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1/*2 * Copyright © 2018 Alexey Dobriyan <adobriyan@gmail.com>3 *4 * Permission to use, copy, modify, and distribute this software for any5 * purpose with or without fee is hereby granted, provided that the above6 * copyright notice and this permission notice appear in all copies.7 *8 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES9 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF10 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR11 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES12 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN13 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF14 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.15 */16// Test that /proc/$KERNEL_THREAD/fd/ is empty.17 18#undef NDEBUG19#include <sys/syscall.h>20#include <assert.h>21#include <dirent.h>22#include <limits.h>23#include <stdio.h>24#include <string.h>25#include <sys/types.h>26#include <sys/stat.h>27#include <fcntl.h>28#include <unistd.h>29 30#include "proc.h"31 32#define PF_KHTREAD 0x0020000033 34/*35 * Test for kernel threadness atomically with openat().36 *37 * Return /proc/$PID/fd descriptor if process is kernel thread.38 * Return -1 if a process is userspace process.39 */40static int kernel_thread_fd(unsigned int pid)41{42 unsigned int flags = 0;43 char buf[4096];44 int dir_fd, fd;45 ssize_t rv;46 47 snprintf(buf, sizeof(buf), "/proc/%u", pid);48 dir_fd = open(buf, O_RDONLY|O_DIRECTORY);49 if (dir_fd == -1)50 return -1;51 52 /*53 * Believe it or not, struct task_struct::flags is directly exposed54 * to userspace!55 */56 fd = openat(dir_fd, "stat", O_RDONLY);57 if (fd == -1) {58 close(dir_fd);59 return -1;60 }61 rv = read(fd, buf, sizeof(buf));62 close(fd);63 if (0 < rv && rv <= sizeof(buf)) {64 unsigned long long flags_ull;65 char *p, *end;66 int i;67 68 assert(buf[rv - 1] == '\n');69 buf[rv - 1] = '\0';70 71 /* Search backwards: ->comm can contain whitespace and ')'. */72 for (i = 0; i < 43; i++) {73 p = strrchr(buf, ' ');74 assert(p);75 *p = '\0';76 }77 78 p = strrchr(buf, ' ');79 assert(p);80 81 flags_ull = xstrtoull(p + 1, &end);82 assert(*end == '\0');83 assert(flags_ull == (unsigned int)flags_ull);84 85 flags = flags_ull;86 }87 88 fd = -1;89 if (flags & PF_KHTREAD) {90 fd = openat(dir_fd, "fd", O_RDONLY|O_DIRECTORY);91 }92 close(dir_fd);93 return fd;94}95 96static void test_readdir(int fd)97{98 DIR *d;99 struct dirent *de;100 101 d = fdopendir(fd);102 assert(d);103 104 de = xreaddir(d);105 assert(streq(de->d_name, "."));106 assert(de->d_type == DT_DIR);107 108 de = xreaddir(d);109 assert(streq(de->d_name, ".."));110 assert(de->d_type == DT_DIR);111 112 de = xreaddir(d);113 assert(!de);114}115 116static inline int sys_statx(int dirfd, const char *pathname, int flags,117 unsigned int mask, void *stx)118{119 return syscall(SYS_statx, dirfd, pathname, flags, mask, stx);120}121 122static void test_lookup_fail(int fd, const char *pathname)123{124 char stx[256] __attribute__((aligned(8)));125 int rv;126 127 rv = sys_statx(fd, pathname, AT_SYMLINK_NOFOLLOW, 0, (void *)stx);128 assert(rv == -1 && errno == ENOENT);129}130 131static void test_lookup(int fd)132{133 char buf[64];134 unsigned int u;135 int i;136 137 for (i = INT_MIN; i < INT_MIN + 1024; i++) {138 snprintf(buf, sizeof(buf), "%d", i);139 test_lookup_fail(fd, buf);140 }141 for (i = -1024; i < 1024; i++) {142 snprintf(buf, sizeof(buf), "%d", i);143 test_lookup_fail(fd, buf);144 }145 for (u = INT_MAX - 1024; u < (unsigned int)INT_MAX + 1024; u++) {146 snprintf(buf, sizeof(buf), "%u", u);147 test_lookup_fail(fd, buf);148 }149 for (u = UINT_MAX - 1024; u != 0; u++) {150 snprintf(buf, sizeof(buf), "%u", u);151 test_lookup_fail(fd, buf);152 }153}154 155int main(void)156{157 unsigned int pid;158 int fd;159 160 /*161 * In theory this will loop indefinitely if kernel threads are exiled162 * from /proc.163 *164 * Start with kthreadd.165 */166 pid = 2;167 while ((fd = kernel_thread_fd(pid)) == -1 && pid < 1024) {168 pid++;169 }170 /* EACCES if run as non-root. */171 if (pid >= 1024)172 return 1;173 174 test_readdir(fd);175 test_lookup(fd);176 177 return 0;178}179