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
chown_ok(const struct inode * inode,kuid_t uid)21 static bool chown_ok(const struct inode *inode, kuid_t uid)
22 {
23 if (uid_eq(current_fsuid(), inode->i_uid) &&
24 uid_eq(uid, inode->i_uid))
25 return true;
26 if (capable_wrt_inode_uidgid(inode, CAP_CHOWN))
27 return true;
28 if (uid_eq(inode->i_uid, INVALID_UID) &&
29 ns_capable(inode->i_sb->s_user_ns, CAP_CHOWN))
30 return true;
31 return false;
32 }
33
chgrp_ok(const struct inode * inode,kgid_t gid)34 static bool chgrp_ok(const struct inode *inode, kgid_t gid)
35 {
36 if (uid_eq(current_fsuid(), inode->i_uid) &&
37 (in_group_p(gid) || gid_eq(gid, inode->i_gid)))
38 return true;
39 if (capable_wrt_inode_uidgid(inode, CAP_CHOWN))
40 return true;
41 if (gid_eq(inode->i_gid, INVALID_GID) &&
42 ns_capable(inode->i_sb->s_user_ns, CAP_CHOWN))
43 return true;
44 return false;
45 }
46
47 /**
48 * setattr_prepare - check if attribute changes to a dentry are allowed
49 * @dentry: dentry to check
50 * @attr: attributes to change
51 *
52 * Check if we are allowed to change the attributes contained in @attr
53 * in the given dentry. This includes the normal unix access permission
54 * checks, as well as checks for rlimits and others. The function also clears
55 * SGID bit from mode if user is not allowed to set it. Also file capabilities
56 * and IMA extended attributes are cleared if ATTR_KILL_PRIV is set.
57 *
58 * Should be called as the first thing in ->setattr implementations,
59 * possibly after taking additional locks.
60 */
setattr_prepare(struct dentry * dentry,struct iattr * attr)61 int setattr_prepare(struct dentry *dentry, struct iattr *attr)
62 {
63 struct inode *inode = d_inode(dentry);
64 unsigned int ia_valid = attr->ia_valid;
65
66 /*
67 * First check size constraints. These can't be overriden using
68 * ATTR_FORCE.
69 */
70 if (ia_valid & ATTR_SIZE) {
71 int error = inode_newsize_ok(inode, attr->ia_size);
72 if (error)
73 return error;
74 }
75
76 /* If force is set do it anyway. */
77 if (ia_valid & ATTR_FORCE)
78 goto kill_priv;
79
80 /* Make sure a caller can chown. */
81 if ((ia_valid & ATTR_UID) && !chown_ok(inode, attr->ia_uid))
82 return -EPERM;
83
84 /* Make sure caller can chgrp. */
85 if ((ia_valid & ATTR_GID) && !chgrp_ok(inode, attr->ia_gid))
86 return -EPERM;
87
88 /* Make sure a caller can chmod. */
89 if (ia_valid & ATTR_MODE) {
90 if (!inode_owner_or_capable(inode))
91 return -EPERM;
92 /* Also check the setgid bit! */
93 if (!in_group_p((ia_valid & ATTR_GID) ? attr->ia_gid :
94 inode->i_gid) &&
95 !capable_wrt_inode_uidgid(inode, CAP_FSETID))
96 attr->ia_mode &= ~S_ISGID;
97 }
98
99 /* Check for setting the inode time. */
100 if (ia_valid & (ATTR_MTIME_SET | ATTR_ATIME_SET | ATTR_TIMES_SET)) {
101 if (!inode_owner_or_capable(inode))
102 return -EPERM;
103 }
104
105 kill_priv:
106 /* User has permission for the change */
107 if (ia_valid & ATTR_KILL_PRIV) {
108 int error;
109
110 error = security_inode_killpriv(dentry);
111 if (error)
112 return error;
113 }
114
115 return 0;
116 }
117 EXPORT_SYMBOL(setattr_prepare);
118
119 /**
120 * inode_newsize_ok - may this inode be truncated to a given size
121 * @inode: the inode to be truncated
122 * @offset: the new size to assign to the inode
123 *
124 * inode_newsize_ok must be called with i_mutex held.
125 *
126 * inode_newsize_ok will check filesystem limits and ulimits to check that the
127 * new inode size is within limits. inode_newsize_ok will also send SIGXFSZ
128 * when necessary. Caller must not proceed with inode size change if failure is
129 * returned. @inode must be a file (not directory), with appropriate
130 * permissions to allow truncate (inode_newsize_ok does NOT check these
131 * conditions).
132 *
133 * Return: 0 on success, -ve errno on failure
134 */
inode_newsize_ok(const struct inode * inode,loff_t offset)135 int inode_newsize_ok(const struct inode *inode, loff_t offset)
136 {
137 if (offset < 0)
138 return -EINVAL;
139 if (inode->i_size < offset) {
140 unsigned long limit;
141
142 limit = rlimit(RLIMIT_FSIZE);
143 if (limit != RLIM_INFINITY && offset > limit)
144 goto out_sig;
145 if (offset > inode->i_sb->s_maxbytes)
146 goto out_big;
147 } else {
148 /*
149 * truncation of in-use swapfiles is disallowed - it would
150 * cause subsequent swapout to scribble on the now-freed
151 * blocks.
152 */
153 if (IS_SWAPFILE(inode))
154 return -ETXTBSY;
155 }
156
157 return 0;
158 out_sig:
159 send_sig(SIGXFSZ, current, 0);
160 out_big:
161 return -EFBIG;
162 }
163 EXPORT_SYMBOL(inode_newsize_ok);
164
165 /**
166 * setattr_copy - copy simple metadata updates into the generic inode
167 * @inode: the inode to be updated
168 * @attr: the new attributes
169 *
170 * setattr_copy must be called with i_mutex held.
171 *
172 * setattr_copy updates the inode's metadata with that specified
173 * in attr. Noticeably missing is inode size update, which is more complex
174 * as it requires pagecache updates.
175 *
176 * The inode is not marked as dirty after this operation. The rationale is
177 * that for "simple" filesystems, the struct inode is the inode storage.
178 * The caller is free to mark the inode dirty afterwards if needed.
179 */
setattr_copy(struct inode * inode,const struct iattr * attr)180 void setattr_copy(struct inode *inode, const struct iattr *attr)
181 {
182 unsigned int ia_valid = attr->ia_valid;
183
184 if (ia_valid & ATTR_UID)
185 inode->i_uid = attr->ia_uid;
186 if (ia_valid & ATTR_GID)
187 inode->i_gid = attr->ia_gid;
188 if (ia_valid & ATTR_ATIME)
189 inode->i_atime = timespec64_trunc(attr->ia_atime,
190 inode->i_sb->s_time_gran);
191 if (ia_valid & ATTR_MTIME)
192 inode->i_mtime = timespec64_trunc(attr->ia_mtime,
193 inode->i_sb->s_time_gran);
194 if (ia_valid & ATTR_CTIME)
195 inode->i_ctime = timespec64_trunc(attr->ia_ctime,
196 inode->i_sb->s_time_gran);
197 if (ia_valid & ATTR_MODE) {
198 umode_t mode = attr->ia_mode;
199
200 if (!in_group_p(inode->i_gid) &&
201 !capable_wrt_inode_uidgid(inode, CAP_FSETID))
202 mode &= ~S_ISGID;
203 inode->i_mode = mode;
204 }
205 }
206 EXPORT_SYMBOL(setattr_copy);
207
208 /**
209 * notify_change - modify attributes of a filesytem object
210 * @dentry: object affected
211 * @attr: new attributes
212 * @delegated_inode: returns inode, if the inode is delegated
213 *
214 * The caller must hold the i_mutex on the affected object.
215 *
216 * If notify_change discovers a delegation in need of breaking,
217 * it will return -EWOULDBLOCK and return a reference to the inode in
218 * delegated_inode. The caller should then break the delegation and
219 * retry. Because breaking a delegation may take a long time, the
220 * caller should drop the i_mutex before doing so.
221 *
222 * Alternatively, a caller may pass NULL for delegated_inode. This may
223 * be appropriate for callers that expect the underlying filesystem not
224 * to be NFS exported. Also, passing NULL is fine for callers holding
225 * the file open for write, as there can be no conflicting delegation in
226 * that case.
227 */
notify_change(struct dentry * dentry,struct iattr * attr,struct inode ** delegated_inode)228 int notify_change(struct dentry * dentry, struct iattr * attr, struct inode **delegated_inode)
229 {
230 struct inode *inode = dentry->d_inode;
231 umode_t mode = inode->i_mode;
232 int error;
233 struct timespec64 now;
234 unsigned int ia_valid = attr->ia_valid;
235
236 WARN_ON_ONCE(!inode_is_locked(inode));
237
238 if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID | ATTR_TIMES_SET)) {
239 if (IS_IMMUTABLE(inode) || IS_APPEND(inode))
240 return -EPERM;
241 }
242
243 /*
244 * If utimes(2) and friends are called with times == NULL (or both
245 * times are UTIME_NOW), then we need to check for write permission
246 */
247 if (ia_valid & ATTR_TOUCH) {
248 if (IS_IMMUTABLE(inode))
249 return -EPERM;
250
251 if (!inode_owner_or_capable(inode)) {
252 error = inode_permission(inode, MAY_WRITE);
253 if (error)
254 return error;
255 }
256 }
257
258 if ((ia_valid & ATTR_MODE)) {
259 /*
260 * Don't allow changing the mode of symlinks:
261 *
262 * (1) The vfs doesn't take the mode of symlinks into account
263 * during permission checking.
264 * (2) This has never worked correctly. Most major filesystems
265 * did return EOPNOTSUPP due to interactions with POSIX ACLs
266 * but did still updated the mode of the symlink.
267 * This inconsistency led system call wrapper providers such
268 * as libc to block changing the mode of symlinks with
269 * EOPNOTSUPP already.
270 * (3) To even do this in the first place one would have to use
271 * specific file descriptors and quite some effort.
272 */
273 if (S_ISLNK(inode->i_mode))
274 return -EOPNOTSUPP;
275
276 /* Flag setting protected by i_mutex */
277 if (is_sxid(attr->ia_mode))
278 inode->i_flags &= ~S_NOSEC;
279 }
280
281 now = current_time(inode);
282
283 attr->ia_ctime = now;
284 if (!(ia_valid & ATTR_ATIME_SET))
285 attr->ia_atime = now;
286 if (!(ia_valid & ATTR_MTIME_SET))
287 attr->ia_mtime = now;
288 if (ia_valid & ATTR_KILL_PRIV) {
289 error = security_inode_need_killpriv(dentry);
290 if (error < 0)
291 return error;
292 if (error == 0)
293 ia_valid = attr->ia_valid &= ~ATTR_KILL_PRIV;
294 }
295
296 /*
297 * We now pass ATTR_KILL_S*ID to the lower level setattr function so
298 * that the function has the ability to reinterpret a mode change
299 * that's due to these bits. This adds an implicit restriction that
300 * no function will ever call notify_change with both ATTR_MODE and
301 * ATTR_KILL_S*ID set.
302 */
303 if ((ia_valid & (ATTR_KILL_SUID|ATTR_KILL_SGID)) &&
304 (ia_valid & ATTR_MODE))
305 BUG();
306
307 if (ia_valid & ATTR_KILL_SUID) {
308 if (mode & S_ISUID) {
309 ia_valid = attr->ia_valid |= ATTR_MODE;
310 attr->ia_mode = (inode->i_mode & ~S_ISUID);
311 }
312 }
313 if (ia_valid & ATTR_KILL_SGID) {
314 if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP)) {
315 if (!(ia_valid & ATTR_MODE)) {
316 ia_valid = attr->ia_valid |= ATTR_MODE;
317 attr->ia_mode = inode->i_mode;
318 }
319 attr->ia_mode &= ~S_ISGID;
320 }
321 }
322 if (!(attr->ia_valid & ~(ATTR_KILL_SUID | ATTR_KILL_SGID)))
323 return 0;
324
325 /*
326 * Verify that uid/gid changes are valid in the target
327 * namespace of the superblock.
328 */
329 if (ia_valid & ATTR_UID &&
330 !kuid_has_mapping(inode->i_sb->s_user_ns, attr->ia_uid))
331 return -EOVERFLOW;
332 if (ia_valid & ATTR_GID &&
333 !kgid_has_mapping(inode->i_sb->s_user_ns, attr->ia_gid))
334 return -EOVERFLOW;
335
336 /* Don't allow modifications of files with invalid uids or
337 * gids unless those uids & gids are being made valid.
338 */
339 if (!(ia_valid & ATTR_UID) && !uid_valid(inode->i_uid))
340 return -EOVERFLOW;
341 if (!(ia_valid & ATTR_GID) && !gid_valid(inode->i_gid))
342 return -EOVERFLOW;
343
344 error = security_inode_setattr(dentry, attr);
345 if (error)
346 return error;
347 error = try_break_deleg(inode, delegated_inode);
348 if (error)
349 return error;
350
351 if (inode->i_op->setattr)
352 error = inode->i_op->setattr(dentry, attr);
353 else
354 error = simple_setattr(dentry, attr);
355
356 if (!error) {
357 fsnotify_change(dentry, ia_valid);
358 ima_inode_post_setattr(dentry);
359 evm_inode_post_setattr(dentry, ia_valid);
360 }
361
362 return error;
363 }
364 EXPORT_SYMBOL(notify_change);
365