1 | // SPDX-License-Identifier: GPL-2.0 |
2 | /* |
3 | * linux/fs/attr.c |
4 | * |
5 | * Copyright (C) 1991, 1992 Linus Torvalds |
6 | * changes by Thomas Schoebel-Theuer |
7 | */ |
8 | |
9 | #include <linux/export.h> |
10 | #include <linux/time.h> |
11 | #include <linux/mm.h> |
12 | #include <linux/string.h> |
13 | #include <linux/sched/signal.h> |
14 | #include <linux/capability.h> |
15 | #include <linux/fsnotify.h> |
16 | #include <linux/fcntl.h> |
17 | #include <linux/filelock.h> |
18 | #include <linux/security.h> |
19 | |
20 | #include "internal.h" |
21 | |
22 | /** |
23 | * setattr_should_drop_sgid - determine whether the setgid bit needs to be |
24 | * removed |
25 | * @idmap: idmap of the mount @inode was found from |
26 | * @inode: inode to check |
27 | * |
28 | * This function determines whether the setgid bit needs to be removed. |
29 | * We retain backwards compatibility and require setgid bit to be removed |
30 | * unconditionally if S_IXGRP is set. Otherwise we have the exact same |
31 | * requirements as setattr_prepare() and setattr_copy(). |
32 | * |
33 | * Return: ATTR_KILL_SGID if setgid bit needs to be removed, 0 otherwise. |
34 | */ |
35 | int setattr_should_drop_sgid(struct mnt_idmap *idmap, |
36 | const struct inode *inode) |
37 | { |
38 | umode_t mode = inode->i_mode; |
39 | |
40 | if (!(mode & S_ISGID)) |
41 | return 0; |
42 | if (mode & S_IXGRP) |
43 | return ATTR_KILL_SGID; |
44 | if (!in_group_or_capable(idmap, inode, vfsgid: i_gid_into_vfsgid(idmap, inode))) |
45 | return ATTR_KILL_SGID; |
46 | return 0; |
47 | } |
48 | EXPORT_SYMBOL(setattr_should_drop_sgid); |
49 | |
50 | /** |
51 | * setattr_should_drop_suidgid - determine whether the set{g,u}id bit needs to |
52 | * be dropped |
53 | * @idmap: idmap of the mount @inode was found from |
54 | * @inode: inode to check |
55 | * |
56 | * This function determines whether the set{g,u}id bits need to be removed. |
57 | * If the setuid bit needs to be removed ATTR_KILL_SUID is returned. If the |
58 | * setgid bit needs to be removed ATTR_KILL_SGID is returned. If both |
59 | * set{g,u}id bits need to be removed the corresponding mask of both flags is |
60 | * returned. |
61 | * |
62 | * Return: A mask of ATTR_KILL_S{G,U}ID indicating which - if any - setid bits |
63 | * to remove, 0 otherwise. |
64 | */ |
65 | int setattr_should_drop_suidgid(struct mnt_idmap *idmap, |
66 | struct inode *inode) |
67 | { |
68 | umode_t mode = inode->i_mode; |
69 | int kill = 0; |
70 | |
71 | /* suid always must be killed */ |
72 | if (unlikely(mode & S_ISUID)) |
73 | kill = ATTR_KILL_SUID; |
74 | |
75 | kill |= setattr_should_drop_sgid(idmap, inode); |
76 | |
77 | if (unlikely(kill && !capable(CAP_FSETID) && S_ISREG(mode))) |
78 | return kill; |
79 | |
80 | return 0; |
81 | } |
82 | EXPORT_SYMBOL(setattr_should_drop_suidgid); |
83 | |
84 | /** |
85 | * chown_ok - verify permissions to chown inode |
86 | * @idmap: idmap of the mount @inode was found from |
87 | * @inode: inode to check permissions on |
88 | * @ia_vfsuid: uid to chown @inode to |
89 | * |
90 | * If the inode has been found through an idmapped mount the idmap of |
91 | * the vfsmount must be passed through @idmap. This function will then |
92 | * take care to map the inode according to @idmap before checking |
93 | * permissions. On non-idmapped mounts or if permission checking is to be |
94 | * performed on the raw inode simply pass @nop_mnt_idmap. |
95 | */ |
96 | static bool chown_ok(struct mnt_idmap *idmap, |
97 | const struct inode *inode, vfsuid_t ia_vfsuid) |
98 | { |
99 | vfsuid_t vfsuid = i_uid_into_vfsuid(idmap, inode); |
100 | if (vfsuid_eq_kuid(vfsuid, current_fsuid()) && |
101 | vfsuid_eq(left: ia_vfsuid, right: vfsuid)) |
102 | return true; |
103 | if (capable_wrt_inode_uidgid(idmap, inode, CAP_CHOWN)) |
104 | return true; |
105 | if (!vfsuid_valid(uid: vfsuid) && |
106 | ns_capable(ns: inode->i_sb->s_user_ns, CAP_CHOWN)) |
107 | return true; |
108 | return false; |
109 | } |
110 | |
111 | /** |
112 | * chgrp_ok - verify permissions to chgrp inode |
113 | * @idmap: idmap of the mount @inode was found from |
114 | * @inode: inode to check permissions on |
115 | * @ia_vfsgid: gid to chown @inode to |
116 | * |
117 | * If the inode has been found through an idmapped mount the idmap of |
118 | * the vfsmount must be passed through @idmap. This function will then |
119 | * take care to map the inode according to @idmap before checking |
120 | * permissions. On non-idmapped mounts or if permission checking is to be |
121 | * performed on the raw inode simply pass @nop_mnt_idmap. |
122 | */ |
123 | static bool chgrp_ok(struct mnt_idmap *idmap, |
124 | const struct inode *inode, vfsgid_t ia_vfsgid) |
125 | { |
126 | vfsgid_t vfsgid = i_gid_into_vfsgid(idmap, inode); |
127 | vfsuid_t vfsuid = i_uid_into_vfsuid(idmap, inode); |
128 | if (vfsuid_eq_kuid(vfsuid, current_fsuid())) { |
129 | if (vfsgid_eq(left: ia_vfsgid, right: vfsgid)) |
130 | return true; |
131 | if (vfsgid_in_group_p(vfsgid: ia_vfsgid)) |
132 | return true; |
133 | } |
134 | if (capable_wrt_inode_uidgid(idmap, inode, CAP_CHOWN)) |
135 | return true; |
136 | if (!vfsgid_valid(gid: vfsgid) && |
137 | ns_capable(ns: inode->i_sb->s_user_ns, CAP_CHOWN)) |
138 | return true; |
139 | return false; |
140 | } |
141 | |
142 | /** |
143 | * setattr_prepare - check if attribute changes to a dentry are allowed |
144 | * @idmap: idmap of the mount the inode was found from |
145 | * @dentry: dentry to check |
146 | * @attr: attributes to change |
147 | * |
148 | * Check if we are allowed to change the attributes contained in @attr |
149 | * in the given dentry. This includes the normal unix access permission |
150 | * checks, as well as checks for rlimits and others. The function also clears |
151 | * SGID bit from mode if user is not allowed to set it. Also file capabilities |
152 | * and IMA extended attributes are cleared if ATTR_KILL_PRIV is set. |
153 | * |
154 | * If the inode has been found through an idmapped mount the idmap of |
155 | * the vfsmount must be passed through @idmap. This function will then |
156 | * take care to map the inode according to @idmap before checking |
157 | * permissions. On non-idmapped mounts or if permission checking is to be |
158 | * performed on the raw inode simply pass @nop_mnt_idmap. |
159 | * |
160 | * Should be called as the first thing in ->setattr implementations, |
161 | * possibly after taking additional locks. |
162 | */ |
163 | int setattr_prepare(struct mnt_idmap *idmap, struct dentry *dentry, |
164 | struct iattr *attr) |
165 | { |
166 | struct inode *inode = d_inode(dentry); |
167 | unsigned int ia_valid = attr->ia_valid; |
168 | |
169 | /* |
170 | * First check size constraints. These can't be overriden using |
171 | * ATTR_FORCE. |
172 | */ |
173 | if (ia_valid & ATTR_SIZE) { |
174 | int error = inode_newsize_ok(inode, offset: attr->ia_size); |
175 | if (error) |
176 | return error; |
177 | } |
178 | |
179 | /* If force is set do it anyway. */ |
180 | if (ia_valid & ATTR_FORCE) |
181 | goto kill_priv; |
182 | |
183 | /* Make sure a caller can chown. */ |
184 | if ((ia_valid & ATTR_UID) && |
185 | !chown_ok(idmap, inode, ia_vfsuid: attr->ia_vfsuid)) |
186 | return -EPERM; |
187 | |
188 | /* Make sure caller can chgrp. */ |
189 | if ((ia_valid & ATTR_GID) && |
190 | !chgrp_ok(idmap, inode, ia_vfsgid: attr->ia_vfsgid)) |
191 | return -EPERM; |
192 | |
193 | /* Make sure a caller can chmod. */ |
194 | if (ia_valid & ATTR_MODE) { |
195 | vfsgid_t vfsgid; |
196 | |
197 | if (!inode_owner_or_capable(idmap, inode)) |
198 | return -EPERM; |
199 | |
200 | if (ia_valid & ATTR_GID) |
201 | vfsgid = attr->ia_vfsgid; |
202 | else |
203 | vfsgid = i_gid_into_vfsgid(idmap, inode); |
204 | |
205 | /* Also check the setgid bit! */ |
206 | if (!in_group_or_capable(idmap, inode, vfsgid)) |
207 | attr->ia_mode &= ~S_ISGID; |
208 | } |
209 | |
210 | /* Check for setting the inode time. */ |
211 | if (ia_valid & (ATTR_MTIME_SET | ATTR_ATIME_SET | ATTR_TIMES_SET)) { |
212 | if (!inode_owner_or_capable(idmap, inode)) |
213 | return -EPERM; |
214 | } |
215 | |
216 | kill_priv: |
217 | /* User has permission for the change */ |
218 | if (ia_valid & ATTR_KILL_PRIV) { |
219 | int error; |
220 | |
221 | error = security_inode_killpriv(idmap, dentry); |
222 | if (error) |
223 | return error; |
224 | } |
225 | |
226 | return 0; |
227 | } |
228 | EXPORT_SYMBOL(setattr_prepare); |
229 | |
230 | /** |
231 | * inode_newsize_ok - may this inode be truncated to a given size |
232 | * @inode: the inode to be truncated |
233 | * @offset: the new size to assign to the inode |
234 | * |
235 | * inode_newsize_ok must be called with i_mutex held. |
236 | * |
237 | * inode_newsize_ok will check filesystem limits and ulimits to check that the |
238 | * new inode size is within limits. inode_newsize_ok will also send SIGXFSZ |
239 | * when necessary. Caller must not proceed with inode size change if failure is |
240 | * returned. @inode must be a file (not directory), with appropriate |
241 | * permissions to allow truncate (inode_newsize_ok does NOT check these |
242 | * conditions). |
243 | * |
244 | * Return: 0 on success, -ve errno on failure |
245 | */ |
246 | int inode_newsize_ok(const struct inode *inode, loff_t offset) |
247 | { |
248 | if (offset < 0) |
249 | return -EINVAL; |
250 | if (inode->i_size < offset) { |
251 | unsigned long limit; |
252 | |
253 | limit = rlimit(RLIMIT_FSIZE); |
254 | if (limit != RLIM_INFINITY && offset > limit) |
255 | goto out_sig; |
256 | if (offset > inode->i_sb->s_maxbytes) |
257 | goto out_big; |
258 | } else { |
259 | /* |
260 | * truncation of in-use swapfiles is disallowed - it would |
261 | * cause subsequent swapout to scribble on the now-freed |
262 | * blocks. |
263 | */ |
264 | if (IS_SWAPFILE(inode)) |
265 | return -ETXTBSY; |
266 | } |
267 | |
268 | return 0; |
269 | out_sig: |
270 | send_sig(SIGXFSZ, current, 0); |
271 | out_big: |
272 | return -EFBIG; |
273 | } |
274 | EXPORT_SYMBOL(inode_newsize_ok); |
275 | |
276 | /** |
277 | * setattr_copy - copy simple metadata updates into the generic inode |
278 | * @idmap: idmap of the mount the inode was found from |
279 | * @inode: the inode to be updated |
280 | * @attr: the new attributes |
281 | * |
282 | * setattr_copy must be called with i_mutex held. |
283 | * |
284 | * setattr_copy updates the inode's metadata with that specified |
285 | * in attr on idmapped mounts. Necessary permission checks to determine |
286 | * whether or not the S_ISGID property needs to be removed are performed with |
287 | * the correct idmapped mount permission helpers. |
288 | * Noticeably missing is inode size update, which is more complex |
289 | * as it requires pagecache updates. |
290 | * |
291 | * If the inode has been found through an idmapped mount the idmap of |
292 | * the vfsmount must be passed through @idmap. This function will then |
293 | * take care to map the inode according to @idmap before checking |
294 | * permissions. On non-idmapped mounts or if permission checking is to be |
295 | * performed on the raw inode simply pass @nop_mnt_idmap. |
296 | * |
297 | * The inode is not marked as dirty after this operation. The rationale is |
298 | * that for "simple" filesystems, the struct inode is the inode storage. |
299 | * The caller is free to mark the inode dirty afterwards if needed. |
300 | */ |
301 | void setattr_copy(struct mnt_idmap *idmap, struct inode *inode, |
302 | const struct iattr *attr) |
303 | { |
304 | unsigned int ia_valid = attr->ia_valid; |
305 | |
306 | i_uid_update(idmap, attr, inode); |
307 | i_gid_update(idmap, attr, inode); |
308 | if (ia_valid & ATTR_ATIME) |
309 | inode_set_atime_to_ts(inode, ts: attr->ia_atime); |
310 | if (ia_valid & ATTR_MTIME) |
311 | inode_set_mtime_to_ts(inode, ts: attr->ia_mtime); |
312 | if (ia_valid & ATTR_CTIME) |
313 | inode_set_ctime_to_ts(inode, ts: attr->ia_ctime); |
314 | if (ia_valid & ATTR_MODE) { |
315 | umode_t mode = attr->ia_mode; |
316 | if (!in_group_or_capable(idmap, inode, |
317 | vfsgid: i_gid_into_vfsgid(idmap, inode))) |
318 | mode &= ~S_ISGID; |
319 | inode->i_mode = mode; |
320 | } |
321 | } |
322 | EXPORT_SYMBOL(setattr_copy); |
323 | |
324 | int may_setattr(struct mnt_idmap *idmap, struct inode *inode, |
325 | unsigned int ia_valid) |
326 | { |
327 | int error; |
328 | |
329 | if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID | ATTR_TIMES_SET)) { |
330 | if (IS_IMMUTABLE(inode) || IS_APPEND(inode)) |
331 | return -EPERM; |
332 | } |
333 | |
334 | /* |
335 | * If utimes(2) and friends are called with times == NULL (or both |
336 | * times are UTIME_NOW), then we need to check for write permission |
337 | */ |
338 | if (ia_valid & ATTR_TOUCH) { |
339 | if (IS_IMMUTABLE(inode)) |
340 | return -EPERM; |
341 | |
342 | if (!inode_owner_or_capable(idmap, inode)) { |
343 | error = inode_permission(idmap, inode, MAY_WRITE); |
344 | if (error) |
345 | return error; |
346 | } |
347 | } |
348 | return 0; |
349 | } |
350 | EXPORT_SYMBOL(may_setattr); |
351 | |
352 | /** |
353 | * notify_change - modify attributes of a filesystem object |
354 | * @idmap: idmap of the mount the inode was found from |
355 | * @dentry: object affected |
356 | * @attr: new attributes |
357 | * @delegated_inode: returns inode, if the inode is delegated |
358 | * |
359 | * The caller must hold the i_mutex on the affected object. |
360 | * |
361 | * If notify_change discovers a delegation in need of breaking, |
362 | * it will return -EWOULDBLOCK and return a reference to the inode in |
363 | * delegated_inode. The caller should then break the delegation and |
364 | * retry. Because breaking a delegation may take a long time, the |
365 | * caller should drop the i_mutex before doing so. |
366 | * |
367 | * Alternatively, a caller may pass NULL for delegated_inode. This may |
368 | * be appropriate for callers that expect the underlying filesystem not |
369 | * to be NFS exported. Also, passing NULL is fine for callers holding |
370 | * the file open for write, as there can be no conflicting delegation in |
371 | * that case. |
372 | * |
373 | * If the inode has been found through an idmapped mount the idmap of |
374 | * the vfsmount must be passed through @idmap. This function will then |
375 | * take care to map the inode according to @idmap before checking |
376 | * permissions. On non-idmapped mounts or if permission checking is to be |
377 | * performed on the raw inode simply pass @nop_mnt_idmap. |
378 | */ |
379 | int notify_change(struct mnt_idmap *idmap, struct dentry *dentry, |
380 | struct iattr *attr, struct inode **delegated_inode) |
381 | { |
382 | struct inode *inode = dentry->d_inode; |
383 | umode_t mode = inode->i_mode; |
384 | int error; |
385 | struct timespec64 now; |
386 | unsigned int ia_valid = attr->ia_valid; |
387 | |
388 | WARN_ON_ONCE(!inode_is_locked(inode)); |
389 | |
390 | error = may_setattr(idmap, inode, ia_valid); |
391 | if (error) |
392 | return error; |
393 | |
394 | if ((ia_valid & ATTR_MODE)) { |
395 | /* |
396 | * Don't allow changing the mode of symlinks: |
397 | * |
398 | * (1) The vfs doesn't take the mode of symlinks into account |
399 | * during permission checking. |
400 | * (2) This has never worked correctly. Most major filesystems |
401 | * did return EOPNOTSUPP due to interactions with POSIX ACLs |
402 | * but did still updated the mode of the symlink. |
403 | * This inconsistency led system call wrapper providers such |
404 | * as libc to block changing the mode of symlinks with |
405 | * EOPNOTSUPP already. |
406 | * (3) To even do this in the first place one would have to use |
407 | * specific file descriptors and quite some effort. |
408 | */ |
409 | if (S_ISLNK(inode->i_mode)) |
410 | return -EOPNOTSUPP; |
411 | |
412 | /* Flag setting protected by i_mutex */ |
413 | if (is_sxid(mode: attr->ia_mode)) |
414 | inode->i_flags &= ~S_NOSEC; |
415 | } |
416 | |
417 | now = current_time(inode); |
418 | |
419 | attr->ia_ctime = now; |
420 | if (!(ia_valid & ATTR_ATIME_SET)) |
421 | attr->ia_atime = now; |
422 | else |
423 | attr->ia_atime = timestamp_truncate(t: attr->ia_atime, inode); |
424 | if (!(ia_valid & ATTR_MTIME_SET)) |
425 | attr->ia_mtime = now; |
426 | else |
427 | attr->ia_mtime = timestamp_truncate(t: attr->ia_mtime, inode); |
428 | |
429 | if (ia_valid & ATTR_KILL_PRIV) { |
430 | error = security_inode_need_killpriv(dentry); |
431 | if (error < 0) |
432 | return error; |
433 | if (error == 0) |
434 | ia_valid = attr->ia_valid &= ~ATTR_KILL_PRIV; |
435 | } |
436 | |
437 | /* |
438 | * We now pass ATTR_KILL_S*ID to the lower level setattr function so |
439 | * that the function has the ability to reinterpret a mode change |
440 | * that's due to these bits. This adds an implicit restriction that |
441 | * no function will ever call notify_change with both ATTR_MODE and |
442 | * ATTR_KILL_S*ID set. |
443 | */ |
444 | if ((ia_valid & (ATTR_KILL_SUID|ATTR_KILL_SGID)) && |
445 | (ia_valid & ATTR_MODE)) |
446 | BUG(); |
447 | |
448 | if (ia_valid & ATTR_KILL_SUID) { |
449 | if (mode & S_ISUID) { |
450 | ia_valid = attr->ia_valid |= ATTR_MODE; |
451 | attr->ia_mode = (inode->i_mode & ~S_ISUID); |
452 | } |
453 | } |
454 | if (ia_valid & ATTR_KILL_SGID) { |
455 | if (mode & S_ISGID) { |
456 | if (!(ia_valid & ATTR_MODE)) { |
457 | ia_valid = attr->ia_valid |= ATTR_MODE; |
458 | attr->ia_mode = inode->i_mode; |
459 | } |
460 | attr->ia_mode &= ~S_ISGID; |
461 | } |
462 | } |
463 | if (!(attr->ia_valid & ~(ATTR_KILL_SUID | ATTR_KILL_SGID))) |
464 | return 0; |
465 | |
466 | /* |
467 | * Verify that uid/gid changes are valid in the target |
468 | * namespace of the superblock. |
469 | */ |
470 | if (ia_valid & ATTR_UID && |
471 | !vfsuid_has_fsmapping(idmap, fs_userns: inode->i_sb->s_user_ns, |
472 | vfsuid: attr->ia_vfsuid)) |
473 | return -EOVERFLOW; |
474 | if (ia_valid & ATTR_GID && |
475 | !vfsgid_has_fsmapping(idmap, fs_userns: inode->i_sb->s_user_ns, |
476 | vfsgid: attr->ia_vfsgid)) |
477 | return -EOVERFLOW; |
478 | |
479 | /* Don't allow modifications of files with invalid uids or |
480 | * gids unless those uids & gids are being made valid. |
481 | */ |
482 | if (!(ia_valid & ATTR_UID) && |
483 | !vfsuid_valid(uid: i_uid_into_vfsuid(idmap, inode))) |
484 | return -EOVERFLOW; |
485 | if (!(ia_valid & ATTR_GID) && |
486 | !vfsgid_valid(gid: i_gid_into_vfsgid(idmap, inode))) |
487 | return -EOVERFLOW; |
488 | |
489 | error = security_inode_setattr(idmap, dentry, attr); |
490 | if (error) |
491 | return error; |
492 | error = try_break_deleg(inode, delegated_inode); |
493 | if (error) |
494 | return error; |
495 | |
496 | if (inode->i_op->setattr) |
497 | error = inode->i_op->setattr(idmap, dentry, attr); |
498 | else |
499 | error = simple_setattr(idmap, dentry, attr); |
500 | |
501 | if (!error) { |
502 | fsnotify_change(dentry, ia_valid); |
503 | security_inode_post_setattr(idmap, dentry, ia_valid); |
504 | } |
505 | |
506 | return error; |
507 | } |
508 | EXPORT_SYMBOL(notify_change); |
509 | |