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 inode_permission(inode, mask);
  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->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 = memdup_user(value, size);
 241                 if (IS_ERR(kvalue))
 242                         return PTR_ERR(kvalue);
 243         }
 244
 245         error = vfs_setxattr(d, kname, kvalue, size, flags);
 246         kfree(kvalue);
 247         return error;
 248 }
 249
 250 SYSCALL_DEFINE5(setxattr, const char __user *, pathname,
 251                 const char __user *, name, const void __user *, value,
 252                 size_t, size, int, flags)
 253 {
 254         struct path path;
 255         int error;
 256
 257         error = user_path(pathname, &path);
 258         if (error)
 259                 return error;
 260         error = mnt_want_write(path.mnt);
 261         if (!error) {
 262                 error = setxattr(path.dentry, name, value, size, flags);
 263                 mnt_drop_write(path.mnt);
 264         }
 265         path_put(&path);
 266         return error;
 267 }
 268
 269 SYSCALL_DEFINE5(lsetxattr, const char __user *, pathname,
 270                 const char __user *, name, const void __user *, value,
 271                 size_t, size, int, flags)
 272 {
 273         struct path path;
 274         int error;
 275
 276         error = user_lpath(pathname, &path);
 277         if (error)
 278                 return error;
 279         error = mnt_want_write(path.mnt);
 280         if (!error) {
 281                 error = setxattr(path.dentry, name, value, size, flags);
 282                 mnt_drop_write(path.mnt);
 283         }
 284         path_put(&path);
 285         return error;
 286 }
 287
 288 SYSCALL_DEFINE5(fsetxattr, int, fd, const char __user *, name,
 289                 const void __user *,value, size_t, size, int, flags)
 290 {
 291         struct file *f;
 292         struct dentry *dentry;
 293         int error = -EBADF;
 294
 295         f = fget(fd);
 296         if (!f)
 297                 return error;
 298         dentry = f->f_path.dentry;
 299         audit_inode(NULL, dentry);
 300         error = mnt_want_write_file(f);
 301         if (!error) {
 302                 error = setxattr(dentry, name, value, size, flags);
 303                 mnt_drop_write(f->f_path.mnt);
 304         }
 305         fput(f);
 306         return error;
 307 }
 308
 309 /*
 310  * Extended attribute GET operations
 311  */
 312 static ssize_t
 313 getxattr(struct dentry *d, const char __user *name, void __user *value,
 314          size_t size)
 315 {
 316         ssize_t error;
 317         void *kvalue = NULL;
 318         char kname[XATTR_NAME_MAX + 1];
 319
 320         error = strncpy_from_user(kname, name, sizeof(kname));
 321         if (error == 0 || error == sizeof(kname))
 322                 error = -ERANGE;
 323         if (error < 0)
 324                 return error;
 325
 326         if (size) {
 327                 if (size > XATTR_SIZE_MAX)
 328                         size = XATTR_SIZE_MAX;
 329                 kvalue = kzalloc(size, GFP_KERNEL);
 330                 if (!kvalue)
 331                         return -ENOMEM;
 332         }
 333
 334         error = vfs_getxattr(d, kname, kvalue, size);
 335         if (error > 0) {
 336                 if (size && copy_to_user(value, kvalue, error))
 337                         error = -EFAULT;
 338         } else if (error == -ERANGE && size >= XATTR_SIZE_MAX) {
 339                 /* The file system tried to returned a value bigger
 340                    than XATTR_SIZE_MAX bytes. Not possible. */
 341                 error = -E2BIG;
 342         }
 343         kfree(kvalue);
 344         return error;
 345 }
 346
 347 SYSCALL_DEFINE4(getxattr, const char __user *, pathname,
 348                 const char __user *, name, void __user *, value, size_t, size)
 349 {
 350         struct path path;
 351         ssize_t error;
 352
 353         error = user_path(pathname, &path);
 354         if (error)
 355                 return error;
 356         error = getxattr(path.dentry, name, value, size);
 357         path_put(&path);
 358         return error;
 359 }
 360
 361 SYSCALL_DEFINE4(lgetxattr, const char __user *, pathname,
 362                 const char __user *, name, void __user *, value, size_t, size)
 363 {
 364         struct path path;
 365         ssize_t error;
 366
 367         error = user_lpath(pathname, &path);
 368         if (error)
 369                 return error;
 370         error = getxattr(path.dentry, name, value, size);
 371         path_put(&path);
 372         return error;
 373 }
 374
 375 SYSCALL_DEFINE4(fgetxattr, int, fd, const char __user *, name,
 376                 void __user *, value, size_t, size)
 377 {
 378         struct file *f;
 379         ssize_t error = -EBADF;
 380
 381         f = fget(fd);
 382         if (!f)
 383                 return error;
 384         audit_inode(NULL, f->f_path.dentry);
 385         error = getxattr(f->f_path.dentry, name, value, size);
 386         fput(f);
 387         return error;
 388 }
 389
 390 /*
 391  * Extended attribute LIST operations
 392  */
 393 static ssize_t
 394 listxattr(struct dentry *d, char __user *list, size_t size)
 395 {
 396         ssize_t error;
 397         char *klist = NULL;
 398
 399         if (size) {
 400                 if (size > XATTR_LIST_MAX)
 401                         size = XATTR_LIST_MAX;
 402                 klist = kmalloc(size, GFP_KERNEL);
 403                 if (!klist)
 404                         return -ENOMEM;
 405         }
 406
 407         error = vfs_listxattr(d, klist, size);
 408         if (error > 0) {
 409                 if (size && copy_to_user(list, klist, error))
 410                         error = -EFAULT;
 411         } else if (error == -ERANGE && size >= XATTR_LIST_MAX) {
 412                 /* The file system tried to returned a list bigger
 413                    than XATTR_LIST_MAX bytes. Not possible. */
 414                 error = -E2BIG;
 415         }
 416         kfree(klist);
 417         return error;
 418 }
 419
 420 SYSCALL_DEFINE3(listxattr, const char __user *, pathname, char __user *, list,
 421                 size_t, size)
 422 {
 423         struct path path;
 424         ssize_t error;
 425
 426         error = user_path(pathname, &path);
 427         if (error)
 428                 return error;
 429         error = listxattr(path.dentry, list, size);
 430         path_put(&path);
 431         return error;
 432 }
 433
 434 SYSCALL_DEFINE3(llistxattr, const char __user *, pathname, char __user *, list,
 435                 size_t, size)
 436 {
 437         struct path path;
 438         ssize_t error;
 439
 440         error = user_lpath(pathname, &path);
 441         if (error)
 442                 return error;
 443         error = listxattr(path.dentry, list, size);
 444         path_put(&path);
 445         return error;
 446 }
 447
 448 SYSCALL_DEFINE3(flistxattr, int, fd, char __user *, list, size_t, size)
 449 {
 450         struct file *f;
 451         ssize_t error = -EBADF;
 452
 453         f = fget(fd);
 454         if (!f)
 455                 return error;
 456         audit_inode(NULL, f->f_path.dentry);
 457         error = listxattr(f->f_path.dentry, list, size);
 458         fput(f);
 459         return error;
 460 }
 461
 462 /*
 463  * Extended attribute REMOVE operations
 464  */
 465 static long
 466 removexattr(struct dentry *d, const char __user *name)
 467 {
 468         int error;
 469         char kname[XATTR_NAME_MAX + 1];
 470
 471         error = strncpy_from_user(kname, name, sizeof(kname));
 472         if (error == 0 || error == sizeof(kname))
 473                 error = -ERANGE;
 474         if (error < 0)
 475                 return error;
 476
 477         return vfs_removexattr(d, kname);
 478 }
 479
 480 SYSCALL_DEFINE2(removexattr, const char __user *, pathname,
 481                 const char __user *, name)
 482 {
 483         struct path path;
 484         int error;
 485
 486         error = user_path(pathname, &path);
 487         if (error)
 488                 return error;
 489         error = mnt_want_write(path.mnt);
 490         if (!error) {
 491                 error = removexattr(path.dentry, name);
 492                 mnt_drop_write(path.mnt);
 493         }
 494         path_put(&path);
 495         return error;
 496 }
 497
 498 SYSCALL_DEFINE2(lremovexattr, const char __user *, pathname,
 499                 const char __user *, name)
 500 {
 501         struct path path;
 502         int error;
 503
 504         error = user_lpath(pathname, &path);
 505         if (error)
 506                 return error;
 507         error = mnt_want_write(path.mnt);
 508         if (!error) {
 509                 error = removexattr(path.dentry, name);
 510                 mnt_drop_write(path.mnt);
 511         }
 512         path_put(&path);
 513         return error;
 514 }
 515
 516 SYSCALL_DEFINE2(fremovexattr, int, fd, const char __user *, name)
 517 {
 518         struct file *f;
 519         struct dentry *dentry;
 520         int error = -EBADF;
 521
 522         f = fget(fd);
 523         if (!f)
 524                 return error;
 525         dentry = f->f_path.dentry;
 526         audit_inode(NULL, dentry);
 527         error = mnt_want_write_file(f);
 528         if (!error) {
 529                 error = removexattr(dentry, name);
 530                 mnt_drop_write(f->f_path.mnt);
 531         }
 532         fput(f);
 533         return error;
 534 }
 535
 536
 537 static const char *
 538 strcmp_prefix(const char *a, const char *a_prefix)
 539 {
 540         while (*a_prefix && *a == *a_prefix) {
 541                 a++;
 542                 a_prefix++;
 543         }
 544         return *a_prefix ? NULL : a;
 545 }
 546
 547 /*
 548  * In order to implement different sets of xattr operations for each xattr
 549  * prefix with the generic xattr API, a filesystem should create a
 550  * null-terminated array of struct xattr_handler (one for each prefix) and
 551  * hang a pointer to it off of the s_xattr field of the superblock.
 552  *
 553  * The generic_fooxattr() functions will use this list to dispatch xattr
 554  * operations to the correct xattr_handler.
 555  */
 556 #define for_each_xattr_handler(handlers, handler)               \
 557                 for ((handler) = *(handlers)++;                 \
 558                         (handler) != NULL;                      \
 559                         (handler) = *(handlers)++)
 560
 561 /*
 562  * Find the xattr_handler with the matching prefix.
 563  */
 564 static struct xattr_handler *
 565 xattr_resolve_name(struct xattr_handler **handlers, const char **name)
 566 {
 567         struct xattr_handler *handler;
 568
 569         if (!*name)
 570                 return NULL;
 571
 572         for_each_xattr_handler(handlers, handler) {
 573                 const char *n = strcmp_prefix(*name, handler->prefix);
 574                 if (n) {
 575                         *name = n;
 576                         break;
 577                 }
 578         }
 579         return handler;
 580 }
 581
 582 /*
 583  * Find the handler for the prefix and dispatch its get() operation.
 584  */
 585 ssize_t
 586 generic_getxattr(struct dentry *dentry, const char *name, void *buffer, size_t size)
 587 {
 588         struct xattr_handler *handler;
 589         struct inode *inode = dentry->d_inode;
 590
 591         handler = xattr_resolve_name(inode->i_sb->s_xattr, &name);
 592         if (!handler)
 593                 return -EOPNOTSUPP;
 594         return handler->get(inode, name, buffer, size);
 595 }
 596
 597 /*
 598  * Combine the results of the list() operation from every xattr_handler in the
 599  * list.
 600  */
 601 ssize_t
 602 generic_listxattr(struct dentry *dentry, char *buffer, size_t buffer_size)
 603 {
 604         struct inode *inode = dentry->d_inode;
 605         struct xattr_handler *handler, **handlers = inode->i_sb->s_xattr;
 606         unsigned int size = 0;
 607
 608         if (!buffer) {
 609                 for_each_xattr_handler(handlers, handler)
 610                         size += handler->list(inode, NULL, 0, NULL, 0);
 611         } else {
 612                 char *buf = buffer;
 613
 614                 for_each_xattr_handler(handlers, handler) {
 615                         size = handler->list(inode, buf, buffer_size, NULL, 0);
 616                         if (size > buffer_size)
 617                                 return -ERANGE;
 618                         buf += size;
 619                         buffer_size -= size;
 620                 }
 621                 size = buf - buffer;
 622         }
 623         return size;
 624 }
 625
 626 /*
 627  * Find the handler for the prefix and dispatch its set() operation.
 628  */
 629 int
 630 generic_setxattr(struct dentry *dentry, const char *name, const void *value, size_t size, int flags)
 631 {
 632         struct xattr_handler *handler;
 633         struct inode *inode = dentry->d_inode;
 634
 635         if (size == 0)
 636                 value = "";  /* empty EA, do not remove */
 637         handler = xattr_resolve_name(inode->i_sb->s_xattr, &name);
 638         if (!handler)
 639                 return -EOPNOTSUPP;
 640         return handler->set(inode, name, value, size, flags);
 641 }
 642
 643 /*
 644  * Find the handler for the prefix and dispatch its set() operation to remove
 645  * any associated extended attribute.
 646  */
 647 int
 648 generic_removexattr(struct dentry *dentry, const char *name)
 649 {
 650         struct xattr_handler *handler;
 651         struct inode *inode = dentry->d_inode;
 652
 653         handler = xattr_resolve_name(inode->i_sb->s_xattr, &name);
 654         if (!handler)
 655                 return -EOPNOTSUPP;
 656         return handler->set(inode, name, NULL, 0, XATTR_REPLACE);
 657 }
 658
 659 EXPORT_SYMBOL(generic_getxattr);
 660 EXPORT_SYMBOL(generic_listxattr);
 661 EXPORT_SYMBOL(generic_setxattr);
 662 EXPORT_SYMBOL(generic_removexattr);