fs/xattr.c

   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
  24 #include <asm/uaccess.h>
  25
  26 /*
  27  * Check permissions for extended attribute access.  This is a bit complicated
  28  * because different namespaces have very different rules.
  29  */
  30 static int
  31 xattr_permission(struct inode *inode, const char *name, int mask)
  32 {
  33         /*
  34          * We can never set or remove an extended attribute on a read-only
  35          * filesystem  or on an immutable / append-only inode.
  36          */
  37         if (mask & MAY_WRITE) {
  38                 if (IS_IMMUTABLE(inode) || IS_APPEND(inode))
  39                         return -EPERM;
  40         }
  41
  42         /*
  43          * No restriction for security.* and system.* from the VFS.  Decision
  44          * on these is left to the underlying filesystem / security module.
  45          */
  46         if (!strncmp(name, XATTR_SECURITY_PREFIX, XATTR_SECURITY_PREFIX_LEN) ||
  47             !strncmp(name, XATTR_SYSTEM_PREFIX, XATTR_SYSTEM_PREFIX_LEN))
  48                 return 0;
  49
  50         /*
  51          * The trusted.* namespace can only be accessed by privileged users.
  52          */
  53         if (!strncmp(name, XATTR_TRUSTED_PREFIX, XATTR_TRUSTED_PREFIX_LEN)) {
  54                 if (!capable(CAP_SYS_ADMIN))
  55                         return (mask & MAY_WRITE) ? -EPERM : -ENODATA;
  56                 return 0;
  57         }
  58
  59         /*
  60          * In the user.* namespace, only regular files and directories can have
  61          * extended attributes. For sticky directories, only the owner and
  62          * privileged users can write attributes.
  63          */
  64         if (!strncmp(name, XATTR_USER_PREFIX, XATTR_USER_PREFIX_LEN)) {
  65                 if (!S_ISREG(inode->i_mode) && !S_ISDIR(inode->i_mode))
  66                         return (mask & MAY_WRITE) ? -EPERM : -ENODATA;
  67                 if (S_ISDIR(inode->i_mode) && (inode->i_mode & S_ISVTX) &&
  68                     (mask & MAY_WRITE) && !inode_owner_or_capable(inode))
  69                         return -EPERM;
  70         }
  71
  72         return inode_permission(inode, mask);
  73 }
  74
  75 /**
  76  *  __vfs_setxattr_noperm - perform setxattr operation without performing
  77  *  permission checks.
  78  *
  79  *  @dentry - object to perform setxattr on
  80  *  @name - xattr name to set
  81  *  @value - value to set @name to
  82  *  @size - size of @value
  83  *  @flags - flags to pass into filesystem operations
  84  *
  85  *  returns the result of the internal setxattr or setsecurity operations.
  86  *
  87  *  This function requires the caller to lock the inode's i_mutex before it
  88  *  is executed. It also assumes that the caller will make the appropriate
  89  *  permission checks.
  90  */
  91 int __vfs_setxattr_noperm(struct dentry *dentry, const char *name,
  92                 const void *value, size_t size, int flags)
  93 {
  94         struct inode *inode = dentry->d_inode;
  95         int error = -EOPNOTSUPP;
  96         int issec = !strncmp(name, XATTR_SECURITY_PREFIX,
  97                                    XATTR_SECURITY_PREFIX_LEN);
  98
  99         if (issec)
 100                 inode->i_flags &= ~S_NOSEC;
 101         if (inode->i_op->setxattr) {
 102                 error = inode->i_op->setxattr(dentry, name, value, size, flags);
 103                 if (!error) {
 104                         fsnotify_xattr(dentry);
 105                         security_inode_post_setxattr(dentry, name, value,
 106                                                      size, flags);
 107                 }
 108         } else if (issec) {
 109                 const char *suffix = name + XATTR_SECURITY_PREFIX_LEN;
 110                 error = security_inode_setsecurity(inode, suffix, value,
 111                                                    size, flags);
 112                 if (!error)
 113                         fsnotify_xattr(dentry);
 114         }
 115
 116         return error;
 117 }
 118
 119
 120 int
 121 vfs_setxattr(struct dentry *dentry, const char *name, const void *value,
 122                 size_t size, int flags)
 123 {
 124         struct inode *inode = dentry->d_inode;
 125         int error;
 126
 127         error = xattr_permission(inode, name, MAY_WRITE);
 128         if (error)
 129                 return error;
 130
 131         mutex_lock(&inode->i_mutex);
 132         error = security_inode_setxattr(dentry, name, value, size, flags);
 133         if (error)
 134                 goto out;
 135
 136         error = __vfs_setxattr_noperm(dentry, name, value, size, flags);
 137
 138 out:
 139         mutex_unlock(&inode->i_mutex);
 140         return error;
 141 }
 142 EXPORT_SYMBOL_GPL(vfs_setxattr);
 143
 144 ssize_t
 145 xattr_getsecurity(struct inode *inode, const char *name, void *value,
 146                         size_t size)
 147 {
 148         void *buffer = NULL;
 149         ssize_t len;
 150
 151         if (!value || !size) {
 152                 len = security_inode_getsecurity(inode, name, &buffer, false);
 153                 goto out_noalloc;
 154         }
 155
 156         len = security_inode_getsecurity(inode, name, &buffer, true);
 157         if (len < 0)
 158                 return len;
 159         if (size < len) {
 160                 len = -ERANGE;
 161                 goto out;
 162         }
 163         memcpy(value, buffer, len);
 164 out:
 165         security_release_secctx(buffer, len);
 166 out_noalloc:
 167         return len;
 168 }
 169 EXPORT_SYMBOL_GPL(xattr_getsecurity);
 170
 171 /*
 172  * vfs_getxattr_alloc - allocate memory, if necessary, before calling getxattr
 173  *
 174  * Allocate memory, if not already allocated, or re-allocate correct size,
 175  * before retrieving the extended attribute.
 176  *
 177  * Returns the result of alloc, if failed, or the getxattr operation.
 178  */
 179 ssize_t
 180 vfs_getxattr_alloc(struct dentry *dentry, const char *name, char **xattr_value,
 181                    size_t xattr_size, gfp_t flags)
 182 {
 183         struct inode *inode = dentry->d_inode;
 184         char *value = *xattr_value;
 185         int error;
 186
 187         error = xattr_permission(inode, name, MAY_READ);
 188         if (error)
 189                 return error;
 190
 191         if (!inode->i_op->getxattr)
 192                 return -EOPNOTSUPP;
 193
 194         error = inode->i_op->getxattr(dentry, name, NULL, 0);
 195         if (error < 0)
 196                 return error;
 197
 198         if (!value || (error > xattr_size)) {
 199                 value = krealloc(*xattr_value, error + 1, flags);
 200                 if (!value)
 201                         return -ENOMEM;
 202                 memset(value, 0, error + 1);
 203         }
 204
 205         error = inode->i_op->getxattr(dentry, name, value, error);
 206         *xattr_value = value;
 207         return error;
 208 }
 209
 210 /* Compare an extended attribute value with the given value */
 211 int vfs_xattr_cmp(struct dentry *dentry, const char *xattr_name,
 212                   const char *value, size_t size, gfp_t flags)
 213 {
 214         char *xattr_value = NULL;
 215         int rc;
 216
 217         rc = vfs_getxattr_alloc(dentry, xattr_name, &xattr_value, 0, flags);
 218         if (rc < 0)
 219                 return rc;
 220
 221         if ((rc != size) || (memcmp(xattr_value, value, rc) != 0))
 222                 rc = -EINVAL;
 223         else
 224                 rc = 0;
 225         kfree(xattr_value);
 226         return rc;
 227 }
 228
 229 ssize_t
 230 vfs_getxattr(struct dentry *dentry, const char *name, void *value, size_t size)
 231 {
 232         struct inode *inode = dentry->d_inode;
 233         int error;
 234
 235         error = xattr_permission(inode, name, MAY_READ);
 236         if (error)
 237                 return error;
 238
 239         error = security_inode_getxattr(dentry, name);
 240         if (error)
 241                 return error;
 242
 243         if (!strncmp(name, XATTR_SECURITY_PREFIX,
 244                                 XATTR_SECURITY_PREFIX_LEN)) {
 245                 const char *suffix = name + XATTR_SECURITY_PREFIX_LEN;
 246                 int ret = xattr_getsecurity(inode, suffix, value, size);
 247                 /*
 248                  * Only overwrite the return value if a security module
 249                  * is actually active.
 250                  */
 251                 if (ret == -EOPNOTSUPP)
 252                         goto nolsm;
 253                 return ret;
 254         }
 255 nolsm:
 256         if (inode->i_op->getxattr)
 257                 error = inode->i_op->getxattr(dentry, name, value, size);
 258         else
 259                 error = -EOPNOTSUPP;
 260
 261         return error;
 262 }
 263 EXPORT_SYMBOL_GPL(vfs_getxattr);
 264
 265 ssize_t
 266 vfs_listxattr(struct dentry *d, char *list, size_t size)
 267 {
 268         ssize_t error;
 269
 270         error = security_inode_listxattr(d);
 271         if (error)
 272                 return error;
 273         error = -EOPNOTSUPP;
 274         if (d->d_inode->i_op->listxattr) {
 275                 error = d->d_inode->i_op->listxattr(d, list, size);
 276         } else {
 277                 error = security_inode_listsecurity(d->d_inode, list, size);
 278                 if (size && error > size)
 279                         error = -ERANGE;
 280         }
 281         return error;
 282 }
 283 EXPORT_SYMBOL_GPL(vfs_listxattr);
 284
 285 int
 286 vfs_removexattr(struct dentry *dentry, const char *name)
 287 {
 288         struct inode *inode = dentry->d_inode;
 289         int error;
 290
 291         if (!inode->i_op->removexattr)
 292                 return -EOPNOTSUPP;
 293
 294         error = xattr_permission(inode, name, MAY_WRITE);
 295         if (error)
 296                 return error;
 297
 298         error = security_inode_removexattr(dentry, name);
 299         if (error)
 300                 return error;
 301
 302         mutex_lock(&inode->i_mutex);
 303         error = inode->i_op->removexattr(dentry, name);
 304         mutex_unlock(&inode->i_mutex);
 305
 306         if (!error) {
 307                 fsnotify_xattr(dentry);
 308                 evm_inode_post_removexattr(dentry, name);
 309         }
 310         return error;
 311 }
 312 EXPORT_SYMBOL_GPL(vfs_removexattr);
 313
 314
 315 /*
 316  * Extended attribute SET operations
 317  */
 318 static long
 319 setxattr(struct dentry *d, const char __user *name, const void __user *value,
 320          size_t size, int flags)
 321 {
 322         int error;
 323         void *kvalue = NULL;
 324         void *vvalue = NULL;    /* If non-NULL, we used vmalloc() */
 325         char kname[XATTR_NAME_MAX + 1];
 326
 327         if (flags & ~(XATTR_CREATE|XATTR_REPLACE))
 328                 return -EINVAL;
 329
 330         error = strncpy_from_user(kname, name, sizeof(kname));
 331         if (error == 0 || error == sizeof(kname))
 332                 error = -ERANGE;
 333         if (error < 0)
 334                 return error;
 335
 336         if (size) {
 337                 if (size > XATTR_SIZE_MAX)
 338                         return -E2BIG;
 339                 kvalue = kmalloc(size, GFP_KERNEL | __GFP_NOWARN);
 340                 if (!kvalue) {
 341                         vvalue = vmalloc(size);
 342                         if (!vvalue)
 343                                 return -ENOMEM;
 344                         kvalue = vvalue;
 345                 }
 346                 if (copy_from_user(kvalue, value, size)) {
 347                         error = -EFAULT;
 348                         goto out;
 349                 }
 350         }
 351
 352         error = vfs_setxattr(d, kname, kvalue, size, flags);
 353 out:
 354         if (vvalue)
 355                 vfree(vvalue);
 356         else
 357                 kfree(kvalue);
 358         return error;
 359 }
 360
 361 SYSCALL_DEFINE5(setxattr, const char __user *, pathname,
 362                 const char __user *, name, const void __user *, value,
 363                 size_t, size, int, flags)
 364 {
 365         struct path path;
 366         int error;
 367
 368         error = user_path(pathname, &path);
 369         if (error)
 370                 return error;
 371         error = mnt_want_write(path.mnt);
 372         if (!error) {
 373                 error = setxattr(path.dentry, name, value, size, flags);
 374                 mnt_drop_write(path.mnt);
 375         }
 376         path_put(&path);
 377         return error;
 378 }
 379
 380 SYSCALL_DEFINE5(lsetxattr, const char __user *, pathname,
 381                 const char __user *, name, const void __user *, value,
 382                 size_t, size, int, flags)
 383 {
 384         struct path path;
 385         int error;
 386
 387         error = user_lpath(pathname, &path);
 388         if (error)
 389                 return error;
 390         error = mnt_want_write(path.mnt);
 391         if (!error) {
 392                 error = setxattr(path.dentry, name, value, size, flags);
 393                 mnt_drop_write(path.mnt);
 394         }
 395         path_put(&path);
 396         return error;
 397 }
 398
 399 SYSCALL_DEFINE5(fsetxattr, int, fd, const char __user *, name,
 400                 const void __user *,value, size_t, size, int, flags)
 401 {
 402         struct file *f;
 403         struct dentry *dentry;
 404         int error = -EBADF;
 405
 406         f = fget(fd);
 407         if (!f)
 408                 return error;
 409         dentry = f->f_path.dentry;
 410         audit_inode(NULL, dentry);
 411         error = mnt_want_write_file(f);
 412         if (!error) {
 413                 error = setxattr(dentry, name, value, size, flags);
 414                 mnt_drop_write_file(f);
 415         }
 416         fput(f);
 417         return error;
 418 }
 419
 420 /*
 421  * Extended attribute GET operations
 422  */
 423 static ssize_t
 424 getxattr(struct dentry *d, const char __user *name, void __user *value,
 425          size_t size)
 426 {
 427         ssize_t error;
 428         void *kvalue = NULL;
 429         char kname[XATTR_NAME_MAX + 1];
 430
 431         error = strncpy_from_user(kname, name, sizeof(kname));
 432         if (error == 0 || error == sizeof(kname))
 433                 error = -ERANGE;
 434         if (error < 0)
 435                 return error;
 436
 437         if (size) {
 438                 if (size > XATTR_SIZE_MAX)
 439                         size = XATTR_SIZE_MAX;
 440                 kvalue = kzalloc(size, GFP_KERNEL);
 441                 if (!kvalue)
 442                         return -ENOMEM;
 443         }
 444
 445         error = vfs_getxattr(d, kname, kvalue, size);
 446         if (error > 0) {
 447                 if (size && copy_to_user(value, kvalue, error))
 448                         error = -EFAULT;
 449         } else if (error == -ERANGE && size >= XATTR_SIZE_MAX) {
 450                 /* The file system tried to returned a value bigger
 451                    than XATTR_SIZE_MAX bytes. Not possible. */
 452                 error = -E2BIG;
 453         }
 454         kfree(kvalue);
 455         return error;
 456 }
 457
 458 SYSCALL_DEFINE4(getxattr, const char __user *, pathname,
 459                 const char __user *, name, void __user *, value, size_t, size)
 460 {
 461         struct path path;
 462         ssize_t error;
 463
 464         error = user_path(pathname, &path);
 465         if (error)
 466                 return error;
 467         error = getxattr(path.dentry, name, value, size);
 468         path_put(&path);
 469         return error;
 470 }
 471
 472 SYSCALL_DEFINE4(lgetxattr, const char __user *, pathname,
 473                 const char __user *, name, void __user *, value, size_t, size)
 474 {
 475         struct path path;
 476         ssize_t error;
 477
 478         error = user_lpath(pathname, &path);
 479         if (error)
 480                 return error;
 481         error = getxattr(path.dentry, name, value, size);
 482         path_put(&path);
 483         return error;
 484 }
 485
 486 SYSCALL_DEFINE4(fgetxattr, int, fd, const char __user *, name,
 487                 void __user *, value, size_t, size)
 488 {
 489         struct file *f;
 490         ssize_t error = -EBADF;
 491
 492         f = fget(fd);
 493         if (!f)
 494                 return error;
 495         audit_inode(NULL, f->f_path.dentry);
 496         error = getxattr(f->f_path.dentry, name, value, size);
 497         fput(f);
 498         return error;
 499 }
 500
 501 /*
 502  * Extended attribute LIST operations
 503  */
 504 static ssize_t
 505 listxattr(struct dentry *d, char __user *list, size_t size)
 506 {
 507         ssize_t error;
 508         char *klist = NULL;
 509         char *vlist = NULL;     /* If non-NULL, we used vmalloc() */
 510
 511         if (size) {
 512                 if (size > XATTR_LIST_MAX)
 513                         size = XATTR_LIST_MAX;
 514                 klist = kmalloc(size, __GFP_NOWARN | GFP_KERNEL);
 515                 if (!klist) {
 516                         vlist = vmalloc(size);
 517                         if (!vlist)
 518                                 return -ENOMEM;
 519                         klist = vlist;
 520                 }
 521         }
 522
 523         error = vfs_listxattr(d, klist, size);
 524         if (error > 0) {
 525                 if (size && copy_to_user(list, klist, error))
 526                         error = -EFAULT;
 527         } else if (error == -ERANGE && size >= XATTR_LIST_MAX) {
 528                 /* The file system tried to returned a list bigger
 529                    than XATTR_LIST_MAX bytes. Not possible. */
 530                 error = -E2BIG;
 531         }
 532         if (vlist)
 533                 vfree(vlist);
 534         else
 535                 kfree(klist);
 536         return error;
 537 }
 538
 539 SYSCALL_DEFINE3(listxattr, const char __user *, pathname, char __user *, list,
 540                 size_t, size)
 541 {
 542         struct path path;
 543         ssize_t error;
 544
 545         error = user_path(pathname, &path);
 546         if (error)
 547                 return error;
 548         error = listxattr(path.dentry, list, size);
 549         path_put(&path);
 550         return error;
 551 }
 552
 553 SYSCALL_DEFINE3(llistxattr, const char __user *, pathname, char __user *, list,
 554                 size_t, size)
 555 {
 556         struct path path;
 557         ssize_t error;
 558
 559         error = user_lpath(pathname, &path);
 560         if (error)
 561                 return error;
 562         error = listxattr(path.dentry, list, size);
 563         path_put(&path);
 564         return error;
 565 }
 566
 567 SYSCALL_DEFINE3(flistxattr, int, fd, char __user *, list, size_t, size)
 568 {
 569         struct file *f;
 570         ssize_t error = -EBADF;
 571
 572         f = fget(fd);
 573         if (!f)
 574                 return error;
 575         audit_inode(NULL, f->f_path.dentry);
 576         error = listxattr(f->f_path.dentry, list, size);
 577         fput(f);
 578         return error;
 579 }
 580
 581 /*
 582  * Extended attribute REMOVE operations
 583  */
 584 static long
 585 removexattr(struct dentry *d, const char __user *name)
 586 {
 587         int error;
 588         char kname[XATTR_NAME_MAX + 1];
 589
 590         error = strncpy_from_user(kname, name, sizeof(kname));
 591         if (error == 0 || error == sizeof(kname))
 592                 error = -ERANGE;
 593         if (error < 0)
 594                 return error;
 595
 596         return vfs_removexattr(d, kname);
 597 }
 598
 599 SYSCALL_DEFINE2(removexattr, const char __user *, pathname,
 600                 const char __user *, name)
 601 {
 602         struct path path;
 603         int error;
 604
 605         error = user_path(pathname, &path);
 606         if (error)
 607                 return error;
 608         error = mnt_want_write(path.mnt);
 609         if (!error) {
 610                 error = removexattr(path.dentry, name);
 611                 mnt_drop_write(path.mnt);
 612         }
 613         path_put(&path);
 614         return error;
 615 }
 616
 617 SYSCALL_DEFINE2(lremovexattr, const char __user *, pathname,
 618                 const char __user *, name)
 619 {
 620         struct path path;
 621         int error;
 622
 623         error = user_lpath(pathname, &path);
 624         if (error)
 625                 return error;
 626         error = mnt_want_write(path.mnt);
 627         if (!error) {
 628                 error = removexattr(path.dentry, name);
 629                 mnt_drop_write(path.mnt);
 630         }
 631         path_put(&path);
 632         return error;
 633 }
 634
 635 SYSCALL_DEFINE2(fremovexattr, int, fd, const char __user *, name)
 636 {
 637         struct file *f;
 638         struct dentry *dentry;
 639         int error = -EBADF;
 640
 641         f = fget(fd);
 642         if (!f)
 643                 return error;
 644         dentry = f->f_path.dentry;
 645         audit_inode(NULL, dentry);
 646         error = mnt_want_write_file(f);
 647         if (!error) {
 648                 error = removexattr(dentry, name);
 649                 mnt_drop_write_file(f);
 650         }
 651         fput(f);
 652         return error;
 653 }
 654
 655
 656 static const char *
 657 strcmp_prefix(const char *a, const char *a_prefix)
 658 {
 659         while (*a_prefix && *a == *a_prefix) {
 660                 a++;
 661                 a_prefix++;
 662         }
 663         return *a_prefix ? NULL : a;
 664 }
 665
 666 /*
 667  * In order to implement different sets of xattr operations for each xattr
 668  * prefix with the generic xattr API, a filesystem should create a
 669  * null-terminated array of struct xattr_handler (one for each prefix) and
 670  * hang a pointer to it off of the s_xattr field of the superblock.
 671  *
 672  * The generic_fooxattr() functions will use this list to dispatch xattr
 673  * operations to the correct xattr_handler.
 674  */
 675 #define for_each_xattr_handler(handlers, handler)               \
 676                 for ((handler) = *(handlers)++;                 \
 677                         (handler) != NULL;                      \
 678                         (handler) = *(handlers)++)
 679
 680 /*
 681  * Find the xattr_handler with the matching prefix.
 682  */
 683 static const struct xattr_handler *
 684 xattr_resolve_name(const struct xattr_handler **handlers, const char **name)
 685 {
 686         const struct xattr_handler *handler;
 687
 688         if (!*name)
 689                 return NULL;
 690
 691         for_each_xattr_handler(handlers, handler) {
 692                 const char *n = strcmp_prefix(*name, handler->prefix);
 693                 if (n) {
 694                         *name = n;
 695                         break;
 696                 }
 697         }
 698         return handler;
 699 }
 700
 701 /*
 702  * Find the handler for the prefix and dispatch its get() operation.
 703  */
 704 ssize_t
 705 generic_getxattr(struct dentry *dentry, const char *name, void *buffer, size_t size)
 706 {
 707         const struct xattr_handler *handler;
 708
 709         handler = xattr_resolve_name(dentry->d_sb->s_xattr, &name);
 710         if (!handler)
 711                 return -EOPNOTSUPP;
 712         return handler->get(dentry, name, buffer, size, handler->flags);
 713 }
 714
 715 /*
 716  * Combine the results of the list() operation from every xattr_handler in the
 717  * list.
 718  */
 719 ssize_t
 720 generic_listxattr(struct dentry *dentry, char *buffer, size_t buffer_size)
 721 {
 722         const struct xattr_handler *handler, **handlers = dentry->d_sb->s_xattr;
 723         unsigned int size = 0;
 724
 725         if (!buffer) {
 726                 for_each_xattr_handler(handlers, handler) {
 727                         size += handler->list(dentry, NULL, 0, NULL, 0,
 728                                               handler->flags);
 729                 }
 730         } else {
 731                 char *buf = buffer;
 732
 733                 for_each_xattr_handler(handlers, handler) {
 734                         size = handler->list(dentry, buf, buffer_size,
 735                                              NULL, 0, handler->flags);
 736                         if (size > buffer_size)
 737                                 return -ERANGE;
 738                         buf += size;
 739                         buffer_size -= size;
 740                 }
 741                 size = buf - buffer;
 742         }
 743         return size;
 744 }
 745
 746 /*
 747  * Find the handler for the prefix and dispatch its set() operation.
 748  */
 749 int
 750 generic_setxattr(struct dentry *dentry, const char *name, const void *value, size_t size, int flags)
 751 {
 752         const struct xattr_handler *handler;
 753
 754         if (size == 0)
 755                 value = "";  /* empty EA, do not remove */
 756         handler = xattr_resolve_name(dentry->d_sb->s_xattr, &name);
 757         if (!handler)
 758                 return -EOPNOTSUPP;
 759         return handler->set(dentry, name, value, size, flags, handler->flags);
 760 }
 761
 762 /*
 763  * Find the handler for the prefix and dispatch its set() operation to remove
 764  * any associated extended attribute.
 765  */
 766 int
 767 generic_removexattr(struct dentry *dentry, const char *name)
 768 {
 769         const struct xattr_handler *handler;
 770
 771         handler = xattr_resolve_name(dentry->d_sb->s_xattr, &name);
 772         if (!handler)
 773                 return -EOPNOTSUPP;
 774         return handler->set(dentry, name, NULL, 0,
 775                             XATTR_REPLACE, handler->flags);
 776 }
 777
 778 EXPORT_SYMBOL(generic_getxattr);
 779 EXPORT_SYMBOL(generic_listxattr);
 780 EXPORT_SYMBOL(generic_setxattr);
 781 EXPORT_SYMBOL(generic_removexattr);