1 /* SPDX-License-Identifier: LGPL-2.1-or-later */
2
3 #include <errno.h>
4 #include <fcntl.h>
5 #include <sys/mount.h>
6
7 #include "alloc-util.h"
8 #include "chase-symlinks.h"
9 #include "fd-util.h"
10 #include "fileio.h"
11 #include "filesystems.h"
12 #include "fs-util.h"
13 #include "missing_stat.h"
14 #include "missing_syscall.h"
15 #include "mkdir.h"
16 #include "mountpoint-util.h"
17 #include "nulstr-util.h"
18 #include "parse-util.h"
19 #include "path-util.h"
20 #include "stat-util.h"
21 #include "stdio-util.h"
22 #include "strv.h"
23 #include "user-util.h"
24
25 /* This is the original MAX_HANDLE_SZ definition from the kernel, when the API was introduced. We use that in place of
26 * any more currently defined value to future-proof things: if the size is increased in the API headers, and our code
27 * is recompiled then it would cease working on old kernels, as those refuse any sizes larger than this value with
28 * EINVAL right-away. Hence, let's disconnect ourselves from any such API changes, and stick to the original definition
29 * from when it was introduced. We use it as a start value only anyway (see below), and hence should be able to deal
30 * with large file handles anyway. */
31 #define ORIGINAL_MAX_HANDLE_SZ 128
32
name_to_handle_at_loop(int fd,const char * path,struct file_handle ** ret_handle,int * ret_mnt_id,int flags)33 int name_to_handle_at_loop(
34 int fd,
35 const char *path,
36 struct file_handle **ret_handle,
37 int *ret_mnt_id,
38 int flags) {
39
40 _cleanup_free_ struct file_handle *h = NULL;
41 size_t n = ORIGINAL_MAX_HANDLE_SZ;
42
43 assert((flags & ~(AT_SYMLINK_FOLLOW|AT_EMPTY_PATH)) == 0);
44
45 /* We need to invoke name_to_handle_at() in a loop, given that it might return EOVERFLOW when the specified
46 * buffer is too small. Note that in contrast to what the docs might suggest, MAX_HANDLE_SZ is only good as a
47 * start value, it is not an upper bound on the buffer size required.
48 *
49 * This improves on raw name_to_handle_at() also in one other regard: ret_handle and ret_mnt_id can be passed
50 * as NULL if there's no interest in either. */
51
52 for (;;) {
53 int mnt_id = -1;
54
55 h = malloc0(offsetof(struct file_handle, f_handle) + n);
56 if (!h)
57 return -ENOMEM;
58
59 h->handle_bytes = n;
60
61 if (name_to_handle_at(fd, path, h, &mnt_id, flags) >= 0) {
62
63 if (ret_handle)
64 *ret_handle = TAKE_PTR(h);
65
66 if (ret_mnt_id)
67 *ret_mnt_id = mnt_id;
68
69 return 0;
70 }
71 if (errno != EOVERFLOW)
72 return -errno;
73
74 if (!ret_handle && ret_mnt_id && mnt_id >= 0) {
75
76 /* As it appears, name_to_handle_at() fills in mnt_id even when it returns EOVERFLOW when the
77 * buffer is too small, but that's undocumented. Hence, let's make use of this if it appears to
78 * be filled in, and the caller was interested in only the mount ID an nothing else. */
79
80 *ret_mnt_id = mnt_id;
81 return 0;
82 }
83
84 /* If name_to_handle_at() didn't increase the byte size, then this EOVERFLOW is caused by something
85 * else (apparently EOVERFLOW is returned for untriggered nfs4 mounts sometimes), not by the too small
86 * buffer. In that case propagate EOVERFLOW */
87 if (h->handle_bytes <= n)
88 return -EOVERFLOW;
89
90 /* The buffer was too small. Size the new buffer by what name_to_handle_at() returned. */
91 n = h->handle_bytes;
92 if (offsetof(struct file_handle, f_handle) + n < n) /* check for addition overflow */
93 return -EOVERFLOW;
94
95 h = mfree(h);
96 }
97 }
98
fd_fdinfo_mnt_id(int fd,const char * filename,int flags,int * ret_mnt_id)99 static int fd_fdinfo_mnt_id(int fd, const char *filename, int flags, int *ret_mnt_id) {
100 char path[STRLEN("/proc/self/fdinfo/") + DECIMAL_STR_MAX(int)];
101 _cleanup_free_ char *fdinfo = NULL;
102 _cleanup_close_ int subfd = -1;
103 char *p;
104 int r;
105
106 assert(ret_mnt_id);
107 assert((flags & ~(AT_SYMLINK_FOLLOW|AT_EMPTY_PATH)) == 0);
108
109 if ((flags & AT_EMPTY_PATH) && isempty(filename))
110 xsprintf(path, "/proc/self/fdinfo/%i", fd);
111 else {
112 subfd = openat(fd, filename, O_CLOEXEC|O_PATH|(flags & AT_SYMLINK_FOLLOW ? 0 : O_NOFOLLOW));
113 if (subfd < 0)
114 return -errno;
115
116 xsprintf(path, "/proc/self/fdinfo/%i", subfd);
117 }
118
119 r = read_full_virtual_file(path, &fdinfo, NULL);
120 if (r == -ENOENT) /* The fdinfo directory is a relatively new addition */
121 return -EOPNOTSUPP;
122 if (r < 0)
123 return r;
124
125 p = startswith(fdinfo, "mnt_id:");
126 if (!p) {
127 p = strstr(fdinfo, "\nmnt_id:");
128 if (!p) /* The mnt_id field is a relatively new addition */
129 return -EOPNOTSUPP;
130
131 p += 8;
132 }
133
134 p += strspn(p, WHITESPACE);
135 p[strcspn(p, WHITESPACE)] = 0;
136
137 return safe_atoi(p, ret_mnt_id);
138 }
139
filename_possibly_with_slash_suffix(const char * s)140 static bool filename_possibly_with_slash_suffix(const char *s) {
141 const char *slash, *copied;
142
143 /* Checks whether the specified string is either file name, or a filename with a suffix of
144 * slashes. But nothing else.
145 *
146 * this is OK: foo, bar, foo/, bar/, foo//, bar///
147 * this is not OK: "", "/", "/foo", "foo/bar", ".", ".." … */
148
149 slash = strchr(s, '/');
150 if (!slash)
151 return filename_is_valid(s);
152
153 if (slash - s > PATH_MAX) /* We want to allocate on the stack below, hence do a size check first */
154 return false;
155
156 if (slash[strspn(slash, "/")] != 0) /* Check that the suffix consist only of one or more slashes */
157 return false;
158
159 copied = strndupa_safe(s, slash - s);
160 return filename_is_valid(copied);
161 }
162
is_name_to_handle_at_fatal_error(int err)163 static bool is_name_to_handle_at_fatal_error(int err) {
164 /* name_to_handle_at() can return "acceptable" errors that are due to the context. For
165 * example the kernel does not support name_to_handle_at() at all (ENOSYS), or the syscall
166 * was blocked (EACCES/EPERM; maybe through seccomp, because we are running inside of a
167 * container), or the mount point is not triggered yet (EOVERFLOW, think nfs4), or some
168 * general name_to_handle_at() flakiness (EINVAL). However other errors are not supposed to
169 * happen and therefore are considered fatal ones. */
170
171 assert(err < 0);
172
173 return !IN_SET(err, -EOPNOTSUPP, -ENOSYS, -EACCES, -EPERM, -EOVERFLOW, -EINVAL);
174 }
175
fd_is_mount_point(int fd,const char * filename,int flags)176 int fd_is_mount_point(int fd, const char *filename, int flags) {
177 _cleanup_free_ struct file_handle *h = NULL, *h_parent = NULL;
178 int mount_id = -1, mount_id_parent = -1;
179 bool nosupp = false, check_st_dev = true;
180 STRUCT_STATX_DEFINE(sx);
181 struct stat a, b;
182 int r;
183
184 assert(fd >= 0);
185 assert(filename);
186 assert((flags & ~(AT_SYMLINK_FOLLOW|AT_EMPTY_PATH)) == 0);
187
188 /* Insist that the specified filename is actually a filename, and not a path, i.e. some inode further
189 * up or down the tree then immediately below the specified directory fd. */
190 if (!filename_possibly_with_slash_suffix(filename))
191 return -EINVAL;
192
193 /* First we will try statx()' STATX_ATTR_MOUNT_ROOT attribute, which is our ideal API, available
194 * since kernel 5.8.
195 *
196 * If that fails, our second try is the name_to_handle_at() syscall, which tells us the mount id and
197 * an opaque file "handle". It is not supported everywhere though (kernel compile-time option, not
198 * all file systems are hooked up). If it works the mount id is usually good enough to tell us
199 * whether something is a mount point.
200 *
201 * If that didn't work we will try to read the mount id from /proc/self/fdinfo/<fd>. This is almost
202 * as good as name_to_handle_at(), however, does not return the opaque file handle. The opaque file
203 * handle is pretty useful to detect the root directory, which we should always consider a mount
204 * point. Hence we use this only as fallback. Exporting the mnt_id in fdinfo is a pretty recent
205 * kernel addition.
206 *
207 * As last fallback we do traditional fstat() based st_dev comparisons. This is how things were
208 * traditionally done, but unionfs breaks this since it exposes file systems with a variety of st_dev
209 * reported. Also, btrfs subvolumes have different st_dev, even though they aren't real mounts of
210 * their own. */
211
212 if (statx(fd, filename, (FLAGS_SET(flags, AT_SYMLINK_FOLLOW) ? 0 : AT_SYMLINK_NOFOLLOW) |
213 (flags & AT_EMPTY_PATH) |
214 AT_NO_AUTOMOUNT, STATX_TYPE, &sx) < 0) {
215 if (!ERRNO_IS_NOT_SUPPORTED(errno) && !ERRNO_IS_PRIVILEGE(errno))
216 return -errno;
217
218 /* If statx() is not available or forbidden, fall back to name_to_handle_at() below */
219 } else if (FLAGS_SET(sx.stx_attributes_mask, STATX_ATTR_MOUNT_ROOT)) /* yay! */
220 return FLAGS_SET(sx.stx_attributes, STATX_ATTR_MOUNT_ROOT);
221 else if (FLAGS_SET(sx.stx_mask, STATX_TYPE) && S_ISLNK(sx.stx_mode))
222 return false; /* symlinks are never mount points */
223
224 r = name_to_handle_at_loop(fd, filename, &h, &mount_id, flags);
225 if (r < 0) {
226 if (is_name_to_handle_at_fatal_error(r))
227 return r;
228 if (r != -EOPNOTSUPP)
229 goto fallback_fdinfo;
230
231 /* This kernel or file system does not support name_to_handle_at(), hence let's see
232 * if the upper fs supports it (in which case it is a mount point), otherwise fall
233 * back to the traditional stat() logic */
234 nosupp = true;
235 }
236
237 r = name_to_handle_at_loop(fd, "", &h_parent, &mount_id_parent, AT_EMPTY_PATH);
238 if (r < 0) {
239 if (is_name_to_handle_at_fatal_error(r))
240 return r;
241 if (r != -EOPNOTSUPP)
242 goto fallback_fdinfo;
243 if (nosupp)
244 /* Both the parent and the directory can't do name_to_handle_at() */
245 goto fallback_fdinfo;
246
247 /* The parent can't do name_to_handle_at() but the directory we are
248 * interested in can? If so, it must be a mount point. */
249 return 1;
250 }
251
252 /* The parent can do name_to_handle_at() but the directory we are interested in can't? If
253 * so, it must be a mount point. */
254 if (nosupp)
255 return 1;
256
257 /* If the file handle for the directory we are interested in and its parent are identical,
258 * we assume this is the root directory, which is a mount point. */
259
260 if (h->handle_bytes == h_parent->handle_bytes &&
261 h->handle_type == h_parent->handle_type &&
262 memcmp(h->f_handle, h_parent->f_handle, h->handle_bytes) == 0)
263 return 1;
264
265 return mount_id != mount_id_parent;
266
267 fallback_fdinfo:
268 r = fd_fdinfo_mnt_id(fd, filename, flags, &mount_id);
269 if (IN_SET(r, -EOPNOTSUPP, -EACCES, -EPERM))
270 goto fallback_fstat;
271 if (r < 0)
272 return r;
273
274 r = fd_fdinfo_mnt_id(fd, "", AT_EMPTY_PATH, &mount_id_parent);
275 if (r < 0)
276 return r;
277
278 if (mount_id != mount_id_parent)
279 return 1;
280
281 /* Hmm, so, the mount ids are the same. This leaves one special case though for the root file
282 * system. For that, let's see if the parent directory has the same inode as we are interested
283 * in. Hence, let's also do fstat() checks now, too, but avoid the st_dev comparisons, since they
284 * aren't that useful on unionfs mounts. */
285 check_st_dev = false;
286
287 fallback_fstat:
288 /* yay for fstatat() taking a different set of flags than the other _at() above */
289 if (flags & AT_SYMLINK_FOLLOW)
290 flags &= ~AT_SYMLINK_FOLLOW;
291 else
292 flags |= AT_SYMLINK_NOFOLLOW;
293 if (fstatat(fd, filename, &a, flags) < 0)
294 return -errno;
295 if (S_ISLNK(a.st_mode)) /* Symlinks are never mount points */
296 return false;
297
298 if (fstatat(fd, "", &b, AT_EMPTY_PATH) < 0)
299 return -errno;
300
301 /* A directory with same device and inode as its parent? Must be the root directory */
302 if (stat_inode_same(&a, &b))
303 return 1;
304
305 return check_st_dev && (a.st_dev != b.st_dev);
306 }
307
308 /* flags can be AT_SYMLINK_FOLLOW or 0 */
path_is_mount_point(const char * t,const char * root,int flags)309 int path_is_mount_point(const char *t, const char *root, int flags) {
310 _cleanup_free_ char *canonical = NULL;
311 _cleanup_close_ int fd = -1;
312 int r;
313
314 assert(t);
315 assert((flags & ~AT_SYMLINK_FOLLOW) == 0);
316
317 if (path_equal(t, "/"))
318 return 1;
319
320 /* we need to resolve symlinks manually, we can't just rely on
321 * fd_is_mount_point() to do that for us; if we have a structure like
322 * /bin -> /usr/bin/ and /usr is a mount point, then the parent that we
323 * look at needs to be /usr, not /. */
324 if (flags & AT_SYMLINK_FOLLOW) {
325 r = chase_symlinks(t, root, CHASE_TRAIL_SLASH, &canonical, NULL);
326 if (r < 0)
327 return r;
328
329 t = canonical;
330 }
331
332 fd = open_parent(t, O_PATH|O_CLOEXEC, 0);
333 if (fd < 0)
334 return fd;
335
336 return fd_is_mount_point(fd, last_path_component(t), flags);
337 }
338
path_get_mnt_id(const char * path,int * ret)339 int path_get_mnt_id(const char *path, int *ret) {
340 STRUCT_NEW_STATX_DEFINE(buf);
341 int r;
342
343 if (statx(AT_FDCWD, path, AT_SYMLINK_NOFOLLOW|AT_NO_AUTOMOUNT, STATX_MNT_ID, &buf.sx) < 0) {
344 if (!ERRNO_IS_NOT_SUPPORTED(errno) && !ERRNO_IS_PRIVILEGE(errno))
345 return -errno;
346
347 /* Fall back to name_to_handle_at() and then fdinfo if statx is not supported or we lack
348 * privileges */
349
350 } else if (FLAGS_SET(buf.nsx.stx_mask, STATX_MNT_ID)) {
351 *ret = buf.nsx.stx_mnt_id;
352 return 0;
353 }
354
355 r = name_to_handle_at_loop(AT_FDCWD, path, NULL, ret, 0);
356 if (r == 0 || is_name_to_handle_at_fatal_error(r))
357 return r;
358
359 return fd_fdinfo_mnt_id(AT_FDCWD, path, 0, ret);
360 }
361
fstype_is_network(const char * fstype)362 bool fstype_is_network(const char *fstype) {
363 const char *x;
364
365 x = startswith(fstype, "fuse.");
366 if (x)
367 fstype = x;
368
369 if (nulstr_contains(filesystem_sets[FILESYSTEM_SET_NETWORK].value, fstype))
370 return true;
371
372 /* Filesystems not present in the internal database */
373 return STR_IN_SET(fstype,
374 "davfs",
375 "glusterfs",
376 "lustre",
377 "sshfs");
378 }
379
fstype_is_api_vfs(const char * fstype)380 bool fstype_is_api_vfs(const char *fstype) {
381 const FilesystemSet *fs;
382
383 FOREACH_POINTER(fs,
384 filesystem_sets + FILESYSTEM_SET_BASIC_API,
385 filesystem_sets + FILESYSTEM_SET_AUXILIARY_API,
386 filesystem_sets + FILESYSTEM_SET_PRIVILEGED_API,
387 filesystem_sets + FILESYSTEM_SET_TEMPORARY)
388 if (nulstr_contains(fs->value, fstype))
389 return true;
390
391 /* Filesystems not present in the internal database */
392 return STR_IN_SET(fstype,
393 "autofs",
394 "cpuset",
395 "devtmpfs");
396 }
397
fstype_is_blockdev_backed(const char * fstype)398 bool fstype_is_blockdev_backed(const char *fstype) {
399 const char *x;
400
401 x = startswith(fstype, "fuse.");
402 if (x)
403 fstype = x;
404
405 return !streq(fstype, "9p") && !fstype_is_network(fstype) && !fstype_is_api_vfs(fstype);
406 }
407
fstype_is_ro(const char * fstype)408 bool fstype_is_ro(const char *fstype) {
409 /* All Linux file systems that are necessarily read-only */
410 return STR_IN_SET(fstype,
411 "DM_verity_hash",
412 "cramfs",
413 "erofs",
414 "iso9660",
415 "squashfs");
416 }
417
fstype_can_discard(const char * fstype)418 bool fstype_can_discard(const char *fstype) {
419 return STR_IN_SET(fstype,
420 "btrfs",
421 "f2fs",
422 "ext4",
423 "vfat",
424 "xfs");
425 }
426
fstype_can_uid_gid(const char * fstype)427 bool fstype_can_uid_gid(const char *fstype) {
428
429 /* All file systems that have a uid=/gid= mount option that fixates the owners of all files and directories,
430 * current and future. */
431
432 return STR_IN_SET(fstype,
433 "adfs",
434 "exfat",
435 "fat",
436 "hfs",
437 "hpfs",
438 "iso9660",
439 "msdos",
440 "ntfs",
441 "vfat");
442 }
443
dev_is_devtmpfs(void)444 int dev_is_devtmpfs(void) {
445 _cleanup_fclose_ FILE *proc_self_mountinfo = NULL;
446 int mount_id, r;
447 char *e;
448
449 r = path_get_mnt_id("/dev", &mount_id);
450 if (r < 0)
451 return r;
452
453 r = fopen_unlocked("/proc/self/mountinfo", "re", &proc_self_mountinfo);
454 if (r < 0)
455 return r;
456
457 for (;;) {
458 _cleanup_free_ char *line = NULL;
459 int mid;
460
461 r = read_line(proc_self_mountinfo, LONG_LINE_MAX, &line);
462 if (r < 0)
463 return r;
464 if (r == 0)
465 break;
466
467 if (sscanf(line, "%i", &mid) != 1)
468 continue;
469
470 if (mid != mount_id)
471 continue;
472
473 e = strstr(line, " - ");
474 if (!e)
475 continue;
476
477 /* accept any name that starts with the currently expected type */
478 if (startswith(e + 3, "devtmpfs"))
479 return true;
480 }
481
482 return false;
483 }
484
mount_propagation_flags_to_string(unsigned long flags)485 const char *mount_propagation_flags_to_string(unsigned long flags) {
486
487 switch (flags & (MS_SHARED|MS_SLAVE|MS_PRIVATE)) {
488 case 0:
489 return "";
490 case MS_SHARED:
491 return "shared";
492 case MS_SLAVE:
493 return "slave";
494 case MS_PRIVATE:
495 return "private";
496 }
497
498 return NULL;
499 }
500
mount_propagation_flags_from_string(const char * name,unsigned long * ret)501 int mount_propagation_flags_from_string(const char *name, unsigned long *ret) {
502
503 if (isempty(name))
504 *ret = 0;
505 else if (streq(name, "shared"))
506 *ret = MS_SHARED;
507 else if (streq(name, "slave"))
508 *ret = MS_SLAVE;
509 else if (streq(name, "private"))
510 *ret = MS_PRIVATE;
511 else
512 return -EINVAL;
513 return 0;
514 }
515