linux-kernel - Re: [PATCH] proc: test subset=pid

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Date:   Sat, 20 Mar 2021 18:54:29 +0100
From:   Alexey Gladkov <gladkov.alexey@...il.com>
To:     Alexey Dobriyan <adobriyan@...il.com>
Cc:     akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] proc: test subset=pid

On Sat, Mar 20, 2021 at 06:48:55PM +0300, Alexey Dobriyan wrote:
> Test that /proc instance mounted with
> 
> 	mount -t proc -o subset=pid
> 
> contains only ".", "..", "self", "thread-self" and pid directories.
> 
> Note:
> Currently "subset=pid" doesn't return "." and ".." via readdir.
> This must be a bug.

Ops. Good catch! Looks good to me.

Acked-by: Alexey Gladkov <gladkov.alexey@...il.com>

> Signed-off-by: Alexey Dobriyan <adobriyan@...il.com>
> ---
> 
>  tools/testing/selftests/proc/Makefile          |    1 
>  tools/testing/selftests/proc/proc-subset-pid.c |  121 +++++++++++++++++++++++++
>  2 files changed, 122 insertions(+)
> 
> --- a/tools/testing/selftests/proc/Makefile
> +++ b/tools/testing/selftests/proc/Makefile
> @@ -12,6 +12,7 @@ TEST_GEN_PROGS += proc-self-map-files-001
>  TEST_GEN_PROGS += proc-self-map-files-002
>  TEST_GEN_PROGS += proc-self-syscall
>  TEST_GEN_PROGS += proc-self-wchan
> +TEST_GEN_PROGS += proc-subset-pid
>  TEST_GEN_PROGS += proc-uptime-001
>  TEST_GEN_PROGS += proc-uptime-002
>  TEST_GEN_PROGS += read
> new file mode 100644
> --- /dev/null
> +++ b/tools/testing/selftests/proc/proc-subset-pid.c
> @@ -0,0 +1,121 @@
> +/*
> + * Copyright (c) 2021 Alexey Dobriyan <adobriyan@...il.com>
> + *
> + * Permission to use, copy, modify, and distribute this software for any
> + * purpose with or without fee is hereby granted, provided that the above
> + * copyright notice and this permission notice appear in all copies.
> + *
> + * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
> + * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
> + * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
> + * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
> + * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
> + * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
> + * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
> + */
> +/*
> + * Test that "mount -t proc -o subset=pid" hides everything but pids,
> + * /proc/self and /proc/thread-self.
> + */
> +#undef NDEBUG
> +#include <assert.h>
> +#include <errno.h>
> +#include <sched.h>
> +#include <stdbool.h>
> +#include <stdlib.h>
> +#include <string.h>
> +#include <sys/mount.h>
> +#include <sys/types.h>
> +#include <sys/stat.h>
> +#include <fcntl.h>
> +#include <dirent.h>
> +#include <unistd.h>
> +#include <stdio.h>
> +
> +static inline bool streq(const char *a, const char *b)
> +{
> +	return strcmp(a, b) == 0;
> +}
> +
> +static void make_private_proc(void)
> +{
> +	if (unshare(CLONE_NEWNS) == -1) {
> +		if (errno == ENOSYS || errno == EPERM) {
> +			exit(4);
> +		}
> +		exit(1);
> +	}
> +	if (mount(NULL, "/", NULL, MS_PRIVATE|MS_REC, NULL) == -1) {
> +		exit(1);
> +	}
> +	if (mount(NULL, "/proc", "proc", 0, "subset=pid") == -1) {
> +		exit(1);
> +	}
> +}
> +
> +static bool string_is_pid(const char *s)
> +{
> +	while (1) {
> +		switch (*s++) {
> +		case '0':case '1':case '2':case '3':case '4':
> +		case '5':case '6':case '7':case '8':case '9':
> +			continue;
> +
> +		case '\0':
> +			return true;
> +
> +		default:
> +			return false;
> +		}
> +	}
> +}
> +
> +int main(void)
> +{
> +	make_private_proc();
> +
> +	DIR *d = opendir("/proc");
> +	assert(d);
> +
> +	struct dirent *de;
> +
> +	bool dot = false;
> +	bool dot_dot = false;
> +	bool self = false;
> +	bool thread_self = false;
> +
> +	while ((de = readdir(d))) {
> +		if (streq(de->d_name, ".")) {
> +			assert(!dot);
> +			dot = true;
> +			assert(de->d_type == DT_DIR);
> +		} else if (streq(de->d_name, "..")) {
> +			assert(!dot_dot);
> +			dot_dot = true;
> +			assert(de->d_type == DT_DIR);
> +		} else if (streq(de->d_name, "self")) {
> +			assert(!self);
> +			self = true;
> +			assert(de->d_type == DT_LNK);
> +		} else if (streq(de->d_name, "thread-self")) {
> +			assert(!thread_self);
> +			thread_self = true;
> +			assert(de->d_type == DT_LNK);
> +		} else {
> +			if (!string_is_pid(de->d_name)) {
> +				fprintf(stderr, "d_name '%s'\n", de->d_name);
> +				assert(0);
> +			}
> +			assert(de->d_type == DT_DIR);
> +		}
> +	}
> +
> +	char c;
> +	int rv = readlink("/proc/cpuinfo", &c, 1);
> +	assert(rv == -1 && errno == ENOENT);
> +
> +	int fd = open("/proc/cpuinfo", O_RDONLY);
> +	assert(fd == -1 && errno == ENOENT);
> +
> +	return 0;
> +}
> 

-- 
Rgrds, legion