zdtm: Check c/r of anonymous mounts

"anonymous" mounts are those created via open_tree with OPEN_TREE_CLONE
and get unmounted when the fd returned by open_tree is closed. They can
also be mounted to the filesystem using move_mount() and openat2() can
be used to create files inside them.

Signed-off-by: Bhavik Sachdev <b.sachdev1904@gmail.com>

test/zdtm/static/Makefile

@@ -398,6 +398,7 @@ TST_DIR		=				\
 		cwd00				\
 		cwd01				\
 		cwd02				\
+		anonymous_mount			\
 		unmounted_mount			\
 		unmounted_bind_mount		\
 		overmount_dev			\

test/zdtm/static/anonymous_mount.c

@@ -0,0 +1,140 @@
+#include <fcntl.h>
+#include <linux/limits.h>
+#include <linux/openat2.h>
+#include <stdint.h>
+#include <sys/types.h>
+#include <unistd.h>
+#include <sys/stat.h>
+#include <sys/syscall.h>
+#include <inttypes.h>
+#include <sys/mount.h>
+
+#include "zdtmtst.h"
+
+const char *test_doc = "Check whether CRIU can c/r a fd pointing to a anonymous mount created using open_tree";
+const char *test_author = "Bhavik Sachdev <b.sachdev1904@gmail.com>";
+
+char *dirname;
+TEST_OPTION(dirname, string, "directory name", 1);
+
+#define TEST_FILE "anonymous-mount-file"
+#define BUFLEN	  1000
+
+#ifndef OPEN_TREE_CLONE
+#define OPEN_TREE_CLONE (1 << 0)
+#endif
+
+#ifndef MOVE_MOUNT_F_EMPTY_PATH
+#define MOVE_MOUNT_F_EMPTY_PATH 0x00000004
+#endif
+
+long sys_openat2(int dirfd, const char *pathname, struct open_how *how, size_t size)
+{
+	return syscall(__NR_openat2, dirfd, pathname, how, size);
+}
+
+long sys_open_tree(int dirfd, char *filename, unsigned int flags)
+{
+	return syscall(__NR_open_tree, dirfd, filename, flags);
+}
+
+long sys_move_mount(int from_dfd, char *from_pathname, int to_dfd,
+		    char *to_pathname, unsigned int flags)
+{
+	return syscall(__NR_move_mount, from_dfd, from_pathname, to_dfd,
+		       to_pathname, flags);
+}
+
+int main(int argc, char *argv[])
+{
+	int mntfd, fd, ret = 1;
+	uint32_t crc = ~0;
+	struct open_how how = {};
+	uint8_t buf[BUFLEN];
+
+	test_init(argc, argv);
+
+	if (mkdir(dirname, 0700)) {
+		pr_perror("mkdir %s", dirname);
+		return 1;
+	}
+
+	/* create a mount point at dirname */
+	if (mount("none", dirname, "tmpfs", 0, NULL)) {
+		pr_perror("mount %s", dirname);
+		return 1;
+	}
+
+	/* create a abstract (detached) clone mount of this mount */
+	mntfd = sys_open_tree(AT_FDCWD, dirname, OPEN_TREE_CLONE);
+	if (mntfd < 0) {
+		pr_perror("open_tree");
+		return 1;
+	}
+
+	how.flags = O_CREAT | O_RDWR;
+	how.mode = 0600;
+	how.resolve = 0;
+	/* open a file inside the (detached) clone */
+	fd = sys_openat2(mntfd, TEST_FILE, &how, sizeof(how));
+	if (fd < 0) {
+		pr_perror("openat2");
+		return 1;
+	}
+
+	datagen(buf, BUFLEN, &crc);
+	if (write(fd, buf, BUFLEN) != BUFLEN) {
+		pr_perror("write");
+		return 1;
+	}
+
+	/* unmount the original */
+	if (umount(dirname)) {
+		pr_perror("umount %s", dirname);
+		return 1;
+	}
+
+	close(fd);
+
+	test_daemon();
+	test_waitsig();
+
+	/* verify the contents of the file inside anonymous mount */
+	how.flags = O_RDONLY;
+	how.mode = 0;
+	how.resolve = 0;
+
+	fd = sys_openat2(mntfd, TEST_FILE, &how, sizeof(how));
+	if (fd < 0) {
+		pr_perror("openat2");
+		close(mntfd);
+		return 1;
+	}
+
+	if (read(fd, buf, BUFLEN) != BUFLEN) {
+		pr_perror("read");
+		goto out;
+	}
+
+	crc = ~0;
+	if (datachk(buf, BUFLEN, &crc)) {
+		fail("Data mismatch");
+		goto out;
+	}
+
+	/* we should still be able to create mount using mntfd */
+	if (sys_move_mount(mntfd, "", AT_FDCWD, dirname, MOVE_MOUNT_F_EMPTY_PATH)) {
+		if (errno != ENOSYS) {
+			pr_perror("move_mount");
+			goto out;
+		}
+	}
+
+	pass();
+	ret = 0;
+out:
+	close(fd);
+	umount(dirname);
+	close(mntfd);
+	return ret;
+}

test/zdtm/static/anonymous_mount.desc

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