[LTP] [PATCH STAGING v2 09/16] fchroot06: test path walks under failfs root

[Cyril Hrubis]

Hi!
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * Copyright (C) 2026 SUSE LLC Andrea Cervesato <andrea.cervesato@suse.com>
> + */
> +
> +/*\
> + * Test path walks under the failfs root.
> + *
> + * Once :manpage:`fchroot(2)` moved the process root into failfs, only
> + * lookups anchored at a file descriptor keep working:
> + *
> + * - lookups relative to the working directory, which stays in the real
> + *   filesystem, keep working
> + * - lookups anchored at a pre-opened directory fd keep working, including
> + *   resolution of relative symlinks
> + * - absolute symlinks restart the walk at the failfs root and fail with
> + *   ``EOPNOTSUPP``
> + * - ".." walks clamp at the top of the mount tree, not at the failfs
> + *   root, so walking up from the working directory lands on the real
> + *   root
> + *
> + * Root is required because entering failfs with the ``FD_FAILFS_ROOT``
> + * sentinel requires ``CAP_SYS_CHROOT``.
> + *
> + * The test runs in a forked child so the root of the parent process is
> + * left untouched.
> + */
> +
> +#define _GNU_SOURCE
> +#include <fcntl.h>
> +#include <sys/stat.h>
> +#include "tst_test.h"
> +#include "lapi/fcntl.h"
> +#include "lapi/syscalls.h"
> +#include "tst_safe_file_at.h"
> +
> +#define RELDIR "rel"
> +#define ABSDIR "abs"
> +
> +static char upwards[PATH_MAX];
> +
> +static void run(void)
> +{
> +	if (SAFE_FORK())
> +		return;
> +
> +	struct stat realroot, st;
> +	int dfd, fd;
> +
> +	SAFE_STAT("/", &realroot);
> +	dfd = SAFE_OPEN(".", O_RDONLY | O_DIRECTORY);
> +
> +	TST_EXP_PASS(tst_syscall(__NR_fchroot, FD_FAILFS_ROOT, 0),
> +		"fchroot() with the FD_FAILFS_ROOT sentinel");
> +
> +	fd = SAFE_OPENAT(AT_FDCWD, ".", O_RDONLY | O_DIRECTORY);
> +	SAFE_CLOSE(fd);

This is a test right? So it should be TST_EXP_FD(openat(...));

> +	fd = SAFE_OPENAT(dfd, "canary", O_WRONLY | O_CREAT, 0600);
> +	SAFE_WRITE(SAFE_WRITE_ALL, fd, "x", 1);
> +	SAFE_CLOSE(fd);
> +
> +	fd = SAFE_OPENAT(dfd, RELDIR, O_RDONLY);
> +	SAFE_CLOSE(fd);

These as well.

> +	TST_EXP_FAIL2(openat(dfd, ABSDIR, O_RDONLY), EOPNOTSUPP,
> +		"resolution of an absolute symlink");
> +
> +	fd = SAFE_OPENAT(AT_FDCWD, upwards, O_PATH);
> +	SAFE_FSTAT(fd, &st);
> +	SAFE_CLOSE(fd);

And here.

> +	TST_EXP_EXPR(st.st_dev == realroot.st_dev &&
> +		st.st_ino == realroot.st_ino,
> +		"'..' walk clamps at the top of the mount tree");
> +
> +	SAFE_CLOSE(dfd);
> +
> +	exit(0);
> +}
> +
> +static void setup(void)
> +{
> +	char *tmpdir;
> +	char abs_path[PATH_MAX];
> +	struct stat root_st, st;
> +	int fd, off;
> +
> +	tmpdir = tst_tmpdir_path();
> +	snprintf(abs_path, sizeof(abs_path), "%s/%s", tmpdir, "target");
> +
> +	SAFE_TOUCH("target", 0644, NULL);
> +	SAFE_SYMLINK("target", RELDIR);
> +	SAFE_SYMLINK(abs_path, ABSDIR);
> +
> +	SAFE_STAT("/", &root_st);
> +
> +	off = snprintf(upwards, sizeof(upwards), "..");
> +	while (1) {
> +		fd = SAFE_OPENAT(AT_FDCWD, upwards, O_PATH);
> +		SAFE_FSTAT(fd, &st);
> +		SAFE_CLOSE(fd);
> +
> +		if (st.st_dev == root_st.st_dev && st.st_ino == root_st.st_ino)
> +			break;
> +
> +		off += snprintf(upwards + off, sizeof(upwards) - off, "/..");
> +	}
> +}
> +
> +static struct tst_test test = {
> +	.setup = setup,
> +	.test_all = run,
> +	.needs_root = 1,
> +	.needs_tmpdir = 1,
> +	.forks_child = 1,
> +};
> 
> -- 
> 2.51.0
> 
> 
> -- 
> Mailing list info: https://lists.linux.it/listinfo/ltp

-- 
Cyril Hrubis
chrubis@suse.cz