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