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/$KERNEL_THREAD/fd/ is empty.
17 #define _GNU_SOURCE
18 #undef NDEBUG
19 #include <sys/syscall.h>
20 #include <assert.h>
21 #include <dirent.h>
22 #include <limits.h>
23 #include <stdio.h>
24 #include <string.h>
25 #include <sys/types.h>
26 #include <sys/stat.h>
27 #include <fcntl.h>
28 #include <unistd.h>
29
30 #include "proc.h"
31
32 #define PF_KHTREAD 0x00200000
33
34 /*
35 * Test for kernel threadness atomically with openat().
36 *
37 * Return /proc/$PID/fd descriptor if process is kernel thread.
38 * Return -1 if a process is userspace process.
39 */
kernel_thread_fd(unsigned int pid)40 static 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
test_readdir(int fd)96 static 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
sys_statx(int dirfd,const char * pathname,int flags,unsigned int mask,void * stx)116 static 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
test_lookup_fail(int fd,const char * pathname)122 static 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
test_lookup(int fd)131 static 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
main(void)155 int 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
