2 * Copyright © 2018 Alexey Dobriyan <adobriyan@gmail.com>
4 * Permission to use, copy, modify, and distribute this software for any
5 * purpose with or without fee is hereby granted, provided that the above
6 * copyright notice and this permission notice appear in all copies.
8 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
9 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
10 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
11 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
12 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
13 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
14 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
16 // Test that /proc/$KERNEL_THREAD/fd/ is empty.
19 #include <sys/syscall.h>
25 #include <sys/types.h>
32 #define PF_KHTREAD 0x00200000
35 * Test for kernel threadness atomically with openat().
37 * Return /proc/$PID/fd descriptor if process is kernel thread.
38 * Return -1 if a process is userspace process.
40 static int kernel_thread_fd(unsigned int pid)
42 unsigned int flags = 0;
47 snprintf(buf, sizeof(buf), "/proc/%u", pid);
48 dir_fd = open(buf, O_RDONLY|O_DIRECTORY);
53 * Believe it or not, struct task_struct::flags is directly exposed
56 fd = openat(dir_fd, "stat", O_RDONLY);
61 rv = read(fd, buf, sizeof(buf));
63 if (0 < rv && rv <= sizeof(buf)) {
64 unsigned long long flags_ull;
68 assert(buf[rv - 1] == '\n');
71 /* Search backwards: ->comm can contain whitespace and ')'. */
72 for (i = 0; i < 43; i++) {
73 p = strrchr(buf, ' ');
78 p = strrchr(buf, ' ');
81 flags_ull = xstrtoull(p + 1, &end);
83 assert(flags_ull == (unsigned int)flags_ull);
89 if (flags & PF_KHTREAD) {
90 fd = openat(dir_fd, "fd", O_RDONLY|O_DIRECTORY);
96 static void test_readdir(int fd)
105 assert(streq(de->d_name, "."));
106 assert(de->d_type == DT_DIR);
109 assert(streq(de->d_name, ".."));
110 assert(de->d_type == DT_DIR);
116 static inline int sys_statx(int dirfd, const char *pathname, int flags,
117 unsigned int mask, void *stx)
119 return syscall(SYS_statx, dirfd, pathname, flags, mask, stx);
122 static void test_lookup_fail(int fd, const char *pathname)
124 char stx[256] __attribute__((aligned(8)));
127 rv = sys_statx(fd, pathname, AT_SYMLINK_NOFOLLOW, 0, (void *)stx);
128 assert(rv == -1 && errno == ENOENT);
131 static void test_lookup(int fd)
137 for (i = INT_MIN; i < INT_MIN + 1024; i++) {
138 snprintf(buf, sizeof(buf), "%d", i);
139 test_lookup_fail(fd, buf);
141 for (i = -1024; i < 1024; i++) {
142 snprintf(buf, sizeof(buf), "%d", i);
143 test_lookup_fail(fd, buf);
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);
149 for (u = UINT_MAX - 1024; u != 0; u++) {
150 snprintf(buf, sizeof(buf), "%u", u);
151 test_lookup_fail(fd, buf);
161 * In theory this will loop indefinitely if kernel threads are exiled
164 * Start with kthreadd.
167 while ((fd = kernel_thread_fd(pid)) == -1 && pid < 1024) {
170 /* EACCES if run as non-root. */