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/evm.h>
  18 #include <linux/syscalls.h>
  19 #include <linux/export.h>
  20 #include <linux/fsnotify.h>
  21 #include <linux/audit.h>
  22 #include <linux/vmalloc.h>
  23 #include <linux/posix_acl_xattr.h>
  24
  25 #include <asm/uaccess.h>
  26
  27 /*
  28  * Check permissions for extended attribute access.  This is a bit complicated
  29  * because different namespaces have very different rules.
  30  */
  31 static int
  32 xattr_permission(struct inode *inode, const char *name, int mask)
  33 {
  34         /*
  35          * We can never set or remove an extended attribute on a read-only
  36          * filesystem  or on an immutable / append-only inode.
  37          */
  38         if (mask & MAY_WRITE) {
  39                 if (IS_IMMUTABLE(inode) || IS_APPEND(inode))
  40                         return -EPERM;
  41         }
  42
  43         /*
  44          * No restriction for security.* and system.* from the VFS.  Decision
  45          * on these is left to the underlying filesystem / security module.
  46          */
  47         if (!strncmp(name, XATTR_SECURITY_PREFIX, XATTR_SECURITY_PREFIX_LEN) ||
  48             !strncmp(name, XATTR_SYSTEM_PREFIX, XATTR_SYSTEM_PREFIX_LEN))
  49                 return 0;
  50
  51         /*
  52          * The trusted.* namespace can only be accessed by privileged users.
  53          */
  54         if (!strncmp(name, XATTR_TRUSTED_PREFIX, XATTR_TRUSTED_PREFIX_LEN)) {
  55                 if (!capable(CAP_SYS_ADMIN))
  56                         return (mask & MAY_WRITE) ? -EPERM : -ENODATA;
  57                 return 0;
  58         }
  59
  60         /*
  61          * In the user.* namespace, only regular files and directories can have
  62          * extended attributes. For sticky directories, only the owner and
  63          * privileged users can write attributes.
  64          */
  65         if (!strncmp(name, XATTR_USER_PREFIX, XATTR_USER_PREFIX_LEN)) {
  66                 if (!S_ISREG(inode->i_mode) && !S_ISDIR(inode->i_mode))
  67                         return (mask & MAY_WRITE) ? -EPERM : -ENODATA;
  68                 if (S_ISDIR(inode->i_mode) && (inode->i_mode & S_ISVTX) &&
  69                     (mask & MAY_WRITE) && !inode_owner_or_capable(inode))
  70                         return -EPERM;
  71         }
  72
  73         return inode_permission(inode, mask);
  74 }
  75
  76 /**
  77  *  __vfs_setxattr_noperm - perform setxattr operation without performing
  78  *  permission checks.
  79  *
  80  *  @dentry - object to perform setxattr on
  81  *  @name - xattr name to set
  82  *  @value - value to set @name to
  83  *  @size - size of @value
  84  *  @flags - flags to pass into filesystem operations
  85  *
  86  *  returns the result of the internal setxattr or setsecurity operations.
  87  *
  88  *  This function requires the caller to lock the inode's i_mutex before it
  89  *  is executed. It also assumes that the caller will make the appropriate
  90  *  permission checks.
  91  */
  92 int __vfs_setxattr_noperm(struct dentry *dentry, const char *name,
  93                 const void *value, size_t size, int flags)
  94 {
  95         struct inode *inode = dentry->d_inode;
  96         int error = -EOPNOTSUPP;
  97         int issec = !strncmp(name, XATTR_SECURITY_PREFIX,
  98                                    XATTR_SECURITY_PREFIX_LEN);
  99
 100         if (issec)
 101                 inode->i_flags &= ~S_NOSEC;
 102         if (inode->i_op->setxattr) {
 103                 error = inode->i_op->setxattr(dentry, name, value, size, flags);
 104                 if (!error) {
 105                         fsnotify_xattr(dentry);
 106                         security_inode_post_setxattr(dentry, name, value,
 107                                                      size, flags);
 108                 }
 109         } else if (issec) {
 110                 const char *suffix = name + XATTR_SECURITY_PREFIX_LEN;
 111                 error = security_inode_setsecurity(inode, suffix, value,
 112                                                    size, flags);
 113                 if (!error)
 114                         fsnotify_xattr(dentry);
 115         }
 116
 117         return error;
 118 }
 119
 120
 121 int
 122 vfs_setxattr(struct dentry *dentry, const char *name, const void *value,
 123                 size_t size, int flags)
 124 {
 125         struct inode *inode = dentry->d_inode;
 126         int error;
 127
 128         error = xattr_permission(inode, name, MAY_WRITE);
 129         if (error)
 130                 return error;
 131
 132         mutex_lock(&inode->i_mutex);
 133         error = security_inode_setxattr(dentry, name, value, size, flags);
 134         if (error)
 135                 goto out;
 136
 137         error = __vfs_setxattr_noperm(dentry, name, value, size, flags);
 138
 139 out:
 140         mutex_unlock(&inode->i_mutex);
 141         return error;
 142 }
 143 EXPORT_SYMBOL_GPL(vfs_setxattr);
 144
 145 ssize_t
 146 xattr_getsecurity(struct inode *inode, const char *name, void *value,
 147                         size_t size)
 148 {
 149         void *buffer = NULL;
 150         ssize_t len;
 151
 152         if (!value || !size) {
 153                 len = security_inode_getsecurity(inode, name, &buffer, false);
 154                 goto out_noalloc;
 155         }
 156
 157         len = security_inode_getsecurity(inode, name, &buffer, true);
 158         if (len < 0)
 159                 return len;
 160         if (size < len) {
 161                 len = -ERANGE;
 162                 goto out;
 163         }
 164         memcpy(value, buffer, len);
 165 out:
 166         kfree(buffer);
 167 out_noalloc:
 168         return len;
 169 }
 170 EXPORT_SYMBOL_GPL(xattr_getsecurity);
 171
 172 /*
 173  * vfs_getxattr_alloc - allocate memory, if necessary, before calling getxattr
 174  *
 175  * Allocate memory, if not already allocated, or re-allocate correct size,
 176  * before retrieving the extended attribute.
 177  *
 178  * Returns the result of alloc, if failed, or the getxattr operation.
 179  */
 180 ssize_t
 181 vfs_getxattr_alloc(struct dentry *dentry, const char *name, char **xattr_value,
 182                    size_t xattr_size, gfp_t flags)
 183 {
 184         struct inode *inode = dentry->d_inode;
 185         char *value = *xattr_value;
 186         int error;
 187
 188         error = xattr_permission(inode, name, MAY_READ);
 189         if (error)
 190                 return error;
 191
 192         if (!inode->i_op->getxattr)
 193                 return -EOPNOTSUPP;
 194
 195         error = inode->i_op->getxattr(dentry, name, NULL, 0);
 196         if (error < 0)
 197                 return error;
 198
 199         if (!value || (error > xattr_size)) {
 200                 value = krealloc(*xattr_value, error + 1, flags);
 201                 if (!value)
 202                         return -ENOMEM;
 203                 memset(value, 0, error + 1);
 204         }
 205
 206         error = inode->i_op->getxattr(dentry, name, value, error);
 207         *xattr_value = value;
 208         return error;
 209 }
 210
 211 /* Compare an extended attribute value with the given value */
 212 int vfs_xattr_cmp(struct dentry *dentry, const char *xattr_name,
 213                   const char *value, size_t size, gfp_t flags)
 214 {
 215         char *xattr_value = NULL;
 216         int rc;
 217
 218         rc = vfs_getxattr_alloc(dentry, xattr_name, &xattr_value, 0, flags);
 219         if (rc < 0)
 220                 return rc;
 221
 222         if ((rc != size) || (memcmp(xattr_value, value, rc) != 0))
 223                 rc = -EINVAL;
 224         else
 225                 rc = 0;
 226         kfree(xattr_value);
 227         return rc;
 228 }
 229
 230 ssize_t
 231 vfs_getxattr(struct dentry *dentry, const char *name, void *value, size_t size)
 232 {
 233         struct inode *inode = dentry->d_inode;
 234         int error;
 235
 236         error = xattr_permission(inode, name, MAY_READ);
 237         if (error)
 238                 return error;
 239
 240         error = security_inode_getxattr(dentry, name);
 241         if (error)
 242                 return error;
 243
 244         if (!strncmp(name, XATTR_SECURITY_PREFIX,
 245                                 XATTR_SECURITY_PREFIX_LEN)) {
 246                 const char *suffix = name + XATTR_SECURITY_PREFIX_LEN;
 247                 int ret = xattr_getsecurity(inode, suffix, value, size);
 248                 /*
 249                  * Only overwrite the return value if a security module
 250                  * is actually active.
 251                  */
 252                 if (ret == -EOPNOTSUPP)
 253                         goto nolsm;
 254                 return ret;
 255         }
 256 nolsm:
 257         if (inode->i_op->getxattr)
 258                 error = inode->i_op->getxattr(dentry, name, value, size);
 259         else
 260                 error = -EOPNOTSUPP;
 261
 262         return error;
 263 }
 264 EXPORT_SYMBOL_GPL(vfs_getxattr);
 265
 266 ssize_t
 267 vfs_listxattr(struct dentry *d, char *list, size_t size)
 268 {
 269         ssize_t error;
 270
 271         error = security_inode_listxattr(d);
 272         if (error)
 273                 return error;
 274         error = -EOPNOTSUPP;
 275         if (d->d_inode->i_op->listxattr) {
 276                 error = d->d_inode->i_op->listxattr(d, list, size);
 277         } else {
 278                 error = security_inode_listsecurity(d->d_inode, list, size);
 279                 if (size && error > size)
 280                         error = -ERANGE;
 281         }
 282         return error;
 283 }
 284 EXPORT_SYMBOL_GPL(vfs_listxattr);
 285
 286 int
 287 vfs_removexattr(struct dentry *dentry, const char *name)
 288 {
 289         struct inode *inode = dentry->d_inode;
 290         int error;
 291
 292         if (!inode->i_op->removexattr)
 293                 return -EOPNOTSUPP;
 294
 295         error = xattr_permission(inode, name, MAY_WRITE);
 296         if (error)
 297                 return error;
 298
 299         mutex_lock(&inode->i_mutex);
 300         error = security_inode_removexattr(dentry, name);
 301         if (error)
 302                 goto out;
 303
 304         error = inode->i_op->removexattr(dentry, name);
 305
 306         if (!error) {
 307                 fsnotify_xattr(dentry);
 308                 evm_inode_post_removexattr(dentry, name);
 309         }
 310
 311 out:
 312         mutex_unlock(&inode->i_mutex);
 313         return error;
 314 }
 315 EXPORT_SYMBOL_GPL(vfs_removexattr);
 316
 317
 318 /*
 319  * Extended attribute SET operations
 320  */
 321 static long
 322 setxattr(struct dentry *d, const char __user *name, const void __user *value,
 323          size_t size, int flags)
 324 {
 325         int error;
 326         void *kvalue = NULL;
 327         void *vvalue = NULL;    /* If non-NULL, we used vmalloc() */
 328         char kname[XATTR_NAME_MAX + 1];
 329
 330         if (flags & ~(XATTR_CREATE|XATTR_REPLACE))
 331                 return -EINVAL;
 332
 333         error = strncpy_from_user(kname, name, sizeof(kname));
 334         if (error == 0 || error == sizeof(kname))
 335                 error = -ERANGE;
 336         if (error < 0)
 337                 return error;
 338
 339         if (size) {
 340                 if (size > XATTR_SIZE_MAX)
 341                         return -E2BIG;
 342                 kvalue = kmalloc(size, GFP_KERNEL | __GFP_NOWARN);
 343                 if (!kvalue) {
 344                         vvalue = vmalloc(size);
 345                         if (!vvalue)
 346                                 return -ENOMEM;
 347                         kvalue = vvalue;
 348                 }
 349                 if (copy_from_user(kvalue, value, size)) {
 350                         error = -EFAULT;
 351                         goto out;
 352                 }
 353                 if ((strcmp(kname, XATTR_NAME_POSIX_ACL_ACCESS) == 0) ||
 354                     (strcmp(kname, XATTR_NAME_POSIX_ACL_DEFAULT) == 0))
 355                         posix_acl_fix_xattr_from_user(kvalue, size);
 356         }
 357
 358         error = vfs_setxattr(d, kname, kvalue, size, flags);
 359 out:
 360         if (vvalue)
 361                 vfree(vvalue);
 362         else
 363                 kfree(kvalue);
 364         return error;
 365 }
 366
 367 static int path_setxattr(const char __user *pathname,
 368                          const char __user *name, const void __user *value,
 369                          size_t size, int flags, unsigned int lookup_flags)
 370 {
 371         struct path path;
 372         int error;
 373 retry:
 374         error = user_path_at(AT_FDCWD, pathname, lookup_flags, &path);
 375         if (error)
 376                 return error;
 377         error = mnt_want_write(path.mnt);
 378         if (!error) {
 379                 error = setxattr(path.dentry, name, value, size, flags);
 380                 mnt_drop_write(path.mnt);
 381         }
 382         path_put(&path);
 383         if (retry_estale(error, lookup_flags)) {
 384                 lookup_flags |= LOOKUP_REVAL;
 385                 goto retry;
 386         }
 387         return error;
 388 }
 389
 390 SYSCALL_DEFINE5(setxattr, const char __user *, pathname,
 391                 const char __user *, name, const void __user *, value,
 392                 size_t, size, int, flags)
 393 {
 394         return path_setxattr(pathname, name, value, size, flags, LOOKUP_FOLLOW);
 395 }
 396
 397 SYSCALL_DEFINE5(lsetxattr, const char __user *, pathname,
 398                 const char __user *, name, const void __user *, value,
 399                 size_t, size, int, flags)
 400 {
 401         return path_setxattr(pathname, name, value, size, flags, 0);
 402 }
 403
 404 SYSCALL_DEFINE5(fsetxattr, int, fd, const char __user *, name,
 405                 const void __user *,value, size_t, size, int, flags)
 406 {
 407         struct fd f = fdget(fd);
 408         int error = -EBADF;
 409
 410         if (!f.file)
 411                 return error;
 412         audit_file(f.file);
 413         error = mnt_want_write_file(f.file);
 414         if (!error) {
 415                 error = setxattr(f.file->f_path.dentry, name, value, size, flags);
 416                 mnt_drop_write_file(f.file);
 417         }
 418         fdput(f);
 419         return error;
 420 }
 421
 422 /*
 423  * Extended attribute GET operations
 424  */
 425 static ssize_t
 426 getxattr(struct dentry *d, const char __user *name, void __user *value,
 427          size_t size)
 428 {
 429         ssize_t error;
 430         void *kvalue = NULL;
 431         void *vvalue = NULL;
 432         char kname[XATTR_NAME_MAX + 1];
 433
 434         error = strncpy_from_user(kname, name, sizeof(kname));
 435         if (error == 0 || error == sizeof(kname))
 436                 error = -ERANGE;
 437         if (error < 0)
 438                 return error;
 439
 440         if (size) {
 441                 if (size > XATTR_SIZE_MAX)
 442                         size = XATTR_SIZE_MAX;
 443                 kvalue = kzalloc(size, GFP_KERNEL | __GFP_NOWARN);
 444                 if (!kvalue) {
 445                         vvalue = vzalloc(size);
 446                         if (!vvalue)
 447                                 return -ENOMEM;
 448                         kvalue = vvalue;
 449                 }
 450         }
 451
 452         error = vfs_getxattr(d, kname, kvalue, size);
 453         if (error > 0) {
 454                 if ((strcmp(kname, XATTR_NAME_POSIX_ACL_ACCESS) == 0) ||
 455                     (strcmp(kname, XATTR_NAME_POSIX_ACL_DEFAULT) == 0))
 456                         posix_acl_fix_xattr_to_user(kvalue, error);
 457                 if (size && copy_to_user(value, kvalue, error))
 458                         error = -EFAULT;
 459         } else if (error == -ERANGE && size >= XATTR_SIZE_MAX) {
 460                 /* The file system tried to returned a value bigger
 461                    than XATTR_SIZE_MAX bytes. Not possible. */
 462                 error = -E2BIG;
 463         }
 464         if (vvalue)
 465                 vfree(vvalue);
 466         else
 467                 kfree(kvalue);
 468         return error;
 469 }
 470
 471 static ssize_t path_getxattr(const char __user *pathname,
 472                              const char __user *name, void __user *value,
 473                              size_t size, unsigned int lookup_flags)
 474 {
 475         struct path path;
 476         ssize_t error;
 477 retry:
 478         error = user_path_at(AT_FDCWD, pathname, lookup_flags, &path);
 479         if (error)
 480                 return error;
 481         error = getxattr(path.dentry, name, value, size);
 482         path_put(&path);
 483         if (retry_estale(error, lookup_flags)) {
 484                 lookup_flags |= LOOKUP_REVAL;
 485                 goto retry;
 486         }
 487         return error;
 488 }
 489
 490 SYSCALL_DEFINE4(getxattr, const char __user *, pathname,
 491                 const char __user *, name, void __user *, value, size_t, size)
 492 {
 493         return path_getxattr(pathname, name, value, size, LOOKUP_FOLLOW);
 494 }
 495
 496 SYSCALL_DEFINE4(lgetxattr, const char __user *, pathname,
 497                 const char __user *, name, void __user *, value, size_t, size)
 498 {
 499         return path_getxattr(pathname, name, value, size, 0);
 500 }
 501
 502 SYSCALL_DEFINE4(fgetxattr, int, fd, const char __user *, name,
 503                 void __user *, value, size_t, size)
 504 {
 505         struct fd f = fdget(fd);
 506         ssize_t error = -EBADF;
 507
 508         if (!f.file)
 509                 return error;
 510         audit_file(f.file);
 511         error = getxattr(f.file->f_path.dentry, name, value, size);
 512         fdput(f);
 513         return error;
 514 }
 515
 516 /*
 517  * Extended attribute LIST operations
 518  */
 519 static ssize_t
 520 listxattr(struct dentry *d, char __user *list, size_t size)
 521 {
 522         ssize_t error;
 523         char *klist = NULL;
 524         char *vlist = NULL;     /* If non-NULL, we used vmalloc() */
 525
 526         if (size) {
 527                 if (size > XATTR_LIST_MAX)
 528                         size = XATTR_LIST_MAX;
 529                 klist = kmalloc(size, __GFP_NOWARN | GFP_KERNEL);
 530                 if (!klist) {
 531                         vlist = vmalloc(size);
 532                         if (!vlist)
 533                                 return -ENOMEM;
 534                         klist = vlist;
 535                 }
 536         }
 537
 538         error = vfs_listxattr(d, klist, size);
 539         if (error > 0) {
 540                 if (size && copy_to_user(list, klist, error))
 541                         error = -EFAULT;
 542         } else if (error == -ERANGE && size >= XATTR_LIST_MAX) {
 543                 /* The file system tried to returned a list bigger
 544                    than XATTR_LIST_MAX bytes. Not possible. */
 545                 error = -E2BIG;
 546         }
 547         if (vlist)
 548                 vfree(vlist);
 549         else
 550                 kfree(klist);
 551         return error;
 552 }
 553
 554 static ssize_t path_listxattr(const char __user *pathname, char __user *list,
 555                               size_t size, unsigned int lookup_flags)
 556 {
 557         struct path path;
 558         ssize_t error;
 559 retry:
 560         error = user_path_at(AT_FDCWD, pathname, lookup_flags, &path);
 561         if (error)
 562                 return error;
 563         error = listxattr(path.dentry, list, size);
 564         path_put(&path);
 565         if (retry_estale(error, lookup_flags)) {
 566                 lookup_flags |= LOOKUP_REVAL;
 567                 goto retry;
 568         }
 569         return error;
 570 }
 571
 572 SYSCALL_DEFINE3(listxattr, const char __user *, pathname, char __user *, list,
 573                 size_t, size)
 574 {
 575         return path_listxattr(pathname, list, size, LOOKUP_FOLLOW);
 576 }
 577
 578 SYSCALL_DEFINE3(llistxattr, const char __user *, pathname, char __user *, list,
 579                 size_t, size)
 580 {
 581         return path_listxattr(pathname, list, size, 0);
 582 }
 583
 584 SYSCALL_DEFINE3(flistxattr, int, fd, char __user *, list, size_t, size)
 585 {
 586         struct fd f = fdget(fd);
 587         ssize_t error = -EBADF;
 588
 589         if (!f.file)
 590                 return error;
 591         audit_file(f.file);
 592         error = listxattr(f.file->f_path.dentry, list, size);
 593         fdput(f);
 594         return error;
 595 }
 596
 597 /*
 598  * Extended attribute REMOVE operations
 599  */
 600 static long
 601 removexattr(struct dentry *d, const char __user *name)
 602 {
 603         int error;
 604         char kname[XATTR_NAME_MAX + 1];
 605
 606         error = strncpy_from_user(kname, name, sizeof(kname));
 607         if (error == 0 || error == sizeof(kname))
 608                 error = -ERANGE;
 609         if (error < 0)
 610                 return error;
 611
 612         return vfs_removexattr(d, kname);
 613 }
 614
 615 static int path_removexattr(const char __user *pathname,
 616                             const char __user *name, unsigned int lookup_flags)
 617 {
 618         struct path path;
 619         int error;
 620 retry:
 621         error = user_path_at(AT_FDCWD, pathname, lookup_flags, &path);
 622         if (error)
 623                 return error;
 624         error = mnt_want_write(path.mnt);
 625         if (!error) {
 626                 error = removexattr(path.dentry, name);
 627                 mnt_drop_write(path.mnt);
 628         }
 629         path_put(&path);
 630         if (retry_estale(error, lookup_flags)) {
 631                 lookup_flags |= LOOKUP_REVAL;
 632                 goto retry;
 633         }
 634         return error;
 635 }
 636
 637 SYSCALL_DEFINE2(removexattr, const char __user *, pathname,
 638                 const char __user *, name)
 639 {
 640         return path_removexattr(pathname, name, LOOKUP_FOLLOW);
 641 }
 642
 643 SYSCALL_DEFINE2(lremovexattr, const char __user *, pathname,
 644                 const char __user *, name)
 645 {
 646         return path_removexattr(pathname, name, 0);
 647 }
 648
 649 SYSCALL_DEFINE2(fremovexattr, int, fd, const char __user *, name)
 650 {
 651         struct fd f = fdget(fd);
 652         int error = -EBADF;
 653
 654         if (!f.file)
 655                 return error;
 656         audit_file(f.file);
 657         error = mnt_want_write_file(f.file);
 658         if (!error) {
 659                 error = removexattr(f.file->f_path.dentry, name);
 660                 mnt_drop_write_file(f.file);
 661         }
 662         fdput(f);
 663         return error;
 664 }
 665
 666
 667 static const char *
 668 strcmp_prefix(const char *a, const char *a_prefix)
 669 {
 670         while (*a_prefix && *a == *a_prefix) {
 671                 a++;
 672                 a_prefix++;
 673         }
 674         return *a_prefix ? NULL : a;
 675 }
 676
 677 /*
 678  * In order to implement different sets of xattr operations for each xattr
 679  * prefix with the generic xattr API, a filesystem should create a
 680  * null-terminated array of struct xattr_handler (one for each prefix) and
 681  * hang a pointer to it off of the s_xattr field of the superblock.
 682  *
 683  * The generic_fooxattr() functions will use this list to dispatch xattr
 684  * operations to the correct xattr_handler.
 685  */
 686 #define for_each_xattr_handler(handlers, handler)               \
 687                 for ((handler) = *(handlers)++;                 \
 688                         (handler) != NULL;                      \
 689                         (handler) = *(handlers)++)
 690
 691 /*
 692  * Find the xattr_handler with the matching prefix.
 693  */
 694 static const struct xattr_handler *
 695 xattr_resolve_name(const struct xattr_handler **handlers, const char **name)
 696 {
 697         const struct xattr_handler *handler;
 698
 699         if (!*name)
 700                 return NULL;
 701
 702         for_each_xattr_handler(handlers, handler) {
 703                 const char *n = strcmp_prefix(*name, handler->prefix);
 704                 if (n) {
 705                         *name = n;
 706                         break;
 707                 }
 708         }
 709         return handler;
 710 }
 711
 712 /*
 713  * Find the handler for the prefix and dispatch its get() operation.
 714  */
 715 ssize_t
 716 generic_getxattr(struct dentry *dentry, const char *name, void *buffer, size_t size)
 717 {
 718         const struct xattr_handler *handler;
 719
 720         handler = xattr_resolve_name(dentry->d_sb->s_xattr, &name);
 721         if (!handler)
 722                 return -EOPNOTSUPP;
 723         return handler->get(handler, dentry, name, buffer, size);
 724 }
 725
 726 /*
 727  * Combine the results of the list() operation from every xattr_handler in the
 728  * list.
 729  */
 730 ssize_t
 731 generic_listxattr(struct dentry *dentry, char *buffer, size_t buffer_size)
 732 {
 733         const struct xattr_handler *handler, **handlers = dentry->d_sb->s_xattr;
 734         unsigned int size = 0;
 735
 736         if (!buffer) {
 737                 for_each_xattr_handler(handlers, handler) {
 738                         size += handler->list(handler, dentry, NULL, 0,
 739                                               NULL, 0);
 740                 }
 741         } else {
 742                 char *buf = buffer;
 743
 744                 for_each_xattr_handler(handlers, handler) {
 745                         size = handler->list(handler, dentry, buf, buffer_size,
 746                                              NULL, 0);
 747                         if (size > buffer_size)
 748                                 return -ERANGE;
 749                         buf += size;
 750                         buffer_size -= size;
 751                 }
 752                 size = buf - buffer;
 753         }
 754         return size;
 755 }
 756
 757 /*
 758  * Find the handler for the prefix and dispatch its set() operation.
 759  */
 760 int
 761 generic_setxattr(struct dentry *dentry, const char *name, const void *value, size_t size, int flags)
 762 {
 763         const struct xattr_handler *handler;
 764
 765         if (size == 0)
 766                 value = "";  /* empty EA, do not remove */
 767         handler = xattr_resolve_name(dentry->d_sb->s_xattr, &name);
 768         if (!handler)
 769                 return -EOPNOTSUPP;
 770         return handler->set(handler, dentry, name, value, size, flags);
 771 }
 772
 773 /*
 774  * Find the handler for the prefix and dispatch its set() operation to remove
 775  * any associated extended attribute.
 776  */
 777 int
 778 generic_removexattr(struct dentry *dentry, const char *name)
 779 {
 780         const struct xattr_handler *handler;
 781
 782         handler = xattr_resolve_name(dentry->d_sb->s_xattr, &name);
 783         if (!handler)
 784                 return -EOPNOTSUPP;
 785         return handler->set(handler, dentry, name, NULL, 0, XATTR_REPLACE);
 786 }
 787
 788 EXPORT_SYMBOL(generic_getxattr);
 789 EXPORT_SYMBOL(generic_listxattr);
 790 EXPORT_SYMBOL(generic_setxattr);
 791 EXPORT_SYMBOL(generic_removexattr);
 792
 793 /**
 794  * xattr_full_name  -  Compute full attribute name from suffix
 795  *
 796  * @handler:    handler of the xattr_handler operation
 797  * @name:       name passed to the xattr_handler operation
 798  *
 799  * The get and set xattr handler operations are called with the remainder of
 800  * the attribute name after skipping the handler's prefix: for example, "foo"
 801  * is passed to the get operation of a handler with prefix "user." to get
 802  * attribute "user.foo".  The full name is still "there" in the name though.
 803  *
 804  * Note: the list xattr handler operation when called from the vfs is passed a
 805  * NULL name; some file systems use this operation internally, with varying
 806  * semantics.
 807  */
 808 const char *xattr_full_name(const struct xattr_handler *handler,
 809                             const char *name)
 810 {
 811         size_t prefix_len = strlen(handler->prefix);
 812
 813         return name - prefix_len;
 814 }
 815 EXPORT_SYMBOL(xattr_full_name);
 816
 817 /*
 818  * Allocate new xattr and copy in the value; but leave the name to callers.
 819  */
 820 struct simple_xattr *simple_xattr_alloc(const void *value, size_t size)
 821 {
 822         struct simple_xattr *new_xattr;
 823         size_t len;
 824
 825         /* wrap around? */
 826         len = sizeof(*new_xattr) + size;
 827         if (len < sizeof(*new_xattr))
 828                 return NULL;
 829
 830         new_xattr = kmalloc(len, GFP_KERNEL);
 831         if (!new_xattr)
 832                 return NULL;
 833
 834         new_xattr->size = size;
 835         memcpy(new_xattr->value, value, size);
 836         return new_xattr;
 837 }
 838
 839 /*
 840  * xattr GET operation for in-memory/pseudo filesystems
 841  */
 842 int simple_xattr_get(struct simple_xattrs *xattrs, const char *name,
 843                      void *buffer, size_t size)
 844 {
 845         struct simple_xattr *xattr;
 846         int ret = -ENODATA;
 847
 848         spin_lock(&xattrs->lock);
 849         list_for_each_entry(xattr, &xattrs->head, list) {
 850                 if (strcmp(name, xattr->name))
 851                         continue;
 852
 853                 ret = xattr->size;
 854                 if (buffer) {
 855                         if (size < xattr->size)
 856                                 ret = -ERANGE;
 857                         else
 858                                 memcpy(buffer, xattr->value, xattr->size);
 859                 }
 860                 break;
 861         }
 862         spin_unlock(&xattrs->lock);
 863         return ret;
 864 }
 865
 866 static int __simple_xattr_set(struct simple_xattrs *xattrs, const char *name,
 867                               const void *value, size_t size, int flags)
 868 {
 869         struct simple_xattr *xattr;
 870         struct simple_xattr *new_xattr = NULL;
 871         int err = 0;
 872
 873         /* value == NULL means remove */
 874         if (value) {
 875                 new_xattr = simple_xattr_alloc(value, size);
 876                 if (!new_xattr)
 877                         return -ENOMEM;
 878
 879                 new_xattr->name = kstrdup(name, GFP_KERNEL);
 880                 if (!new_xattr->name) {
 881                         kfree(new_xattr);
 882                         return -ENOMEM;
 883                 }
 884         }
 885
 886         spin_lock(&xattrs->lock);
 887         list_for_each_entry(xattr, &xattrs->head, list) {
 888                 if (!strcmp(name, xattr->name)) {
 889                         if (flags & XATTR_CREATE) {
 890                                 xattr = new_xattr;
 891                                 err = -EEXIST;
 892                         } else if (new_xattr) {
 893                                 list_replace(&xattr->list, &new_xattr->list);
 894                         } else {
 895                                 list_del(&xattr->list);
 896                         }
 897                         goto out;
 898                 }
 899         }
 900         if (flags & XATTR_REPLACE) {
 901                 xattr = new_xattr;
 902                 err = -ENODATA;
 903         } else {
 904                 list_add(&new_xattr->list, &xattrs->head);
 905                 xattr = NULL;
 906         }
 907 out:
 908         spin_unlock(&xattrs->lock);
 909         if (xattr) {
 910                 kfree(xattr->name);
 911                 kfree(xattr);
 912         }
 913         return err;
 914
 915 }
 916
 917 /**
 918  * simple_xattr_set - xattr SET operation for in-memory/pseudo filesystems
 919  * @xattrs: target simple_xattr list
 920  * @name: name of the new extended attribute
 921  * @value: value of the new xattr. If %NULL, will remove the attribute
 922  * @size: size of the new xattr
 923  * @flags: %XATTR_{CREATE|REPLACE}
 924  *
 925  * %XATTR_CREATE is set, the xattr shouldn't exist already; otherwise fails
 926  * with -EEXIST.  If %XATTR_REPLACE is set, the xattr should exist;
 927  * otherwise, fails with -ENODATA.
 928  *
 929  * Returns 0 on success, -errno on failure.
 930  */
 931 int simple_xattr_set(struct simple_xattrs *xattrs, const char *name,
 932                      const void *value, size_t size, int flags)
 933 {
 934         if (size == 0)
 935                 value = ""; /* empty EA, do not remove */
 936         return __simple_xattr_set(xattrs, name, value, size, flags);
 937 }
 938
 939 /*
 940  * xattr REMOVE operation for in-memory/pseudo filesystems
 941  */
 942 int simple_xattr_remove(struct simple_xattrs *xattrs, const char *name)
 943 {
 944         return __simple_xattr_set(xattrs, name, NULL, 0, XATTR_REPLACE);
 945 }
 946
 947 static bool xattr_is_trusted(const char *name)
 948 {
 949         return !strncmp(name, XATTR_TRUSTED_PREFIX, XATTR_TRUSTED_PREFIX_LEN);
 950 }
 951
 952 /*
 953  * xattr LIST operation for in-memory/pseudo filesystems
 954  */
 955 ssize_t simple_xattr_list(struct simple_xattrs *xattrs, char *buffer,
 956                           size_t size)
 957 {
 958         bool trusted = capable(CAP_SYS_ADMIN);
 959         struct simple_xattr *xattr;
 960         size_t used = 0;
 961
 962         spin_lock(&xattrs->lock);
 963         list_for_each_entry(xattr, &xattrs->head, list) {
 964                 size_t len;
 965
 966                 /* skip "trusted." attributes for unprivileged callers */
 967                 if (!trusted && xattr_is_trusted(xattr->name))
 968                         continue;
 969
 970                 len = strlen(xattr->name) + 1;
 971                 used += len;
 972                 if (buffer) {
 973                         if (size < used) {
 974                                 used = -ERANGE;
 975                                 break;
 976                         }
 977                         memcpy(buffer, xattr->name, len);
 978                         buffer += len;
 979                 }
 980         }
 981         spin_unlock(&xattrs->lock);
 982
 983         return used;
 984 }
 985
 986 /*
 987  * Adds an extended attribute to the list
 988  */
 989 void simple_xattr_list_add(struct simple_xattrs *xattrs,
 990                            struct simple_xattr *new_xattr)
 991 {
 992         spin_lock(&xattrs->lock);
 993         list_add(&new_xattr->list, &xattrs->head);
 994         spin_unlock(&xattrs->lock);
 995 }