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/*
* 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;
}
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