c

	if (s2n_result_is_error(s2n_new_inet_socket_pair(&io_pair))) {
	/* We should be able to setup AF_INET sockets everywhere, but if
	* we can't, don't block the build unless the build explicitly expects
	* to be able to test ktls.
	*/
	EXPECT_FALSE(ktls_expected);
	END_TEST();
	}

However, that would leads to a very small number of tests passed, since this check is located at the beginning of the test. I checked the number of tests that passed after the change which is 682, that means the function didn't failed and the test is fully executed.

Testing:

• Test it locally, and all opened AF_INET sockets are closed in s2n_self_talk_ktls_test.c.
• Test it in codebuild with the newly proposed open fds check.
• The test for this PR is ran in a branch which has valgrind open fds check.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.