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Linux/tools/testing/selftests/mount/unprivileged-remount-test.c

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  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("vsnprintf failed: %s\n",
 67                     strerror(errno));
 68         }
 69         if (buf_len >= sizeof(buf)) {
 70                 die("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("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("short write to %s\n", filename);
 84                 } else {
 85                         die("write to %s failed: %s\n",
 86                                 filename, strerror(errno));
 87                 }
 88         }
 89         if (close(fd) != 0) {
 90                 die("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("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("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("/proc/self/setgroups", "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("child did not terminate cleanly\n");
206                 }
207                 return WEXITSTATUS(status) == EXIT_SUCCESS ? true : false;
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("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("child did not terminate cleanly\n");
284                 }
285                 return WEXITSTATUS(status) == EXIT_SUCCESS ? true : false;
286         }
287 
288         orig_mnt_flags = read_mnt_flags(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(dest_path);
312         if (orig_mnt_flags != remount_mnt_flags) {
313                 die("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("MS_RDONLY malfunctions\n");
323         }
324         if (!test_unpriv_remount("devpts", "newinstance", MS_NODEV, MS_NODEV, 0)) {
325                 die("MS_NODEV malfunctions\n");
326         }
327         if (!test_unpriv_remount_simple(MS_NOSUID)) {
328                 die("MS_NOSUID malfunctions\n");
329         }
330         if (!test_unpriv_remount_simple(MS_NOEXEC)) {
331                 die("MS_NOEXEC malfunctions\n");
332         }
333         if (!test_unpriv_remount_atime(MS_RELATIME,
334                                        MS_NOATIME))
335         {
336                 die("MS_RELATIME malfunctions\n");
337         }
338         if (!test_unpriv_remount_atime(MS_STRICTATIME,
339                                        MS_NOATIME))
340         {
341                 die("MS_STRICTATIME malfunctions\n");
342         }
343         if (!test_unpriv_remount_atime(MS_NOATIME,
344                                        MS_STRICTATIME))
345         {
346                 die("MS_NOATIME malfunctions\n");
347         }
348         if (!test_unpriv_remount_atime(MS_RELATIME|MS_NODIRATIME,
349                                        MS_NOATIME))
350         {
351                 die("MS_RELATIME|MS_NODIRATIME malfunctions\n");
352         }
353         if (!test_unpriv_remount_atime(MS_STRICTATIME|MS_NODIRATIME,
354                                        MS_NOATIME))
355         {
356                 die("MS_STRICTATIME|MS_NODIRATIME malfunctions\n");
357         }
358         if (!test_unpriv_remount_atime(MS_NOATIME|MS_NODIRATIME,
359                                        MS_STRICTATIME))
360         {
361                 die("MS_NOATIME|MS_DIRATIME malfunctions\n");
362         }
363         if (!test_unpriv_remount("ramfs", NULL, MS_STRICTATIME, 0, MS_NOATIME))
364         {
365                 die("Default atime malfunctions\n");
366         }
367         if (!test_priv_mount_unpriv_remount()) {
368                 die("Mount flags unexpectedly changed after remount\n");
369         }
370         return EXIT_SUCCESS;
371 }
372 

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