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 = attr->ia_atime;
190 if (ia_valid & ATTR_MTIME)
191 inode->i_mtime = attr->ia_mtime;
192 if (ia_valid & ATTR_CTIME)
193 inode->i_ctime = attr->ia_ctime;
194 if (ia_valid & ATTR_MODE) {
195 umode_t mode = attr->ia_mode;
196
197 if (!in_group_p(inode->i_gid) &&
198 !capable_wrt_inode_uidgid(inode, CAP_FSETID))
199 mode &= ~S_ISGID;
200 inode->i_mode = mode;
201 }
202 }
203 EXPORT_SYMBOL(setattr_copy);
204
205 /**
206 * notify_change - modify attributes of a filesytem object
207 * @dentry: object affected
208 * @attr: new attributes
209 * @delegated_inode: returns inode, if the inode is delegated
210 *
211 * The caller must hold the i_mutex on the affected object.
212 *
213 * If notify_change discovers a delegation in need of breaking,
214 * it will return -EWOULDBLOCK and return a reference to the inode in
215 * delegated_inode. The caller should then break the delegation and
216 * retry. Because breaking a delegation may take a long time, the
217 * caller should drop the i_mutex before doing so.
218 *
219 * Alternatively, a caller may pass NULL for delegated_inode. This may
220 * be appropriate for callers that expect the underlying filesystem not
221 * to be NFS exported. Also, passing NULL is fine for callers holding
222 * the file open for write, as there can be no conflicting delegation in
223 * that case.
224 */
notify_change(struct dentry * dentry,struct iattr * attr,struct inode ** delegated_inode)225 int notify_change(struct dentry * dentry, struct iattr * attr, struct inode **delegated_inode)
226 {
227 struct inode *inode = dentry->d_inode;
228 umode_t mode = inode->i_mode;
229 int error;
230 struct timespec64 now;
231 unsigned int ia_valid = attr->ia_valid;
232
233 WARN_ON_ONCE(!inode_is_locked(inode));
234
235 if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID | ATTR_TIMES_SET)) {
236 if (IS_IMMUTABLE(inode) || IS_APPEND(inode))
237 return -EPERM;
238 }
239
240 /*
241 * If utimes(2) and friends are called with times == NULL (or both
242 * times are UTIME_NOW), then we need to check for write permission
243 */
244 if (ia_valid & ATTR_TOUCH) {
245 if (IS_IMMUTABLE(inode))
246 return -EPERM;
247
248 if (!inode_owner_or_capable(inode)) {
249 error = inode_permission(inode, MAY_WRITE);
250 if (error)
251 return error;
252 }
253 }
254
255 if ((ia_valid & ATTR_MODE)) {
256 umode_t amode = attr->ia_mode;
257 /* Flag setting protected by i_mutex */
258 if (is_sxid(amode))
259 inode->i_flags &= ~S_NOSEC;
260 }
261
262 now = current_time(inode);
263
264 attr->ia_ctime = now;
265 if (!(ia_valid & ATTR_ATIME_SET))
266 attr->ia_atime = now;
267 else
268 attr->ia_atime = timestamp_truncate(attr->ia_atime, inode);
269 if (!(ia_valid & ATTR_MTIME_SET))
270 attr->ia_mtime = now;
271 else
272 attr->ia_mtime = timestamp_truncate(attr->ia_mtime, inode);
273
274 if (ia_valid & ATTR_KILL_PRIV) {
275 error = security_inode_need_killpriv(dentry);
276 if (error < 0)
277 return error;
278 if (error == 0)
279 ia_valid = attr->ia_valid &= ~ATTR_KILL_PRIV;
280 }
281
282 /*
283 * We now pass ATTR_KILL_S*ID to the lower level setattr function so
284 * that the function has the ability to reinterpret a mode change
285 * that's due to these bits. This adds an implicit restriction that
286 * no function will ever call notify_change with both ATTR_MODE and
287 * ATTR_KILL_S*ID set.
288 */
289 if ((ia_valid & (ATTR_KILL_SUID|ATTR_KILL_SGID)) &&
290 (ia_valid & ATTR_MODE))
291 BUG();
292
293 if (ia_valid & ATTR_KILL_SUID) {
294 if (mode & S_ISUID) {
295 ia_valid = attr->ia_valid |= ATTR_MODE;
296 attr->ia_mode = (inode->i_mode & ~S_ISUID);
297 }
298 }
299 if (ia_valid & ATTR_KILL_SGID) {
300 if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP)) {
301 if (!(ia_valid & ATTR_MODE)) {
302 ia_valid = attr->ia_valid |= ATTR_MODE;
303 attr->ia_mode = inode->i_mode;
304 }
305 attr->ia_mode &= ~S_ISGID;
306 }
307 }
308 if (!(attr->ia_valid & ~(ATTR_KILL_SUID | ATTR_KILL_SGID)))
309 return 0;
310
311 /*
312 * Verify that uid/gid changes are valid in the target
313 * namespace of the superblock.
314 */
315 if (ia_valid & ATTR_UID &&
316 !kuid_has_mapping(inode->i_sb->s_user_ns, attr->ia_uid))
317 return -EOVERFLOW;
318 if (ia_valid & ATTR_GID &&
319 !kgid_has_mapping(inode->i_sb->s_user_ns, attr->ia_gid))
320 return -EOVERFLOW;
321
322 /* Don't allow modifications of files with invalid uids or
323 * gids unless those uids & gids are being made valid.
324 */
325 if (!(ia_valid & ATTR_UID) && !uid_valid(inode->i_uid))
326 return -EOVERFLOW;
327 if (!(ia_valid & ATTR_GID) && !gid_valid(inode->i_gid))
328 return -EOVERFLOW;
329
330 error = security_inode_setattr(dentry, attr);
331 if (error)
332 return error;
333 error = try_break_deleg(inode, delegated_inode);
334 if (error)
335 return error;
336
337 if (inode->i_op->setattr)
338 error = inode->i_op->setattr(dentry, attr);
339 else
340 error = simple_setattr(dentry, attr);
341
342 if (!error) {
343 fsnotify_change(dentry, ia_valid);
344 ima_inode_post_setattr(dentry);
345 evm_inode_post_setattr(dentry, ia_valid);
346 }
347
348 return error;
349 }
350 EXPORT_SYMBOL(notify_change);
351