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