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