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1 /***
2 This file is part of systemd.
3
4 Copyright 2010 Lennart Poettering
5
6 systemd is free software; you can redistribute it and/or modify it
7 under the terms of the GNU Lesser General Public License as published by
8 the Free Software Foundation; either version 2.1 of the License, or
9 (at your option) any later version.
10
11 systemd is distributed in the hope that it will be useful, but
12 WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 Lesser General Public License for more details.
15
16 You should have received a copy of the GNU Lesser General Public License
17 along with systemd; If not, see <http://www.gnu.org/licenses/>.
18 ***/
19
20 #include <errno.h>
21 #include <stdlib.h>
22 #include <string.h>
23 #include <sys/mount.h>
24 #include <sys/stat.h>
25 #include <sys/statvfs.h>
26 #include <unistd.h>
27
28 #include "alloc-util.h"
29 #include "escape.h"
30 #include "fd-util.h"
31 #include "fileio.h"
32 #include "hashmap.h"
33 #include "mount-util.h"
34 #include "parse-util.h"
35 #include "path-util.h"
36 #include "set.h"
37 #include "stdio-util.h"
38 #include "string-util.h"
39
40 static int fd_fdinfo_mnt_id(int fd, const char *filename, int flags, int *mnt_id) {
41 char path[strlen("/proc/self/fdinfo/") + DECIMAL_STR_MAX(int)];
42 _cleanup_free_ char *fdinfo = NULL;
43 _cleanup_close_ int subfd = -1;
44 char *p;
45 int r;
46
47 if ((flags & AT_EMPTY_PATH) && isempty(filename))
48 xsprintf(path, "/proc/self/fdinfo/%i", fd);
49 else {
50 subfd = openat(fd, filename, O_RDONLY|O_CLOEXEC|O_NOCTTY|O_PATH);
51 if (subfd < 0)
52 return -errno;
53
54 xsprintf(path, "/proc/self/fdinfo/%i", subfd);
55 }
56
57 r = read_full_file(path, &fdinfo, NULL);
58 if (r == -ENOENT) /* The fdinfo directory is a relatively new addition */
59 return -EOPNOTSUPP;
60 if (r < 0)
61 return -errno;
62
63 p = startswith(fdinfo, "mnt_id:");
64 if (!p) {
65 p = strstr(fdinfo, "\nmnt_id:");
66 if (!p) /* The mnt_id field is a relatively new addition */
67 return -EOPNOTSUPP;
68
69 p += 8;
70 }
71
72 p += strspn(p, WHITESPACE);
73 p[strcspn(p, WHITESPACE)] = 0;
74
75 return safe_atoi(p, mnt_id);
76 }
77
78
79 int fd_is_mount_point(int fd, const char *filename, int flags) {
80 union file_handle_union h = FILE_HANDLE_INIT, h_parent = FILE_HANDLE_INIT;
81 int mount_id = -1, mount_id_parent = -1;
82 bool nosupp = false, check_st_dev = true;
83 struct stat a, b;
84 int r;
85
86 assert(fd >= 0);
87 assert(filename);
88
89 /* First we will try the name_to_handle_at() syscall, which
90 * tells us the mount id and an opaque file "handle". It is
91 * not supported everywhere though (kernel compile-time
92 * option, not all file systems are hooked up). If it works
93 * the mount id is usually good enough to tell us whether
94 * something is a mount point.
95 *
96 * If that didn't work we will try to read the mount id from
97 * /proc/self/fdinfo/<fd>. This is almost as good as
98 * name_to_handle_at(), however, does not return the
99 * opaque file handle. The opaque file handle is pretty useful
100 * to detect the root directory, which we should always
101 * consider a mount point. Hence we use this only as
102 * fallback. Exporting the mnt_id in fdinfo is a pretty recent
103 * kernel addition.
104 *
105 * As last fallback we do traditional fstat() based st_dev
106 * comparisons. This is how things were traditionally done,
107 * but unionfs breaks breaks this since it exposes file
108 * systems with a variety of st_dev reported. Also, btrfs
109 * subvolumes have different st_dev, even though they aren't
110 * real mounts of their own. */
111
112 r = name_to_handle_at(fd, filename, &h.handle, &mount_id, flags);
113 if (r < 0) {
114 if (errno == ENOSYS)
115 /* This kernel does not support name_to_handle_at()
116 * fall back to simpler logic. */
117 goto fallback_fdinfo;
118 else if (errno == EOPNOTSUPP)
119 /* This kernel or file system does not support
120 * name_to_handle_at(), hence let's see if the
121 * upper fs supports it (in which case it is a
122 * mount point), otherwise fallback to the
123 * traditional stat() logic */
124 nosupp = true;
125 else
126 return -errno;
127 }
128
129 r = name_to_handle_at(fd, "", &h_parent.handle, &mount_id_parent, AT_EMPTY_PATH);
130 if (r < 0) {
131 if (errno == EOPNOTSUPP) {
132 if (nosupp)
133 /* Neither parent nor child do name_to_handle_at()?
134 We have no choice but to fall back. */
135 goto fallback_fdinfo;
136 else
137 /* The parent can't do name_to_handle_at() but the
138 * directory we are interested in can?
139 * If so, it must be a mount point. */
140 return 1;
141 } else
142 return -errno;
143 }
144
145 /* The parent can do name_to_handle_at() but the
146 * directory we are interested in can't? If so, it
147 * must be a mount point. */
148 if (nosupp)
149 return 1;
150
151 /* If the file handle for the directory we are
152 * interested in and its parent are identical, we
153 * assume this is the root directory, which is a mount
154 * point. */
155
156 if (h.handle.handle_bytes == h_parent.handle.handle_bytes &&
157 h.handle.handle_type == h_parent.handle.handle_type &&
158 memcmp(h.handle.f_handle, h_parent.handle.f_handle, h.handle.handle_bytes) == 0)
159 return 1;
160
161 return mount_id != mount_id_parent;
162
163 fallback_fdinfo:
164 r = fd_fdinfo_mnt_id(fd, filename, flags, &mount_id);
165 if (r == -EOPNOTSUPP)
166 goto fallback_fstat;
167 if (r < 0)
168 return r;
169
170 r = fd_fdinfo_mnt_id(fd, "", AT_EMPTY_PATH, &mount_id_parent);
171 if (r < 0)
172 return r;
173
174 if (mount_id != mount_id_parent)
175 return 1;
176
177 /* Hmm, so, the mount ids are the same. This leaves one
178 * special case though for the root file system. For that,
179 * let's see if the parent directory has the same inode as we
180 * are interested in. Hence, let's also do fstat() checks now,
181 * too, but avoid the st_dev comparisons, since they aren't
182 * that useful on unionfs mounts. */
183 check_st_dev = false;
184
185 fallback_fstat:
186 /* yay for fstatat() taking a different set of flags than the other
187 * _at() above */
188 if (flags & AT_SYMLINK_FOLLOW)
189 flags &= ~AT_SYMLINK_FOLLOW;
190 else
191 flags |= AT_SYMLINK_NOFOLLOW;
192 if (fstatat(fd, filename, &a, flags) < 0)
193 return -errno;
194
195 if (fstatat(fd, "", &b, AT_EMPTY_PATH) < 0)
196 return -errno;
197
198 /* A directory with same device and inode as its parent? Must
199 * be the root directory */
200 if (a.st_dev == b.st_dev &&
201 a.st_ino == b.st_ino)
202 return 1;
203
204 return check_st_dev && (a.st_dev != b.st_dev);
205 }
206
207 /* flags can be AT_SYMLINK_FOLLOW or 0 */
208 int path_is_mount_point(const char *t, int flags) {
209 _cleanup_close_ int fd = -1;
210 _cleanup_free_ char *canonical = NULL, *parent = NULL;
211
212 assert(t);
213
214 if (path_equal(t, "/"))
215 return 1;
216
217 /* we need to resolve symlinks manually, we can't just rely on
218 * fd_is_mount_point() to do that for us; if we have a structure like
219 * /bin -> /usr/bin/ and /usr is a mount point, then the parent that we
220 * look at needs to be /usr, not /. */
221 if (flags & AT_SYMLINK_FOLLOW) {
222 canonical = canonicalize_file_name(t);
223 if (!canonical)
224 return -errno;
225
226 t = canonical;
227 }
228
229 parent = dirname_malloc(t);
230 if (!parent)
231 return -ENOMEM;
232
233 fd = openat(AT_FDCWD, parent, O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC|O_PATH);
234 if (fd < 0)
235 return -errno;
236
237 return fd_is_mount_point(fd, basename(t), flags);
238 }
239
240 int umount_recursive(const char *prefix, int flags) {
241 bool again;
242 int n = 0, r;
243
244 /* Try to umount everything recursively below a
245 * directory. Also, take care of stacked mounts, and keep
246 * unmounting them until they are gone. */
247
248 do {
249 _cleanup_fclose_ FILE *proc_self_mountinfo = NULL;
250
251 again = false;
252 r = 0;
253
254 proc_self_mountinfo = fopen("/proc/self/mountinfo", "re");
255 if (!proc_self_mountinfo)
256 return -errno;
257
258 for (;;) {
259 _cleanup_free_ char *path = NULL, *p = NULL;
260 int k;
261
262 k = fscanf(proc_self_mountinfo,
263 "%*s " /* (1) mount id */
264 "%*s " /* (2) parent id */
265 "%*s " /* (3) major:minor */
266 "%*s " /* (4) root */
267 "%ms " /* (5) mount point */
268 "%*s" /* (6) mount options */
269 "%*[^-]" /* (7) optional fields */
270 "- " /* (8) separator */
271 "%*s " /* (9) file system type */
272 "%*s" /* (10) mount source */
273 "%*s" /* (11) mount options 2 */
274 "%*[^\n]", /* some rubbish at the end */
275 &path);
276 if (k != 1) {
277 if (k == EOF)
278 break;
279
280 continue;
281 }
282
283 r = cunescape(path, UNESCAPE_RELAX, &p);
284 if (r < 0)
285 return r;
286
287 if (!path_startswith(p, prefix))
288 continue;
289
290 if (umount2(p, flags) < 0) {
291 r = -errno;
292 continue;
293 }
294
295 again = true;
296 n++;
297
298 break;
299 }
300
301 } while (again);
302
303 return r ? r : n;
304 }
305
306 static int get_mount_flags(const char *path, unsigned long *flags) {
307 struct statvfs buf;
308
309 if (statvfs(path, &buf) < 0)
310 return -errno;
311 *flags = buf.f_flag;
312 return 0;
313 }
314
315 int bind_remount_recursive(const char *prefix, bool ro) {
316 _cleanup_set_free_free_ Set *done = NULL;
317 _cleanup_free_ char *cleaned = NULL;
318 int r;
319
320 /* Recursively remount a directory (and all its submounts)
321 * read-only or read-write. If the directory is already
322 * mounted, we reuse the mount and simply mark it
323 * MS_BIND|MS_RDONLY (or remove the MS_RDONLY for read-write
324 * operation). If it isn't we first make it one. Afterwards we
325 * apply MS_BIND|MS_RDONLY (or remove MS_RDONLY) to all
326 * submounts we can access, too. When mounts are stacked on
327 * the same mount point we only care for each individual
328 * "top-level" mount on each point, as we cannot
329 * influence/access the underlying mounts anyway. We do not
330 * have any effect on future submounts that might get
331 * propagated, they migt be writable. This includes future
332 * submounts that have been triggered via autofs. */
333
334 cleaned = strdup(prefix);
335 if (!cleaned)
336 return -ENOMEM;
337
338 path_kill_slashes(cleaned);
339
340 done = set_new(&string_hash_ops);
341 if (!done)
342 return -ENOMEM;
343
344 for (;;) {
345 _cleanup_fclose_ FILE *proc_self_mountinfo = NULL;
346 _cleanup_set_free_free_ Set *todo = NULL;
347 bool top_autofs = false;
348 char *x;
349 unsigned long orig_flags;
350
351 todo = set_new(&string_hash_ops);
352 if (!todo)
353 return -ENOMEM;
354
355 proc_self_mountinfo = fopen("/proc/self/mountinfo", "re");
356 if (!proc_self_mountinfo)
357 return -errno;
358
359 for (;;) {
360 _cleanup_free_ char *path = NULL, *p = NULL, *type = NULL;
361 int k;
362
363 k = fscanf(proc_self_mountinfo,
364 "%*s " /* (1) mount id */
365 "%*s " /* (2) parent id */
366 "%*s " /* (3) major:minor */
367 "%*s " /* (4) root */
368 "%ms " /* (5) mount point */
369 "%*s" /* (6) mount options (superblock) */
370 "%*[^-]" /* (7) optional fields */
371 "- " /* (8) separator */
372 "%ms " /* (9) file system type */
373 "%*s" /* (10) mount source */
374 "%*s" /* (11) mount options (bind mount) */
375 "%*[^\n]", /* some rubbish at the end */
376 &path,
377 &type);
378 if (k != 2) {
379 if (k == EOF)
380 break;
381
382 continue;
383 }
384
385 r = cunescape(path, UNESCAPE_RELAX, &p);
386 if (r < 0)
387 return r;
388
389 /* Let's ignore autofs mounts. If they aren't
390 * triggered yet, we want to avoid triggering
391 * them, as we don't make any guarantees for
392 * future submounts anyway. If they are
393 * already triggered, then we will find
394 * another entry for this. */
395 if (streq(type, "autofs")) {
396 top_autofs = top_autofs || path_equal(cleaned, p);
397 continue;
398 }
399
400 if (path_startswith(p, cleaned) &&
401 !set_contains(done, p)) {
402
403 r = set_consume(todo, p);
404 p = NULL;
405
406 if (r == -EEXIST)
407 continue;
408 if (r < 0)
409 return r;
410 }
411 }
412
413 /* If we have no submounts to process anymore and if
414 * the root is either already done, or an autofs, we
415 * are done */
416 if (set_isempty(todo) &&
417 (top_autofs || set_contains(done, cleaned)))
418 return 0;
419
420 if (!set_contains(done, cleaned) &&
421 !set_contains(todo, cleaned)) {
422 /* The prefix directory itself is not yet a
423 * mount, make it one. */
424 if (mount(cleaned, cleaned, NULL, MS_BIND|MS_REC, NULL) < 0)
425 return -errno;
426
427 orig_flags = 0;
428 (void) get_mount_flags(cleaned, &orig_flags);
429 orig_flags &= ~MS_RDONLY;
430
431 if (mount(NULL, prefix, NULL, orig_flags|MS_BIND|MS_REMOUNT|(ro ? MS_RDONLY : 0), NULL) < 0)
432 return -errno;
433
434 x = strdup(cleaned);
435 if (!x)
436 return -ENOMEM;
437
438 r = set_consume(done, x);
439 if (r < 0)
440 return r;
441 }
442
443 while ((x = set_steal_first(todo))) {
444
445 r = set_consume(done, x);
446 if (r == -EEXIST || r == 0)
447 continue;
448 if (r < 0)
449 return r;
450
451 /* Try to reuse the original flag set, but
452 * don't care for errors, in case of
453 * obstructed mounts */
454 orig_flags = 0;
455 (void) get_mount_flags(x, &orig_flags);
456 orig_flags &= ~MS_RDONLY;
457
458 if (mount(NULL, x, NULL, orig_flags|MS_BIND|MS_REMOUNT|(ro ? MS_RDONLY : 0), NULL) < 0) {
459
460 /* Deal with mount points that are
461 * obstructed by a later mount */
462
463 if (errno != ENOENT)
464 return -errno;
465 }
466
467 }
468 }
469 }
470
471 int mount_move_root(const char *path) {
472 assert(path);
473
474 if (chdir(path) < 0)
475 return -errno;
476
477 if (mount(path, "/", NULL, MS_MOVE, NULL) < 0)
478 return -errno;
479
480 if (chroot(".") < 0)
481 return -errno;
482
483 if (chdir("/") < 0)
484 return -errno;
485
486 return 0;
487 }
488
489 bool fstype_is_network(const char *fstype) {
490 static const char table[] =
491 "afs\0"
492 "cifs\0"
493 "smbfs\0"
494 "sshfs\0"
495 "ncpfs\0"
496 "ncp\0"
497 "nfs\0"
498 "nfs4\0"
499 "gfs\0"
500 "gfs2\0"
501 "glusterfs\0";
502
503 const char *x;
504
505 x = startswith(fstype, "fuse.");
506 if (x)
507 fstype = x;
508
509 return nulstr_contains(table, fstype);
510 }
511
512 int repeat_unmount(const char *path, int flags) {
513 bool done = false;
514
515 assert(path);
516
517 /* If there are multiple mounts on a mount point, this
518 * removes them all */
519
520 for (;;) {
521 if (umount2(path, flags) < 0) {
522
523 if (errno == EINVAL)
524 return done;
525
526 return -errno;
527 }
528
529 done = true;
530 }
531 }