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