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 = timestamp_truncate(attr->ia_atime,
188 						  inode);
189 	}
190 	if (ia_valid & ATTR_MTIME) {
191 		inode->i_mtime = timestamp_truncate(attr->ia_mtime,
192 						  inode);
193 	}
194 	if (ia_valid & ATTR_CTIME) {
195 		inode->i_ctime = timestamp_truncate(attr->ia_ctime,
196 						  inode);
197 	}
198 	if (ia_valid & ATTR_MODE) {
199 		umode_t mode = attr->ia_mode;
200 
201 		if (!in_group_p(inode->i_gid) &&
202 		    !capable_wrt_inode_uidgid(inode, CAP_FSETID))
203 			mode &= ~S_ISGID;
204 		inode->i_mode = mode;
205 	}
206 }
207 EXPORT_SYMBOL(setattr_copy);
208 
209 /**
210  * notify_change - modify attributes of a filesytem object
211  * @dentry:	object affected
212  * @attr:	new attributes
213  * @delegated_inode: returns inode, if the inode is delegated
214  *
215  * The caller must hold the i_mutex on the affected object.
216  *
217  * If notify_change discovers a delegation in need of breaking,
218  * it will return -EWOULDBLOCK and return a reference to the inode in
219  * delegated_inode.  The caller should then break the delegation and
220  * retry.  Because breaking a delegation may take a long time, the
221  * caller should drop the i_mutex before doing so.
222  *
223  * Alternatively, a caller may pass NULL for delegated_inode.  This may
224  * be appropriate for callers that expect the underlying filesystem not
225  * to be NFS exported.  Also, passing NULL is fine for callers holding
226  * the file open for write, as there can be no conflicting delegation in
227  * that case.
228  */
notify_change(struct dentry * dentry,struct iattr * attr,struct inode ** delegated_inode)229 int notify_change(struct dentry * dentry, struct iattr * attr, struct inode **delegated_inode)
230 {
231 	struct inode *inode = dentry->d_inode;
232 	umode_t mode = inode->i_mode;
233 	int error;
234 	struct timespec64 now;
235 	unsigned int ia_valid = attr->ia_valid;
236 
237 	WARN_ON_ONCE(!inode_is_locked(inode));
238 
239 	if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID | ATTR_TIMES_SET)) {
240 		if (IS_IMMUTABLE(inode) || IS_APPEND(inode))
241 			return -EPERM;
242 	}
243 
244 	/*
245 	 * If utimes(2) and friends are called with times == NULL (or both
246 	 * times are UTIME_NOW), then we need to check for write permission
247 	 */
248 	if (ia_valid & ATTR_TOUCH) {
249 		if (IS_IMMUTABLE(inode))
250 			return -EPERM;
251 
252 		if (!inode_owner_or_capable(inode)) {
253 			error = inode_permission(inode, MAY_WRITE);
254 			if (error)
255 				return error;
256 		}
257 	}
258 
259 	if ((ia_valid & ATTR_MODE)) {
260 		umode_t amode = attr->ia_mode;
261 		/* Flag setting protected by i_mutex */
262 		if (is_sxid(amode))
263 			inode->i_flags &= ~S_NOSEC;
264 	}
265 
266 	now = current_time(inode);
267 
268 	attr->ia_ctime = now;
269 	if (!(ia_valid & ATTR_ATIME_SET))
270 		attr->ia_atime = now;
271 	if (!(ia_valid & ATTR_MTIME_SET))
272 		attr->ia_mtime = now;
273 	if (ia_valid & ATTR_KILL_PRIV) {
274 		error = security_inode_need_killpriv(dentry);
275 		if (error < 0)
276 			return error;
277 		if (error == 0)
278 			ia_valid = attr->ia_valid &= ~ATTR_KILL_PRIV;
279 	}
280 
281 	/*
282 	 * We now pass ATTR_KILL_S*ID to the lower level setattr function so
283 	 * that the function has the ability to reinterpret a mode change
284 	 * that's due to these bits. This adds an implicit restriction that
285 	 * no function will ever call notify_change with both ATTR_MODE and
286 	 * ATTR_KILL_S*ID set.
287 	 */
288 	if ((ia_valid & (ATTR_KILL_SUID|ATTR_KILL_SGID)) &&
289 	    (ia_valid & ATTR_MODE))
290 		BUG();
291 
292 	if (ia_valid & ATTR_KILL_SUID) {
293 		if (mode & S_ISUID) {
294 			ia_valid = attr->ia_valid |= ATTR_MODE;
295 			attr->ia_mode = (inode->i_mode & ~S_ISUID);
296 		}
297 	}
298 	if (ia_valid & ATTR_KILL_SGID) {
299 		if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP)) {
300 			if (!(ia_valid & ATTR_MODE)) {
301 				ia_valid = attr->ia_valid |= ATTR_MODE;
302 				attr->ia_mode = inode->i_mode;
303 			}
304 			attr->ia_mode &= ~S_ISGID;
305 		}
306 	}
307 	if (!(attr->ia_valid & ~(ATTR_KILL_SUID | ATTR_KILL_SGID)))
308 		return 0;
309 
310 	/*
311 	 * Verify that uid/gid changes are valid in the target
312 	 * namespace of the superblock.
313 	 */
314 	if (ia_valid & ATTR_UID &&
315 	    !kuid_has_mapping(inode->i_sb->s_user_ns, attr->ia_uid))
316 		return -EOVERFLOW;
317 	if (ia_valid & ATTR_GID &&
318 	    !kgid_has_mapping(inode->i_sb->s_user_ns, attr->ia_gid))
319 		return -EOVERFLOW;
320 
321 	/* Don't allow modifications of files with invalid uids or
322 	 * gids unless those uids & gids are being made valid.
323 	 */
324 	if (!(ia_valid & ATTR_UID) && !uid_valid(inode->i_uid))
325 		return -EOVERFLOW;
326 	if (!(ia_valid & ATTR_GID) && !gid_valid(inode->i_gid))
327 		return -EOVERFLOW;
328 
329 	error = security_inode_setattr(dentry, attr);
330 	if (error)
331 		return error;
332 	error = try_break_deleg(inode, delegated_inode);
333 	if (error)
334 		return error;
335 
336 	if (inode->i_op->setattr)
337 		error = inode->i_op->setattr(dentry, attr);
338 	else
339 		error = simple_setattr(dentry, attr);
340 
341 	if (!error) {
342 		fsnotify_change(dentry, ia_valid);
343 		ima_inode_post_setattr(dentry);
344 		evm_inode_post_setattr(dentry, ia_valid);
345 	}
346 
347 	return error;
348 }
349 EXPORT_SYMBOL(notify_change);
350