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 (inode->i_size < offset) {
138 unsigned long limit;
139
140 limit = rlimit(RLIMIT_FSIZE);
141 if (limit != RLIM_INFINITY && offset > limit)
142 goto out_sig;
143 if (offset > inode->i_sb->s_maxbytes)
144 goto out_big;
145 } else {
146 /*
147 * truncation of in-use swapfiles is disallowed - it would
148 * cause subsequent swapout to scribble on the now-freed
149 * blocks.
150 */
151 if (IS_SWAPFILE(inode))
152 return -ETXTBSY;
153 }
154
155 return 0;
156 out_sig:
157 send_sig(SIGXFSZ, current, 0);
158 out_big:
159 return -EFBIG;
160 }
161 EXPORT_SYMBOL(inode_newsize_ok);
162
163 /**
164 * setattr_copy - copy simple metadata updates into the generic inode
165 * @inode: the inode to be updated
166 * @attr: the new attributes
167 *
168 * setattr_copy must be called with i_mutex held.
169 *
170 * setattr_copy updates the inode's metadata with that specified
171 * in attr. Noticeably missing is inode size update, which is more complex
172 * as it requires pagecache updates.
173 *
174 * The inode is not marked as dirty after this operation. The rationale is
175 * that for "simple" filesystems, the struct inode is the inode storage.
176 * The caller is free to mark the inode dirty afterwards if needed.
177 */
setattr_copy(struct inode * inode,const struct iattr * attr)178 void setattr_copy(struct inode *inode, const struct iattr *attr)
179 {
180 unsigned int ia_valid = attr->ia_valid;
181
182 if (ia_valid & ATTR_UID)
183 inode->i_uid = attr->ia_uid;
184 if (ia_valid & ATTR_GID)
185 inode->i_gid = attr->ia_gid;
186 if (ia_valid & ATTR_ATIME)
187 inode->i_atime = timespec64_trunc(attr->ia_atime,
188 inode->i_sb->s_time_gran);
189 if (ia_valid & ATTR_MTIME)
190 inode->i_mtime = timespec64_trunc(attr->ia_mtime,
191 inode->i_sb->s_time_gran);
192 if (ia_valid & ATTR_CTIME)
193 inode->i_ctime = timespec64_trunc(attr->ia_ctime,
194 inode->i_sb->s_time_gran);
195 if (ia_valid & ATTR_MODE) {
196 umode_t mode = attr->ia_mode;
197
198 if (!in_group_p(inode->i_gid) &&
199 !capable_wrt_inode_uidgid(inode, CAP_FSETID))
200 mode &= ~S_ISGID;
201 inode->i_mode = mode;
202 }
203 }
204 EXPORT_SYMBOL(setattr_copy);
205
206 /**
207 * notify_change - modify attributes of a filesytem object
208 * @dentry: object affected
209 * @attr: new attributes
210 * @delegated_inode: returns inode, if the inode is delegated
211 *
212 * The caller must hold the i_mutex on the affected object.
213 *
214 * If notify_change discovers a delegation in need of breaking,
215 * it will return -EWOULDBLOCK and return a reference to the inode in
216 * delegated_inode. The caller should then break the delegation and
217 * retry. Because breaking a delegation may take a long time, the
218 * caller should drop the i_mutex before doing so.
219 *
220 * Alternatively, a caller may pass NULL for delegated_inode. This may
221 * be appropriate for callers that expect the underlying filesystem not
222 * to be NFS exported. Also, passing NULL is fine for callers holding
223 * the file open for write, as there can be no conflicting delegation in
224 * that case.
225 */
notify_change(struct dentry * dentry,struct iattr * attr,struct inode ** delegated_inode)226 int notify_change(struct dentry * dentry, struct iattr * attr, struct inode **delegated_inode)
227 {
228 struct inode *inode = dentry->d_inode;
229 umode_t mode = inode->i_mode;
230 int error;
231 struct timespec64 now;
232 unsigned int ia_valid = attr->ia_valid;
233
234 WARN_ON_ONCE(!inode_is_locked(inode));
235
236 if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID | ATTR_TIMES_SET)) {
237 if (IS_IMMUTABLE(inode) || IS_APPEND(inode))
238 return -EPERM;
239 }
240
241 /*
242 * If utimes(2) and friends are called with times == NULL (or both
243 * times are UTIME_NOW), then we need to check for write permission
244 */
245 if (ia_valid & ATTR_TOUCH) {
246 if (IS_IMMUTABLE(inode))
247 return -EPERM;
248
249 if (!inode_owner_or_capable(inode)) {
250 error = inode_permission(inode, MAY_WRITE);
251 if (error)
252 return error;
253 }
254 }
255
256 if ((ia_valid & ATTR_MODE)) {
257 umode_t amode = attr->ia_mode;
258 /* Flag setting protected by i_mutex */
259 if (is_sxid(amode))
260 inode->i_flags &= ~S_NOSEC;
261 }
262
263 now = current_time(inode);
264
265 attr->ia_ctime = now;
266 if (!(ia_valid & ATTR_ATIME_SET))
267 attr->ia_atime = now;
268 if (!(ia_valid & ATTR_MTIME_SET))
269 attr->ia_mtime = now;
270 if (ia_valid & ATTR_KILL_PRIV) {
271 error = security_inode_need_killpriv(dentry);
272 if (error < 0)
273 return error;
274 if (error == 0)
275 ia_valid = attr->ia_valid &= ~ATTR_KILL_PRIV;
276 }
277
278 /*
279 * We now pass ATTR_KILL_S*ID to the lower level setattr function so
280 * that the function has the ability to reinterpret a mode change
281 * that's due to these bits. This adds an implicit restriction that
282 * no function will ever call notify_change with both ATTR_MODE and
283 * ATTR_KILL_S*ID set.
284 */
285 if ((ia_valid & (ATTR_KILL_SUID|ATTR_KILL_SGID)) &&
286 (ia_valid & ATTR_MODE))
287 BUG();
288
289 if (ia_valid & ATTR_KILL_SUID) {
290 if (mode & S_ISUID) {
291 ia_valid = attr->ia_valid |= ATTR_MODE;
292 attr->ia_mode = (inode->i_mode & ~S_ISUID);
293 }
294 }
295 if (ia_valid & ATTR_KILL_SGID) {
296 if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP)) {
297 if (!(ia_valid & ATTR_MODE)) {
298 ia_valid = attr->ia_valid |= ATTR_MODE;
299 attr->ia_mode = inode->i_mode;
300 }
301 attr->ia_mode &= ~S_ISGID;
302 }
303 }
304 if (!(attr->ia_valid & ~(ATTR_KILL_SUID | ATTR_KILL_SGID)))
305 return 0;
306
307 /*
308 * Verify that uid/gid changes are valid in the target
309 * namespace of the superblock.
310 */
311 if (ia_valid & ATTR_UID &&
312 !kuid_has_mapping(inode->i_sb->s_user_ns, attr->ia_uid))
313 return -EOVERFLOW;
314 if (ia_valid & ATTR_GID &&
315 !kgid_has_mapping(inode->i_sb->s_user_ns, attr->ia_gid))
316 return -EOVERFLOW;
317
318 /* Don't allow modifications of files with invalid uids or
319 * gids unless those uids & gids are being made valid.
320 */
321 if (!(ia_valid & ATTR_UID) && !uid_valid(inode->i_uid))
322 return -EOVERFLOW;
323 if (!(ia_valid & ATTR_GID) && !gid_valid(inode->i_gid))
324 return -EOVERFLOW;
325
326 error = security_inode_setattr(dentry, attr);
327 if (error)
328 return error;
329 error = try_break_deleg(inode, delegated_inode);
330 if (error)
331 return error;
332
333 if (inode->i_op->setattr)
334 error = inode->i_op->setattr(dentry, attr);
335 else
336 error = simple_setattr(dentry, attr);
337
338 if (!error) {
339 fsnotify_change(dentry, ia_valid);
340 ima_inode_post_setattr(dentry);
341 evm_inode_post_setattr(dentry, ia_valid);
342 }
343
344 return error;
345 }
346 EXPORT_SYMBOL(notify_change);
347
