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/mount.h>
15 #include <linux/namei.h>
16 #include <linux/security.h>
17 #include <linux/syscalls.h>
18 #include <linux/module.h>
19 #include <linux/fsnotify.h>
20 #include <linux/audit.h>
21 #include <asm/uaccess.h>
22
23
24 /*
25 * Check permissions for extended attribute access. This is a bit complicated
26 * because different namespaces have very different rules.
27 */
28 static int
xattr_permission(struct inode * inode,const char * name,int mask)29 xattr_permission(struct inode *inode, const char *name, int mask)
30 {
31 /*
32 * We can never set or remove an extended attribute on a read-only
33 * filesystem or on an immutable / append-only inode.
34 */
35 if (mask & MAY_WRITE) {
36 if (IS_IMMUTABLE(inode) || IS_APPEND(inode))
37 return -EPERM;
38 }
39
40 /*
41 * No restriction for security.* and system.* from the VFS. Decision
42 * on these is left to the underlying filesystem / security module.
43 */
44 if (!strncmp(name, XATTR_SECURITY_PREFIX, XATTR_SECURITY_PREFIX_LEN) ||
45 !strncmp(name, XATTR_SYSTEM_PREFIX, XATTR_SYSTEM_PREFIX_LEN))
46 return 0;
47
48 /*
49 * The trusted.* namespace can only be accessed by a privileged user.
50 */
51 if (!strncmp(name, XATTR_TRUSTED_PREFIX, XATTR_TRUSTED_PREFIX_LEN))
52 return (capable(CAP_SYS_ADMIN) ? 0 : -EPERM);
53
54 /* In user.* namespace, only regular files and directories can have
55 * extended attributes. For sticky directories, only the owner and
56 * privileged user can write attributes.
57 */
58 if (!strncmp(name, XATTR_USER_PREFIX, XATTR_USER_PREFIX_LEN)) {
59 if (!S_ISREG(inode->i_mode) && !S_ISDIR(inode->i_mode))
60 return -EPERM;
61 if (S_ISDIR(inode->i_mode) && (inode->i_mode & S_ISVTX) &&
62 (mask & MAY_WRITE) && !inode_owner_or_capable(inode))
63 return -EPERM;
64 }
65
66 return inode_permission(inode, mask);
67 }
68
69 /**
70 * __vfs_setxattr_noperm - perform setxattr operation without performing
71 * permission checks.
72 *
73 * @dentry - object to perform setxattr on
74 * @name - xattr name to set
75 * @value - value to set @name to
76 * @size - size of @value
77 * @flags - flags to pass into filesystem operations
78 *
79 * returns the result of the internal setxattr or setsecurity operations.
80 *
81 * This function requires the caller to lock the inode's i_mutex before it
82 * is executed. It also assumes that the caller will make the appropriate
83 * permission checks.
84 */
__vfs_setxattr_noperm(struct dentry * dentry,const char * name,const void * value,size_t size,int flags)85 int __vfs_setxattr_noperm(struct dentry *dentry, const char *name,
86 const void *value, size_t size, int flags)
87 {
88 struct inode *inode = dentry->d_inode;
89 int error = -EOPNOTSUPP;
90
91 if (inode->i_op->setxattr) {
92 error = inode->i_op->setxattr(dentry, name, value, size, flags);
93 if (!error) {
94 fsnotify_xattr(dentry);
95 security_inode_post_setxattr(dentry, name, value,
96 size, flags);
97 }
98 } else if (!strncmp(name, XATTR_SECURITY_PREFIX,
99 XATTR_SECURITY_PREFIX_LEN)) {
100 const char *suffix = name + XATTR_SECURITY_PREFIX_LEN;
101 error = security_inode_setsecurity(inode, suffix, value,
102 size, flags);
103 if (!error)
104 fsnotify_xattr(dentry);
105 }
106
107 return error;
108 }
109
110
111 int
vfs_setxattr(struct dentry * dentry,const char * name,const void * value,size_t size,int flags)112 vfs_setxattr(struct dentry *dentry, const char *name, const void *value,
113 size_t size, int flags)
114 {
115 struct inode *inode = dentry->d_inode;
116 int error;
117
118 error = xattr_permission(inode, name, MAY_WRITE);
119 if (error)
120 return error;
121
122 mutex_lock(&inode->i_mutex);
123 error = security_inode_setxattr(dentry, name, value, size, flags);
124 if (error)
125 goto out;
126
127 error = __vfs_setxattr_noperm(dentry, name, value, size, flags);
128
129 out:
130 mutex_unlock(&inode->i_mutex);
131 return error;
132 }
133 EXPORT_SYMBOL_GPL(vfs_setxattr);
134
135 ssize_t
xattr_getsecurity(struct inode * inode,const char * name,void * value,size_t size)136 xattr_getsecurity(struct inode *inode, const char *name, void *value,
137 size_t size)
138 {
139 void *buffer = NULL;
140 ssize_t len;
141
142 if (!value || !size) {
143 len = security_inode_getsecurity(inode, name, &buffer, false);
144 goto out_noalloc;
145 }
146
147 len = security_inode_getsecurity(inode, name, &buffer, true);
148 if (len < 0)
149 return len;
150 if (size < len) {
151 len = -ERANGE;
152 goto out;
153 }
154 memcpy(value, buffer, len);
155 out:
156 security_release_secctx(buffer, len);
157 out_noalloc:
158 return len;
159 }
160 EXPORT_SYMBOL_GPL(xattr_getsecurity);
161
162 ssize_t
vfs_getxattr(struct dentry * dentry,const char * name,void * value,size_t size)163 vfs_getxattr(struct dentry *dentry, const char *name, void *value, size_t size)
164 {
165 struct inode *inode = dentry->d_inode;
166 int error;
167
168 error = xattr_permission(inode, name, MAY_READ);
169 if (error)
170 return error;
171
172 error = security_inode_getxattr(dentry, name);
173 if (error)
174 return error;
175
176 if (!strncmp(name, XATTR_SECURITY_PREFIX,
177 XATTR_SECURITY_PREFIX_LEN)) {
178 const char *suffix = name + XATTR_SECURITY_PREFIX_LEN;
179 int ret = xattr_getsecurity(inode, suffix, value, size);
180 /*
181 * Only overwrite the return value if a security module
182 * is actually active.
183 */
184 if (ret == -EOPNOTSUPP)
185 goto nolsm;
186 return ret;
187 }
188 nolsm:
189 if (inode->i_op->getxattr)
190 error = inode->i_op->getxattr(dentry, name, value, size);
191 else
192 error = -EOPNOTSUPP;
193
194 return error;
195 }
196 EXPORT_SYMBOL_GPL(vfs_getxattr);
197
198 ssize_t
vfs_listxattr(struct dentry * d,char * list,size_t size)199 vfs_listxattr(struct dentry *d, char *list, size_t size)
200 {
201 ssize_t error;
202
203 error = security_inode_listxattr(d);
204 if (error)
205 return error;
206 error = -EOPNOTSUPP;
207 if (d->d_inode->i_op->listxattr) {
208 error = d->d_inode->i_op->listxattr(d, list, size);
209 } else {
210 error = security_inode_listsecurity(d->d_inode, list, size);
211 if (size && error > size)
212 error = -ERANGE;
213 }
214 return error;
215 }
216 EXPORT_SYMBOL_GPL(vfs_listxattr);
217
218 int
vfs_removexattr(struct dentry * dentry,const char * name)219 vfs_removexattr(struct dentry *dentry, const char *name)
220 {
221 struct inode *inode = dentry->d_inode;
222 int error;
223
224 if (!inode->i_op->removexattr)
225 return -EOPNOTSUPP;
226
227 error = xattr_permission(inode, name, MAY_WRITE);
228 if (error)
229 return error;
230
231 error = security_inode_removexattr(dentry, name);
232 if (error)
233 return error;
234
235 mutex_lock(&inode->i_mutex);
236 error = inode->i_op->removexattr(dentry, name);
237 mutex_unlock(&inode->i_mutex);
238
239 if (!error)
240 fsnotify_xattr(dentry);
241 return error;
242 }
243 EXPORT_SYMBOL_GPL(vfs_removexattr);
244
245
246 /*
247 * Extended attribute SET operations
248 */
249 static long
setxattr(struct dentry * d,const char __user * name,const void __user * value,size_t size,int flags)250 setxattr(struct dentry *d, const char __user *name, const void __user *value,
251 size_t size, int flags)
252 {
253 int error;
254 void *kvalue = NULL;
255 char kname[XATTR_NAME_MAX + 1];
256
257 if (flags & ~(XATTR_CREATE|XATTR_REPLACE))
258 return -EINVAL;
259
260 error = strncpy_from_user(kname, name, sizeof(kname));
261 if (error == 0 || error == sizeof(kname))
262 error = -ERANGE;
263 if (error < 0)
264 return error;
265
266 if (size) {
267 if (size > XATTR_SIZE_MAX)
268 return -E2BIG;
269 kvalue = memdup_user(value, size);
270 if (IS_ERR(kvalue))
271 return PTR_ERR(kvalue);
272 }
273
274 error = vfs_setxattr(d, kname, kvalue, size, flags);
275 kfree(kvalue);
276 return error;
277 }
278
SYSCALL_DEFINE5(setxattr,const char __user *,pathname,const char __user *,name,const void __user *,value,size_t,size,int,flags)279 SYSCALL_DEFINE5(setxattr, const char __user *, pathname,
280 const char __user *, name, const void __user *, value,
281 size_t, size, int, flags)
282 {
283 struct path path;
284 int error;
285
286 error = user_path(pathname, &path);
287 if (error)
288 return error;
289 error = mnt_want_write(path.mnt);
290 if (!error) {
291 error = setxattr(path.dentry, name, value, size, flags);
292 mnt_drop_write(path.mnt);
293 }
294 path_put(&path);
295 return error;
296 }
297
SYSCALL_DEFINE5(lsetxattr,const char __user *,pathname,const char __user *,name,const void __user *,value,size_t,size,int,flags)298 SYSCALL_DEFINE5(lsetxattr, const char __user *, pathname,
299 const char __user *, name, const void __user *, value,
300 size_t, size, int, flags)
301 {
302 struct path path;
303 int error;
304
305 error = user_lpath(pathname, &path);
306 if (error)
307 return error;
308 error = mnt_want_write(path.mnt);
309 if (!error) {
310 error = setxattr(path.dentry, name, value, size, flags);
311 mnt_drop_write(path.mnt);
312 }
313 path_put(&path);
314 return error;
315 }
316
SYSCALL_DEFINE5(fsetxattr,int,fd,const char __user *,name,const void __user *,value,size_t,size,int,flags)317 SYSCALL_DEFINE5(fsetxattr, int, fd, const char __user *, name,
318 const void __user *,value, size_t, size, int, flags)
319 {
320 struct file *f;
321 struct dentry *dentry;
322 int error = -EBADF;
323
324 f = fget(fd);
325 if (!f)
326 return error;
327 dentry = f->f_path.dentry;
328 audit_inode(NULL, dentry);
329 error = mnt_want_write_file(f);
330 if (!error) {
331 error = setxattr(dentry, name, value, size, flags);
332 mnt_drop_write(f->f_path.mnt);
333 }
334 fput(f);
335 return error;
336 }
337
338 /*
339 * Extended attribute GET operations
340 */
341 static ssize_t
getxattr(struct dentry * d,const char __user * name,void __user * value,size_t size)342 getxattr(struct dentry *d, const char __user *name, void __user *value,
343 size_t size)
344 {
345 ssize_t error;
346 void *kvalue = NULL;
347 char kname[XATTR_NAME_MAX + 1];
348
349 error = strncpy_from_user(kname, name, sizeof(kname));
350 if (error == 0 || error == sizeof(kname))
351 error = -ERANGE;
352 if (error < 0)
353 return error;
354
355 if (size) {
356 if (size > XATTR_SIZE_MAX)
357 size = XATTR_SIZE_MAX;
358 kvalue = kzalloc(size, GFP_KERNEL);
359 if (!kvalue)
360 return -ENOMEM;
361 }
362
363 error = vfs_getxattr(d, kname, kvalue, size);
364 if (error > 0) {
365 if (size && copy_to_user(value, kvalue, error))
366 error = -EFAULT;
367 } else if (error == -ERANGE && size >= XATTR_SIZE_MAX) {
368 /* The file system tried to returned a value bigger
369 than XATTR_SIZE_MAX bytes. Not possible. */
370 error = -E2BIG;
371 }
372 kfree(kvalue);
373 return error;
374 }
375
SYSCALL_DEFINE4(getxattr,const char __user *,pathname,const char __user *,name,void __user *,value,size_t,size)376 SYSCALL_DEFINE4(getxattr, const char __user *, pathname,
377 const char __user *, name, void __user *, value, size_t, size)
378 {
379 struct path path;
380 ssize_t error;
381
382 error = user_path(pathname, &path);
383 if (error)
384 return error;
385 error = getxattr(path.dentry, name, value, size);
386 path_put(&path);
387 return error;
388 }
389
SYSCALL_DEFINE4(lgetxattr,const char __user *,pathname,const char __user *,name,void __user *,value,size_t,size)390 SYSCALL_DEFINE4(lgetxattr, const char __user *, pathname,
391 const char __user *, name, void __user *, value, size_t, size)
392 {
393 struct path path;
394 ssize_t error;
395
396 error = user_lpath(pathname, &path);
397 if (error)
398 return error;
399 error = getxattr(path.dentry, name, value, size);
400 path_put(&path);
401 return error;
402 }
403
SYSCALL_DEFINE4(fgetxattr,int,fd,const char __user *,name,void __user *,value,size_t,size)404 SYSCALL_DEFINE4(fgetxattr, int, fd, const char __user *, name,
405 void __user *, value, size_t, size)
406 {
407 struct file *f;
408 ssize_t error = -EBADF;
409
410 f = fget(fd);
411 if (!f)
412 return error;
413 audit_inode(NULL, f->f_path.dentry);
414 error = getxattr(f->f_path.dentry, name, value, size);
415 fput(f);
416 return error;
417 }
418
419 /*
420 * Extended attribute LIST operations
421 */
422 static ssize_t
listxattr(struct dentry * d,char __user * list,size_t size)423 listxattr(struct dentry *d, char __user *list, size_t size)
424 {
425 ssize_t error;
426 char *klist = NULL;
427
428 if (size) {
429 if (size > XATTR_LIST_MAX)
430 size = XATTR_LIST_MAX;
431 klist = kmalloc(size, GFP_KERNEL);
432 if (!klist)
433 return -ENOMEM;
434 }
435
436 error = vfs_listxattr(d, klist, size);
437 if (error > 0) {
438 if (size && copy_to_user(list, klist, error))
439 error = -EFAULT;
440 } else if (error == -ERANGE && size >= XATTR_LIST_MAX) {
441 /* The file system tried to returned a list bigger
442 than XATTR_LIST_MAX bytes. Not possible. */
443 error = -E2BIG;
444 }
445 kfree(klist);
446 return error;
447 }
448
SYSCALL_DEFINE3(listxattr,const char __user *,pathname,char __user *,list,size_t,size)449 SYSCALL_DEFINE3(listxattr, const char __user *, pathname, char __user *, list,
450 size_t, size)
451 {
452 struct path path;
453 ssize_t error;
454
455 error = user_path(pathname, &path);
456 if (error)
457 return error;
458 error = listxattr(path.dentry, list, size);
459 path_put(&path);
460 return error;
461 }
462
SYSCALL_DEFINE3(llistxattr,const char __user *,pathname,char __user *,list,size_t,size)463 SYSCALL_DEFINE3(llistxattr, const char __user *, pathname, char __user *, list,
464 size_t, size)
465 {
466 struct path path;
467 ssize_t error;
468
469 error = user_lpath(pathname, &path);
470 if (error)
471 return error;
472 error = listxattr(path.dentry, list, size);
473 path_put(&path);
474 return error;
475 }
476
SYSCALL_DEFINE3(flistxattr,int,fd,char __user *,list,size_t,size)477 SYSCALL_DEFINE3(flistxattr, int, fd, char __user *, list, size_t, size)
478 {
479 struct file *f;
480 ssize_t error = -EBADF;
481
482 f = fget(fd);
483 if (!f)
484 return error;
485 audit_inode(NULL, f->f_path.dentry);
486 error = listxattr(f->f_path.dentry, list, size);
487 fput(f);
488 return error;
489 }
490
491 /*
492 * Extended attribute REMOVE operations
493 */
494 static long
removexattr(struct dentry * d,const char __user * name)495 removexattr(struct dentry *d, const char __user *name)
496 {
497 int error;
498 char kname[XATTR_NAME_MAX + 1];
499
500 error = strncpy_from_user(kname, name, sizeof(kname));
501 if (error == 0 || error == sizeof(kname))
502 error = -ERANGE;
503 if (error < 0)
504 return error;
505
506 return vfs_removexattr(d, kname);
507 }
508
SYSCALL_DEFINE2(removexattr,const char __user *,pathname,const char __user *,name)509 SYSCALL_DEFINE2(removexattr, const char __user *, pathname,
510 const char __user *, name)
511 {
512 struct path path;
513 int error;
514
515 error = user_path(pathname, &path);
516 if (error)
517 return error;
518 error = mnt_want_write(path.mnt);
519 if (!error) {
520 error = removexattr(path.dentry, name);
521 mnt_drop_write(path.mnt);
522 }
523 path_put(&path);
524 return error;
525 }
526
SYSCALL_DEFINE2(lremovexattr,const char __user *,pathname,const char __user *,name)527 SYSCALL_DEFINE2(lremovexattr, const char __user *, pathname,
528 const char __user *, name)
529 {
530 struct path path;
531 int error;
532
533 error = user_lpath(pathname, &path);
534 if (error)
535 return error;
536 error = mnt_want_write(path.mnt);
537 if (!error) {
538 error = removexattr(path.dentry, name);
539 mnt_drop_write(path.mnt);
540 }
541 path_put(&path);
542 return error;
543 }
544
SYSCALL_DEFINE2(fremovexattr,int,fd,const char __user *,name)545 SYSCALL_DEFINE2(fremovexattr, int, fd, const char __user *, name)
546 {
547 struct file *f;
548 struct dentry *dentry;
549 int error = -EBADF;
550
551 f = fget(fd);
552 if (!f)
553 return error;
554 dentry = f->f_path.dentry;
555 audit_inode(NULL, dentry);
556 error = mnt_want_write_file(f);
557 if (!error) {
558 error = removexattr(dentry, name);
559 mnt_drop_write(f->f_path.mnt);
560 }
561 fput(f);
562 return error;
563 }
564
565
566 static const char *
strcmp_prefix(const char * a,const char * a_prefix)567 strcmp_prefix(const char *a, const char *a_prefix)
568 {
569 while (*a_prefix && *a == *a_prefix) {
570 a++;
571 a_prefix++;
572 }
573 return *a_prefix ? NULL : a;
574 }
575
576 /*
577 * In order to implement different sets of xattr operations for each xattr
578 * prefix with the generic xattr API, a filesystem should create a
579 * null-terminated array of struct xattr_handler (one for each prefix) and
580 * hang a pointer to it off of the s_xattr field of the superblock.
581 *
582 * The generic_fooxattr() functions will use this list to dispatch xattr
583 * operations to the correct xattr_handler.
584 */
585 #define for_each_xattr_handler(handlers, handler) \
586 for ((handler) = *(handlers)++; \
587 (handler) != NULL; \
588 (handler) = *(handlers)++)
589
590 /*
591 * Find the xattr_handler with the matching prefix.
592 */
593 static const struct xattr_handler *
xattr_resolve_name(const struct xattr_handler ** handlers,const char ** name)594 xattr_resolve_name(const struct xattr_handler **handlers, const char **name)
595 {
596 const struct xattr_handler *handler;
597
598 if (!*name)
599 return NULL;
600
601 for_each_xattr_handler(handlers, handler) {
602 const char *n = strcmp_prefix(*name, handler->prefix);
603 if (n) {
604 *name = n;
605 break;
606 }
607 }
608 return handler;
609 }
610
611 /*
612 * Find the handler for the prefix and dispatch its get() operation.
613 */
614 ssize_t
generic_getxattr(struct dentry * dentry,const char * name,void * buffer,size_t size)615 generic_getxattr(struct dentry *dentry, const char *name, void *buffer, size_t size)
616 {
617 const struct xattr_handler *handler;
618
619 handler = xattr_resolve_name(dentry->d_sb->s_xattr, &name);
620 if (!handler)
621 return -EOPNOTSUPP;
622 return handler->get(dentry, name, buffer, size, handler->flags);
623 }
624
625 /*
626 * Combine the results of the list() operation from every xattr_handler in the
627 * list.
628 */
629 ssize_t
generic_listxattr(struct dentry * dentry,char * buffer,size_t buffer_size)630 generic_listxattr(struct dentry *dentry, char *buffer, size_t buffer_size)
631 {
632 const struct xattr_handler *handler, **handlers = dentry->d_sb->s_xattr;
633 unsigned int size = 0;
634
635 if (!buffer) {
636 for_each_xattr_handler(handlers, handler) {
637 size += handler->list(dentry, NULL, 0, NULL, 0,
638 handler->flags);
639 }
640 } else {
641 char *buf = buffer;
642
643 for_each_xattr_handler(handlers, handler) {
644 size = handler->list(dentry, buf, buffer_size,
645 NULL, 0, handler->flags);
646 if (size > buffer_size)
647 return -ERANGE;
648 buf += size;
649 buffer_size -= size;
650 }
651 size = buf - buffer;
652 }
653 return size;
654 }
655
656 /*
657 * Find the handler for the prefix and dispatch its set() operation.
658 */
659 int
generic_setxattr(struct dentry * dentry,const char * name,const void * value,size_t size,int flags)660 generic_setxattr(struct dentry *dentry, const char *name, const void *value, size_t size, int flags)
661 {
662 const struct xattr_handler *handler;
663
664 if (size == 0)
665 value = ""; /* empty EA, do not remove */
666 handler = xattr_resolve_name(dentry->d_sb->s_xattr, &name);
667 if (!handler)
668 return -EOPNOTSUPP;
669 return handler->set(dentry, name, value, size, flags, handler->flags);
670 }
671
672 /*
673 * Find the handler for the prefix and dispatch its set() operation to remove
674 * any associated extended attribute.
675 */
676 int
generic_removexattr(struct dentry * dentry,const char * name)677 generic_removexattr(struct dentry *dentry, const char *name)
678 {
679 const struct xattr_handler *handler;
680
681 handler = xattr_resolve_name(dentry->d_sb->s_xattr, &name);
682 if (!handler)
683 return -EOPNOTSUPP;
684 return handler->set(dentry, name, NULL, 0,
685 XATTR_REPLACE, handler->flags);
686 }
687
688 EXPORT_SYMBOL(generic_getxattr);
689 EXPORT_SYMBOL(generic_listxattr);
690 EXPORT_SYMBOL(generic_setxattr);
691 EXPORT_SYMBOL(generic_removexattr);
692