zdtm: add mntns_pivot_root test

This creates nested mntns and does pivot_root to tmpfs mount, so that
roots of original test mntns and in nested mntns are different.

Before allowing nested mntnses with different roots in previous patch
this would fail.

Signed-off-by: Pavel Tikhomirov <ptikhomirov@virtuozzo.com>

test/zdtm/static/Makefile

@@ -401,6 +401,7 @@ TST_DIR		=				\
 		mnt_ext_dev			\
 		mnt_ext_root			\
 		mnt_ext_collision		\
+		mntns_pivot_root		\
 		mnt_tracefs			\
 		mntns_deleted			\
 		unlink_regular00		\

test/zdtm/static/mntns_pivot_root.c

@@ -0,0 +1,150 @@
+#include <sched.h>
+#include <signal.h>
+#include <fcntl.h>
+#include <sys/mman.h>
+#include <sys/mount.h>
+#include <sys/stat.h>
+#include <sys/wait.h>
+#include <linux/limits.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+
+#include "zdtmtst.h"
+#include "lock.h"
+
+const char *test_doc = "Check nested mntns with different root";
+const char *test_author = "Pavel Tikhomirov <ptikhomirov@virtuozzo.com>";
+
+char *dirname = "mntns_pivot_root.test";
+TEST_OPTION(dirname, string, "directory name", 1);
+
+char *source = "mntns_pivot_root";
+
+enum {
+	TEST_INIT = 0,
+	TEST_CHILD,
+	TEST_CHECK,
+	TEST_EXIT,
+	EMERGENCY_ABORT,
+};
+
+futex_t *futex;
+
+static int sys_pivot_root(const char *new_root, const char *put_old)
+{
+	return syscall(SYS_pivot_root, new_root, put_old);
+}
+
+#define BUF_SIZE 4096
+
+static int child(void)
+{
+	char *put_root = "put_root";
+	char *testfile = "testfile";
+	int fd;
+
+	if (unshare(CLONE_NEWNS)) {
+		pr_perror("unshare");
+		goto err;
+	}
+	/*
+	 * Setup new root
+	 */
+	mkdir(dirname, 0755);
+
+	if (mount(source, dirname, "tmpfs", 0, NULL)) {
+		pr_perror("mount tmpfs");
+		goto err;
+	}
+
+	if (mount(NULL, dirname, NULL, MS_PRIVATE, NULL)) {
+		pr_perror("make private");
+		goto err;
+	}
+
+	if (chdir(dirname)) {
+		pr_perror("chdir");
+		goto err;
+	}
+
+	mkdir(put_root, 0755);
+
+	if (sys_pivot_root(".", put_root)) {
+		pr_perror("pivot_root");
+		goto err;
+	}
+
+	if (umount2(put_root, MNT_DETACH)) {
+		pr_perror("umount2");
+		goto err;
+	}
+
+	fd = open(testfile, O_RDWR | O_CREAT | O_EXCL, 0666);
+	if (fd < 0) {
+		pr_perror("open");
+		goto err;
+	}
+	close(fd);
+
+	futex_set_and_wake(futex, TEST_CHILD);
+	futex_wait_while_lt(futex, TEST_CHECK);
+
+	if (access(testfile, F_OK)) {
+		pr_perror("access");
+		goto err;
+	}
+
+	futex_set_and_wake(futex, TEST_EXIT);
+	return 0;
+err:
+	futex_set_and_wake(futex, EMERGENCY_ABORT);
+	return 1;
+}
+
+int main(int argc, char **argv)
+{
+	int pid;
+
+	test_init(argc, argv);
+
+	/*
+	 * Setup futex for processes syncronization
+	 */
+	futex = mmap(NULL, sizeof(futex), PROT_WRITE | PROT_READ, MAP_SHARED | MAP_ANONYMOUS, -1, 0);
+	if (futex == MAP_FAILED) {
+		pr_perror("mmap");
+		return 1;
+	}
+	futex_init(futex);
+
+	/*
+	 * Fork child which would have nested mntns
+	 */
+	pid = fork();
+	if (pid < 0) {
+		pr_perror("fork");
+		return 1;
+	} else if (pid == 0) {
+		exit(child());
+	}
+
+	futex_wait_while_lt(futex, TEST_CHILD);
+	if (futex_get(futex) == EMERGENCY_ABORT) {
+		pr_err("Fail in child\n");
+		return 1;
+	}
+
+	test_daemon();
+	test_waitsig();
+
+	futex_set_and_wake(futex, TEST_CHECK);
+	futex_wait_while_lt(futex, TEST_EXIT);
+	if (futex_get(futex) == EMERGENCY_ABORT) {
+		fail("Fail in child on check stage");
+		return 1;
+	}
+
+	waitpid(pid, NULL, 0);
+	pass();
+	return 0;
+}

test/zdtm/static/mntns_pivot_root.desc

@@ -0,0 +1 @@
+{'flavor': 'ns uns', 'flags': 'suid'}