1 /*
2 * linux/fs/attr.c
3 *
4 * Copyright (C) 1991, 1992 Linus Torvalds
5 * changes by Thomas Schoebel-Theuer
6 */
7
8 #include <linux/export.h>
9 #include <linux/time.h>
10 #include <linux/mm.h>
11 #include <linux/string.h>
12 #include <linux/capability.h>
13 #include <linux/fsnotify.h>
14 #include <linux/fcntl.h>
15 #include <linux/security.h>
16 #include <linux/evm.h>
17 #include <linux/ima.h>
18
19 /**
20 * setattr_prepare - check if attribute changes to a dentry are allowed
21 * @dentry: dentry to check
22 * @attr: attributes to change
23 *
24 * Check if we are allowed to change the attributes contained in @attr
25 * in the given dentry. This includes the normal unix access permission
26 * checks, as well as checks for rlimits and others. The function also clears
27 * SGID bit from mode if user is not allowed to set it. Also file capabilities
28 * and IMA extended attributes are cleared if ATTR_KILL_PRIV is set.
29 *
30 * Should be called as the first thing in ->setattr implementations,
31 * possibly after taking additional locks.
32 */
setattr_prepare(struct dentry * dentry,struct iattr * attr)33 int setattr_prepare(struct dentry *dentry, struct iattr *attr)
34 {
35 struct inode *inode = d_inode(dentry);
36 unsigned int ia_valid = attr->ia_valid;
37
38 /*
39 * First check size constraints. These can't be overriden using
40 * ATTR_FORCE.
41 */
42 if (ia_valid & ATTR_SIZE) {
43 int error = inode_newsize_ok(inode, attr->ia_size);
44 if (error)
45 return error;
46 }
47
48 /* If force is set do it anyway. */
49 if (ia_valid & ATTR_FORCE)
50 goto kill_priv;
51
52 /* Make sure a caller can chown. */
53 if ((ia_valid & ATTR_UID) &&
54 (!uid_eq(current_fsuid(), inode->i_uid) ||
55 !uid_eq(attr->ia_uid, inode->i_uid)) &&
56 !capable_wrt_inode_uidgid(inode, CAP_CHOWN))
57 return -EPERM;
58
59 /* Make sure caller can chgrp. */
60 if ((ia_valid & ATTR_GID) &&
61 (!uid_eq(current_fsuid(), inode->i_uid) ||
62 (!in_group_p(attr->ia_gid) && !gid_eq(attr->ia_gid, inode->i_gid))) &&
63 !capable_wrt_inode_uidgid(inode, CAP_CHOWN))
64 return -EPERM;
65
66 /* Make sure a caller can chmod. */
67 if (ia_valid & ATTR_MODE) {
68 if (!inode_owner_or_capable(inode))
69 return -EPERM;
70 /* Also check the setgid bit! */
71 if (!in_group_p((ia_valid & ATTR_GID) ? attr->ia_gid :
72 inode->i_gid) &&
73 !capable_wrt_inode_uidgid(inode, CAP_FSETID))
74 attr->ia_mode &= ~S_ISGID;
75 }
76
77 /* Check for setting the inode time. */
78 if (ia_valid & (ATTR_MTIME_SET | ATTR_ATIME_SET | ATTR_TIMES_SET)) {
79 if (!inode_owner_or_capable(inode))
80 return -EPERM;
81 }
82
83 kill_priv:
84 /* User has permission for the change */
85 if (ia_valid & ATTR_KILL_PRIV) {
86 int error;
87
88 error = security_inode_killpriv(dentry);
89 if (error)
90 return error;
91 }
92
93 return 0;
94 }
95 EXPORT_SYMBOL(setattr_prepare);
96
97 /**
98 * inode_newsize_ok - may this inode be truncated to a given size
99 * @inode: the inode to be truncated
100 * @offset: the new size to assign to the inode
101 * @Returns: 0 on success, -ve errno on failure
102 *
103 * inode_newsize_ok must be called with i_mutex held.
104 *
105 * inode_newsize_ok will check filesystem limits and ulimits to check that the
106 * new inode size is within limits. inode_newsize_ok will also send SIGXFSZ
107 * when necessary. Caller must not proceed with inode size change if failure is
108 * returned. @inode must be a file (not directory), with appropriate
109 * permissions to allow truncate (inode_newsize_ok does NOT check these
110 * conditions).
111 */
inode_newsize_ok(const struct inode * inode,loff_t offset)112 int inode_newsize_ok(const struct inode *inode, loff_t offset)
113 {
114 if (inode->i_size < offset) {
115 unsigned long limit;
116
117 limit = rlimit(RLIMIT_FSIZE);
118 if (limit != RLIM_INFINITY && offset > limit)
119 goto out_sig;
120 if (offset > inode->i_sb->s_maxbytes)
121 goto out_big;
122 } else {
123 /*
124 * truncation of in-use swapfiles is disallowed - it would
125 * cause subsequent swapout to scribble on the now-freed
126 * blocks.
127 */
128 if (IS_SWAPFILE(inode))
129 return -ETXTBSY;
130 }
131
132 return 0;
133 out_sig:
134 send_sig(SIGXFSZ, current, 0);
135 out_big:
136 return -EFBIG;
137 }
138 EXPORT_SYMBOL(inode_newsize_ok);
139
140 /**
141 * setattr_copy - copy simple metadata updates into the generic inode
142 * @inode: the inode to be updated
143 * @attr: the new attributes
144 *
145 * setattr_copy must be called with i_mutex held.
146 *
147 * setattr_copy updates the inode's metadata with that specified
148 * in attr. Noticeably missing is inode size update, which is more complex
149 * as it requires pagecache updates.
150 *
151 * The inode is not marked as dirty after this operation. The rationale is
152 * that for "simple" filesystems, the struct inode is the inode storage.
153 * The caller is free to mark the inode dirty afterwards if needed.
154 */
setattr_copy(struct inode * inode,const struct iattr * attr)155 void setattr_copy(struct inode *inode, const struct iattr *attr)
156 {
157 unsigned int ia_valid = attr->ia_valid;
158
159 if (ia_valid & ATTR_UID)
160 inode->i_uid = attr->ia_uid;
161 if (ia_valid & ATTR_GID)
162 inode->i_gid = attr->ia_gid;
163 if (ia_valid & ATTR_ATIME)
164 inode->i_atime = timespec_trunc(attr->ia_atime,
165 inode->i_sb->s_time_gran);
166 if (ia_valid & ATTR_MTIME)
167 inode->i_mtime = timespec_trunc(attr->ia_mtime,
168 inode->i_sb->s_time_gran);
169 if (ia_valid & ATTR_CTIME)
170 inode->i_ctime = timespec_trunc(attr->ia_ctime,
171 inode->i_sb->s_time_gran);
172 if (ia_valid & ATTR_MODE) {
173 umode_t mode = attr->ia_mode;
174
175 if (!in_group_p(inode->i_gid) &&
176 !capable_wrt_inode_uidgid(inode, CAP_FSETID))
177 mode &= ~S_ISGID;
178 inode->i_mode = mode;
179 }
180 }
181 EXPORT_SYMBOL(setattr_copy);
182
183 /**
184 * notify_change - modify attributes of a filesytem object
185 * @dentry: object affected
186 * @iattr: new attributes
187 * @delegated_inode: returns inode, if the inode is delegated
188 *
189 * The caller must hold the i_mutex on the affected object.
190 *
191 * If notify_change discovers a delegation in need of breaking,
192 * it will return -EWOULDBLOCK and return a reference to the inode in
193 * delegated_inode. The caller should then break the delegation and
194 * retry. Because breaking a delegation may take a long time, the
195 * caller should drop the i_mutex before doing so.
196 *
197 * Alternatively, a caller may pass NULL for delegated_inode. This may
198 * be appropriate for callers that expect the underlying filesystem not
199 * to be NFS exported. Also, passing NULL is fine for callers holding
200 * the file open for write, as there can be no conflicting delegation in
201 * that case.
202 */
notify_change2(struct vfsmount * mnt,struct dentry * dentry,struct iattr * attr,struct inode ** delegated_inode)203 int notify_change2(struct vfsmount *mnt, struct dentry * dentry, struct iattr * attr, struct inode **delegated_inode)
204 {
205 struct inode *inode = dentry->d_inode;
206 umode_t mode = inode->i_mode;
207 int error;
208 struct timespec now;
209 unsigned int ia_valid = attr->ia_valid;
210
211 WARN_ON_ONCE(!inode_is_locked(inode));
212
213 if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID | ATTR_TIMES_SET)) {
214 if (IS_IMMUTABLE(inode) || IS_APPEND(inode))
215 return -EPERM;
216 }
217
218 /*
219 * If utimes(2) and friends are called with times == NULL (or both
220 * times are UTIME_NOW), then we need to check for write permission
221 */
222 if (ia_valid & ATTR_TOUCH) {
223 if (IS_IMMUTABLE(inode))
224 return -EPERM;
225
226 if (!inode_owner_or_capable(inode)) {
227 error = inode_permission2(mnt, inode, MAY_WRITE);
228 if (error)
229 return error;
230 }
231 }
232
233 if ((ia_valid & ATTR_MODE)) {
234 umode_t amode = attr->ia_mode;
235 /* Flag setting protected by i_mutex */
236 if (is_sxid(amode))
237 inode->i_flags &= ~S_NOSEC;
238 }
239
240 now = current_time(inode);
241
242 attr->ia_ctime = now;
243 if (!(ia_valid & ATTR_ATIME_SET))
244 attr->ia_atime = now;
245 if (!(ia_valid & ATTR_MTIME_SET))
246 attr->ia_mtime = now;
247 if (ia_valid & ATTR_KILL_PRIV) {
248 error = security_inode_need_killpriv(dentry);
249 if (error < 0)
250 return error;
251 if (error == 0)
252 ia_valid = attr->ia_valid &= ~ATTR_KILL_PRIV;
253 }
254
255 /*
256 * We now pass ATTR_KILL_S*ID to the lower level setattr function so
257 * that the function has the ability to reinterpret a mode change
258 * that's due to these bits. This adds an implicit restriction that
259 * no function will ever call notify_change with both ATTR_MODE and
260 * ATTR_KILL_S*ID set.
261 */
262 if ((ia_valid & (ATTR_KILL_SUID|ATTR_KILL_SGID)) &&
263 (ia_valid & ATTR_MODE))
264 BUG();
265
266 if (ia_valid & ATTR_KILL_SUID) {
267 if (mode & S_ISUID) {
268 ia_valid = attr->ia_valid |= ATTR_MODE;
269 attr->ia_mode = (inode->i_mode & ~S_ISUID);
270 }
271 }
272 if (ia_valid & ATTR_KILL_SGID) {
273 if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP)) {
274 if (!(ia_valid & ATTR_MODE)) {
275 ia_valid = attr->ia_valid |= ATTR_MODE;
276 attr->ia_mode = inode->i_mode;
277 }
278 attr->ia_mode &= ~S_ISGID;
279 }
280 }
281 if (!(attr->ia_valid & ~(ATTR_KILL_SUID | ATTR_KILL_SGID)))
282 return 0;
283
284 /*
285 * Verify that uid/gid changes are valid in the target
286 * namespace of the superblock.
287 */
288 if (ia_valid & ATTR_UID &&
289 !kuid_has_mapping(inode->i_sb->s_user_ns, attr->ia_uid))
290 return -EOVERFLOW;
291 if (ia_valid & ATTR_GID &&
292 !kgid_has_mapping(inode->i_sb->s_user_ns, attr->ia_gid))
293 return -EOVERFLOW;
294
295 /* Don't allow modifications of files with invalid uids or
296 * gids unless those uids & gids are being made valid.
297 */
298 if (!(ia_valid & ATTR_UID) && !uid_valid(inode->i_uid))
299 return -EOVERFLOW;
300 if (!(ia_valid & ATTR_GID) && !gid_valid(inode->i_gid))
301 return -EOVERFLOW;
302
303 error = security_inode_setattr(dentry, attr);
304 if (error)
305 return error;
306 error = try_break_deleg(inode, delegated_inode);
307 if (error)
308 return error;
309
310 if (mnt && inode->i_op->setattr2)
311 error = inode->i_op->setattr2(mnt, dentry, attr);
312 else if (inode->i_op->setattr)
313 error = inode->i_op->setattr(dentry, attr);
314 else
315 error = simple_setattr(dentry, attr);
316
317 if (!error) {
318 fsnotify_change(dentry, ia_valid);
319 ima_inode_post_setattr(dentry);
320 evm_inode_post_setattr(dentry, ia_valid);
321 }
322
323 return error;
324 }
325 EXPORT_SYMBOL(notify_change2);
326
notify_change(struct dentry * dentry,struct iattr * attr,struct inode ** delegated_inode)327 int notify_change(struct dentry * dentry, struct iattr * attr, struct inode **delegated_inode)
328 {
329 return notify_change2(NULL, dentry, attr, delegated_inode);
330 }
331 EXPORT_SYMBOL(notify_change);
332