fix: close all /dev/urandom open fds

[boquan-fang]

Resolved issues:

Partially solve #4005

Description of changes:

• Directly call s2n_rand_cleanup to close /dev/urandom in s2n_drbg_test.c and s2n_override_openssl_random_test.c.
  • s2n_drbg_test.c and s2n_override_openssl_random_test.c calls s2n_rand_set_callbacks function which resets the default cleanup callback functions.
  • The rand_cleanup_callback parameter is supposed to close /dev/urandom, but s2n_cleanup no longer calls that function, since that parameter is overwritten to some other clean up functions, like nist_fake_entropy_init_cleanup.
  • Hence, I call s2n_rand_cleanup to run those fake clean up call back functions, and reset those call back functions back to default.
  • In that way, END_TEST will cleanup the default callbacks set by BEGIN_TEST, so that the default callbacks won't leak fds.
  • The solution is to call s2n_rand_cleanup to cleanup the default random callbacks. Then we call s2n_rand_init to reinitiate the randomness engine again.
• Some other options I tried for the previous problem
  • Implement another possible fix. Look for that comment for reasons why it wouldn't work.
  • Call s2n_rand_set_callbacks before BEGIN_TEST.
    • s2n_drbg_test.c wants to pass two different generators to s2n_rand_set_callbacks, so fix a generator before BEGIN_TEST will change the test itself.
• Close /dev/urandom in s2n_fork_generation_number_test.c.
  • Call s2n_rand_clean_up() directly for the reason of this comment.
• Close dev_urandom in s2n_random_test.c for both test 0 and 1.
  • For test 1, we need to close the original fd for dev_urandom before we make that fd invalid.

Call-outs:

• See PR#4833 and PR#4834 for fixes of other open fds.
• I didn't add a test in this PR. The test to detect all opened fds will be in a separate PR.

Testing:

• Test locally.
  • Add --track-fds=yes to CTest memcheck and direct all Valgrind output to MemoryTester.log files.
  • Search in VS Code for Open File Descriptors of /dev/urandom.
    • Previously opened /dev/urandom in tests that are fixed.
  • This is similar to the check in ./codebuild/bin/test_exec_leak.sh.
    

    s2n-tls/codebuild/bin/test_exec_leak.sh

    Lines 82 to 97 in 6bb195c

    	# run valgrind with track-fds enabled
    	valgrind_log_dir=valgrind_log_dir
    	for test_file in detect_exec_leak detect_exec_leak_finish; do
    	LD_LIBRARY_PATH="build/lib:$TARGET_LIBCRYPTO_PATH/lib:$LD_LIBRARY_PATH" S2N_VALGRIND=1 \
    	valgrind --leak-check=full --show-leak-kinds=all --errors-for-leak-kinds=all \
    	--run-libc-freeres=yes -q --gen-suppressions=all --track-fds=yes \
    	--leak-resolution=high --undef-value-errors=no --trace-children=yes \
    	--suppressions=tests/unit/valgrind.suppressions --log-file="build/$valgrind_log_dir/$test_file" \
    	build/bin/$test_file
    	# search for all leaked file descriptors, excluding the valgrind_log_dir file
    	cat build/$valgrind_log_dir/$test_file | \
    	grep "Open file descriptor" | \
    	grep --invert-match $valgrind_log_dir \
    	&& fail "file leak detected while running $test_file"
    	done

• Open fds test will be implemented once PR#4851 is merged.

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

[lrstewart]

As discussed offline, this change needs better documentation / explanation. That means some combination of code comments, expanding the PR description, and moving the s2n_rand_cleanup calls closer to the code that requires the cleanup.

It's not obvious that you're calling s2n_rand_cleanup to cleanup/reset custom callbacks, so that END_TEST will cleanup the default callbacks set by BEGIN_TEST, so that the default callbacks won't leak fds.