Re: [LTP] [PATCH STAGING v4 11/16] fchroot08: test failfs root fork inheritance

[Cyril Hrubis <chrubis@suse.cz>]

Hi!
> Verify that the root moved into failfs by fchroot() lives in the
> fs_struct which is duplicated on fork, so a child of a process with
> the failfs root also fails every absolute path lookup with
> EOPNOTSUPP.
> 
> Signed-off-by: Andrea Cervesato <andrea.cervesato@suse.com>
> ---
>  runtest/staging                               |  1 +
>  testcases/kernel/syscalls/fchroot/.gitignore  |  1 +
>  testcases/kernel/syscalls/fchroot/fchroot08.c | 69 +++++++++++++++++++++++++++
>  3 files changed, 71 insertions(+)
> 
> diff --git a/runtest/staging b/runtest/staging
> index b8954bb5a..8dfe95c4a 100644
> --- a/runtest/staging
> +++ b/runtest/staging
> @@ -7,3 +7,4 @@ fchroot04 fchroot04
>  fchroot05 fchroot05
>  fchroot06 fchroot06
>  fchroot07 fchroot07
> +fchroot08 fchroot08
> diff --git a/testcases/kernel/syscalls/fchroot/.gitignore b/testcases/kernel/syscalls/fchroot/.gitignore
> index bfa2a8ce1..0a2510d8a 100644
> --- a/testcases/kernel/syscalls/fchroot/.gitignore
> +++ b/testcases/kernel/syscalls/fchroot/.gitignore
> @@ -6,3 +6,4 @@ fchroot05
>  fchroot06
>  fchroot07
>  fchroot07_child
> +fchroot08
> diff --git a/testcases/kernel/syscalls/fchroot/fchroot08.c b/testcases/kernel/syscalls/fchroot/fchroot08.c
> new file mode 100644
> index 000000000..3180191e7
> --- /dev/null
> +++ b/testcases/kernel/syscalls/fchroot/fchroot08.c
> @@ -0,0 +1,69 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * Copyright (C) 2026 SUSE LLC Andrea Cervesato <andrea.cervesato@suse.com>
> + */
> +
> +/*\
> + * Test that the failfs root is inherited across :manpage:`fork(2)`.
> + *
> + * The root moved into failfs by :manpage:`fchroot(2)` lives in the
> + * fs_struct which is duplicated on :manpage:`fork(2)`, so a child of a process with the
> + * failfs root also fails every absolute path lookup with ``EOPNOTSUPP``.
> + *
> + * 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/wait.h>
> +#include "tst_test.h"
> +#include "lapi/fcntl.h"
> +#include "lapi/syscalls.h"
> +
> +#define ABSDIR "abs"
> +
> +static void run(void)
> +{
> +	if (SAFE_FORK())
> +		return;
> +
> +	pid_t pid;
> +
> +	TST_EXP_PASS(tst_syscall(__NR_fchroot, FD_FAILFS_ROOT, 0),
> +		"fchroot() with the FD_FAILFS_ROOT sentinel");
> +
> +	pid = SAFE_FORK();
> +	if (!pid) {
> +		TST_EXP_FAIL2(open(ABSDIR, O_PATH), EOPNOTSUPP,
> +			"absolute lookup in a forked child");
> +		exit(0);
> +	}
> +
> +	SAFE_WAITPID(pid, NULL, 0);
> +
> +	exit(0);
> +}
> +
> +static void setup(void)
> +{
> +	char *tmpdir;
> +	char abs_path[PATH_MAX];
> +
> +	tmpdir = tst_tmpdir_path();
> +	snprintf(abs_path, sizeof(abs_path), "%s/%s", tmpdir, "target");
> +
> +	SAFE_TOUCH("target", 0644, NULL);
> +	SAFE_SYMLINK(abs_path, ABSDIR);

I do not understand why we do the symlink here?

Why don't we pass the abs_path to the syscall directly?

> +}
> +
> +static struct tst_test test = {
> +	.test_all = run,
> +	.setup = setup,
> +	.needs_root = 1,
> +	.forks_child = 1,
> +	.needs_tmpdir = 1,
> +};
> 
> -- 
> 2.51.0
> 
> 
> -- 
> Mailing list info: https://lists.linux.it/listinfo/ltp

-- 
Cyril Hrubis
chrubis@suse.cz

-- 
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