1/*
2 * Copyright �� 2018 Alexey Dobriyan <adobriyan@gmail.com>
3 *
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.
7 *
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.
15 */
16// Test that /proc/$KERNEL_THREAD/fd/ is empty.
17
18#undef NDEBUG
19#include <sys/syscall.h>
20#include <assert.h>
21#include <dirent.h>
22#include <limits.h>
23#include <stdio.h>
24#include <string.h>
25#include <sys/types.h>
26#include <sys/stat.h>
27#include <fcntl.h>
28#include <unistd.h>
29
30#include "proc.h"
31
32#define PF_KHTREAD 0x00200000
33
34/*
35 * Test for kernel threadness atomically with openat().
36 *
37 * Return /proc/$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 exposed
54	 * 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 exiled
162	 * 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