Commit b2f5de03 authored by Alexey Dobriyan's avatar Alexey Dobriyan Committed by Linus Torvalds

tools/testing/selftests/proc: test /proc/*/fd a bit (+ PF_KTHREAD is ABI!)

* Test lookup in /proc/self/fd.
  "map_files" lookup story showed that lookup is not that simple.

* Test that all those symlinks open the same file.
  Check with (st_dev, st_info).

* Test that kernel threads do not have anything in their /proc/*/fd/
  directory.

Now this is where things get interesting.

First, kernel threads aren't pinned by /proc/self or equivalent,
thus some "atomicity" is required.

Second, ->comm can contain whitespace and ')'.
No, they are not escaped.

Third, the only reliable way to check if process is kernel thread
appears to be field #9 in /proc/*/stat.

This field is struct task_struct::flags in decimal!
Check is done by testing PF_KTHREAD flags like we do in kernel.

	PF_KTREAD value is a part of userspace ABI !!!

Other methods for determining kernel threadness are not reliable:
* RSS can be 0 if everything is swapped, even while reading
  from /proc/self.

* ->total_vm CAN BE ZERO if process is finishing

	munmap(NULL, whole address space);

* /proc/*/maps and similar files can be empty because unmapping
  everything works. Read returning 0 can't distinguish between
  kernel thread and such suicide process.

Link: http://lkml.kernel.org/r/20180505000414.GA15090@avx2Signed-off-by: default avatarAlexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 5d008fb4
/fd-001-lookup
/fd-002-posix-eq
/fd-003-kthread
/proc-loadavg-001
/proc-self-map-files-001
/proc-self-map-files-002
......
CFLAGS += -Wall -O2
CFLAGS += -Wall -O2 -Wno-unused-function
TEST_GEN_PROGS :=
TEST_GEN_PROGS += fd-001-lookup
TEST_GEN_PROGS += fd-002-posix-eq
TEST_GEN_PROGS += fd-003-kthread
TEST_GEN_PROGS += proc-loadavg-001
TEST_GEN_PROGS += proc-self-map-files-001
TEST_GEN_PROGS += proc-self-map-files-002
......
/*
* Copyright © 2018 Alexey Dobriyan <adobriyan@gmail.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 /proc/*/fd lookup.
#define _GNU_SOURCE
#undef NDEBUG
#include <assert.h>
#include <dirent.h>
#include <errno.h>
#include <limits.h>
#include <sched.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include "proc.h"
/* lstat(2) has more "coverage" in case non-symlink pops up somehow. */
static void test_lookup_pass(const char *pathname)
{
struct stat st;
ssize_t rv;
memset(&st, 0, sizeof(struct stat));
rv = lstat(pathname, &st);
assert(rv == 0);
assert(S_ISLNK(st.st_mode));
}
static void test_lookup_fail(const char *pathname)
{
struct stat st;
ssize_t rv;
rv = lstat(pathname, &st);
assert(rv == -1 && errno == ENOENT);
}
static void test_lookup(unsigned int fd)
{
char buf[64];
unsigned int c;
unsigned int u;
int i;
snprintf(buf, sizeof(buf), "/proc/self/fd/%u", fd);
test_lookup_pass(buf);
/* leading junk */
for (c = 1; c <= 255; c++) {
if (c == '/')
continue;
snprintf(buf, sizeof(buf), "/proc/self/fd/%c%u", c, fd);
test_lookup_fail(buf);
}
/* trailing junk */
for (c = 1; c <= 255; c++) {
if (c == '/')
continue;
snprintf(buf, sizeof(buf), "/proc/self/fd/%u%c", fd, c);
test_lookup_fail(buf);
}
for (i = INT_MIN; i < INT_MIN + 1024; i++) {
snprintf(buf, sizeof(buf), "/proc/self/fd/%d", i);
test_lookup_fail(buf);
}
for (i = -1024; i < 0; i++) {
snprintf(buf, sizeof(buf), "/proc/self/fd/%d", i);
test_lookup_fail(buf);
}
for (u = INT_MAX - 1024; u <= (unsigned int)INT_MAX + 1024; u++) {
snprintf(buf, sizeof(buf), "/proc/self/fd/%u", u);
test_lookup_fail(buf);
}
for (u = UINT_MAX - 1024; u != 0; u++) {
snprintf(buf, sizeof(buf), "/proc/self/fd/%u", u);
test_lookup_fail(buf);
}
}
int main(void)
{
struct dirent *de;
unsigned int fd, target_fd;
if (unshare(CLONE_FILES) == -1)
return 1;
/* Wipe fdtable. */
do {
DIR *d;
d = opendir("/proc/self/fd");
if (!d)
return 1;
de = xreaddir(d);
assert(de->d_type == DT_DIR);
assert(streq(de->d_name, "."));
de = xreaddir(d);
assert(de->d_type == DT_DIR);
assert(streq(de->d_name, ".."));
next:
de = xreaddir(d);
if (de) {
unsigned long long fd_ull;
unsigned int fd;
char *end;
assert(de->d_type == DT_LNK);
fd_ull = xstrtoull(de->d_name, &end);
assert(*end == '\0');
assert(fd_ull == (unsigned int)fd_ull);
fd = fd_ull;
if (fd == dirfd(d))
goto next;
close(fd);
}
closedir(d);
} while (de);
/* Now fdtable is clean. */
fd = open("/", O_PATH|O_DIRECTORY);
assert(fd == 0);
test_lookup(fd);
close(fd);
/* Clean again! */
fd = open("/", O_PATH|O_DIRECTORY);
assert(fd == 0);
/* Default RLIMIT_NOFILE-1 */
target_fd = 1023;
while (target_fd > 0) {
if (dup2(fd, target_fd) == target_fd)
break;
target_fd /= 2;
}
assert(target_fd > 0);
close(fd);
test_lookup(target_fd);
close(target_fd);
return 0;
}
/*
* Copyright © 2018 Alexey Dobriyan <adobriyan@gmail.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 open(/proc/*/fd/*) opens the same file.
#undef NDEBUG
#include <assert.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
int main(void)
{
int fd0, fd1, fd2;
struct stat st0, st1, st2;
char buf[64];
int rv;
fd0 = open("/", O_DIRECTORY|O_RDONLY);
assert(fd0 >= 0);
snprintf(buf, sizeof(buf), "/proc/self/fd/%u", fd0);
fd1 = open(buf, O_RDONLY);
assert(fd1 >= 0);
snprintf(buf, sizeof(buf), "/proc/thread-self/fd/%u", fd0);
fd2 = open(buf, O_RDONLY);
assert(fd2 >= 0);
rv = fstat(fd0, &st0);
assert(rv == 0);
rv = fstat(fd1, &st1);
assert(rv == 0);
rv = fstat(fd2, &st2);
assert(rv == 0);
assert(st0.st_dev == st1.st_dev);
assert(st0.st_ino == st1.st_ino);
assert(st0.st_dev == st2.st_dev);
assert(st0.st_ino == st2.st_ino);
return 0;
}
/*
* Copyright © 2018 Alexey Dobriyan <adobriyan@gmail.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 /proc/$KERNEL_THREAD/fd/ is empty.
#define _GNU_SOURCE
#undef NDEBUG
#include <sys/syscall.h>
#include <assert.h>
#include <dirent.h>
#include <limits.h>
#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include "proc.h"
#define PF_KHTREAD 0x00200000
/*
* Test for kernel threadness atomically with openat().
*
* Return /proc/$PID/fd descriptor if process is kernel thread.
* Return -1 if a process is userspace process.
*/
static int kernel_thread_fd(unsigned int pid)
{
unsigned int flags = 0;
char buf[4096];
int dir_fd, fd;
ssize_t rv;
snprintf(buf, sizeof(buf), "/proc/%u", pid);
dir_fd = open(buf, O_RDONLY|O_DIRECTORY);
if (dir_fd == -1)
return -1;
/*
* Believe it or not, struct task_struct::flags is directly exposed
* to userspace!
*/
fd = openat(dir_fd, "stat", O_RDONLY);
if (fd == -1) {
close(dir_fd);
return -1;
}
rv = read(fd, buf, sizeof(buf));
close(fd);
if (0 < rv && rv <= sizeof(buf)) {
unsigned long long flags_ull;
char *p, *end;
int i;
assert(buf[rv - 1] == '\n');
buf[rv - 1] = '\0';
/* Search backwards: ->comm can contain whitespace and ')'. */
for (i = 0; i < 43; i++) {
p = strrchr(buf, ' ');
assert(p);
*p = '\0';
}
p = strrchr(buf, ' ');
assert(p);
flags_ull = xstrtoull(p + 1, &end);
assert(*end == '\0');
assert(flags_ull == (unsigned int)flags_ull);
flags = flags_ull;
}
fd = -1;
if (flags & PF_KHTREAD) {
fd = openat(dir_fd, "fd", O_RDONLY|O_DIRECTORY);
}
close(dir_fd);
return fd;
}
static void test_readdir(int fd)
{
DIR *d;
struct dirent *de;
d = fdopendir(fd);
assert(d);
de = xreaddir(d);
assert(streq(de->d_name, "."));
assert(de->d_type == DT_DIR);
de = xreaddir(d);
assert(streq(de->d_name, ".."));
assert(de->d_type == DT_DIR);
de = xreaddir(d);
assert(!de);
}
static inline int sys_statx(int dirfd, const char *pathname, int flags,
unsigned int mask, void *stx)
{
return syscall(SYS_statx, dirfd, pathname, flags, mask, stx);
}
static void test_lookup_fail(int fd, const char *pathname)
{
char stx[256] __attribute__((aligned(8)));
int rv;
rv = sys_statx(fd, pathname, AT_SYMLINK_NOFOLLOW, 0, (void *)stx);
assert(rv == -1 && errno == ENOENT);
}
static void test_lookup(int fd)
{
char buf[64];
unsigned int u;
int i;
for (i = INT_MIN; i < INT_MIN + 1024; i++) {
snprintf(buf, sizeof(buf), "%d", i);
test_lookup_fail(fd, buf);
}
for (i = -1024; i < 1024; i++) {
snprintf(buf, sizeof(buf), "%d", i);
test_lookup_fail(fd, buf);
}
for (u = INT_MAX - 1024; u < (unsigned int)INT_MAX + 1024; u++) {
snprintf(buf, sizeof(buf), "%u", u);
test_lookup_fail(fd, buf);
}
for (u = UINT_MAX - 1024; u != 0; u++) {
snprintf(buf, sizeof(buf), "%u", u);
test_lookup_fail(fd, buf);
}
}
int main(void)
{
unsigned int pid;
int fd;
/*
* In theory this will loop indefinitely if kernel threads are exiled
* from /proc.
*
* Start with kthreadd.
*/
pid = 2;
while ((fd = kernel_thread_fd(pid)) == -1 && pid < 1024) {
pid++;
}
/* EACCES if run as non-root. */
if (pid >= 1024)
return 1;
test_readdir(fd);
test_lookup(fd);
return 0;
}
......@@ -20,21 +20,7 @@
#include <stdlib.h>
#include <unistd.h>
static unsigned long long xstrtoull(const char *p, char **end)
{
if (*p == '0') {
*end = (char *)p + 1;
return 0;
} else if ('1' <= *p && *p <= '9') {
unsigned long long val;
errno = 0;
val = strtoull(p, end, 10);
assert(errno == 0);
return val;
} else
assert(0);
}
#include "proc.h"
static void proc_uptime(int fd, uint64_t *uptime, uint64_t *idle)
{
......
#pragma once
#undef NDEBUG
#include <assert.h>
#include <dirent.h>
#include <errno.h>
#include <stdbool.h>
#include <stdlib.h>
#include <string.h>
static inline bool streq(const char *s1, const char *s2)
{
return strcmp(s1, s2) == 0;
}
static unsigned long long xstrtoull(const char *p, char **end)
{
if (*p == '0') {
*end = (char *)p + 1;
return 0;
} else if ('1' <= *p && *p <= '9') {
unsigned long long val;
errno = 0;
val = strtoull(p, end, 10);
assert(errno == 0);
return val;
} else
assert(0);
}
static struct dirent *xreaddir(DIR *d)
{
struct dirent *de;
errno = 0;
de = readdir(d);
assert(de || errno == 0);
return de;
}
......@@ -31,22 +31,7 @@
#include <fcntl.h>
#include <unistd.h>
static inline bool streq(const char *s1, const char *s2)
{
return strcmp(s1, s2) == 0;
}
static struct dirent *xreaddir(DIR *d)
{
struct dirent *de;
errno = 0;
de = readdir(d);
if (!de && errno != 0) {
exit(1);
}
return de;
}
#include "proc.h"
static void f_reg(DIR *d, const char *filename)
{
......
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