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 permission(inode, mask, NULL);
  67 }
  68
  69 int
  70 vfs_setxattr(struct dentry *dentry, char *name, 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, 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, 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, char __user *name, 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 asmlinkage long
 255 sys_setxattr(char __user *path, char __user *name, void __user *value,
 256              size_t size, int flags)
 257 {
 258         struct nameidata nd;
 259         int error;
 260
 261         error = user_path_walk(path, &nd);
 262         if (error)
 263                 return error;
 264         error = mnt_want_write(nd.path.mnt);
 265         if (!error) {
 266                 error = setxattr(nd.path.dentry, name, value, size, flags);
 267                 mnt_drop_write(nd.path.mnt);
 268         }
 269         path_put(&nd.path);
 270         return error;
 271 }
 272
 273 asmlinkage long
 274 sys_lsetxattr(char __user *path, char __user *name, void __user *value,
 275               size_t size, int flags)
 276 {
 277         struct nameidata nd;
 278         int error;
 279
 280         error = user_path_walk_link(path, &nd);
 281         if (error)
 282                 return error;
 283         error = mnt_want_write(nd.path.mnt);
 284         if (!error) {
 285                 error = setxattr(nd.path.dentry, name, value, size, flags);
 286                 mnt_drop_write(nd.path.mnt);
 287         }
 288         path_put(&nd.path);
 289         return error;
 290 }
 291
 292 asmlinkage long
 293 sys_fsetxattr(int fd, char __user *name, void __user *value,
 294               size_t size, int flags)
 295 {
 296         struct file *f;
 297         struct dentry *dentry;
 298         int error = -EBADF;
 299
 300         f = fget(fd);
 301         if (!f)
 302                 return error;
 303         dentry = f->f_path.dentry;
 304         audit_inode(NULL, dentry);
 305         error = mnt_want_write(f->f_path.mnt);
 306         if (!error) {
 307                 error = setxattr(dentry, name, value, size, flags);
 308                 mnt_drop_write(f->f_path.mnt);
 309         }
 310         fput(f);
 311         return error;
 312 }
 313
 314 /*
 315  * Extended attribute GET operations
 316  */
 317 static ssize_t
 318 getxattr(struct dentry *d, char __user *name, void __user *value, 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 asmlinkage ssize_t
 352 sys_getxattr(char __user *path, char __user *name, void __user *value,
 353              size_t size)
 354 {
 355         struct nameidata nd;
 356         ssize_t error;
 357
 358         error = user_path_walk(path, &nd);
 359         if (error)
 360                 return error;
 361         error = getxattr(nd.path.dentry, name, value, size);
 362         path_put(&nd.path);
 363         return error;
 364 }
 365
 366 asmlinkage ssize_t
 367 sys_lgetxattr(char __user *path, char __user *name, void __user *value,
 368               size_t size)
 369 {
 370         struct nameidata nd;
 371         ssize_t error;
 372
 373         error = user_path_walk_link(path, &nd);
 374         if (error)
 375                 return error;
 376         error = getxattr(nd.path.dentry, name, value, size);
 377         path_put(&nd.path);
 378         return error;
 379 }
 380
 381 asmlinkage ssize_t
 382 sys_fgetxattr(int fd, char __user *name, void __user *value, size_t size)
 383 {
 384         struct file *f;
 385         ssize_t error = -EBADF;
 386
 387         f = fget(fd);
 388         if (!f)
 389                 return error;
 390         audit_inode(NULL, f->f_path.dentry);
 391         error = getxattr(f->f_path.dentry, name, value, size);
 392         fput(f);
 393         return error;
 394 }
 395
 396 /*
 397  * Extended attribute LIST operations
 398  */
 399 static ssize_t
 400 listxattr(struct dentry *d, char __user *list, size_t size)
 401 {
 402         ssize_t error;
 403         char *klist = NULL;
 404
 405         if (size) {
 406                 if (size > XATTR_LIST_MAX)
 407                         size = XATTR_LIST_MAX;
 408                 klist = kmalloc(size, GFP_KERNEL);
 409                 if (!klist)
 410                         return -ENOMEM;
 411         }
 412
 413         error = vfs_listxattr(d, klist, size);
 414         if (error > 0) {
 415                 if (size && copy_to_user(list, klist, error))
 416                         error = -EFAULT;
 417         } else if (error == -ERANGE && size >= XATTR_LIST_MAX) {
 418                 /* The file system tried to returned a list bigger
 419                    than XATTR_LIST_MAX bytes. Not possible. */
 420                 error = -E2BIG;
 421         }
 422         kfree(klist);
 423         return error;
 424 }
 425
 426 asmlinkage ssize_t
 427 sys_listxattr(char __user *path, char __user *list, size_t size)
 428 {
 429         struct nameidata nd;
 430         ssize_t error;
 431
 432         error = user_path_walk(path, &nd);
 433         if (error)
 434                 return error;
 435         error = listxattr(nd.path.dentry, list, size);
 436         path_put(&nd.path);
 437         return error;
 438 }
 439
 440 asmlinkage ssize_t
 441 sys_llistxattr(char __user *path, char __user *list, size_t size)
 442 {
 443         struct nameidata nd;
 444         ssize_t error;
 445
 446         error = user_path_walk_link(path, &nd);
 447         if (error)
 448                 return error;
 449         error = listxattr(nd.path.dentry, list, size);
 450         path_put(&nd.path);
 451         return error;
 452 }
 453
 454 asmlinkage ssize_t
 455 sys_flistxattr(int fd, char __user *list, size_t size)
 456 {
 457         struct file *f;
 458         ssize_t error = -EBADF;
 459
 460         f = fget(fd);
 461         if (!f)
 462                 return error;
 463         audit_inode(NULL, f->f_path.dentry);
 464         error = listxattr(f->f_path.dentry, list, size);
 465         fput(f);
 466         return error;
 467 }
 468
 469 /*
 470  * Extended attribute REMOVE operations
 471  */
 472 static long
 473 removexattr(struct dentry *d, char __user *name)
 474 {
 475         int error;
 476         char kname[XATTR_NAME_MAX + 1];
 477
 478         error = strncpy_from_user(kname, name, sizeof(kname));
 479         if (error == 0 || error == sizeof(kname))
 480                 error = -ERANGE;
 481         if (error < 0)
 482                 return error;
 483
 484         return vfs_removexattr(d, kname);
 485 }
 486
 487 asmlinkage long
 488 sys_removexattr(char __user *path, char __user *name)
 489 {
 490         struct nameidata nd;
 491         int error;
 492
 493         error = user_path_walk(path, &nd);
 494         if (error)
 495                 return error;
 496         error = mnt_want_write(nd.path.mnt);
 497         if (!error) {
 498                 error = removexattr(nd.path.dentry, name);
 499                 mnt_drop_write(nd.path.mnt);
 500         }
 501         path_put(&nd.path);
 502         return error;
 503 }
 504
 505 asmlinkage long
 506 sys_lremovexattr(char __user *path, char __user *name)
 507 {
 508         struct nameidata nd;
 509         int error;
 510
 511         error = user_path_walk_link(path, &nd);
 512         if (error)
 513                 return error;
 514         error = mnt_want_write(nd.path.mnt);
 515         if (!error) {
 516                 error = removexattr(nd.path.dentry, name);
 517                 mnt_drop_write(nd.path.mnt);
 518         }
 519         path_put(&nd.path);
 520         return error;
 521 }
 522
 523 asmlinkage long
 524 sys_fremovexattr(int fd, char __user *name)
 525 {
 526         struct file *f;
 527         struct dentry *dentry;
 528         int error = -EBADF;
 529
 530         f = fget(fd);
 531         if (!f)
 532                 return error;
 533         dentry = f->f_path.dentry;
 534         audit_inode(NULL, dentry);
 535         error = mnt_want_write(f->f_path.mnt);
 536         if (!error) {
 537                 error = removexattr(dentry, name);
 538                 mnt_drop_write(f->f_path.mnt);
 539         }
 540         fput(f);
 541         return error;
 542 }
 543
 544
 545 static const char *
 546 strcmp_prefix(const char *a, const char *a_prefix)
 547 {
 548         while (*a_prefix && *a == *a_prefix) {
 549                 a++;
 550                 a_prefix++;
 551         }
 552         return *a_prefix ? NULL : a;
 553 }
 554
 555 /*
 556  * In order to implement different sets of xattr operations for each xattr
 557  * prefix with the generic xattr API, a filesystem should create a
 558  * null-terminated array of struct xattr_handler (one for each prefix) and
 559  * hang a pointer to it off of the s_xattr field of the superblock.
 560  *
 561  * The generic_fooxattr() functions will use this list to dispatch xattr
 562  * operations to the correct xattr_handler.
 563  */
 564 #define for_each_xattr_handler(handlers, handler)               \
 565                 for ((handler) = *(handlers)++;                 \
 566                         (handler) != NULL;                      \
 567                         (handler) = *(handlers)++)
 568
 569 /*
 570  * Find the xattr_handler with the matching prefix.
 571  */
 572 static struct xattr_handler *
 573 xattr_resolve_name(struct xattr_handler **handlers, const char **name)
 574 {
 575         struct xattr_handler *handler;
 576
 577         if (!*name)
 578                 return NULL;
 579
 580         for_each_xattr_handler(handlers, handler) {
 581                 const char *n = strcmp_prefix(*name, handler->prefix);
 582                 if (n) {
 583                         *name = n;
 584                         break;
 585                 }
 586         }
 587         return handler;
 588 }
 589
 590 /*
 591  * Find the handler for the prefix and dispatch its get() operation.
 592  */
 593 ssize_t
 594 generic_getxattr(struct dentry *dentry, const char *name, void *buffer, size_t size)
 595 {
 596         struct xattr_handler *handler;
 597         struct inode *inode = dentry->d_inode;
 598
 599         handler = xattr_resolve_name(inode->i_sb->s_xattr, &name);
 600         if (!handler)
 601                 return -EOPNOTSUPP;
 602         return handler->get(inode, name, buffer, size);
 603 }
 604
 605 /*
 606  * Combine the results of the list() operation from every xattr_handler in the
 607  * list.
 608  */
 609 ssize_t
 610 generic_listxattr(struct dentry *dentry, char *buffer, size_t buffer_size)
 611 {
 612         struct inode *inode = dentry->d_inode;
 613         struct xattr_handler *handler, **handlers = inode->i_sb->s_xattr;
 614         unsigned int size = 0;
 615
 616         if (!buffer) {
 617                 for_each_xattr_handler(handlers, handler)
 618                         size += handler->list(inode, NULL, 0, NULL, 0);
 619         } else {
 620                 char *buf = buffer;
 621
 622                 for_each_xattr_handler(handlers, handler) {
 623                         size = handler->list(inode, buf, buffer_size, NULL, 0);
 624                         if (size > buffer_size)
 625                                 return -ERANGE;
 626                         buf += size;
 627                         buffer_size -= size;
 628                 }
 629                 size = buf - buffer;
 630         }
 631         return size;
 632 }
 633
 634 /*
 635  * Find the handler for the prefix and dispatch its set() operation.
 636  */
 637 int
 638 generic_setxattr(struct dentry *dentry, const char *name, const void *value, size_t size, int flags)
 639 {
 640         struct xattr_handler *handler;
 641         struct inode *inode = dentry->d_inode;
 642
 643         if (size == 0)
 644                 value = "";  /* empty EA, do not remove */
 645         handler = xattr_resolve_name(inode->i_sb->s_xattr, &name);
 646         if (!handler)
 647                 return -EOPNOTSUPP;
 648         return handler->set(inode, name, value, size, flags);
 649 }
 650
 651 /*
 652  * Find the handler for the prefix and dispatch its set() operation to remove
 653  * any associated extended attribute.
 654  */
 655 int
 656 generic_removexattr(struct dentry *dentry, const char *name)
 657 {
 658         struct xattr_handler *handler;
 659         struct inode *inode = dentry->d_inode;
 660
 661         handler = xattr_resolve_name(inode->i_sb->s_xattr, &name);
 662         if (!handler)
 663                 return -EOPNOTSUPP;
 664         return handler->set(inode, name, NULL, 0, XATTR_REPLACE);
 665 }
 666
 667 EXPORT_SYMBOL(generic_getxattr);
 668 EXPORT_SYMBOL(generic_listxattr);
 669 EXPORT_SYMBOL(generic_setxattr);
 670 EXPORT_SYMBOL(generic_removexattr);