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Linux/fs/xattr.c

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  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/evm.h>
 18 #include <linux/syscalls.h>
 19 #include <linux/export.h>
 20 #include <linux/fsnotify.h>
 21 #include <linux/audit.h>
 22 #include <linux/vmalloc.h>
 23 #include <linux/posix_acl_xattr.h>
 24 
 25 #include <linux/uaccess.h>
 26 
 27 static const char *
 28 strcmp_prefix(const char *a, const char *a_prefix)
 29 {
 30         while (*a_prefix && *a == *a_prefix) {
 31                 a++;
 32                 a_prefix++;
 33         }
 34         return *a_prefix ? NULL : a;
 35 }
 36 
 37 /*
 38  * In order to implement different sets of xattr operations for each xattr
 39  * prefix, a filesystem should create a null-terminated array of struct
 40  * xattr_handler (one for each prefix) and hang a pointer to it off of the
 41  * s_xattr field of the superblock.
 42  */
 43 #define for_each_xattr_handler(handlers, handler)               \
 44         if (handlers)                                           \
 45                 for ((handler) = *(handlers)++;                 \
 46                         (handler) != NULL;                      \
 47                         (handler) = *(handlers)++)
 48 
 49 /*
 50  * Find the xattr_handler with the matching prefix.
 51  */
 52 static const struct xattr_handler *
 53 xattr_resolve_name(struct inode *inode, const char **name)
 54 {
 55         const struct xattr_handler **handlers = inode->i_sb->s_xattr;
 56         const struct xattr_handler *handler;
 57 
 58         if (!(inode->i_opflags & IOP_XATTR)) {
 59                 if (unlikely(is_bad_inode(inode)))
 60                         return ERR_PTR(-EIO);
 61                 return ERR_PTR(-EOPNOTSUPP);
 62         }
 63         for_each_xattr_handler(handlers, handler) {
 64                 const char *n;
 65 
 66                 n = strcmp_prefix(*name, xattr_prefix(handler));
 67                 if (n) {
 68                         if (!handler->prefix ^ !*n) {
 69                                 if (*n)
 70                                         continue;
 71                                 return ERR_PTR(-EINVAL);
 72                         }
 73                         *name = n;
 74                         return handler;
 75                 }
 76         }
 77         return ERR_PTR(-EOPNOTSUPP);
 78 }
 79 
 80 /*
 81  * Check permissions for extended attribute access.  This is a bit complicated
 82  * because different namespaces have very different rules.
 83  */
 84 static int
 85 xattr_permission(struct inode *inode, const char *name, int mask)
 86 {
 87         /*
 88          * We can never set or remove an extended attribute on a read-only
 89          * filesystem  or on an immutable / append-only inode.
 90          */
 91         if (mask & MAY_WRITE) {
 92                 if (IS_IMMUTABLE(inode) || IS_APPEND(inode))
 93                         return -EPERM;
 94                 /*
 95                  * Updating an xattr will likely cause i_uid and i_gid
 96                  * to be writen back improperly if their true value is
 97                  * unknown to the vfs.
 98                  */
 99                 if (HAS_UNMAPPED_ID(inode))
100                         return -EPERM;
101         }
102 
103         /*
104          * No restriction for security.* and system.* from the VFS.  Decision
105          * on these is left to the underlying filesystem / security module.
106          */
107         if (!strncmp(name, XATTR_SECURITY_PREFIX, XATTR_SECURITY_PREFIX_LEN) ||
108             !strncmp(name, XATTR_SYSTEM_PREFIX, XATTR_SYSTEM_PREFIX_LEN))
109                 return 0;
110 
111         /*
112          * The trusted.* namespace can only be accessed by privileged users.
113          */
114         if (!strncmp(name, XATTR_TRUSTED_PREFIX, XATTR_TRUSTED_PREFIX_LEN)) {
115                 if (!capable(CAP_SYS_ADMIN))
116                         return (mask & MAY_WRITE) ? -EPERM : -ENODATA;
117                 return 0;
118         }
119 
120         /*
121          * In the user.* namespace, only regular files and directories can have
122          * extended attributes. For sticky directories, only the owner and
123          * privileged users can write attributes.
124          */
125         if (!strncmp(name, XATTR_USER_PREFIX, XATTR_USER_PREFIX_LEN)) {
126                 if (!S_ISREG(inode->i_mode) && !S_ISDIR(inode->i_mode))
127                         return (mask & MAY_WRITE) ? -EPERM : -ENODATA;
128                 if (S_ISDIR(inode->i_mode) && (inode->i_mode & S_ISVTX) &&
129                     (mask & MAY_WRITE) && !inode_owner_or_capable(inode))
130                         return -EPERM;
131         }
132 
133         return inode_permission(inode, mask);
134 }
135 
136 int
137 __vfs_setxattr(struct dentry *dentry, struct inode *inode, const char *name,
138                const void *value, size_t size, int flags)
139 {
140         const struct xattr_handler *handler;
141 
142         handler = xattr_resolve_name(inode, &name);
143         if (IS_ERR(handler))
144                 return PTR_ERR(handler);
145         if (!handler->set)
146                 return -EOPNOTSUPP;
147         if (size == 0)
148                 value = "";  /* empty EA, do not remove */
149         return handler->set(handler, dentry, inode, name, value, size, flags);
150 }
151 EXPORT_SYMBOL(__vfs_setxattr);
152 
153 /**
154  *  __vfs_setxattr_noperm - perform setxattr operation without performing
155  *  permission checks.
156  *
157  *  @dentry - object to perform setxattr on
158  *  @name - xattr name to set
159  *  @value - value to set @name to
160  *  @size - size of @value
161  *  @flags - flags to pass into filesystem operations
162  *
163  *  returns the result of the internal setxattr or setsecurity operations.
164  *
165  *  This function requires the caller to lock the inode's i_mutex before it
166  *  is executed. It also assumes that the caller will make the appropriate
167  *  permission checks.
168  */
169 int __vfs_setxattr_noperm(struct dentry *dentry, const char *name,
170                 const void *value, size_t size, int flags)
171 {
172         struct inode *inode = dentry->d_inode;
173         int error = -EAGAIN;
174         int issec = !strncmp(name, XATTR_SECURITY_PREFIX,
175                                    XATTR_SECURITY_PREFIX_LEN);
176 
177         if (issec)
178                 inode->i_flags &= ~S_NOSEC;
179         if (inode->i_opflags & IOP_XATTR) {
180                 error = __vfs_setxattr(dentry, inode, name, value, size, flags);
181                 if (!error) {
182                         fsnotify_xattr(dentry);
183                         security_inode_post_setxattr(dentry, name, value,
184                                                      size, flags);
185                 }
186         } else {
187                 if (unlikely(is_bad_inode(inode)))
188                         return -EIO;
189         }
190         if (error == -EAGAIN) {
191                 error = -EOPNOTSUPP;
192 
193                 if (issec) {
194                         const char *suffix = name + XATTR_SECURITY_PREFIX_LEN;
195 
196                         error = security_inode_setsecurity(inode, suffix, value,
197                                                            size, flags);
198                         if (!error)
199                                 fsnotify_xattr(dentry);
200                 }
201         }
202 
203         return error;
204 }
205 
206 
207 int
208 vfs_setxattr(struct dentry *dentry, const char *name, const void *value,
209                 size_t size, int flags)
210 {
211         struct inode *inode = dentry->d_inode;
212         int error;
213 
214         error = xattr_permission(inode, name, MAY_WRITE);
215         if (error)
216                 return error;
217 
218         inode_lock(inode);
219         error = security_inode_setxattr(dentry, name, value, size, flags);
220         if (error)
221                 goto out;
222 
223         error = __vfs_setxattr_noperm(dentry, name, value, size, flags);
224 
225 out:
226         inode_unlock(inode);
227         return error;
228 }
229 EXPORT_SYMBOL_GPL(vfs_setxattr);
230 
231 ssize_t
232 xattr_getsecurity(struct inode *inode, const char *name, void *value,
233                         size_t size)
234 {
235         void *buffer = NULL;
236         ssize_t len;
237 
238         if (!value || !size) {
239                 len = security_inode_getsecurity(inode, name, &buffer, false);
240                 goto out_noalloc;
241         }
242 
243         len = security_inode_getsecurity(inode, name, &buffer, true);
244         if (len < 0)
245                 return len;
246         if (size < len) {
247                 len = -ERANGE;
248                 goto out;
249         }
250         memcpy(value, buffer, len);
251 out:
252         kfree(buffer);
253 out_noalloc:
254         return len;
255 }
256 EXPORT_SYMBOL_GPL(xattr_getsecurity);
257 
258 /*
259  * vfs_getxattr_alloc - allocate memory, if necessary, before calling getxattr
260  *
261  * Allocate memory, if not already allocated, or re-allocate correct size,
262  * before retrieving the extended attribute.
263  *
264  * Returns the result of alloc, if failed, or the getxattr operation.
265  */
266 ssize_t
267 vfs_getxattr_alloc(struct dentry *dentry, const char *name, char **xattr_value,
268                    size_t xattr_size, gfp_t flags)
269 {
270         const struct xattr_handler *handler;
271         struct inode *inode = dentry->d_inode;
272         char *value = *xattr_value;
273         int error;
274 
275         error = xattr_permission(inode, name, MAY_READ);
276         if (error)
277                 return error;
278 
279         handler = xattr_resolve_name(inode, &name);
280         if (IS_ERR(handler))
281                 return PTR_ERR(handler);
282         if (!handler->get)
283                 return -EOPNOTSUPP;
284         error = handler->get(handler, dentry, inode, name, NULL, 0);
285         if (error < 0)
286                 return error;
287 
288         if (!value || (error > xattr_size)) {
289                 value = krealloc(*xattr_value, error + 1, flags);
290                 if (!value)
291                         return -ENOMEM;
292                 memset(value, 0, error + 1);
293         }
294 
295         error = handler->get(handler, dentry, inode, name, value, error);
296         *xattr_value = value;
297         return error;
298 }
299 
300 ssize_t
301 __vfs_getxattr(struct dentry *dentry, struct inode *inode, const char *name,
302                void *value, size_t size)
303 {
304         const struct xattr_handler *handler;
305 
306         handler = xattr_resolve_name(inode, &name);
307         if (IS_ERR(handler))
308                 return PTR_ERR(handler);
309         if (!handler->get)
310                 return -EOPNOTSUPP;
311         return handler->get(handler, dentry, inode, name, value, size);
312 }
313 EXPORT_SYMBOL(__vfs_getxattr);
314 
315 ssize_t
316 vfs_getxattr(struct dentry *dentry, const char *name, void *value, size_t size)
317 {
318         struct inode *inode = dentry->d_inode;
319         int error;
320 
321         error = xattr_permission(inode, name, MAY_READ);
322         if (error)
323                 return error;
324 
325         error = security_inode_getxattr(dentry, name);
326         if (error)
327                 return error;
328 
329         if (!strncmp(name, XATTR_SECURITY_PREFIX,
330                                 XATTR_SECURITY_PREFIX_LEN)) {
331                 const char *suffix = name + XATTR_SECURITY_PREFIX_LEN;
332                 int ret = xattr_getsecurity(inode, suffix, value, size);
333                 /*
334                  * Only overwrite the return value if a security module
335                  * is actually active.
336                  */
337                 if (ret == -EOPNOTSUPP)
338                         goto nolsm;
339                 return ret;
340         }
341 nolsm:
342         return __vfs_getxattr(dentry, inode, name, value, size);
343 }
344 EXPORT_SYMBOL_GPL(vfs_getxattr);
345 
346 ssize_t
347 vfs_listxattr(struct dentry *dentry, char *list, size_t size)
348 {
349         struct inode *inode = d_inode(dentry);
350         ssize_t error;
351 
352         error = security_inode_listxattr(dentry);
353         if (error)
354                 return error;
355         if (inode->i_op->listxattr && (inode->i_opflags & IOP_XATTR)) {
356                 error = -EOPNOTSUPP;
357                 error = inode->i_op->listxattr(dentry, list, size);
358         } else {
359                 error = security_inode_listsecurity(inode, list, size);
360                 if (size && error > size)
361                         error = -ERANGE;
362         }
363         return error;
364 }
365 EXPORT_SYMBOL_GPL(vfs_listxattr);
366 
367 int
368 __vfs_removexattr(struct dentry *dentry, const char *name)
369 {
370         struct inode *inode = d_inode(dentry);
371         const struct xattr_handler *handler;
372 
373         handler = xattr_resolve_name(inode, &name);
374         if (IS_ERR(handler))
375                 return PTR_ERR(handler);
376         if (!handler->set)
377                 return -EOPNOTSUPP;
378         return handler->set(handler, dentry, inode, name, NULL, 0, XATTR_REPLACE);
379 }
380 EXPORT_SYMBOL(__vfs_removexattr);
381 
382 int
383 vfs_removexattr(struct dentry *dentry, const char *name)
384 {
385         struct inode *inode = dentry->d_inode;
386         int error;
387 
388         error = xattr_permission(inode, name, MAY_WRITE);
389         if (error)
390                 return error;
391 
392         inode_lock(inode);
393         error = security_inode_removexattr(dentry, name);
394         if (error)
395                 goto out;
396 
397         error = __vfs_removexattr(dentry, name);
398 
399         if (!error) {
400                 fsnotify_xattr(dentry);
401                 evm_inode_post_removexattr(dentry, name);
402         }
403 
404 out:
405         inode_unlock(inode);
406         return error;
407 }
408 EXPORT_SYMBOL_GPL(vfs_removexattr);
409 
410 
411 /*
412  * Extended attribute SET operations
413  */
414 static long
415 setxattr(struct dentry *d, const char __user *name, const void __user *value,
416          size_t size, int flags)
417 {
418         int error;
419         void *kvalue = NULL;
420         char kname[XATTR_NAME_MAX + 1];
421 
422         if (flags & ~(XATTR_CREATE|XATTR_REPLACE))
423                 return -EINVAL;
424 
425         error = strncpy_from_user(kname, name, sizeof(kname));
426         if (error == 0 || error == sizeof(kname))
427                 error = -ERANGE;
428         if (error < 0)
429                 return error;
430 
431         if (size) {
432                 if (size > XATTR_SIZE_MAX)
433                         return -E2BIG;
434                 kvalue = kvmalloc(size, GFP_KERNEL);
435                 if (!kvalue)
436                         return -ENOMEM;
437                 if (copy_from_user(kvalue, value, size)) {
438                         error = -EFAULT;
439                         goto out;
440                 }
441                 if ((strcmp(kname, XATTR_NAME_POSIX_ACL_ACCESS) == 0) ||
442                     (strcmp(kname, XATTR_NAME_POSIX_ACL_DEFAULT) == 0))
443                         posix_acl_fix_xattr_from_user(kvalue, size);
444         }
445 
446         error = vfs_setxattr(d, kname, kvalue, size, flags);
447 out:
448         kvfree(kvalue);
449 
450         return error;
451 }
452 
453 static int path_setxattr(const char __user *pathname,
454                          const char __user *name, const void __user *value,
455                          size_t size, int flags, unsigned int lookup_flags)
456 {
457         struct path path;
458         int error;
459 retry:
460         error = user_path_at(AT_FDCWD, pathname, lookup_flags, &path);
461         if (error)
462                 return error;
463         error = mnt_want_write(path.mnt);
464         if (!error) {
465                 error = setxattr(path.dentry, name, value, size, flags);
466                 mnt_drop_write(path.mnt);
467         }
468         path_put(&path);
469         if (retry_estale(error, lookup_flags)) {
470                 lookup_flags |= LOOKUP_REVAL;
471                 goto retry;
472         }
473         return error;
474 }
475 
476 SYSCALL_DEFINE5(setxattr, const char __user *, pathname,
477                 const char __user *, name, const void __user *, value,
478                 size_t, size, int, flags)
479 {
480         return path_setxattr(pathname, name, value, size, flags, LOOKUP_FOLLOW);
481 }
482 
483 SYSCALL_DEFINE5(lsetxattr, const char __user *, pathname,
484                 const char __user *, name, const void __user *, value,
485                 size_t, size, int, flags)
486 {
487         return path_setxattr(pathname, name, value, size, flags, 0);
488 }
489 
490 SYSCALL_DEFINE5(fsetxattr, int, fd, const char __user *, name,
491                 const void __user *,value, size_t, size, int, flags)
492 {
493         struct fd f = fdget(fd);
494         int error = -EBADF;
495 
496         if (!f.file)
497                 return error;
498         audit_file(f.file);
499         error = mnt_want_write_file(f.file);
500         if (!error) {
501                 error = setxattr(f.file->f_path.dentry, name, value, size, flags);
502                 mnt_drop_write_file(f.file);
503         }
504         fdput(f);
505         return error;
506 }
507 
508 /*
509  * Extended attribute GET operations
510  */
511 static ssize_t
512 getxattr(struct dentry *d, const char __user *name, void __user *value,
513          size_t size)
514 {
515         ssize_t error;
516         void *kvalue = NULL;
517         char kname[XATTR_NAME_MAX + 1];
518 
519         error = strncpy_from_user(kname, name, sizeof(kname));
520         if (error == 0 || error == sizeof(kname))
521                 error = -ERANGE;
522         if (error < 0)
523                 return error;
524 
525         if (size) {
526                 if (size > XATTR_SIZE_MAX)
527                         size = XATTR_SIZE_MAX;
528                 kvalue = kvzalloc(size, GFP_KERNEL);
529                 if (!kvalue)
530                         return -ENOMEM;
531         }
532 
533         error = vfs_getxattr(d, kname, kvalue, size);
534         if (error > 0) {
535                 if ((strcmp(kname, XATTR_NAME_POSIX_ACL_ACCESS) == 0) ||
536                     (strcmp(kname, XATTR_NAME_POSIX_ACL_DEFAULT) == 0))
537                         posix_acl_fix_xattr_to_user(kvalue, size);
538                 if (size && copy_to_user(value, kvalue, error))
539                         error = -EFAULT;
540         } else if (error == -ERANGE && size >= XATTR_SIZE_MAX) {
541                 /* The file system tried to returned a value bigger
542                    than XATTR_SIZE_MAX bytes. Not possible. */
543                 error = -E2BIG;
544         }
545 
546         kvfree(kvalue);
547 
548         return error;
549 }
550 
551 static ssize_t path_getxattr(const char __user *pathname,
552                              const char __user *name, void __user *value,
553                              size_t size, unsigned int lookup_flags)
554 {
555         struct path path;
556         ssize_t error;
557 retry:
558         error = user_path_at(AT_FDCWD, pathname, lookup_flags, &path);
559         if (error)
560                 return error;
561         error = getxattr(path.dentry, name, value, size);
562         path_put(&path);
563         if (retry_estale(error, lookup_flags)) {
564                 lookup_flags |= LOOKUP_REVAL;
565                 goto retry;
566         }
567         return error;
568 }
569 
570 SYSCALL_DEFINE4(getxattr, const char __user *, pathname,
571                 const char __user *, name, void __user *, value, size_t, size)
572 {
573         return path_getxattr(pathname, name, value, size, LOOKUP_FOLLOW);
574 }
575 
576 SYSCALL_DEFINE4(lgetxattr, const char __user *, pathname,
577                 const char __user *, name, void __user *, value, size_t, size)
578 {
579         return path_getxattr(pathname, name, value, size, 0);
580 }
581 
582 SYSCALL_DEFINE4(fgetxattr, int, fd, const char __user *, name,
583                 void __user *, value, size_t, size)
584 {
585         struct fd f = fdget(fd);
586         ssize_t error = -EBADF;
587 
588         if (!f.file)
589                 return error;
590         audit_file(f.file);
591         error = getxattr(f.file->f_path.dentry, name, value, size);
592         fdput(f);
593         return error;
594 }
595 
596 /*
597  * Extended attribute LIST operations
598  */
599 static ssize_t
600 listxattr(struct dentry *d, char __user *list, size_t size)
601 {
602         ssize_t error;
603         char *klist = NULL;
604 
605         if (size) {
606                 if (size > XATTR_LIST_MAX)
607                         size = XATTR_LIST_MAX;
608                 klist = kvmalloc(size, GFP_KERNEL);
609                 if (!klist)
610                         return -ENOMEM;
611         }
612 
613         error = vfs_listxattr(d, klist, size);
614         if (error > 0) {
615                 if (size && copy_to_user(list, klist, error))
616                         error = -EFAULT;
617         } else if (error == -ERANGE && size >= XATTR_LIST_MAX) {
618                 /* The file system tried to returned a list bigger
619                    than XATTR_LIST_MAX bytes. Not possible. */
620                 error = -E2BIG;
621         }
622 
623         kvfree(klist);
624 
625         return error;
626 }
627 
628 static ssize_t path_listxattr(const char __user *pathname, char __user *list,
629                               size_t size, unsigned int lookup_flags)
630 {
631         struct path path;
632         ssize_t error;
633 retry:
634         error = user_path_at(AT_FDCWD, pathname, lookup_flags, &path);
635         if (error)
636                 return error;
637         error = listxattr(path.dentry, list, size);
638         path_put(&path);
639         if (retry_estale(error, lookup_flags)) {
640                 lookup_flags |= LOOKUP_REVAL;
641                 goto retry;
642         }
643         return error;
644 }
645 
646 SYSCALL_DEFINE3(listxattr, const char __user *, pathname, char __user *, list,
647                 size_t, size)
648 {
649         return path_listxattr(pathname, list, size, LOOKUP_FOLLOW);
650 }
651 
652 SYSCALL_DEFINE3(llistxattr, const char __user *, pathname, char __user *, list,
653                 size_t, size)
654 {
655         return path_listxattr(pathname, list, size, 0);
656 }
657 
658 SYSCALL_DEFINE3(flistxattr, int, fd, char __user *, list, size_t, size)
659 {
660         struct fd f = fdget(fd);
661         ssize_t error = -EBADF;
662 
663         if (!f.file)
664                 return error;
665         audit_file(f.file);
666         error = listxattr(f.file->f_path.dentry, list, size);
667         fdput(f);
668         return error;
669 }
670 
671 /*
672  * Extended attribute REMOVE operations
673  */
674 static long
675 removexattr(struct dentry *d, const char __user *name)
676 {
677         int error;
678         char kname[XATTR_NAME_MAX + 1];
679 
680         error = strncpy_from_user(kname, name, sizeof(kname));
681         if (error == 0 || error == sizeof(kname))
682                 error = -ERANGE;
683         if (error < 0)
684                 return error;
685 
686         return vfs_removexattr(d, kname);
687 }
688 
689 static int path_removexattr(const char __user *pathname,
690                             const char __user *name, unsigned int lookup_flags)
691 {
692         struct path path;
693         int error;
694 retry:
695         error = user_path_at(AT_FDCWD, pathname, lookup_flags, &path);
696         if (error)
697                 return error;
698         error = mnt_want_write(path.mnt);
699         if (!error) {
700                 error = removexattr(path.dentry, name);
701                 mnt_drop_write(path.mnt);
702         }
703         path_put(&path);
704         if (retry_estale(error, lookup_flags)) {
705                 lookup_flags |= LOOKUP_REVAL;
706                 goto retry;
707         }
708         return error;
709 }
710 
711 SYSCALL_DEFINE2(removexattr, const char __user *, pathname,
712                 const char __user *, name)
713 {
714         return path_removexattr(pathname, name, LOOKUP_FOLLOW);
715 }
716 
717 SYSCALL_DEFINE2(lremovexattr, const char __user *, pathname,
718                 const char __user *, name)
719 {
720         return path_removexattr(pathname, name, 0);
721 }
722 
723 SYSCALL_DEFINE2(fremovexattr, int, fd, const char __user *, name)
724 {
725         struct fd f = fdget(fd);
726         int error = -EBADF;
727 
728         if (!f.file)
729                 return error;
730         audit_file(f.file);
731         error = mnt_want_write_file(f.file);
732         if (!error) {
733                 error = removexattr(f.file->f_path.dentry, name);
734                 mnt_drop_write_file(f.file);
735         }
736         fdput(f);
737         return error;
738 }
739 
740 /*
741  * Combine the results of the list() operation from every xattr_handler in the
742  * list.
743  */
744 ssize_t
745 generic_listxattr(struct dentry *dentry, char *buffer, size_t buffer_size)
746 {
747         const struct xattr_handler *handler, **handlers = dentry->d_sb->s_xattr;
748         unsigned int size = 0;
749 
750         if (!buffer) {
751                 for_each_xattr_handler(handlers, handler) {
752                         if (!handler->name ||
753                             (handler->list && !handler->list(dentry)))
754                                 continue;
755                         size += strlen(handler->name) + 1;
756                 }
757         } else {
758                 char *buf = buffer;
759                 size_t len;
760 
761                 for_each_xattr_handler(handlers, handler) {
762                         if (!handler->name ||
763                             (handler->list && !handler->list(dentry)))
764                                 continue;
765                         len = strlen(handler->name);
766                         if (len + 1 > buffer_size)
767                                 return -ERANGE;
768                         memcpy(buf, handler->name, len + 1);
769                         buf += len + 1;
770                         buffer_size -= len + 1;
771                 }
772                 size = buf - buffer;
773         }
774         return size;
775 }
776 EXPORT_SYMBOL(generic_listxattr);
777 
778 /**
779  * xattr_full_name  -  Compute full attribute name from suffix
780  *
781  * @handler:    handler of the xattr_handler operation
782  * @name:       name passed to the xattr_handler operation
783  *
784  * The get and set xattr handler operations are called with the remainder of
785  * the attribute name after skipping the handler's prefix: for example, "foo"
786  * is passed to the get operation of a handler with prefix "user." to get
787  * attribute "user.foo".  The full name is still "there" in the name though.
788  *
789  * Note: the list xattr handler operation when called from the vfs is passed a
790  * NULL name; some file systems use this operation internally, with varying
791  * semantics.
792  */
793 const char *xattr_full_name(const struct xattr_handler *handler,
794                             const char *name)
795 {
796         size_t prefix_len = strlen(xattr_prefix(handler));
797 
798         return name - prefix_len;
799 }
800 EXPORT_SYMBOL(xattr_full_name);
801 
802 /*
803  * Allocate new xattr and copy in the value; but leave the name to callers.
804  */
805 struct simple_xattr *simple_xattr_alloc(const void *value, size_t size)
806 {
807         struct simple_xattr *new_xattr;
808         size_t len;
809 
810         /* wrap around? */
811         len = sizeof(*new_xattr) + size;
812         if (len < sizeof(*new_xattr))
813                 return NULL;
814 
815         new_xattr = kmalloc(len, GFP_KERNEL);
816         if (!new_xattr)
817                 return NULL;
818 
819         new_xattr->size = size;
820         memcpy(new_xattr->value, value, size);
821         return new_xattr;
822 }
823 
824 /*
825  * xattr GET operation for in-memory/pseudo filesystems
826  */
827 int simple_xattr_get(struct simple_xattrs *xattrs, const char *name,
828                      void *buffer, size_t size)
829 {
830         struct simple_xattr *xattr;
831         int ret = -ENODATA;
832 
833         spin_lock(&xattrs->lock);
834         list_for_each_entry(xattr, &xattrs->head, list) {
835                 if (strcmp(name, xattr->name))
836                         continue;
837 
838                 ret = xattr->size;
839                 if (buffer) {
840                         if (size < xattr->size)
841                                 ret = -ERANGE;
842                         else
843                                 memcpy(buffer, xattr->value, xattr->size);
844                 }
845                 break;
846         }
847         spin_unlock(&xattrs->lock);
848         return ret;
849 }
850 
851 /**
852  * simple_xattr_set - xattr SET operation for in-memory/pseudo filesystems
853  * @xattrs: target simple_xattr list
854  * @name: name of the extended attribute
855  * @value: value of the xattr. If %NULL, will remove the attribute.
856  * @size: size of the new xattr
857  * @flags: %XATTR_{CREATE|REPLACE}
858  *
859  * %XATTR_CREATE is set, the xattr shouldn't exist already; otherwise fails
860  * with -EEXIST.  If %XATTR_REPLACE is set, the xattr should exist;
861  * otherwise, fails with -ENODATA.
862  *
863  * Returns 0 on success, -errno on failure.
864  */
865 int simple_xattr_set(struct simple_xattrs *xattrs, const char *name,
866                      const void *value, size_t size, int flags)
867 {
868         struct simple_xattr *xattr;
869         struct simple_xattr *new_xattr = NULL;
870         int err = 0;
871 
872         /* value == NULL means remove */
873         if (value) {
874                 new_xattr = simple_xattr_alloc(value, size);
875                 if (!new_xattr)
876                         return -ENOMEM;
877 
878                 new_xattr->name = kstrdup(name, GFP_KERNEL);
879                 if (!new_xattr->name) {
880                         kfree(new_xattr);
881                         return -ENOMEM;
882                 }
883         }
884 
885         spin_lock(&xattrs->lock);
886         list_for_each_entry(xattr, &xattrs->head, list) {
887                 if (!strcmp(name, xattr->name)) {
888                         if (flags & XATTR_CREATE) {
889                                 xattr = new_xattr;
890                                 err = -EEXIST;
891                         } else if (new_xattr) {
892                                 list_replace(&xattr->list, &new_xattr->list);
893                         } else {
894                                 list_del(&xattr->list);
895                         }
896                         goto out;
897                 }
898         }
899         if (flags & XATTR_REPLACE) {
900                 xattr = new_xattr;
901                 err = -ENODATA;
902         } else {
903                 list_add(&new_xattr->list, &xattrs->head);
904                 xattr = NULL;
905         }
906 out:
907         spin_unlock(&xattrs->lock);
908         if (xattr) {
909                 kfree(xattr->name);
910                 kfree(xattr);
911         }
912         return err;
913 
914 }
915 
916 static bool xattr_is_trusted(const char *name)
917 {
918         return !strncmp(name, XATTR_TRUSTED_PREFIX, XATTR_TRUSTED_PREFIX_LEN);
919 }
920 
921 static int xattr_list_one(char **buffer, ssize_t *remaining_size,
922                           const char *name)
923 {
924         size_t len = strlen(name) + 1;
925         if (*buffer) {
926                 if (*remaining_size < len)
927                         return -ERANGE;
928                 memcpy(*buffer, name, len);
929                 *buffer += len;
930         }
931         *remaining_size -= len;
932         return 0;
933 }
934 
935 /*
936  * xattr LIST operation for in-memory/pseudo filesystems
937  */
938 ssize_t simple_xattr_list(struct inode *inode, struct simple_xattrs *xattrs,
939                           char *buffer, size_t size)
940 {
941         bool trusted = capable(CAP_SYS_ADMIN);
942         struct simple_xattr *xattr;
943         ssize_t remaining_size = size;
944         int err = 0;
945 
946 #ifdef CONFIG_FS_POSIX_ACL
947         if (inode->i_acl) {
948                 err = xattr_list_one(&buffer, &remaining_size,
949                                      XATTR_NAME_POSIX_ACL_ACCESS);
950                 if (err)
951                         return err;
952         }
953         if (inode->i_default_acl) {
954                 err = xattr_list_one(&buffer, &remaining_size,
955                                      XATTR_NAME_POSIX_ACL_DEFAULT);
956                 if (err)
957                         return err;
958         }
959 #endif
960 
961         spin_lock(&xattrs->lock);
962         list_for_each_entry(xattr, &xattrs->head, list) {
963                 /* skip "trusted." attributes for unprivileged callers */
964                 if (!trusted && xattr_is_trusted(xattr->name))
965                         continue;
966 
967                 err = xattr_list_one(&buffer, &remaining_size, xattr->name);
968                 if (err)
969                         break;
970         }
971         spin_unlock(&xattrs->lock);
972 
973         return err ? err : size - remaining_size;
974 }
975 
976 /*
977  * Adds an extended attribute to the list
978  */
979 void simple_xattr_list_add(struct simple_xattrs *xattrs,
980                            struct simple_xattr *new_xattr)
981 {
982         spin_lock(&xattrs->lock);
983         list_add(&new_xattr->list, &xattrs->head);
984         spin_unlock(&xattrs->lock);
985 }
986 

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