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