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049af8ad ZJS |
1 | /* SPDX-License-Identifier: LGPL-2.1+ */ |
2 | ||
3 | #include <errno.h> | |
4 | #include <fcntl.h> | |
049af8ad ZJS |
5 | #include <sys/mount.h> |
6 | ||
7 | #include "alloc-util.h" | |
8 | #include "fd-util.h" | |
9 | #include "fileio.h" | |
10 | #include "fs-util.h" | |
69b3fa14 LP |
11 | #include "missing_stat.h" |
12 | #include "missing_syscall.h" | |
049af8ad ZJS |
13 | #include "mountpoint-util.h" |
14 | #include "parse-util.h" | |
15 | #include "path-util.h" | |
7cd296c2 | 16 | #include "stat-util.h" |
049af8ad ZJS |
17 | #include "stdio-util.h" |
18 | #include "strv.h" | |
19 | ||
20 | /* This is the original MAX_HANDLE_SZ definition from the kernel, when the API was introduced. We use that in place of | |
21 | * any more currently defined value to future-proof things: if the size is increased in the API headers, and our code | |
22 | * is recompiled then it would cease working on old kernels, as those refuse any sizes larger than this value with | |
23 | * EINVAL right-away. Hence, let's disconnect ourselves from any such API changes, and stick to the original definition | |
24 | * from when it was introduced. We use it as a start value only anyway (see below), and hence should be able to deal | |
25 | * with large file handles anyway. */ | |
26 | #define ORIGINAL_MAX_HANDLE_SZ 128 | |
27 | ||
28 | int name_to_handle_at_loop( | |
29 | int fd, | |
30 | const char *path, | |
31 | struct file_handle **ret_handle, | |
32 | int *ret_mnt_id, | |
33 | int flags) { | |
34 | ||
35 | _cleanup_free_ struct file_handle *h = NULL; | |
36 | size_t n = ORIGINAL_MAX_HANDLE_SZ; | |
37 | ||
ffaf45e4 LP |
38 | assert((flags & ~(AT_SYMLINK_FOLLOW|AT_EMPTY_PATH)) == 0); |
39 | ||
049af8ad ZJS |
40 | /* We need to invoke name_to_handle_at() in a loop, given that it might return EOVERFLOW when the specified |
41 | * buffer is too small. Note that in contrast to what the docs might suggest, MAX_HANDLE_SZ is only good as a | |
42 | * start value, it is not an upper bound on the buffer size required. | |
43 | * | |
44 | * This improves on raw name_to_handle_at() also in one other regard: ret_handle and ret_mnt_id can be passed | |
45 | * as NULL if there's no interest in either. */ | |
46 | ||
47 | for (;;) { | |
48 | int mnt_id = -1; | |
49 | ||
50 | h = malloc0(offsetof(struct file_handle, f_handle) + n); | |
51 | if (!h) | |
52 | return -ENOMEM; | |
53 | ||
54 | h->handle_bytes = n; | |
55 | ||
56 | if (name_to_handle_at(fd, path, h, &mnt_id, flags) >= 0) { | |
57 | ||
58 | if (ret_handle) | |
59 | *ret_handle = TAKE_PTR(h); | |
60 | ||
61 | if (ret_mnt_id) | |
62 | *ret_mnt_id = mnt_id; | |
63 | ||
64 | return 0; | |
65 | } | |
66 | if (errno != EOVERFLOW) | |
67 | return -errno; | |
68 | ||
69 | if (!ret_handle && ret_mnt_id && mnt_id >= 0) { | |
70 | ||
71 | /* As it appears, name_to_handle_at() fills in mnt_id even when it returns EOVERFLOW when the | |
72 | * buffer is too small, but that's undocumented. Hence, let's make use of this if it appears to | |
73 | * be filled in, and the caller was interested in only the mount ID an nothing else. */ | |
74 | ||
75 | *ret_mnt_id = mnt_id; | |
76 | return 0; | |
77 | } | |
78 | ||
79 | /* If name_to_handle_at() didn't increase the byte size, then this EOVERFLOW is caused by something | |
80 | * else (apparently EOVERFLOW is returned for untriggered nfs4 mounts sometimes), not by the too small | |
81 | * buffer. In that case propagate EOVERFLOW */ | |
82 | if (h->handle_bytes <= n) | |
83 | return -EOVERFLOW; | |
84 | ||
85 | /* The buffer was too small. Size the new buffer by what name_to_handle_at() returned. */ | |
86 | n = h->handle_bytes; | |
87 | if (offsetof(struct file_handle, f_handle) + n < n) /* check for addition overflow */ | |
88 | return -EOVERFLOW; | |
89 | ||
90 | h = mfree(h); | |
91 | } | |
92 | } | |
93 | ||
ffaf45e4 | 94 | static int fd_fdinfo_mnt_id(int fd, const char *filename, int flags, int *ret_mnt_id) { |
049af8ad ZJS |
95 | char path[STRLEN("/proc/self/fdinfo/") + DECIMAL_STR_MAX(int)]; |
96 | _cleanup_free_ char *fdinfo = NULL; | |
97 | _cleanup_close_ int subfd = -1; | |
98 | char *p; | |
99 | int r; | |
100 | ||
ffaf45e4 LP |
101 | assert(ret_mnt_id); |
102 | assert((flags & ~(AT_SYMLINK_FOLLOW|AT_EMPTY_PATH)) == 0); | |
103 | ||
049af8ad ZJS |
104 | if ((flags & AT_EMPTY_PATH) && isempty(filename)) |
105 | xsprintf(path, "/proc/self/fdinfo/%i", fd); | |
106 | else { | |
be24321f | 107 | subfd = openat(fd, filename, O_CLOEXEC|O_PATH|(flags & AT_SYMLINK_FOLLOW ? 0 : O_NOFOLLOW)); |
049af8ad ZJS |
108 | if (subfd < 0) |
109 | return -errno; | |
110 | ||
111 | xsprintf(path, "/proc/self/fdinfo/%i", subfd); | |
112 | } | |
113 | ||
114 | r = read_full_file(path, &fdinfo, NULL); | |
115 | if (r == -ENOENT) /* The fdinfo directory is a relatively new addition */ | |
116 | return -EOPNOTSUPP; | |
117 | if (r < 0) | |
118 | return r; | |
119 | ||
120 | p = startswith(fdinfo, "mnt_id:"); | |
121 | if (!p) { | |
122 | p = strstr(fdinfo, "\nmnt_id:"); | |
123 | if (!p) /* The mnt_id field is a relatively new addition */ | |
124 | return -EOPNOTSUPP; | |
125 | ||
126 | p += 8; | |
127 | } | |
128 | ||
129 | p += strspn(p, WHITESPACE); | |
130 | p[strcspn(p, WHITESPACE)] = 0; | |
131 | ||
ffaf45e4 | 132 | return safe_atoi(p, ret_mnt_id); |
049af8ad ZJS |
133 | } |
134 | ||
135 | int fd_is_mount_point(int fd, const char *filename, int flags) { | |
136 | _cleanup_free_ struct file_handle *h = NULL, *h_parent = NULL; | |
137 | int mount_id = -1, mount_id_parent = -1; | |
138 | bool nosupp = false, check_st_dev = true; | |
7cd296c2 | 139 | STRUCT_STATX_DEFINE(sx); |
049af8ad ZJS |
140 | struct stat a, b; |
141 | int r; | |
142 | ||
143 | assert(fd >= 0); | |
144 | assert(filename); | |
5f104080 | 145 | assert((flags & ~(AT_SYMLINK_FOLLOW|AT_EMPTY_PATH)) == 0); |
049af8ad | 146 | |
5f104080 LP |
147 | /* First we will try statx()' STATX_ATTR_MOUNT_ROOT attribute, which is our ideal API, available |
148 | * since kernel 5.8. | |
149 | * | |
150 | * If that fails, our second try is the name_to_handle_at() syscall, which tells us the mount id and | |
151 | * an opaque file "handle". It is not supported everywhere though (kernel compile-time option, not | |
152 | * all file systems are hooked up). If it works the mount id is usually good enough to tell us | |
153 | * whether something is a mount point. | |
049af8ad | 154 | * |
5f104080 LP |
155 | * If that didn't work we will try to read the mount id from /proc/self/fdinfo/<fd>. This is almost |
156 | * as good as name_to_handle_at(), however, does not return the opaque file handle. The opaque file | |
157 | * handle is pretty useful to detect the root directory, which we should always consider a mount | |
158 | * point. Hence we use this only as fallback. Exporting the mnt_id in fdinfo is a pretty recent | |
049af8ad ZJS |
159 | * kernel addition. |
160 | * | |
5f104080 LP |
161 | * As last fallback we do traditional fstat() based st_dev comparisons. This is how things were |
162 | * traditionally done, but unionfs breaks this since it exposes file systems with a variety of st_dev | |
163 | * reported. Also, btrfs subvolumes have different st_dev, even though they aren't real mounts of | |
164 | * their own. */ | |
165 | ||
166 | if (statx(fd, filename, (FLAGS_SET(flags, AT_SYMLINK_FOLLOW) ? 0 : AT_SYMLINK_NOFOLLOW) | | |
167 | (flags & AT_EMPTY_PATH) | | |
168 | AT_NO_AUTOMOUNT, 0, &sx) < 0) { | |
169 | if (!ERRNO_IS_NOT_SUPPORTED(errno) && !ERRNO_IS_PRIVILEGE(errno)) | |
170 | return -errno; | |
171 | ||
2aed63f4 | 172 | /* If statx() is not available or forbidden, fall back to name_to_handle_at() below */ |
5f104080 LP |
173 | } else if (FLAGS_SET(sx.stx_attributes_mask, STATX_ATTR_MOUNT_ROOT)) /* yay! */ |
174 | return FLAGS_SET(sx.stx_attributes, STATX_ATTR_MOUNT_ROOT); | |
049af8ad ZJS |
175 | |
176 | r = name_to_handle_at_loop(fd, filename, &h, &mount_id, flags); | |
177 | if (IN_SET(r, -ENOSYS, -EACCES, -EPERM, -EOVERFLOW, -EINVAL)) | |
178 | /* This kernel does not support name_to_handle_at() at all (ENOSYS), or the syscall was blocked | |
179 | * (EACCES/EPERM; maybe through seccomp, because we are running inside of a container?), or the mount | |
180 | * point is not triggered yet (EOVERFLOW, think nfs4), or some general name_to_handle_at() flakiness | |
181 | * (EINVAL): fall back to simpler logic. */ | |
182 | goto fallback_fdinfo; | |
183 | else if (r == -EOPNOTSUPP) | |
184 | /* This kernel or file system does not support name_to_handle_at(), hence let's see if the upper fs | |
2aed63f4 | 185 | * supports it (in which case it is a mount point), otherwise fall back to the traditional stat() |
049af8ad ZJS |
186 | * logic */ |
187 | nosupp = true; | |
188 | else if (r < 0) | |
189 | return r; | |
190 | ||
191 | r = name_to_handle_at_loop(fd, "", &h_parent, &mount_id_parent, AT_EMPTY_PATH); | |
192 | if (r == -EOPNOTSUPP) { | |
193 | if (nosupp) | |
194 | /* Neither parent nor child do name_to_handle_at()? We have no choice but to fall back. */ | |
195 | goto fallback_fdinfo; | |
196 | else | |
197 | /* The parent can't do name_to_handle_at() but the directory we are interested in can? If so, | |
198 | * it must be a mount point. */ | |
199 | return 1; | |
200 | } else if (r < 0) | |
201 | return r; | |
202 | ||
203 | /* The parent can do name_to_handle_at() but the | |
204 | * directory we are interested in can't? If so, it | |
205 | * must be a mount point. */ | |
206 | if (nosupp) | |
207 | return 1; | |
208 | ||
209 | /* If the file handle for the directory we are | |
210 | * interested in and its parent are identical, we | |
211 | * assume this is the root directory, which is a mount | |
212 | * point. */ | |
213 | ||
214 | if (h->handle_bytes == h_parent->handle_bytes && | |
215 | h->handle_type == h_parent->handle_type && | |
216 | memcmp(h->f_handle, h_parent->f_handle, h->handle_bytes) == 0) | |
217 | return 1; | |
218 | ||
219 | return mount_id != mount_id_parent; | |
220 | ||
221 | fallback_fdinfo: | |
222 | r = fd_fdinfo_mnt_id(fd, filename, flags, &mount_id); | |
223 | if (IN_SET(r, -EOPNOTSUPP, -EACCES, -EPERM)) | |
224 | goto fallback_fstat; | |
225 | if (r < 0) | |
226 | return r; | |
227 | ||
228 | r = fd_fdinfo_mnt_id(fd, "", AT_EMPTY_PATH, &mount_id_parent); | |
229 | if (r < 0) | |
230 | return r; | |
231 | ||
232 | if (mount_id != mount_id_parent) | |
233 | return 1; | |
234 | ||
235 | /* Hmm, so, the mount ids are the same. This leaves one | |
236 | * special case though for the root file system. For that, | |
237 | * let's see if the parent directory has the same inode as we | |
238 | * are interested in. Hence, let's also do fstat() checks now, | |
239 | * too, but avoid the st_dev comparisons, since they aren't | |
240 | * that useful on unionfs mounts. */ | |
241 | check_st_dev = false; | |
242 | ||
243 | fallback_fstat: | |
244 | /* yay for fstatat() taking a different set of flags than the other | |
245 | * _at() above */ | |
246 | if (flags & AT_SYMLINK_FOLLOW) | |
247 | flags &= ~AT_SYMLINK_FOLLOW; | |
248 | else | |
249 | flags |= AT_SYMLINK_NOFOLLOW; | |
250 | if (fstatat(fd, filename, &a, flags) < 0) | |
251 | return -errno; | |
252 | ||
253 | if (fstatat(fd, "", &b, AT_EMPTY_PATH) < 0) | |
254 | return -errno; | |
255 | ||
256 | /* A directory with same device and inode as its parent? Must | |
257 | * be the root directory */ | |
258 | if (a.st_dev == b.st_dev && | |
259 | a.st_ino == b.st_ino) | |
260 | return 1; | |
261 | ||
262 | return check_st_dev && (a.st_dev != b.st_dev); | |
263 | } | |
264 | ||
265 | /* flags can be AT_SYMLINK_FOLLOW or 0 */ | |
266 | int path_is_mount_point(const char *t, const char *root, int flags) { | |
267 | _cleanup_free_ char *canonical = NULL; | |
268 | _cleanup_close_ int fd = -1; | |
269 | int r; | |
270 | ||
271 | assert(t); | |
272 | assert((flags & ~AT_SYMLINK_FOLLOW) == 0); | |
273 | ||
274 | if (path_equal(t, "/")) | |
275 | return 1; | |
276 | ||
277 | /* we need to resolve symlinks manually, we can't just rely on | |
278 | * fd_is_mount_point() to do that for us; if we have a structure like | |
279 | * /bin -> /usr/bin/ and /usr is a mount point, then the parent that we | |
280 | * look at needs to be /usr, not /. */ | |
281 | if (flags & AT_SYMLINK_FOLLOW) { | |
a5648b80 | 282 | r = chase_symlinks(t, root, CHASE_TRAIL_SLASH, &canonical, NULL); |
049af8ad ZJS |
283 | if (r < 0) |
284 | return r; | |
285 | ||
286 | t = canonical; | |
287 | } | |
288 | ||
289 | fd = open_parent(t, O_PATH|O_CLOEXEC, 0); | |
290 | if (fd < 0) | |
89a5385f | 291 | return fd; |
049af8ad ZJS |
292 | |
293 | return fd_is_mount_point(fd, last_path_component(t), flags); | |
294 | } | |
295 | ||
296 | int path_get_mnt_id(const char *path, int *ret) { | |
7cd296c2 | 297 | STRUCT_NEW_STATX_DEFINE(buf); |
049af8ad ZJS |
298 | int r; |
299 | ||
69b3fa14 LP |
300 | if (statx(AT_FDCWD, path, AT_SYMLINK_NOFOLLOW|AT_NO_AUTOMOUNT, STATX_MNT_ID, &buf.sx) < 0) { |
301 | if (!ERRNO_IS_NOT_SUPPORTED(errno) && !ERRNO_IS_PRIVILEGE(errno)) | |
302 | return -errno; | |
303 | ||
304 | /* Fall back to name_to_handle_at() and then fdinfo if statx is not supported or we lack | |
305 | * privileges */ | |
306 | ||
307 | } else if (FLAGS_SET(buf.nsx.stx_mask, STATX_MNT_ID)) { | |
308 | *ret = buf.nsx.stx_mnt_id; | |
309 | return 0; | |
310 | } | |
311 | ||
049af8ad ZJS |
312 | r = name_to_handle_at_loop(AT_FDCWD, path, NULL, ret, 0); |
313 | if (IN_SET(r, -EOPNOTSUPP, -ENOSYS, -EACCES, -EPERM, -EOVERFLOW, -EINVAL)) /* kernel/fs don't support this, or seccomp blocks access, or untriggered mount, or name_to_handle_at() is flaky */ | |
314 | return fd_fdinfo_mnt_id(AT_FDCWD, path, 0, ret); | |
315 | ||
316 | return r; | |
317 | } | |
318 | ||
319 | bool fstype_is_network(const char *fstype) { | |
320 | const char *x; | |
321 | ||
322 | x = startswith(fstype, "fuse."); | |
323 | if (x) | |
324 | fstype = x; | |
325 | ||
326 | return STR_IN_SET(fstype, | |
327 | "afs", | |
c4742de6 | 328 | "ceph", |
049af8ad | 329 | "cifs", |
ff7d6a74 | 330 | "smb3", |
049af8ad ZJS |
331 | "smbfs", |
332 | "sshfs", | |
333 | "ncpfs", | |
334 | "ncp", | |
335 | "nfs", | |
336 | "nfs4", | |
337 | "gfs", | |
338 | "gfs2", | |
339 | "glusterfs", | |
340 | "pvfs2", /* OrangeFS */ | |
341 | "ocfs2", | |
137d4487 | 342 | "lustre", |
343 | "davfs"); | |
049af8ad ZJS |
344 | } |
345 | ||
346 | bool fstype_is_api_vfs(const char *fstype) { | |
347 | return STR_IN_SET(fstype, | |
348 | "autofs", | |
349 | "bpf", | |
350 | "cgroup", | |
351 | "cgroup2", | |
352 | "configfs", | |
353 | "cpuset", | |
354 | "debugfs", | |
355 | "devpts", | |
356 | "devtmpfs", | |
357 | "efivarfs", | |
358 | "fusectl", | |
359 | "hugetlbfs", | |
360 | "mqueue", | |
361 | "proc", | |
362 | "pstore", | |
363 | "ramfs", | |
364 | "securityfs", | |
365 | "sysfs", | |
366 | "tmpfs", | |
367 | "tracefs"); | |
368 | } | |
369 | ||
ac2474e4 Y |
370 | bool fstype_is_blockdev_backed(const char *fstype) { |
371 | const char *x; | |
372 | ||
373 | x = startswith(fstype, "fuse."); | |
374 | if (x) | |
375 | fstype = x; | |
376 | ||
377 | return !streq(fstype, "9p") && !fstype_is_network(fstype) && !fstype_is_api_vfs(fstype); | |
378 | } | |
379 | ||
049af8ad ZJS |
380 | bool fstype_is_ro(const char *fstype) { |
381 | /* All Linux file systems that are necessarily read-only */ | |
382 | return STR_IN_SET(fstype, | |
383 | "DM_verity_hash", | |
384 | "iso9660", | |
385 | "squashfs"); | |
386 | } | |
387 | ||
388 | bool fstype_can_discard(const char *fstype) { | |
389 | return STR_IN_SET(fstype, | |
390 | "btrfs", | |
391 | "ext4", | |
392 | "vfat", | |
393 | "xfs"); | |
394 | } | |
395 | ||
396 | bool fstype_can_uid_gid(const char *fstype) { | |
397 | ||
398 | /* All file systems that have a uid=/gid= mount option that fixates the owners of all files and directories, | |
399 | * current and future. */ | |
400 | ||
401 | return STR_IN_SET(fstype, | |
402 | "adfs", | |
5797a122 | 403 | "exfat", |
049af8ad ZJS |
404 | "fat", |
405 | "hfs", | |
406 | "hpfs", | |
407 | "iso9660", | |
408 | "msdos", | |
409 | "ntfs", | |
410 | "vfat"); | |
411 | } | |
412 | ||
413 | int dev_is_devtmpfs(void) { | |
414 | _cleanup_fclose_ FILE *proc_self_mountinfo = NULL; | |
415 | int mount_id, r; | |
416 | char *e; | |
417 | ||
418 | r = path_get_mnt_id("/dev", &mount_id); | |
419 | if (r < 0) | |
420 | return r; | |
421 | ||
fdeea3f4 ZJS |
422 | r = fopen_unlocked("/proc/self/mountinfo", "re", &proc_self_mountinfo); |
423 | if (r < 0) | |
424 | return r; | |
049af8ad ZJS |
425 | |
426 | for (;;) { | |
427 | _cleanup_free_ char *line = NULL; | |
428 | int mid; | |
429 | ||
430 | r = read_line(proc_self_mountinfo, LONG_LINE_MAX, &line); | |
431 | if (r < 0) | |
432 | return r; | |
433 | if (r == 0) | |
434 | break; | |
435 | ||
436 | if (sscanf(line, "%i", &mid) != 1) | |
437 | continue; | |
438 | ||
439 | if (mid != mount_id) | |
440 | continue; | |
441 | ||
442 | e = strstr(line, " - "); | |
443 | if (!e) | |
444 | continue; | |
445 | ||
446 | /* accept any name that starts with the currently expected type */ | |
447 | if (startswith(e + 3, "devtmpfs")) | |
448 | return true; | |
449 | } | |
450 | ||
451 | return false; | |
452 | } | |
453 | ||
454 | const char *mount_propagation_flags_to_string(unsigned long flags) { | |
455 | ||
456 | switch (flags & (MS_SHARED|MS_SLAVE|MS_PRIVATE)) { | |
457 | case 0: | |
458 | return ""; | |
459 | case MS_SHARED: | |
460 | return "shared"; | |
461 | case MS_SLAVE: | |
462 | return "slave"; | |
463 | case MS_PRIVATE: | |
464 | return "private"; | |
465 | } | |
466 | ||
467 | return NULL; | |
468 | } | |
469 | ||
470 | int mount_propagation_flags_from_string(const char *name, unsigned long *ret) { | |
471 | ||
472 | if (isempty(name)) | |
473 | *ret = 0; | |
474 | else if (streq(name, "shared")) | |
475 | *ret = MS_SHARED; | |
476 | else if (streq(name, "slave")) | |
477 | *ret = MS_SLAVE; | |
478 | else if (streq(name, "private")) | |
479 | *ret = MS_PRIVATE; | |
480 | else | |
481 | return -EINVAL; | |
482 | return 0; | |
483 | } |