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