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