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  */
setattr_should_drop_sgid(struct mnt_idmap * idmap,const struct inode * inode)37 int setattr_should_drop_sgid(struct mnt_idmap *idmap,
38 			     const struct inode *inode)
39 {
40 	umode_t mode = inode->i_mode;
41 
42 	if (!(mode & S_ISGID))
43 		return 0;
44 	if (mode & S_IXGRP)
45 		return ATTR_KILL_SGID;
46 	if (!in_group_or_capable(idmap, inode, i_gid_into_vfsgid(idmap, inode)))
47 		return ATTR_KILL_SGID;
48 	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  */
setattr_should_drop_suidgid(struct mnt_idmap * idmap,struct inode * inode)66 int setattr_should_drop_suidgid(struct mnt_idmap *idmap,
67 				struct inode *inode)
68 {
69 	umode_t mode = inode->i_mode;
70 	int kill = 0;
71 
72 	/* suid always must be killed */
73 	if (unlikely(mode & S_ISUID))
74 		kill = ATTR_KILL_SUID;
75 
76 	kill |= setattr_should_drop_sgid(idmap, inode);
77 
78 	if (unlikely(kill && !capable(CAP_FSETID) && S_ISREG(mode)))
79 		return kill;
80 
81 	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  */
chown_ok(struct mnt_idmap * idmap,const struct inode * inode,vfsuid_t ia_vfsuid)97 static bool chown_ok(struct mnt_idmap *idmap,
98 		     const struct inode *inode, vfsuid_t ia_vfsuid)
99 {
100 	vfsuid_t vfsuid = i_uid_into_vfsuid(idmap, inode);
101 	if (vfsuid_eq_kuid(vfsuid, current_fsuid()) &&
102 	    vfsuid_eq(ia_vfsuid, vfsuid))
103 		return true;
104 	if (capable_wrt_inode_uidgid(idmap, inode, CAP_CHOWN))
105 		return true;
106 	if (!vfsuid_valid(vfsuid) &&
107 	    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  */
chgrp_ok(struct mnt_idmap * idmap,const struct inode * inode,vfsgid_t ia_vfsgid)124 static bool chgrp_ok(struct mnt_idmap *idmap,
125 		     const struct inode *inode, vfsgid_t ia_vfsgid)
126 {
127 	vfsgid_t vfsgid = i_gid_into_vfsgid(idmap, inode);
128 	vfsuid_t vfsuid = i_uid_into_vfsuid(idmap, inode);
129 	if (vfsuid_eq_kuid(vfsuid, current_fsuid())) {
130 		if (vfsgid_eq(ia_vfsgid, vfsgid))
131 			return true;
132 		if (vfsgid_in_group_p(ia_vfsgid))
133 			return true;
134 	}
135 	if (capable_wrt_inode_uidgid(idmap, inode, CAP_CHOWN))
136 		return true;
137 	if (!vfsgid_valid(vfsgid) &&
138 	    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  */
setattr_prepare(struct mnt_idmap * idmap,struct dentry * dentry,struct iattr * attr)164 int setattr_prepare(struct mnt_idmap *idmap, struct dentry *dentry,
165 		    struct iattr *attr)
166 {
167 	struct inode *inode = d_inode(dentry);
168 	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 	if (ia_valid & ATTR_SIZE) {
175 		int error = inode_newsize_ok(inode, attr->ia_size);
176 		if (error)
177 			return error;
178 	}
179 
180 	/* If force is set do it anyway. */
181 	if (ia_valid & ATTR_FORCE)
182 		goto kill_priv;
183 
184 	/* Make sure a caller can chown. */
185 	if ((ia_valid & ATTR_UID) &&
186 	    !chown_ok(idmap, inode, attr->ia_vfsuid))
187 		return -EPERM;
188 
189 	/* Make sure caller can chgrp. */
190 	if ((ia_valid & ATTR_GID) &&
191 	    !chgrp_ok(idmap, inode, attr->ia_vfsgid))
192 		return -EPERM;
193 
194 	/* Make sure a caller can chmod. */
195 	if (ia_valid & ATTR_MODE) {
196 		vfsgid_t vfsgid;
197 
198 		if (!inode_owner_or_capable(idmap, inode))
199 			return -EPERM;
200 
201 		if (ia_valid & ATTR_GID)
202 			vfsgid = attr->ia_vfsgid;
203 		else
204 			vfsgid = i_gid_into_vfsgid(idmap, inode);
205 
206 		/* Also check the setgid bit! */
207 		if (!in_group_or_capable(idmap, inode, vfsgid))
208 			attr->ia_mode &= ~S_ISGID;
209 	}
210 
211 	/* Check for setting the inode time. */
212 	if (ia_valid & (ATTR_MTIME_SET | ATTR_ATIME_SET | ATTR_TIMES_SET)) {
213 		if (!inode_owner_or_capable(idmap, inode))
214 			return -EPERM;
215 	}
216 
217 kill_priv:
218 	/* User has permission for the change */
219 	if (ia_valid & ATTR_KILL_PRIV) {
220 		int error;
221 
222 		error = security_inode_killpriv(idmap, dentry);
223 		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  */
inode_newsize_ok(const struct inode * inode,loff_t offset)247 int inode_newsize_ok(const struct inode *inode, loff_t offset)
248 {
249 	if (offset < 0)
250 		return -EINVAL;
251 	if (inode->i_size < offset) {
252 		unsigned long limit;
253 
254 		limit = rlimit(RLIMIT_FSIZE);
255 		if (limit != RLIM_INFINITY && offset > limit)
256 			goto out_sig;
257 		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 		if (IS_SWAPFILE(inode))
266 			return -ETXTBSY;
267 	}
268 
269 	return 0;
270 out_sig:
271 	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  */
setattr_copy(struct mnt_idmap * idmap,struct inode * inode,const struct iattr * attr)302 void setattr_copy(struct mnt_idmap *idmap, struct inode *inode,
303 		  const struct iattr *attr)
304 {
305 	unsigned int ia_valid = attr->ia_valid;
306 
307 	i_uid_update(idmap, attr, inode);
308 	i_gid_update(idmap, attr, inode);
309 	if (ia_valid & ATTR_ATIME)
310 		inode->i_atime = attr->ia_atime;
311 	if (ia_valid & ATTR_MTIME)
312 		inode->i_mtime = attr->ia_mtime;
313 	if (ia_valid & ATTR_CTIME)
314 		inode->i_ctime = attr->ia_ctime;
315 	if (ia_valid & ATTR_MODE) {
316 		umode_t mode = attr->ia_mode;
317 		if (!in_group_or_capable(idmap, inode,
318 					 i_gid_into_vfsgid(idmap, inode)))
319 			mode &= ~S_ISGID;
320 		inode->i_mode = mode;
321 	}
322 }
323 EXPORT_SYMBOL(setattr_copy);
324 
may_setattr(struct mnt_idmap * idmap,struct inode * inode,unsigned int ia_valid)325 int may_setattr(struct mnt_idmap *idmap, struct inode *inode,
326 		unsigned int ia_valid)
327 {
328 	int error;
329 
330 	if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID | ATTR_TIMES_SET)) {
331 		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 	if (ia_valid & ATTR_TOUCH) {
340 		if (IS_IMMUTABLE(inode))
341 			return -EPERM;
342 
343 		if (!inode_owner_or_capable(idmap, inode)) {
344 			error = inode_permission(idmap, inode, MAY_WRITE);
345 			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  */
notify_change(struct mnt_idmap * idmap,struct dentry * dentry,struct iattr * attr,struct inode ** delegated_inode)380 int notify_change(struct mnt_idmap *idmap, struct dentry *dentry,
381 		  struct iattr *attr, struct inode **delegated_inode)
382 {
383 	struct inode *inode = dentry->d_inode;
384 	umode_t mode = inode->i_mode;
385 	int error;
386 	struct timespec64 now;
387 	unsigned int ia_valid = attr->ia_valid;
388 
389 	WARN_ON_ONCE(!inode_is_locked(inode));
390 
391 	error = may_setattr(idmap, inode, ia_valid);
392 	if (error)
393 		return error;
394 
395 	if ((ia_valid & ATTR_MODE)) {
396 		umode_t amode = attr->ia_mode;
397 		/* Flag setting protected by i_mutex */
398 		if (is_sxid(amode))
399 			inode->i_flags &= ~S_NOSEC;
400 	}
401 
402 	now = current_time(inode);
403 
404 	attr->ia_ctime = now;
405 	if (!(ia_valid & ATTR_ATIME_SET))
406 		attr->ia_atime = now;
407 	else
408 		attr->ia_atime = timestamp_truncate(attr->ia_atime, inode);
409 	if (!(ia_valid & ATTR_MTIME_SET))
410 		attr->ia_mtime = now;
411 	else
412 		attr->ia_mtime = timestamp_truncate(attr->ia_mtime, inode);
413 
414 	if (ia_valid & ATTR_KILL_PRIV) {
415 		error = security_inode_need_killpriv(dentry);
416 		if (error < 0)
417 			return error;
418 		if (error == 0)
419 			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 	if ((ia_valid & (ATTR_KILL_SUID|ATTR_KILL_SGID)) &&
430 	    (ia_valid & ATTR_MODE))
431 		BUG();
432 
433 	if (ia_valid & ATTR_KILL_SUID) {
434 		if (mode & S_ISUID) {
435 			ia_valid = attr->ia_valid |= ATTR_MODE;
436 			attr->ia_mode = (inode->i_mode & ~S_ISUID);
437 		}
438 	}
439 	if (ia_valid & ATTR_KILL_SGID) {
440 		if (mode & S_ISGID) {
441 			if (!(ia_valid & ATTR_MODE)) {
442 				ia_valid = attr->ia_valid |= ATTR_MODE;
443 				attr->ia_mode = inode->i_mode;
444 			}
445 			attr->ia_mode &= ~S_ISGID;
446 		}
447 	}
448 	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 	if (ia_valid & ATTR_UID &&
456 	    !vfsuid_has_fsmapping(idmap, inode->i_sb->s_user_ns,
457 				  attr->ia_vfsuid))
458 		return -EOVERFLOW;
459 	if (ia_valid & ATTR_GID &&
460 	    !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 	if (!(ia_valid & ATTR_UID) &&
468 	    !vfsuid_valid(i_uid_into_vfsuid(idmap, inode)))
469 		return -EOVERFLOW;
470 	if (!(ia_valid & ATTR_GID) &&
471 	    !vfsgid_valid(i_gid_into_vfsgid(idmap, inode)))
472 		return -EOVERFLOW;
473 
474 	error = security_inode_setattr(idmap, dentry, attr);
475 	if (error)
476 		return error;
477 	error = try_break_deleg(inode, delegated_inode);
478 	if (error)
479 		return error;
480 
481 	if (inode->i_op->setattr)
482 		error = inode->i_op->setattr(idmap, dentry, attr);
483 	else
484 		error = simple_setattr(idmap, dentry, attr);
485 
486 	if (!error) {
487 		fsnotify_change(dentry, ia_valid);
488 		ima_inode_post_setattr(idmap, dentry);
489 		evm_inode_post_setattr(dentry, ia_valid);
490 	}
491 
492 	return error;
493 }
494 EXPORT_SYMBOL(notify_change);
495