security/device_cgroup.c

   1 /*
   2  * device_cgroup.c - device cgroup subsystem
   3  *
   4  * Copyright 2007 IBM Corp
   5  */
   6
   7 #include <linux/device_cgroup.h>
   8 #include <linux/cgroup.h>
   9 #include <linux/ctype.h>
  10 #include <linux/list.h>
  11 #include <linux/uaccess.h>
  12 #include <linux/seq_file.h>
  13 #include <linux/slab.h>
  14 #include <linux/rcupdate.h>
  15 #include <linux/mutex.h>
  16
  17 #define ACC_MKNOD 1
  18 #define ACC_READ  2
  19 #define ACC_WRITE 4
  20 #define ACC_MASK (ACC_MKNOD | ACC_READ | ACC_WRITE)
  21
  22 #define DEV_BLOCK 1
  23 #define DEV_CHAR  2
  24 #define DEV_ALL   4  /* this represents all devices */
  25
  26 static DEFINE_MUTEX(devcgroup_mutex);
  27
  28 enum devcg_behavior {
  29         DEVCG_DEFAULT_NONE,
  30         DEVCG_DEFAULT_ALLOW,
  31         DEVCG_DEFAULT_DENY,
  32 };
  33
  34 /*
  35  * exception list locking rules:
  36  * hold devcgroup_mutex for update/read.
  37  * hold rcu_read_lock() for read.
  38  */
  39
  40 struct dev_exception_item {
  41         u32 major, minor;
  42         short type;
  43         short access;
  44         struct list_head list;
  45         struct rcu_head rcu;
  46 };
  47
  48 struct dev_cgroup {
  49         struct cgroup_subsys_state css;
  50         struct list_head exceptions;
  51         enum devcg_behavior behavior;
  52 };
  53
  54 static inline struct dev_cgroup *css_to_devcgroup(struct cgroup_subsys_state *s)
  55 {
  56         return s ? container_of(s, struct dev_cgroup, css) : NULL;
  57 }
  58
  59 static inline struct dev_cgroup *task_devcgroup(struct task_struct *task)
  60 {
  61         return css_to_devcgroup(task_css(task, devices_cgrp_id));
  62 }
  63
  64 /*
  65  * called under devcgroup_mutex
  66  */
  67 static int dev_exceptions_copy(struct list_head *dest, struct list_head *orig)
  68 {
  69         struct dev_exception_item *ex, *tmp, *new;
  70
  71         lockdep_assert_held(&devcgroup_mutex);
  72
  73         list_for_each_entry(ex, orig, list) {
  74                 new = kmemdup(ex, sizeof(*ex), GFP_KERNEL);
  75                 if (!new)
  76                         goto free_and_exit;
  77                 list_add_tail(&new->list, dest);
  78         }
  79
  80         return 0;
  81
  82 free_and_exit:
  83         list_for_each_entry_safe(ex, tmp, dest, list) {
  84                 list_del(&ex->list);
  85                 kfree(ex);
  86         }
  87         return -ENOMEM;
  88 }
  89
  90 /*
  91  * called under devcgroup_mutex
  92  */
  93 static int dev_exception_add(struct dev_cgroup *dev_cgroup,
  94                              struct dev_exception_item *ex)
  95 {
  96         struct dev_exception_item *excopy, *walk;
  97
  98         lockdep_assert_held(&devcgroup_mutex);
  99
 100         excopy = kmemdup(ex, sizeof(*ex), GFP_KERNEL);
 101         if (!excopy)
 102                 return -ENOMEM;
 103
 104         list_for_each_entry(walk, &dev_cgroup->exceptions, list) {
 105                 if (walk->type != ex->type)
 106                         continue;
 107                 if (walk->major != ex->major)
 108                         continue;
 109                 if (walk->minor != ex->minor)
 110                         continue;
 111
 112                 walk->access |= ex->access;
 113                 kfree(excopy);
 114                 excopy = NULL;
 115         }
 116
 117         if (excopy != NULL)
 118                 list_add_tail_rcu(&excopy->list, &dev_cgroup->exceptions);
 119         return 0;
 120 }
 121
 122 /*
 123  * called under devcgroup_mutex
 124  */
 125 static void dev_exception_rm(struct dev_cgroup *dev_cgroup,
 126                              struct dev_exception_item *ex)
 127 {
 128         struct dev_exception_item *walk, *tmp;
 129
 130         lockdep_assert_held(&devcgroup_mutex);
 131
 132         list_for_each_entry_safe(walk, tmp, &dev_cgroup->exceptions, list) {
 133                 if (walk->type != ex->type)
 134                         continue;
 135                 if (walk->major != ex->major)
 136                         continue;
 137                 if (walk->minor != ex->minor)
 138                         continue;
 139
 140                 walk->access &= ~ex->access;
 141                 if (!walk->access) {
 142                         list_del_rcu(&walk->list);
 143                         kfree_rcu(walk, rcu);
 144                 }
 145         }
 146 }
 147
 148 static void __dev_exception_clean(struct dev_cgroup *dev_cgroup)
 149 {
 150         struct dev_exception_item *ex, *tmp;
 151
 152         list_for_each_entry_safe(ex, tmp, &dev_cgroup->exceptions, list) {
 153                 list_del_rcu(&ex->list);
 154                 kfree_rcu(ex, rcu);
 155         }
 156 }
 157
 158 /**
 159  * dev_exception_clean - frees all entries of the exception list
 160  * @dev_cgroup: dev_cgroup with the exception list to be cleaned
 161  *
 162  * called under devcgroup_mutex
 163  */
 164 static void dev_exception_clean(struct dev_cgroup *dev_cgroup)
 165 {
 166         lockdep_assert_held(&devcgroup_mutex);
 167
 168         __dev_exception_clean(dev_cgroup);
 169 }
 170
 171 static inline bool is_devcg_online(const struct dev_cgroup *devcg)
 172 {
 173         return (devcg->behavior != DEVCG_DEFAULT_NONE);
 174 }
 175
 176 /**
 177  * devcgroup_online - initializes devcgroup's behavior and exceptions based on
 178  *                    parent's
 179  * @css: css getting online
 180  * returns 0 in case of success, error code otherwise
 181  */
 182 static int devcgroup_online(struct cgroup_subsys_state *css)
 183 {
 184         struct dev_cgroup *dev_cgroup = css_to_devcgroup(css);
 185         struct dev_cgroup *parent_dev_cgroup = css_to_devcgroup(css_parent(css));
 186         int ret = 0;
 187
 188         mutex_lock(&devcgroup_mutex);
 189
 190         if (parent_dev_cgroup == NULL)
 191                 dev_cgroup->behavior = DEVCG_DEFAULT_ALLOW;
 192         else {
 193                 ret = dev_exceptions_copy(&dev_cgroup->exceptions,
 194                                           &parent_dev_cgroup->exceptions);
 195                 if (!ret)
 196                         dev_cgroup->behavior = parent_dev_cgroup->behavior;
 197         }
 198         mutex_unlock(&devcgroup_mutex);
 199
 200         return ret;
 201 }
 202
 203 static void devcgroup_offline(struct cgroup_subsys_state *css)
 204 {
 205         struct dev_cgroup *dev_cgroup = css_to_devcgroup(css);
 206
 207         mutex_lock(&devcgroup_mutex);
 208         dev_cgroup->behavior = DEVCG_DEFAULT_NONE;
 209         mutex_unlock(&devcgroup_mutex);
 210 }
 211
 212 /*
 213  * called from kernel/cgroup.c with cgroup_lock() held.
 214  */
 215 static struct cgroup_subsys_state *
 216 devcgroup_css_alloc(struct cgroup_subsys_state *parent_css)
 217 {
 218         struct dev_cgroup *dev_cgroup;
 219
 220         dev_cgroup = kzalloc(sizeof(*dev_cgroup), GFP_KERNEL);
 221         if (!dev_cgroup)
 222                 return ERR_PTR(-ENOMEM);
 223         INIT_LIST_HEAD(&dev_cgroup->exceptions);
 224         dev_cgroup->behavior = DEVCG_DEFAULT_NONE;
 225
 226         return &dev_cgroup->css;
 227 }
 228
 229 static void devcgroup_css_free(struct cgroup_subsys_state *css)
 230 {
 231         struct dev_cgroup *dev_cgroup = css_to_devcgroup(css);
 232
 233         __dev_exception_clean(dev_cgroup);
 234         kfree(dev_cgroup);
 235 }
 236
 237 #define DEVCG_ALLOW 1
 238 #define DEVCG_DENY 2
 239 #define DEVCG_LIST 3
 240
 241 #define MAJMINLEN 13
 242 #define ACCLEN 4
 243
 244 static void set_access(char *acc, short access)
 245 {
 246         int idx = 0;
 247         memset(acc, 0, ACCLEN);
 248         if (access & ACC_READ)
 249                 acc[idx++] = 'r';
 250         if (access & ACC_WRITE)
 251                 acc[idx++] = 'w';
 252         if (access & ACC_MKNOD)
 253                 acc[idx++] = 'm';
 254 }
 255
 256 static char type_to_char(short type)
 257 {
 258         if (type == DEV_ALL)
 259                 return 'a';
 260         if (type == DEV_CHAR)
 261                 return 'c';
 262         if (type == DEV_BLOCK)
 263                 return 'b';
 264         return 'X';
 265 }
 266
 267 static void set_majmin(char *str, unsigned m)
 268 {
 269         if (m == ~0)
 270                 strcpy(str, "*");
 271         else
 272                 sprintf(str, "%u", m);
 273 }
 274
 275 static int devcgroup_seq_show(struct seq_file *m, void *v)
 276 {
 277         struct dev_cgroup *devcgroup = css_to_devcgroup(seq_css(m));
 278         struct dev_exception_item *ex;
 279         char maj[MAJMINLEN], min[MAJMINLEN], acc[ACCLEN];
 280
 281         rcu_read_lock();
 282         /*
 283          * To preserve the compatibility:
 284          * - Only show the "all devices" when the default policy is to allow
 285          * - List the exceptions in case the default policy is to deny
 286          * This way, the file remains as a "whitelist of devices"
 287          */
 288         if (devcgroup->behavior == DEVCG_DEFAULT_ALLOW) {
 289                 set_access(acc, ACC_MASK);
 290                 set_majmin(maj, ~0);
 291                 set_majmin(min, ~0);
 292                 seq_printf(m, "%c %s:%s %s\n", type_to_char(DEV_ALL),
 293                            maj, min, acc);
 294         } else {
 295                 list_for_each_entry_rcu(ex, &devcgroup->exceptions, list) {
 296                         set_access(acc, ex->access);
 297                         set_majmin(maj, ex->major);
 298                         set_majmin(min, ex->minor);
 299                         seq_printf(m, "%c %s:%s %s\n", type_to_char(ex->type),
 300                                    maj, min, acc);
 301                 }
 302         }
 303         rcu_read_unlock();
 304
 305         return 0;
 306 }
 307
 308 /**
 309  * may_access - verifies if a new exception is part of what is allowed
 310  *              by a dev cgroup based on the default policy +
 311  *              exceptions. This is used to make sure a child cgroup
 312  *              won't have more privileges than its parent or to
 313  *              verify if a certain access is allowed.
 314  * @dev_cgroup: dev cgroup to be tested against
 315  * @refex: new exception
 316  * @behavior: behavior of the exception
 317  */
 318 static bool may_access(struct dev_cgroup *dev_cgroup,
 319                        struct dev_exception_item *refex,
 320                        enum devcg_behavior behavior)
 321 {
 322         struct dev_exception_item *ex;
 323         bool match = false;
 324
 325         rcu_lockdep_assert(rcu_read_lock_held() ||
 326                            lockdep_is_held(&devcgroup_mutex),
 327                            "device_cgroup::may_access() called without proper synchronization");
 328
 329         list_for_each_entry_rcu(ex, &dev_cgroup->exceptions, list) {
 330                 if ((refex->type & DEV_BLOCK) && !(ex->type & DEV_BLOCK))
 331                         continue;
 332                 if ((refex->type & DEV_CHAR) && !(ex->type & DEV_CHAR))
 333                         continue;
 334                 if (ex->major != ~0 && ex->major != refex->major)
 335                         continue;
 336                 if (ex->minor != ~0 && ex->minor != refex->minor)
 337                         continue;
 338                 if (refex->access & (~ex->access))
 339                         continue;
 340                 match = true;
 341                 break;
 342         }
 343
 344         if (dev_cgroup->behavior == DEVCG_DEFAULT_ALLOW) {
 345                 if (behavior == DEVCG_DEFAULT_ALLOW) {
 346                         /* the exception will deny access to certain devices */
 347                         return true;
 348                 } else {
 349                         /* the exception will allow access to certain devices */
 350                         if (match)
 351                                 /*
 352                                  * a new exception allowing access shouldn't
 353                                  * match an parent's exception
 354                                  */
 355                                 return false;
 356                         return true;
 357                 }
 358         } else {
 359                 /* only behavior == DEVCG_DEFAULT_DENY allowed here */
 360                 if (match)
 361                         /* parent has an exception that matches the proposed */
 362                         return true;
 363                 else
 364                         return false;
 365         }
 366         return false;
 367 }
 368
 369 /*
 370  * parent_has_perm:
 371  * when adding a new allow rule to a device exception list, the rule
 372  * must be allowed in the parent device
 373  */
 374 static int parent_has_perm(struct dev_cgroup *childcg,
 375                                   struct dev_exception_item *ex)
 376 {
 377         struct dev_cgroup *parent = css_to_devcgroup(css_parent(&childcg->css));
 378
 379         if (!parent)
 380                 return 1;
 381         return may_access(parent, ex, childcg->behavior);
 382 }
 383
 384 /**
 385  * may_allow_all - checks if it's possible to change the behavior to
 386  *                 allow based on parent's rules.
 387  * @parent: device cgroup's parent
 388  * returns: != 0 in case it's allowed, 0 otherwise
 389  */
 390 static inline int may_allow_all(struct dev_cgroup *parent)
 391 {
 392         if (!parent)
 393                 return 1;
 394         return parent->behavior == DEVCG_DEFAULT_ALLOW;
 395 }
 396
 397 /**
 398  * revalidate_active_exceptions - walks through the active exception list and
 399  *                                revalidates the exceptions based on parent's
 400  *                                behavior and exceptions. The exceptions that
 401  *                                are no longer valid will be removed.
 402  *                                Called with devcgroup_mutex held.
 403  * @devcg: cgroup which exceptions will be checked
 404  *
 405  * This is one of the three key functions for hierarchy implementation.
 406  * This function is responsible for re-evaluating all the cgroup's active
 407  * exceptions due to a parent's exception change.
 408  * Refer to Documentation/cgroups/devices.txt for more details.
 409  */
 410 static void revalidate_active_exceptions(struct dev_cgroup *devcg)
 411 {
 412         struct dev_exception_item *ex;
 413         struct list_head *this, *tmp;
 414
 415         list_for_each_safe(this, tmp, &devcg->exceptions) {
 416                 ex = container_of(this, struct dev_exception_item, list);
 417                 if (!parent_has_perm(devcg, ex))
 418                         dev_exception_rm(devcg, ex);
 419         }
 420 }
 421
 422 /**
 423  * propagate_exception - propagates a new exception to the children
 424  * @devcg_root: device cgroup that added a new exception
 425  * @ex: new exception to be propagated
 426  *
 427  * returns: 0 in case of success, != 0 in case of error
 428  */
 429 static int propagate_exception(struct dev_cgroup *devcg_root,
 430                                struct dev_exception_item *ex)
 431 {
 432         struct cgroup_subsys_state *pos;
 433         int rc = 0;
 434
 435         rcu_read_lock();
 436
 437         css_for_each_descendant_pre(pos, &devcg_root->css) {
 438                 struct dev_cgroup *devcg = css_to_devcgroup(pos);
 439
 440                 /*
 441                  * Because devcgroup_mutex is held, no devcg will become
 442                  * online or offline during the tree walk (see on/offline
 443                  * methods), and online ones are safe to access outside RCU
 444                  * read lock without bumping refcnt.
 445                  */
 446                 if (pos == &devcg_root->css || !is_devcg_online(devcg))
 447                         continue;
 448
 449                 rcu_read_unlock();
 450
 451                 /*
 452                  * in case both root's behavior and devcg is allow, a new
 453                  * restriction means adding to the exception list
 454                  */
 455                 if (devcg_root->behavior == DEVCG_DEFAULT_ALLOW &&
 456                     devcg->behavior == DEVCG_DEFAULT_ALLOW) {
 457                         rc = dev_exception_add(devcg, ex);
 458                         if (rc)
 459                                 break;
 460                 } else {
 461                         /*
 462                          * in the other possible cases:
 463                          * root's behavior: allow, devcg's: deny
 464                          * root's behavior: deny, devcg's: deny
 465                          * the exception will be removed
 466                          */
 467                         dev_exception_rm(devcg, ex);
 468                 }
 469                 revalidate_active_exceptions(devcg);
 470
 471                 rcu_read_lock();
 472         }
 473
 474         rcu_read_unlock();
 475         return rc;
 476 }
 477
 478 static inline bool has_children(struct dev_cgroup *devcgroup)
 479 {
 480         struct cgroup *cgrp = devcgroup->css.cgroup;
 481
 482         return !list_empty(&cgrp->children);
 483 }
 484
 485 /*
 486  * Modify the exception list using allow/deny rules.
 487  * CAP_SYS_ADMIN is needed for this.  It's at least separate from CAP_MKNOD
 488  * so we can give a container CAP_MKNOD to let it create devices but not
 489  * modify the exception list.
 490  * It seems likely we'll want to add a CAP_CONTAINER capability to allow
 491  * us to also grant CAP_SYS_ADMIN to containers without giving away the
 492  * device exception list controls, but for now we'll stick with CAP_SYS_ADMIN
 493  *
 494  * Taking rules away is always allowed (given CAP_SYS_ADMIN).  Granting
 495  * new access is only allowed if you're in the top-level cgroup, or your
 496  * parent cgroup has the access you're asking for.
 497  */
 498 static int devcgroup_update_access(struct dev_cgroup *devcgroup,
 499                                    int filetype, char *buffer)
 500 {
 501         const char *b;
 502         char temp[12];          /* 11 + 1 characters needed for a u32 */
 503         int count, rc = 0;
 504         struct dev_exception_item ex;
 505         struct dev_cgroup *parent = css_to_devcgroup(css_parent(&devcgroup->css));
 506
 507         if (!capable(CAP_SYS_ADMIN))
 508                 return -EPERM;
 509
 510         memset(&ex, 0, sizeof(ex));
 511         b = buffer;
 512
 513         switch (*b) {
 514         case 'a':
 515                 switch (filetype) {
 516                 case DEVCG_ALLOW:
 517                         if (has_children(devcgroup))
 518                                 return -EINVAL;
 519
 520                         if (!may_allow_all(parent))
 521                                 return -EPERM;
 522                         dev_exception_clean(devcgroup);
 523                         devcgroup->behavior = DEVCG_DEFAULT_ALLOW;
 524                         if (!parent)
 525                                 break;
 526
 527                         rc = dev_exceptions_copy(&devcgroup->exceptions,
 528                                                  &parent->exceptions);
 529                         if (rc)
 530                                 return rc;
 531                         break;
 532                 case DEVCG_DENY:
 533                         if (has_children(devcgroup))
 534                                 return -EINVAL;
 535
 536                         dev_exception_clean(devcgroup);
 537                         devcgroup->behavior = DEVCG_DEFAULT_DENY;
 538                         break;
 539                 default:
 540                         return -EINVAL;
 541                 }
 542                 return 0;
 543         case 'b':
 544                 ex.type = DEV_BLOCK;
 545                 break;
 546         case 'c':
 547                 ex.type = DEV_CHAR;
 548                 break;
 549         default:
 550                 return -EINVAL;
 551         }
 552         b++;
 553         if (!isspace(*b))
 554                 return -EINVAL;
 555         b++;
 556         if (*b == '*') {
 557                 ex.major = ~0;
 558                 b++;
 559         } else if (isdigit(*b)) {
 560                 memset(temp, 0, sizeof(temp));
 561                 for (count = 0; count < sizeof(temp) - 1; count++) {
 562                         temp[count] = *b;
 563                         b++;
 564                         if (!isdigit(*b))
 565                                 break;
 566                 }
 567                 rc = kstrtou32(temp, 10, &ex.major);
 568                 if (rc)
 569                         return -EINVAL;
 570         } else {
 571                 return -EINVAL;
 572         }
 573         if (*b != ':')
 574                 return -EINVAL;
 575         b++;
 576
 577         /* read minor */
 578         if (*b == '*') {
 579                 ex.minor = ~0;
 580                 b++;
 581         } else if (isdigit(*b)) {
 582                 memset(temp, 0, sizeof(temp));
 583                 for (count = 0; count < sizeof(temp) - 1; count++) {
 584                         temp[count] = *b;
 585                         b++;
 586                         if (!isdigit(*b))
 587                                 break;
 588                 }
 589                 rc = kstrtou32(temp, 10, &ex.minor);
 590                 if (rc)
 591                         return -EINVAL;
 592         } else {
 593                 return -EINVAL;
 594         }
 595         if (!isspace(*b))
 596                 return -EINVAL;
 597         for (b++, count = 0; count < 3; count++, b++) {
 598                 switch (*b) {
 599                 case 'r':
 600                         ex.access |= ACC_READ;
 601                         break;
 602                 case 'w':
 603                         ex.access |= ACC_WRITE;
 604                         break;
 605                 case 'm':
 606                         ex.access |= ACC_MKNOD;
 607                         break;
 608                 case '\n':
 609                 case '\0':
 610                         count = 3;
 611                         break;
 612                 default:
 613                         return -EINVAL;
 614                 }
 615         }
 616
 617         switch (filetype) {
 618         case DEVCG_ALLOW:
 619                 if (!parent_has_perm(devcgroup, &ex))
 620                         return -EPERM;
 621                 /*
 622                  * If the default policy is to allow by default, try to remove
 623                  * an matching exception instead. And be silent about it: we
 624                  * don't want to break compatibility
 625                  */
 626                 if (devcgroup->behavior == DEVCG_DEFAULT_ALLOW) {
 627                         dev_exception_rm(devcgroup, &ex);
 628                         return 0;
 629                 }
 630                 rc = dev_exception_add(devcgroup, &ex);
 631                 break;
 632         case DEVCG_DENY:
 633                 /*
 634                  * If the default policy is to deny by default, try to remove
 635                  * an matching exception instead. And be silent about it: we
 636                  * don't want to break compatibility
 637                  */
 638                 if (devcgroup->behavior == DEVCG_DEFAULT_DENY)
 639                         dev_exception_rm(devcgroup, &ex);
 640                 else
 641                         rc = dev_exception_add(devcgroup, &ex);
 642
 643                 if (rc)
 644                         break;
 645                 /* we only propagate new restrictions */
 646                 rc = propagate_exception(devcgroup, &ex);
 647                 break;
 648         default:
 649                 rc = -EINVAL;
 650         }
 651         return rc;
 652 }
 653
 654 static int devcgroup_access_write(struct cgroup_subsys_state *css,
 655                                   struct cftype *cft, char *buffer)
 656 {
 657         int retval;
 658
 659         mutex_lock(&devcgroup_mutex);
 660         retval = devcgroup_update_access(css_to_devcgroup(css),
 661                                          cft->private, buffer);
 662         mutex_unlock(&devcgroup_mutex);
 663         return retval;
 664 }
 665
 666 static struct cftype dev_cgroup_files[] = {
 667         {
 668                 .name = "allow",
 669                 .write_string  = devcgroup_access_write,
 670                 .private = DEVCG_ALLOW,
 671         },
 672         {
 673                 .name = "deny",
 674                 .write_string = devcgroup_access_write,
 675                 .private = DEVCG_DENY,
 676         },
 677         {
 678                 .name = "list",
 679                 .seq_show = devcgroup_seq_show,
 680                 .private = DEVCG_LIST,
 681         },
 682         { }     /* terminate */
 683 };
 684
 685 struct cgroup_subsys devices_cgrp_subsys = {
 686         .css_alloc = devcgroup_css_alloc,
 687         .css_free = devcgroup_css_free,
 688         .css_online = devcgroup_online,
 689         .css_offline = devcgroup_offline,
 690         .base_cftypes = dev_cgroup_files,
 691 };
 692
 693 /**
 694  * __devcgroup_check_permission - checks if an inode operation is permitted
 695  * @dev_cgroup: the dev cgroup to be tested against
 696  * @type: device type
 697  * @major: device major number
 698  * @minor: device minor number
 699  * @access: combination of ACC_WRITE, ACC_READ and ACC_MKNOD
 700  *
 701  * returns 0 on success, -EPERM case the operation is not permitted
 702  */
 703 static int __devcgroup_check_permission(short type, u32 major, u32 minor,
 704                                         short access)
 705 {
 706         struct dev_cgroup *dev_cgroup;
 707         struct dev_exception_item ex;
 708         int rc;
 709
 710         memset(&ex, 0, sizeof(ex));
 711         ex.type = type;
 712         ex.major = major;
 713         ex.minor = minor;
 714         ex.access = access;
 715
 716         rcu_read_lock();
 717         dev_cgroup = task_devcgroup(current);
 718         rc = may_access(dev_cgroup, &ex, dev_cgroup->behavior);
 719         rcu_read_unlock();
 720
 721         if (!rc)
 722                 return -EPERM;
 723
 724         return 0;
 725 }
 726
 727 int __devcgroup_inode_permission(struct inode *inode, int mask)
 728 {
 729         short type, access = 0;
 730
 731         if (S_ISBLK(inode->i_mode))
 732                 type = DEV_BLOCK;
 733         if (S_ISCHR(inode->i_mode))
 734                 type = DEV_CHAR;
 735         if (mask & MAY_WRITE)
 736                 access |= ACC_WRITE;
 737         if (mask & MAY_READ)
 738                 access |= ACC_READ;
 739
 740         return __devcgroup_check_permission(type, imajor(inode), iminor(inode),
 741                         access);
 742 }
 743
 744 int devcgroup_inode_mknod(int mode, dev_t dev)
 745 {
 746         short type;
 747
 748         if (!S_ISBLK(mode) && !S_ISCHR(mode))
 749                 return 0;
 750
 751         if (S_ISBLK(mode))
 752                 type = DEV_BLOCK;
 753         else
 754                 type = DEV_CHAR;
 755
 756         return __devcgroup_check_permission(type, MAJOR(dev), MINOR(dev),
 757                         ACC_MKNOD);
 758
 759 }