1 | // SPDX-License-Identifier: GPL-2.0 |
2 | #define _GNU_SOURCE |
3 | #include <sched.h> |
4 | #include <stdio.h> |
5 | #include <errno.h> |
6 | #include <string.h> |
7 | #include <sys/types.h> |
8 | #include <sys/mount.h> |
9 | #include <sys/wait.h> |
10 | #include <sys/vfs.h> |
11 | #include <sys/statvfs.h> |
12 | #include <stdlib.h> |
13 | #include <unistd.h> |
14 | #include <fcntl.h> |
15 | #include <grp.h> |
16 | #include <stdbool.h> |
17 | #include <stdarg.h> |
18 | |
19 | #ifndef CLONE_NEWNS |
20 | # define CLONE_NEWNS 0x00020000 |
21 | #endif |
22 | #ifndef CLONE_NEWUTS |
23 | # define CLONE_NEWUTS 0x04000000 |
24 | #endif |
25 | #ifndef CLONE_NEWIPC |
26 | # define CLONE_NEWIPC 0x08000000 |
27 | #endif |
28 | #ifndef CLONE_NEWNET |
29 | # define CLONE_NEWNET 0x40000000 |
30 | #endif |
31 | #ifndef CLONE_NEWUSER |
32 | # define CLONE_NEWUSER 0x10000000 |
33 | #endif |
34 | #ifndef CLONE_NEWPID |
35 | # define CLONE_NEWPID 0x20000000 |
36 | #endif |
37 | |
38 | #ifndef MS_REC |
39 | # define MS_REC 16384 |
40 | #endif |
41 | #ifndef MS_RELATIME |
42 | # define MS_RELATIME (1 << 21) |
43 | #endif |
44 | #ifndef MS_STRICTATIME |
45 | # define MS_STRICTATIME (1 << 24) |
46 | #endif |
47 | |
48 | static void die(char *fmt, ...) |
49 | { |
50 | va_list ap; |
51 | va_start(ap, fmt); |
52 | vfprintf(stderr, fmt, ap); |
53 | va_end(ap); |
54 | exit(EXIT_FAILURE); |
55 | } |
56 | |
57 | static void vmaybe_write_file(bool enoent_ok, char *filename, char *fmt, va_list ap) |
58 | { |
59 | char buf[4096]; |
60 | int fd; |
61 | ssize_t written; |
62 | int buf_len; |
63 | |
64 | buf_len = vsnprintf(buf, sizeof(buf), fmt, ap); |
65 | if (buf_len < 0) { |
66 | die(fmt: "vsnprintf failed: %s\n" , |
67 | strerror(errno)); |
68 | } |
69 | if (buf_len >= sizeof(buf)) { |
70 | die(fmt: "vsnprintf output truncated\n" ); |
71 | } |
72 | |
73 | fd = open(filename, O_WRONLY); |
74 | if (fd < 0) { |
75 | if ((errno == ENOENT) && enoent_ok) |
76 | return; |
77 | die(fmt: "open of %s failed: %s\n" , |
78 | filename, strerror(errno)); |
79 | } |
80 | written = write(fd, buf, buf_len); |
81 | if (written != buf_len) { |
82 | if (written >= 0) { |
83 | die(fmt: "short write to %s\n" , filename); |
84 | } else { |
85 | die(fmt: "write to %s failed: %s\n" , |
86 | filename, strerror(errno)); |
87 | } |
88 | } |
89 | if (close(fd) != 0) { |
90 | die(fmt: "close of %s failed: %s\n" , |
91 | filename, strerror(errno)); |
92 | } |
93 | } |
94 | |
95 | static void maybe_write_file(char *filename, char *fmt, ...) |
96 | { |
97 | va_list ap; |
98 | |
99 | va_start(ap, fmt); |
100 | vmaybe_write_file(true, filename, fmt, ap); |
101 | va_end(ap); |
102 | |
103 | } |
104 | |
105 | static void write_file(char *filename, char *fmt, ...) |
106 | { |
107 | va_list ap; |
108 | |
109 | va_start(ap, fmt); |
110 | vmaybe_write_file(false, filename, fmt, ap); |
111 | va_end(ap); |
112 | |
113 | } |
114 | |
115 | static int read_mnt_flags(const char *path) |
116 | { |
117 | int ret; |
118 | struct statvfs stat; |
119 | int mnt_flags; |
120 | |
121 | ret = statvfs(path, &stat); |
122 | if (ret != 0) { |
123 | die(fmt: "statvfs of %s failed: %s\n" , |
124 | path, strerror(errno)); |
125 | } |
126 | if (stat.f_flag & ~(ST_RDONLY | ST_NOSUID | ST_NODEV | \ |
127 | ST_NOEXEC | ST_NOATIME | ST_NODIRATIME | ST_RELATIME | \ |
128 | ST_SYNCHRONOUS | ST_MANDLOCK)) { |
129 | die(fmt: "Unrecognized mount flags\n" ); |
130 | } |
131 | mnt_flags = 0; |
132 | if (stat.f_flag & ST_RDONLY) |
133 | mnt_flags |= MS_RDONLY; |
134 | if (stat.f_flag & ST_NOSUID) |
135 | mnt_flags |= MS_NOSUID; |
136 | if (stat.f_flag & ST_NODEV) |
137 | mnt_flags |= MS_NODEV; |
138 | if (stat.f_flag & ST_NOEXEC) |
139 | mnt_flags |= MS_NOEXEC; |
140 | if (stat.f_flag & ST_NOATIME) |
141 | mnt_flags |= MS_NOATIME; |
142 | if (stat.f_flag & ST_NODIRATIME) |
143 | mnt_flags |= MS_NODIRATIME; |
144 | if (stat.f_flag & ST_RELATIME) |
145 | mnt_flags |= MS_RELATIME; |
146 | if (stat.f_flag & ST_SYNCHRONOUS) |
147 | mnt_flags |= MS_SYNCHRONOUS; |
148 | if (stat.f_flag & ST_MANDLOCK) |
149 | mnt_flags |= ST_MANDLOCK; |
150 | |
151 | return mnt_flags; |
152 | } |
153 | |
154 | static void create_and_enter_userns(void) |
155 | { |
156 | uid_t uid; |
157 | gid_t gid; |
158 | |
159 | uid = getuid(); |
160 | gid = getgid(); |
161 | |
162 | if (unshare(CLONE_NEWUSER) !=0) { |
163 | die("unshare(CLONE_NEWUSER) failed: %s\n" , |
164 | strerror(errno)); |
165 | } |
166 | |
167 | maybe_write_file(filename: "/proc/self/setgroups" , fmt: "deny" ); |
168 | write_file("/proc/self/uid_map" , "0 %d 1" , uid); |
169 | write_file("/proc/self/gid_map" , "0 %d 1" , gid); |
170 | |
171 | if (setgid(0) != 0) { |
172 | die ("setgid(0) failed %s\n" , |
173 | strerror(errno)); |
174 | } |
175 | if (setuid(0) != 0) { |
176 | die("setuid(0) failed %s\n" , |
177 | strerror(errno)); |
178 | } |
179 | } |
180 | |
181 | static |
182 | bool test_unpriv_remount(const char *fstype, const char *mount_options, |
183 | int mount_flags, int remount_flags, int invalid_flags) |
184 | { |
185 | pid_t child; |
186 | |
187 | child = fork(); |
188 | if (child == -1) { |
189 | die("fork failed: %s\n" , |
190 | strerror(errno)); |
191 | } |
192 | if (child != 0) { /* parent */ |
193 | pid_t pid; |
194 | int status; |
195 | pid = waitpid(child, &status, 0); |
196 | if (pid == -1) { |
197 | die("waitpid failed: %s\n" , |
198 | strerror(errno)); |
199 | } |
200 | if (pid != child) { |
201 | die("waited for %d got %d\n" , |
202 | child, pid); |
203 | } |
204 | if (!WIFEXITED(status)) { |
205 | die(fmt: "child did not terminate cleanly\n" ); |
206 | } |
207 | return WEXITSTATUS(status) == EXIT_SUCCESS; |
208 | } |
209 | |
210 | create_and_enter_userns(); |
211 | if (unshare(CLONE_NEWNS) != 0) { |
212 | die("unshare(CLONE_NEWNS) failed: %s\n" , |
213 | strerror(errno)); |
214 | } |
215 | |
216 | if (mount("testing" , "/tmp" , fstype, mount_flags, mount_options) != 0) { |
217 | die("mount of %s with options '%s' on /tmp failed: %s\n" , |
218 | fstype, |
219 | mount_options? mount_options : "" , |
220 | strerror(errno)); |
221 | } |
222 | |
223 | create_and_enter_userns(); |
224 | |
225 | if (unshare(CLONE_NEWNS) != 0) { |
226 | die("unshare(CLONE_NEWNS) failed: %s\n" , |
227 | strerror(errno)); |
228 | } |
229 | |
230 | if (mount("/tmp" , "/tmp" , "none" , |
231 | MS_REMOUNT | MS_BIND | remount_flags, NULL) != 0) { |
232 | /* system("cat /proc/self/mounts"); */ |
233 | die("remount of /tmp failed: %s\n" , |
234 | strerror(errno)); |
235 | } |
236 | |
237 | if (mount("/tmp" , "/tmp" , "none" , |
238 | MS_REMOUNT | MS_BIND | invalid_flags, NULL) == 0) { |
239 | /* system("cat /proc/self/mounts"); */ |
240 | die(fmt: "remount of /tmp with invalid flags " |
241 | "succeeded unexpectedly\n" ); |
242 | } |
243 | exit(EXIT_SUCCESS); |
244 | } |
245 | |
246 | static bool test_unpriv_remount_simple(int mount_flags) |
247 | { |
248 | return test_unpriv_remount("ramfs" , NULL, mount_flags, mount_flags, 0); |
249 | } |
250 | |
251 | static bool test_unpriv_remount_atime(int mount_flags, int invalid_flags) |
252 | { |
253 | return test_unpriv_remount("ramfs" , NULL, mount_flags, mount_flags, |
254 | invalid_flags); |
255 | } |
256 | |
257 | static bool test_priv_mount_unpriv_remount(void) |
258 | { |
259 | pid_t child; |
260 | int ret; |
261 | const char *orig_path = "/dev" ; |
262 | const char *dest_path = "/tmp" ; |
263 | int orig_mnt_flags, remount_mnt_flags; |
264 | |
265 | child = fork(); |
266 | if (child == -1) { |
267 | die("fork failed: %s\n" , |
268 | strerror(errno)); |
269 | } |
270 | if (child != 0) { /* parent */ |
271 | pid_t pid; |
272 | int status; |
273 | pid = waitpid(child, &status, 0); |
274 | if (pid == -1) { |
275 | die("waitpid failed: %s\n" , |
276 | strerror(errno)); |
277 | } |
278 | if (pid != child) { |
279 | die("waited for %d got %d\n" , |
280 | child, pid); |
281 | } |
282 | if (!WIFEXITED(status)) { |
283 | die(fmt: "child did not terminate cleanly\n" ); |
284 | } |
285 | return WEXITSTATUS(status) == EXIT_SUCCESS; |
286 | } |
287 | |
288 | orig_mnt_flags = read_mnt_flags(path: orig_path); |
289 | |
290 | create_and_enter_userns(); |
291 | ret = unshare(CLONE_NEWNS); |
292 | if (ret != 0) { |
293 | die("unshare(CLONE_NEWNS) failed: %s\n" , |
294 | strerror(errno)); |
295 | } |
296 | |
297 | ret = mount(orig_path, dest_path, "bind" , MS_BIND | MS_REC, NULL); |
298 | if (ret != 0) { |
299 | die("recursive bind mount of %s onto %s failed: %s\n" , |
300 | orig_path, dest_path, strerror(errno)); |
301 | } |
302 | |
303 | ret = mount(dest_path, dest_path, "none" , |
304 | MS_REMOUNT | MS_BIND | orig_mnt_flags , NULL); |
305 | if (ret != 0) { |
306 | /* system("cat /proc/self/mounts"); */ |
307 | die("remount of /tmp failed: %s\n" , |
308 | strerror(errno)); |
309 | } |
310 | |
311 | remount_mnt_flags = read_mnt_flags(path: dest_path); |
312 | if (orig_mnt_flags != remount_mnt_flags) { |
313 | die(fmt: "Mount flags unexpectedly changed during remount of %s originally mounted on %s\n" , |
314 | dest_path, orig_path); |
315 | } |
316 | exit(EXIT_SUCCESS); |
317 | } |
318 | |
319 | int main(int argc, char **argv) |
320 | { |
321 | if (!test_unpriv_remount_simple(MS_RDONLY)) { |
322 | die(fmt: "MS_RDONLY malfunctions\n" ); |
323 | } |
324 | if (!test_unpriv_remount("devpts" , "newinstance" , MS_NODEV, MS_NODEV, 0)) { |
325 | die(fmt: "MS_NODEV malfunctions\n" ); |
326 | } |
327 | if (!test_unpriv_remount_simple(MS_NOSUID)) { |
328 | die(fmt: "MS_NOSUID malfunctions\n" ); |
329 | } |
330 | if (!test_unpriv_remount_simple(MS_NOEXEC)) { |
331 | die(fmt: "MS_NOEXEC malfunctions\n" ); |
332 | } |
333 | if (!test_unpriv_remount_atime(MS_RELATIME, |
334 | MS_NOATIME)) |
335 | { |
336 | die(fmt: "MS_RELATIME malfunctions\n" ); |
337 | } |
338 | if (!test_unpriv_remount_atime(MS_STRICTATIME, |
339 | MS_NOATIME)) |
340 | { |
341 | die(fmt: "MS_STRICTATIME malfunctions\n" ); |
342 | } |
343 | if (!test_unpriv_remount_atime(MS_NOATIME, |
344 | MS_STRICTATIME)) |
345 | { |
346 | die(fmt: "MS_NOATIME malfunctions\n" ); |
347 | } |
348 | if (!test_unpriv_remount_atime(MS_RELATIME|MS_NODIRATIME, |
349 | MS_NOATIME)) |
350 | { |
351 | die(fmt: "MS_RELATIME|MS_NODIRATIME malfunctions\n" ); |
352 | } |
353 | if (!test_unpriv_remount_atime(MS_STRICTATIME|MS_NODIRATIME, |
354 | MS_NOATIME)) |
355 | { |
356 | die(fmt: "MS_STRICTATIME|MS_NODIRATIME malfunctions\n" ); |
357 | } |
358 | if (!test_unpriv_remount_atime(MS_NOATIME|MS_NODIRATIME, |
359 | MS_STRICTATIME)) |
360 | { |
361 | die(fmt: "MS_NOATIME|MS_DIRATIME malfunctions\n" ); |
362 | } |
363 | if (!test_unpriv_remount("ramfs" , NULL, MS_STRICTATIME, 0, MS_NOATIME)) |
364 | { |
365 | die(fmt: "Default atime malfunctions\n" ); |
366 | } |
367 | if (!test_priv_mount_unpriv_remount()) { |
368 | die(fmt: "Mount flags unexpectedly changed after remount\n" ); |
369 | } |
370 | return EXIT_SUCCESS; |
371 | } |
372 | |