path: root/fs/attr.c (plain)
blob: c4093c5196be65d35882561c8c8a73859838ca50

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	*/
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	*/
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	*/
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	*/
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
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