github.com/kubiko/snapd@v0.0.0-20201013125620-d4f3094d9ddf/cmd/libsnap-confine-private/locking-test.c

/*
 * Copyright (C) 2017 Canonical Ltd
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 3 as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 */

#include "locking.h"
#include "locking.c"

#include "../libsnap-confine-private/cleanup-funcs.h"
#include "../libsnap-confine-private/test-utils.h"

#include <errno.h>

#include <glib.h>
#include <glib/gstdio.h>

// Set alternate locking directory
static void sc_set_lock_dir(const char *dir)
{
	sc_lock_dir = dir;
}

// A variant of unsetenv that is compatible with GDestroyNotify
static void my_unsetenv(const char *k)
{
	unsetenv(k);
}

// Use temporary directory for locking.
//
// The directory is automatically reset to the real value at the end of the
// test.
static const char *sc_test_use_fake_lock_dir(void)
{
	char *lock_dir = NULL;
	if (g_test_subprocess()) {
		// Check if the environment variable is set. If so then someone is already
		// managing the temporary directory and we should not create a new one.
		lock_dir = getenv("SNAP_CONFINE_LOCK_DIR");
		g_assert_nonnull(lock_dir);
	} else {
		lock_dir = g_dir_make_tmp(NULL, NULL);
		g_assert_nonnull(lock_dir);
		g_test_queue_free(lock_dir);
		g_assert_cmpint(setenv("SNAP_CONFINE_LOCK_DIR", lock_dir, 0),
				==, 0);
		g_test_queue_destroy((GDestroyNotify) my_unsetenv,
				     "SNAP_CONFINE_LOCK_DIR");
		g_test_queue_destroy((GDestroyNotify) rm_rf_tmp, lock_dir);
	}
	g_test_queue_destroy((GDestroyNotify) sc_set_lock_dir, SC_LOCK_DIR);
	sc_set_lock_dir(lock_dir);
	return lock_dir;
}

// Check that locking a namespace actually flock's the mutex with LOCK_EX
static void test_sc_lock_unlock(void)
{
	if (geteuid() != 0) {
		g_test_skip("this test only runs as root");
		return;
	}

	const char *lock_dir = sc_test_use_fake_lock_dir();
	int fd = sc_lock_generic("foo", 123);
	// Construct the name of the lock file
	char *lock_file SC_CLEANUP(sc_cleanup_string) = NULL;
	lock_file = g_strdup_printf("%s/foo.123.lock", lock_dir);
	// Open the lock file again to obtain a separate file descriptor.
	// According to flock(2) locks are associated with an open file table entry
	// so this descriptor will be separate and can compete for the same lock.
	int lock_fd SC_CLEANUP(sc_cleanup_close) = -1;
	lock_fd = open(lock_file, O_RDWR | O_CLOEXEC | O_NOFOLLOW);
	g_assert_cmpint(lock_fd, !=, -1);
	// The non-blocking lock operation should fail with EWOULDBLOCK as the lock
	// file is locked by sc_nlock_ns_mutex() already.
	int err = flock(lock_fd, LOCK_EX | LOCK_NB);
	int saved_errno = errno;
	g_assert_cmpint(err, ==, -1);
	g_assert_cmpint(saved_errno, ==, EWOULDBLOCK);
	// Unlock the lock.
	sc_unlock(fd);
	// Re-attempt the locking operation. This time it should succeed.
	err = flock(lock_fd, LOCK_EX | LOCK_NB);
	g_assert_cmpint(err, ==, 0);
}

// Check that holding a lock is properly detected.
static void test_sc_verify_snap_lock__locked(void)
{
	if (geteuid() != 0) {
		g_test_skip("this test only runs as root");
		return;
	}

	(void)sc_test_use_fake_lock_dir();
	int fd = sc_lock_snap("foo");
	sc_verify_snap_lock("foo");
	sc_unlock(fd);
}

// Check that holding a lock is properly detected.
static void test_sc_verify_snap_lock__unlocked(void)
{
	if (geteuid() != 0) {
		g_test_skip("this test only runs as root");
		return;
	}

	(void)sc_test_use_fake_lock_dir();
	if (g_test_subprocess()) {
		sc_verify_snap_lock("foo");
		return;
	}
	g_test_trap_subprocess(NULL, 0, 0);
	g_test_trap_assert_failed();
	g_test_trap_assert_stderr
	    ("unexpectedly managed to acquire exclusive lock over snap foo\n");
}

static void test_sc_enable_sanity_timeout(void)
{
	if (geteuid() != 0) {
		g_test_skip("this test only runs as root");
		return;
	}

	if (g_test_subprocess()) {
		sc_enable_sanity_timeout();
		debug("waiting...");
		usleep(7 * G_USEC_PER_SEC);
		debug("woke up");
		sc_disable_sanity_timeout();
		return;
	}
	g_test_trap_subprocess(NULL, 1 * G_USEC_PER_SEC,
			       G_TEST_SUBPROCESS_INHERIT_STDERR);
	g_test_trap_assert_failed();
	g_test_trap_assert_stderr
	    ("sanity timeout expired: Interrupted system call\n");
}

static void __attribute__((constructor)) init(void)
{
	g_test_add_func("/locking/sc_lock_unlock", test_sc_lock_unlock);
	g_test_add_func("/locking/sc_enable_sanity_timeout",
			test_sc_enable_sanity_timeout);
	g_test_add_func("/locking/sc_verify_snap_lock__locked",
			test_sc_verify_snap_lock__locked);
	g_test_add_func("/locking/sc_verify_snap_lock__unlocked",
			test_sc_verify_snap_lock__unlocked);
}