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