[LTP] [PATCH v6] mount08.c: Restrict overmounting of ephemeral entities

[Petr Vorel]

Hi Wei, all,

> Add a new test to verify that mount will raise ENOENT if we try to mount
> on magic links under /proc/<pid>/fd/<nr>.
> Refer to the following kernel commit for more information:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=d80b065bb172

...
> --- /dev/null
> +++ b/testcases/kernel/syscalls/mount/mount08.c
> @@ -0,0 +1,57 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * Copyright (C) 2024 Wei Gao <wegao@suse.com>
> + */
> +
> +/*\
> + * Verify that mount will raise ENOENT if we try to mount on magic links
> + * under /proc/<pid>/fd/<nr>.
> + */
> +
> +#include "tst_test.h"
> +#include <sys/mount.h>
> +#include "tst_safe_file_at.h"
> +
> +#define MNTPOINT "mntpoint"
> +#define FOO MNTPOINT "/foo"
> +#define BAR MNTPOINT "/bar"
> +
> +static void run(void)
> +{
> +	char path[PATH_MAX];
> +	int fd, proc_fd;
> +
> +	fd = SAFE_OPEN(FOO, O_RDONLY | O_NONBLOCK, 0640);
> +
> +	sprintf(path, "/proc/%d/fd/%d", getpid(), fd);
> +
> +	proc_fd = SAFE_OPENAT(AT_FDCWD, path, O_PATH | O_NOFOLLOW);
> +
> +	sprintf(path, "/proc/%d/fd/%d", getpid(), proc_fd);
> +
> +	TST_EXP_FAIL(
> +		mount(BAR, path, "", MS_BIND, 0),
> +		ENOENT,
> +		"mount(%s)", path

FYI Test is failing on Tumbleweed 6.15.7, can you please have look?
mount08.c:32: TFAIL: mount(/proc/130511/fd/4) expected ENOENT: EACCES (13)

As Tumbleweed is very close to mainline kernel it will probably fail on mainline
as well. But maybe it's one of few Tumbleweed patches which causes that.

Kind regards,
Petr

> +	);
> +
> +	SAFE_CLOSE(fd);
> +	SAFE_CLOSE(proc_fd);
> +}
> +
> +static void setup(void)
> +{
> +	SAFE_TOUCH(FOO, 0777, NULL);
> +	SAFE_TOUCH(BAR, 0777, NULL);
> +}
> +
> +static struct tst_test test = {
> +	.setup = setup,
> +	.test_all = run,
> +	.needs_root = 1,
> +	.mntpoint = MNTPOINT,
> +	.tags = (const struct tst_tag[]) {
> +		{"linux-git", "d80b065bb172"},
> +		{}
> +	}
> +};