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 : */
33 308 : static bool chown_ok(struct user_namespace *mnt_userns,
34 : const struct inode *inode,
35 : kuid_t uid)
36 : {
37 308 : kuid_t kuid = i_uid_into_mnt(mnt_userns, inode);
38 308 : if (uid_eq(current_fsuid(), kuid) && uid_eq(uid, kuid))
39 : return true;
40 8 : 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 0 : 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 : */
60 308 : static bool chgrp_ok(struct user_namespace *mnt_userns,
61 : const struct inode *inode, kgid_t gid)
62 : {
63 308 : kgid_t kgid = i_gid_into_mnt(mnt_userns, inode);
64 616 : if (uid_eq(current_fsuid(), i_uid_into_mnt(mnt_userns, inode)) &&
65 443 : (in_group_p(gid) || gid_eq(gid, kgid)))
66 : return true;
67 131 : 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 0 : 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 1100 : int setattr_prepare(struct user_namespace *mnt_userns, struct dentry *dentry,
97 : struct iattr *attr)
98 : {
99 1100 : struct inode *inode = d_inode(dentry);
100 1100 : 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 1100 : if (ia_valid & ATTR_SIZE) {
107 64 : int error = inode_newsize_ok(inode, attr->ia_size);
108 64 : if (error)
109 : return error;
110 : }
111 :
112 : /* If force is set do it anyway. */
113 1100 : if (ia_valid & ATTR_FORCE)
114 0 : goto kill_priv;
115 :
116 : /* Make sure a caller can chown. */
117 1100 : if ((ia_valid & ATTR_UID) && !chown_ok(mnt_userns, inode, attr->ia_uid))
118 : return -EPERM;
119 :
120 : /* Make sure caller can chgrp. */
121 1100 : 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 1100 : if (ia_valid & ATTR_MODE) {
126 564 : if (!inode_owner_or_capable(mnt_userns, inode))
127 : return -EPERM;
128 : /* Also check the setgid bit! */
129 1128 : if (!in_group_p((ia_valid & ATTR_GID) ? attr->ia_gid :
130 593 : i_gid_into_mnt(mnt_userns, inode)) &&
131 29 : !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 1100 : if (ia_valid & (ATTR_MTIME_SET | ATTR_ATIME_SET | ATTR_TIMES_SET)) {
137 95 : if (!inode_owner_or_capable(mnt_userns, inode))
138 : return -EPERM;
139 : }
140 :
141 1100 : kill_priv:
142 : /* User has permission for the change */
143 1100 : if (ia_valid & ATTR_KILL_PRIV) {
144 0 : int error;
145 :
146 0 : error = security_inode_killpriv(mnt_userns, dentry);
147 0 : if (error)
148 0 : 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 66 : int inode_newsize_ok(const struct inode *inode, loff_t offset)
172 : {
173 66 : if (inode->i_size < offset) {
174 2 : unsigned long limit;
175 :
176 2 : limit = rlimit(RLIMIT_FSIZE);
177 2 : if (limit != RLIM_INFINITY && offset > limit)
178 0 : goto out_sig;
179 2 : if (offset > inode->i_sb->s_maxbytes)
180 0 : 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 64 : if (IS_SWAPFILE(inode))
188 0 : return -ETXTBSY;
189 : }
190 :
191 : return 0;
192 0 : 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 1100 : void setattr_copy(struct user_namespace *mnt_userns, struct inode *inode,
227 : const struct iattr *attr)
228 : {
229 1100 : unsigned int ia_valid = attr->ia_valid;
230 :
231 1100 : if (ia_valid & ATTR_UID)
232 308 : inode->i_uid = attr->ia_uid;
233 1100 : if (ia_valid & ATTR_GID)
234 308 : inode->i_gid = attr->ia_gid;
235 1100 : if (ia_valid & ATTR_ATIME)
236 262 : inode->i_atime = attr->ia_atime;
237 1100 : if (ia_valid & ATTR_MTIME)
238 335 : inode->i_mtime = attr->ia_mtime;
239 1100 : if (ia_valid & ATTR_CTIME)
240 968 : inode->i_ctime = attr->ia_ctime;
241 1100 : if (ia_valid & ATTR_MODE) {
242 564 : umode_t mode = attr->ia_mode;
243 564 : kgid_t kgid = i_gid_into_mnt(mnt_userns, inode);
244 593 : if (!in_group_p(kgid) &&
245 29 : !capable_wrt_inode_uidgid(mnt_userns, inode, CAP_FSETID))
246 0 : mode &= ~S_ISGID;
247 564 : inode->i_mode = mode;
248 : }
249 1100 : }
250 : EXPORT_SYMBOL(setattr_copy);
251 :
252 : /**
253 : * notify_change - modify attributes of a filesytem object
254 : * @mnt_userns: user namespace of the mount the inode was found from
255 : * @dentry: object affected
256 : * @attr: new attributes
257 : * @delegated_inode: returns inode, if the inode is delegated
258 : *
259 : * The caller must hold the i_mutex on the affected object.
260 : *
261 : * If notify_change discovers a delegation in need of breaking,
262 : * it will return -EWOULDBLOCK and return a reference to the inode in
263 : * delegated_inode. The caller should then break the delegation and
264 : * retry. Because breaking a delegation may take a long time, the
265 : * caller should drop the i_mutex before doing so.
266 : *
267 : * If file ownership is changed notify_change() doesn't map ia_uid and
268 : * ia_gid. It will asssume the caller has already provided the intended values.
269 : *
270 : * Alternatively, a caller may pass NULL for delegated_inode. This may
271 : * be appropriate for callers that expect the underlying filesystem not
272 : * to be NFS exported. Also, passing NULL is fine for callers holding
273 : * the file open for write, as there can be no conflicting delegation in
274 : * that case.
275 : *
276 : * If the inode has been found through an idmapped mount the user namespace of
277 : * the vfsmount must be passed through @mnt_userns. This function will then
278 : * take care to map the inode according to @mnt_userns before checking
279 : * permissions. On non-idmapped mounts or if permission checking is to be
280 : * performed on the raw inode simply passs init_user_ns.
281 : */
282 1100 : int notify_change(struct user_namespace *mnt_userns, struct dentry *dentry,
283 : struct iattr *attr, struct inode **delegated_inode)
284 : {
285 1100 : struct inode *inode = dentry->d_inode;
286 1100 : umode_t mode = inode->i_mode;
287 1100 : int error;
288 1100 : struct timespec64 now;
289 1100 : unsigned int ia_valid = attr->ia_valid;
290 :
291 1100 : WARN_ON_ONCE(!inode_is_locked(inode));
292 :
293 1100 : if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID | ATTR_TIMES_SET)) {
294 849 : if (IS_IMMUTABLE(inode) || IS_APPEND(inode))
295 : return -EPERM;
296 : }
297 :
298 : /*
299 : * If utimes(2) and friends are called with times == NULL (or both
300 : * times are UTIME_NOW), then we need to check for write permission
301 : */
302 1100 : if (ia_valid & ATTR_TOUCH) {
303 179 : if (IS_IMMUTABLE(inode))
304 : return -EPERM;
305 :
306 179 : if (!inode_owner_or_capable(mnt_userns, inode)) {
307 0 : error = inode_permission(mnt_userns, inode, MAY_WRITE);
308 0 : if (error)
309 : return error;
310 : }
311 : }
312 :
313 1100 : if ((ia_valid & ATTR_MODE)) {
314 564 : umode_t amode = attr->ia_mode;
315 : /* Flag setting protected by i_mutex */
316 1128 : if (is_sxid(amode))
317 2 : inode->i_flags &= ~S_NOSEC;
318 : }
319 :
320 1100 : now = current_time(inode);
321 :
322 1100 : attr->ia_ctime = now;
323 1100 : if (!(ia_valid & ATTR_ATIME_SET))
324 1017 : attr->ia_atime = now;
325 : else
326 83 : attr->ia_atime = timestamp_truncate(attr->ia_atime, inode);
327 1100 : if (!(ia_valid & ATTR_MTIME_SET))
328 1005 : attr->ia_mtime = now;
329 : else
330 95 : attr->ia_mtime = timestamp_truncate(attr->ia_mtime, inode);
331 :
332 1100 : if (ia_valid & ATTR_KILL_PRIV) {
333 179 : error = security_inode_need_killpriv(dentry);
334 179 : if (error < 0)
335 : return error;
336 179 : if (error == 0)
337 179 : ia_valid = attr->ia_valid &= ~ATTR_KILL_PRIV;
338 : }
339 :
340 : /*
341 : * We now pass ATTR_KILL_S*ID to the lower level setattr function so
342 : * that the function has the ability to reinterpret a mode change
343 : * that's due to these bits. This adds an implicit restriction that
344 : * no function will ever call notify_change with both ATTR_MODE and
345 : * ATTR_KILL_S*ID set.
346 : */
347 1100 : if ((ia_valid & (ATTR_KILL_SUID|ATTR_KILL_SGID)) &&
348 179 : (ia_valid & ATTR_MODE))
349 0 : BUG();
350 :
351 1100 : if (ia_valid & ATTR_KILL_SUID) {
352 179 : if (mode & S_ISUID) {
353 0 : ia_valid = attr->ia_valid |= ATTR_MODE;
354 0 : attr->ia_mode = (inode->i_mode & ~S_ISUID);
355 : }
356 : }
357 1100 : if (ia_valid & ATTR_KILL_SGID) {
358 179 : if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP)) {
359 0 : if (!(ia_valid & ATTR_MODE)) {
360 0 : ia_valid = attr->ia_valid |= ATTR_MODE;
361 0 : attr->ia_mode = inode->i_mode;
362 : }
363 0 : attr->ia_mode &= ~S_ISGID;
364 : }
365 : }
366 1100 : if (!(attr->ia_valid & ~(ATTR_KILL_SUID | ATTR_KILL_SGID)))
367 : return 0;
368 :
369 : /*
370 : * Verify that uid/gid changes are valid in the target
371 : * namespace of the superblock.
372 : */
373 1100 : if (ia_valid & ATTR_UID &&
374 308 : !kuid_has_mapping(inode->i_sb->s_user_ns, attr->ia_uid))
375 : return -EOVERFLOW;
376 1100 : if (ia_valid & ATTR_GID &&
377 308 : !kgid_has_mapping(inode->i_sb->s_user_ns, attr->ia_gid))
378 : return -EOVERFLOW;
379 :
380 : /* Don't allow modifications of files with invalid uids or
381 : * gids unless those uids & gids are being made valid.
382 : */
383 1100 : if (!(ia_valid & ATTR_UID) &&
384 792 : !uid_valid(i_uid_into_mnt(mnt_userns, inode)))
385 : return -EOVERFLOW;
386 1100 : if (!(ia_valid & ATTR_GID) &&
387 792 : !gid_valid(i_gid_into_mnt(mnt_userns, inode)))
388 : return -EOVERFLOW;
389 :
390 1100 : error = security_inode_setattr(dentry, attr);
391 1100 : if (error)
392 : return error;
393 1100 : error = try_break_deleg(inode, delegated_inode);
394 1100 : if (error)
395 : return error;
396 :
397 1100 : if (inode->i_op->setattr)
398 595 : error = inode->i_op->setattr(mnt_userns, dentry, attr);
399 : else
400 505 : error = simple_setattr(mnt_userns, dentry, attr);
401 :
402 1100 : if (!error) {
403 1100 : fsnotify_change(dentry, ia_valid);
404 1100 : ima_inode_post_setattr(mnt_userns, dentry);
405 1100 : evm_inode_post_setattr(dentry, ia_valid);
406 : }
407 :
408 : return error;
409 : }
410 : EXPORT_SYMBOL(notify_change);
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