1/*
2  File: fs/xattr.c
3
4  Extended attribute handling.
5
6  Copyright (C) 2001 by Andreas Gruenbacher <a.gruenbacher@computer.org>
7  Copyright (C) 2001 SGI - Silicon Graphics, Inc <linux-xfs@oss.sgi.com>
8  Copyright (c) 2004 Red Hat, Inc., James Morris <jmorris@redhat.com>
9 */
10#include <linux/fs.h>
11#include <linux/slab.h>
12#include <linux/file.h>
13#include <linux/xattr.h>
14#include <linux/namei.h>
15#include <linux/security.h>
16#include <linux/syscalls.h>
17#include <linux/module.h>
18#include <linux/fsnotify.h>
19#include <linux/audit.h>
20#include <asm/uaccess.h>
21
22
23/*
24 * Check permissions for extended attribute access.  This is a bit complicated
25 * because different namespaces have very different rules.
26 */
27static int
28xattr_permission(struct inode *inode, const char *name, int mask)
29{
30	/*
31	 * We can never set or remove an extended attribute on a read-only
32	 * filesystem  or on an immutable / append-only inode.
33	 */
34	if (mask & MAY_WRITE) {
35		if (IS_RDONLY(inode))
36			return -EROFS;
37		if (IS_IMMUTABLE(inode) || IS_APPEND(inode))
38			return -EPERM;
39	}
40
41	/*
42	 * No restriction for security.* and system.* from the VFS.  Decision
43	 * on these is left to the underlying filesystem / security module.
44	 */
45	if (!strncmp(name, XATTR_SECURITY_PREFIX, XATTR_SECURITY_PREFIX_LEN) ||
46	    !strncmp(name, XATTR_SYSTEM_PREFIX, XATTR_SYSTEM_PREFIX_LEN))
47		return 0;
48
49	/*
50	 * The trusted.* namespace can only be accessed by a privileged user.
51	 */
52	if (!strncmp(name, XATTR_TRUSTED_PREFIX, XATTR_TRUSTED_PREFIX_LEN))
53		return (capable(CAP_SYS_ADMIN) ? 0 : -EPERM);
54
55	/* In user.* namespace, only regular files and directories can have
56	 * extended attributes. For sticky directories, only the owner and
57	 * privileged user can write attributes.
58	 */
59	if (!strncmp(name, XATTR_USER_PREFIX, XATTR_USER_PREFIX_LEN)) {
60		if (!S_ISREG(inode->i_mode) && !S_ISDIR(inode->i_mode))
61			return -EPERM;
62		if (S_ISDIR(inode->i_mode) && (inode->i_mode & S_ISVTX) &&
63		    (mask & MAY_WRITE) && (current->fsuid != inode->i_uid) &&
64		    !capable(CAP_FOWNER))
65			return -EPERM;
66	}
67
68	return permission(inode, mask, NULL);
69}
70
71int
72vfs_setxattr(struct dentry *dentry, char *name, void *value,
73		size_t size, int flags)
74{
75	struct inode *inode = dentry->d_inode;
76	int error;
77
78	error = xattr_permission(inode, name, MAY_WRITE);
79	if (error)
80		return error;
81
82	mutex_lock(&inode->i_mutex);
83	error = security_inode_setxattr(dentry, name, value, size, flags);
84	if (error)
85		goto out;
86	error = -EOPNOTSUPP;
87	if (inode->i_op->setxattr) {
88		error = inode->i_op->setxattr(dentry, name, value, size, flags);
89		if (!error) {
90			fsnotify_xattr(dentry);
91			security_inode_post_setxattr(dentry, name, value,
92						     size, flags);
93		}
94	} else if (!strncmp(name, XATTR_SECURITY_PREFIX,
95				XATTR_SECURITY_PREFIX_LEN)) {
96		const char *suffix = name + XATTR_SECURITY_PREFIX_LEN;
97		error = security_inode_setsecurity(inode, suffix, value,
98						   size, flags);
99		if (!error)
100			fsnotify_xattr(dentry);
101	}
102out:
103	mutex_unlock(&inode->i_mutex);
104	return error;
105}
106EXPORT_SYMBOL_GPL(vfs_setxattr);
107
108ssize_t
109vfs_getxattr(struct dentry *dentry, char *name, void *value, size_t size)
110{
111	struct inode *inode = dentry->d_inode;
112	int error;
113
114	error = xattr_permission(inode, name, MAY_READ);
115	if (error)
116		return error;
117
118	error = security_inode_getxattr(dentry, name);
119	if (error)
120		return error;
121
122	if (inode->i_op->getxattr)
123		error = inode->i_op->getxattr(dentry, name, value, size);
124	else
125		error = -EOPNOTSUPP;
126
127	if (!strncmp(name, XATTR_SECURITY_PREFIX,
128				XATTR_SECURITY_PREFIX_LEN)) {
129		const char *suffix = name + XATTR_SECURITY_PREFIX_LEN;
130		int ret = security_inode_getsecurity(inode, suffix, value,
131						     size, error);
132		/*
133		 * Only overwrite the return value if a security module
134		 * is actually active.
135		 */
136		if (ret != -EOPNOTSUPP)
137			error = ret;
138	}
139
140	return error;
141}
142EXPORT_SYMBOL_GPL(vfs_getxattr);
143
144ssize_t
145vfs_listxattr(struct dentry *d, char *list, size_t size)
146{
147	ssize_t error;
148
149	error = security_inode_listxattr(d);
150	if (error)
151		return error;
152	error = -EOPNOTSUPP;
153	if (d->d_inode->i_op && d->d_inode->i_op->listxattr) {
154		error = d->d_inode->i_op->listxattr(d, list, size);
155	} else {
156		error = security_inode_listsecurity(d->d_inode, list, size);
157		if (size && error > size)
158			error = -ERANGE;
159	}
160	return error;
161}
162EXPORT_SYMBOL_GPL(vfs_listxattr);
163
164int
165vfs_removexattr(struct dentry *dentry, char *name)
166{
167	struct inode *inode = dentry->d_inode;
168	int error;
169
170	if (!inode->i_op->removexattr)
171		return -EOPNOTSUPP;
172
173	error = xattr_permission(inode, name, MAY_WRITE);
174	if (error)
175		return error;
176
177	error = security_inode_removexattr(dentry, name);
178	if (error)
179		return error;
180
181	mutex_lock(&inode->i_mutex);
182	error = inode->i_op->removexattr(dentry, name);
183	mutex_unlock(&inode->i_mutex);
184
185	if (!error)
186		fsnotify_xattr(dentry);
187	return error;
188}
189EXPORT_SYMBOL_GPL(vfs_removexattr);
190
191
192/*
193 * Extended attribute SET operations
194 */
195static long
196setxattr(struct dentry *d, char __user *name, void __user *value,
197	 size_t size, int flags)
198{
199	int error;
200	void *kvalue = NULL;
201	char kname[XATTR_NAME_MAX + 1];
202
203	if (flags & ~(XATTR_CREATE|XATTR_REPLACE))
204		return -EINVAL;
205
206	error = strncpy_from_user(kname, name, sizeof(kname));
207	if (error == 0 || error == sizeof(kname))
208		error = -ERANGE;
209	if (error < 0)
210		return error;
211
212	if (size) {
213		if (size > XATTR_SIZE_MAX)
214			return -E2BIG;
215		kvalue = kmalloc(size, GFP_KERNEL);
216		if (!kvalue)
217			return -ENOMEM;
218		if (copy_from_user(kvalue, value, size)) {
219			kfree(kvalue);
220			return -EFAULT;
221		}
222	}
223
224	error = vfs_setxattr(d, kname, kvalue, size, flags);
225	kfree(kvalue);
226	return error;
227}
228
229asmlinkage long
230sys_setxattr(char __user *path, char __user *name, void __user *value,
231	     size_t size, int flags)
232{
233	struct nameidata nd;
234	int error;
235
236	error = user_path_walk(path, &nd);
237	if (error)
238		return error;
239	error = setxattr(nd.dentry, name, value, size, flags);
240	path_release(&nd);
241	return error;
242}
243
244asmlinkage long
245sys_lsetxattr(char __user *path, char __user *name, void __user *value,
246	      size_t size, int flags)
247{
248	struct nameidata nd;
249	int error;
250
251	error = user_path_walk_link(path, &nd);
252	if (error)
253		return error;
254	error = setxattr(nd.dentry, name, value, size, flags);
255	path_release(&nd);
256	return error;
257}
258
259asmlinkage long
260sys_fsetxattr(int fd, char __user *name, void __user *value,
261	      size_t size, int flags)
262{
263	struct file *f;
264	struct dentry *dentry;
265	int error = -EBADF;
266
267	f = fget(fd);
268	if (!f)
269		return error;
270	dentry = f->f_path.dentry;
271	audit_inode(NULL, dentry->d_inode);
272	error = setxattr(dentry, name, value, size, flags);
273	fput(f);
274	return error;
275}
276
277/*
278 * Extended attribute GET operations
279 */
280static ssize_t
281getxattr(struct dentry *d, char __user *name, void __user *value, size_t size)
282{
283	ssize_t error;
284	void *kvalue = NULL;
285	char kname[XATTR_NAME_MAX + 1];
286
287	error = strncpy_from_user(kname, name, sizeof(kname));
288	if (error == 0 || error == sizeof(kname))
289		error = -ERANGE;
290	if (error < 0)
291		return error;
292
293	if (size) {
294		if (size > XATTR_SIZE_MAX)
295			size = XATTR_SIZE_MAX;
296		kvalue = kzalloc(size, GFP_KERNEL);
297		if (!kvalue)
298			return -ENOMEM;
299	}
300
301	error = vfs_getxattr(d, kname, kvalue, size);
302	if (error > 0) {
303		if (size && copy_to_user(value, kvalue, error))
304			error = -EFAULT;
305	} else if (error == -ERANGE && size >= XATTR_SIZE_MAX) {
306		/* The file system tried to returned a value bigger
307		   than XATTR_SIZE_MAX bytes. Not possible. */
308		error = -E2BIG;
309	}
310	kfree(kvalue);
311	return error;
312}
313
314asmlinkage ssize_t
315sys_getxattr(char __user *path, char __user *name, void __user *value,
316	     size_t size)
317{
318	struct nameidata nd;
319	ssize_t error;
320
321	error = user_path_walk(path, &nd);
322	if (error)
323		return error;
324	error = getxattr(nd.dentry, name, value, size);
325	path_release(&nd);
326	return error;
327}
328
329asmlinkage ssize_t
330sys_lgetxattr(char __user *path, char __user *name, void __user *value,
331	      size_t size)
332{
333	struct nameidata nd;
334	ssize_t error;
335
336	error = user_path_walk_link(path, &nd);
337	if (error)
338		return error;
339	error = getxattr(nd.dentry, name, value, size);
340	path_release(&nd);
341	return error;
342}
343
344asmlinkage ssize_t
345sys_fgetxattr(int fd, char __user *name, void __user *value, size_t size)
346{
347	struct file *f;
348	ssize_t error = -EBADF;
349
350	f = fget(fd);
351	if (!f)
352		return error;
353	audit_inode(NULL, f->f_path.dentry->d_inode);
354	error = getxattr(f->f_path.dentry, name, value, size);
355	fput(f);
356	return error;
357}
358
359/*
360 * Extended attribute LIST operations
361 */
362static ssize_t
363listxattr(struct dentry *d, char __user *list, size_t size)
364{
365	ssize_t error;
366	char *klist = NULL;
367
368	if (size) {
369		if (size > XATTR_LIST_MAX)
370			size = XATTR_LIST_MAX;
371		klist = kmalloc(size, GFP_KERNEL);
372		if (!klist)
373			return -ENOMEM;
374	}
375
376	error = vfs_listxattr(d, klist, size);
377	if (error > 0) {
378		if (size && copy_to_user(list, klist, error))
379			error = -EFAULT;
380	} else if (error == -ERANGE && size >= XATTR_LIST_MAX) {
381		/* The file system tried to returned a list bigger
382		   than XATTR_LIST_MAX bytes. Not possible. */
383		error = -E2BIG;
384	}
385	kfree(klist);
386	return error;
387}
388
389asmlinkage ssize_t
390sys_listxattr(char __user *path, char __user *list, size_t size)
391{
392	struct nameidata nd;
393	ssize_t error;
394
395	error = user_path_walk(path, &nd);
396	if (error)
397		return error;
398	error = listxattr(nd.dentry, list, size);
399	path_release(&nd);
400	return error;
401}
402
403asmlinkage ssize_t
404sys_llistxattr(char __user *path, char __user *list, size_t size)
405{
406	struct nameidata nd;
407	ssize_t error;
408
409	error = user_path_walk_link(path, &nd);
410	if (error)
411		return error;
412	error = listxattr(nd.dentry, list, size);
413	path_release(&nd);
414	return error;
415}
416
417asmlinkage ssize_t
418sys_flistxattr(int fd, char __user *list, size_t size)
419{
420	struct file *f;
421	ssize_t error = -EBADF;
422
423	f = fget(fd);
424	if (!f)
425		return error;
426	audit_inode(NULL, f->f_path.dentry->d_inode);
427	error = listxattr(f->f_path.dentry, list, size);
428	fput(f);
429	return error;
430}
431
432/*
433 * Extended attribute REMOVE operations
434 */
435static long
436removexattr(struct dentry *d, char __user *name)
437{
438	int error;
439	char kname[XATTR_NAME_MAX + 1];
440
441	error = strncpy_from_user(kname, name, sizeof(kname));
442	if (error == 0 || error == sizeof(kname))
443		error = -ERANGE;
444	if (error < 0)
445		return error;
446
447	return vfs_removexattr(d, kname);
448}
449
450asmlinkage long
451sys_removexattr(char __user *path, char __user *name)
452{
453	struct nameidata nd;
454	int error;
455
456	error = user_path_walk(path, &nd);
457	if (error)
458		return error;
459	error = removexattr(nd.dentry, name);
460	path_release(&nd);
461	return error;
462}
463
464asmlinkage long
465sys_lremovexattr(char __user *path, char __user *name)
466{
467	struct nameidata nd;
468	int error;
469
470	error = user_path_walk_link(path, &nd);
471	if (error)
472		return error;
473	error = removexattr(nd.dentry, name);
474	path_release(&nd);
475	return error;
476}
477
478asmlinkage long
479sys_fremovexattr(int fd, char __user *name)
480{
481	struct file *f;
482	struct dentry *dentry;
483	int error = -EBADF;
484
485	f = fget(fd);
486	if (!f)
487		return error;
488	dentry = f->f_path.dentry;
489	audit_inode(NULL, dentry->d_inode);
490	error = removexattr(dentry, name);
491	fput(f);
492	return error;
493}
494
495
496static const char *
497strcmp_prefix(const char *a, const char *a_prefix)
498{
499	while (*a_prefix && *a == *a_prefix) {
500		a++;
501		a_prefix++;
502	}
503	return *a_prefix ? NULL : a;
504}
505
506/*
507 * In order to implement different sets of xattr operations for each xattr
508 * prefix with the generic xattr API, a filesystem should create a
509 * null-terminated array of struct xattr_handler (one for each prefix) and
510 * hang a pointer to it off of the s_xattr field of the superblock.
511 *
512 * The generic_fooxattr() functions will use this list to dispatch xattr
513 * operations to the correct xattr_handler.
514 */
515#define for_each_xattr_handler(handlers, handler)		\
516		for ((handler) = *(handlers)++;			\
517			(handler) != NULL;			\
518			(handler) = *(handlers)++)
519
520/*
521 * Find the xattr_handler with the matching prefix.
522 */
523static struct xattr_handler *
524xattr_resolve_name(struct xattr_handler **handlers, const char **name)
525{
526	struct xattr_handler *handler;
527
528	if (!*name)
529		return NULL;
530
531	for_each_xattr_handler(handlers, handler) {
532		const char *n = strcmp_prefix(*name, handler->prefix);
533		if (n) {
534			*name = n;
535			break;
536		}
537	}
538	return handler;
539}
540
541/*
542 * Find the handler for the prefix and dispatch its get() operation.
543 */
544ssize_t
545generic_getxattr(struct dentry *dentry, const char *name, void *buffer, size_t size)
546{
547	struct xattr_handler *handler;
548	struct inode *inode = dentry->d_inode;
549
550	handler = xattr_resolve_name(inode->i_sb->s_xattr, &name);
551	if (!handler)
552		return -EOPNOTSUPP;
553	return handler->get(inode, name, buffer, size);
554}
555
556/*
557 * Combine the results of the list() operation from every xattr_handler in the
558 * list.
559 */
560ssize_t
561generic_listxattr(struct dentry *dentry, char *buffer, size_t buffer_size)
562{
563	struct inode *inode = dentry->d_inode;
564	struct xattr_handler *handler, **handlers = inode->i_sb->s_xattr;
565	unsigned int size = 0;
566
567	if (!buffer) {
568		for_each_xattr_handler(handlers, handler)
569			size += handler->list(inode, NULL, 0, NULL, 0);
570	} else {
571		char *buf = buffer;
572
573		for_each_xattr_handler(handlers, handler) {
574			size = handler->list(inode, buf, buffer_size, NULL, 0);
575			if (size > buffer_size)
576				return -ERANGE;
577			buf += size;
578			buffer_size -= size;
579		}
580		size = buf - buffer;
581	}
582	return size;
583}
584
585/*
586 * Find the handler for the prefix and dispatch its set() operation.
587 */
588int
589generic_setxattr(struct dentry *dentry, const char *name, const void *value, size_t size, int flags)
590{
591	struct xattr_handler *handler;
592	struct inode *inode = dentry->d_inode;
593
594	if (size == 0)
595		value = "";  /* empty EA, do not remove */
596	handler = xattr_resolve_name(inode->i_sb->s_xattr, &name);
597	if (!handler)
598		return -EOPNOTSUPP;
599	return handler->set(inode, name, value, size, flags);
600}
601
602/*
603 * Find the handler for the prefix and dispatch its set() operation to remove
604 * any associated extended attribute.
605 */
606int
607generic_removexattr(struct dentry *dentry, const char *name)
608{
609	struct xattr_handler *handler;
610	struct inode *inode = dentry->d_inode;
611
612	handler = xattr_resolve_name(inode->i_sb->s_xattr, &name);
613	if (!handler)
614		return -EOPNOTSUPP;
615	return handler->set(inode, name, NULL, 0, XATTR_REPLACE);
616}
617
618EXPORT_SYMBOL(generic_getxattr);
619EXPORT_SYMBOL(generic_listxattr);
620EXPORT_SYMBOL(generic_setxattr);
621EXPORT_SYMBOL(generic_removexattr);
622