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_subsys_id));
  62 }
  63
  64 struct cgroup_subsys devices_subsys;
  65
  66 /*
  67  * called under devcgroup_mutex
  68  */
  69 static int dev_exceptions_copy(struct list_head *dest, struct list_head *orig)
  70 {
  71         struct dev_exception_item *ex, *tmp, *new;
  72
  73         lockdep_assert_held(&devcgroup_mutex);
  74
  75         list_for_each_entry(ex, orig, list) {
  76                 new = kmemdup(ex, sizeof(*ex), GFP_KERNEL);
  77                 if (!new)
  78                         goto free_and_exit;
  79                 list_add_tail(&new->list, dest);
  80         }
  81
  82         return 0;
  83
  84 free_and_exit:
  85         list_for_each_entry_safe(ex, tmp, dest, list) {
  86                 list_del(&ex->list);
  87                 kfree(ex);
  88         }
  89         return -ENOMEM;
  90 }
  91
  92 /*
  93  * called under devcgroup_mutex
  94  */
  95 static int dev_exception_add(struct dev_cgroup *dev_cgroup,
  96                              struct dev_exception_item *ex)
  97 {
  98         struct dev_exception_item *excopy, *walk;
  99
 100         lockdep_assert_held(&devcgroup_mutex);
 101
 102         excopy = kmemdup(ex, sizeof(*ex), GFP_KERNEL);
 103         if (!excopy)
 104                 return -ENOMEM;
 105
 106         list_for_each_entry(walk, &dev_cgroup->exceptions, list) {
 107                 if (walk->type != ex->type)
 108                         continue;
 109                 if (walk->major != ex->major)
 110                         continue;
 111                 if (walk->minor != ex->minor)
 112                         continue;
 113
 114                 walk->access |= ex->access;
 115                 kfree(excopy);
 116                 excopy = NULL;
 117         }
 118
 119         if (excopy != NULL)
 120                 list_add_tail_rcu(&excopy->list, &dev_cgroup->exceptions);
 121         return 0;
 122 }
 123
 124 /*
 125  * called under devcgroup_mutex
 126  */
 127 static void dev_exception_rm(struct dev_cgroup *dev_cgroup,
 128                              struct dev_exception_item *ex)
 129 {
 130         struct dev_exception_item *walk, *tmp;
 131
 132         lockdep_assert_held(&devcgroup_mutex);
 133
 134         list_for_each_entry_safe(walk, tmp, &dev_cgroup->exceptions, list) {
 135                 if (walk->type != ex->type)
 136                         continue;
 137                 if (walk->major != ex->major)
 138                         continue;
 139                 if (walk->minor != ex->minor)
 140                         continue;
 141
 142                 walk->access &= ~ex->access;
 143                 if (!walk->access) {
 144                         list_del_rcu(&walk->list);
 145                         kfree_rcu(walk, rcu);
 146                 }
 147         }
 148 }
 149
 150 static void __dev_exception_clean(struct dev_cgroup *dev_cgroup)
 151 {
 152         struct dev_exception_item *ex, *tmp;
 153
 154         list_for_each_entry_safe(ex, tmp, &dev_cgroup->exceptions, list) {
 155                 list_del_rcu(&ex->list);
 156                 kfree_rcu(ex, rcu);
 157         }
 158 }
 159
 160 /**
 161  * dev_exception_clean - frees all entries of the exception list
 162  * @dev_cgroup: dev_cgroup with the exception list to be cleaned
 163  *
 164  * called under devcgroup_mutex
 165  */
 166 static void dev_exception_clean(struct dev_cgroup *dev_cgroup)
 167 {
 168         lockdep_assert_held(&devcgroup_mutex);
 169
 170         __dev_exception_clean(dev_cgroup);
 171 }
 172
 173 static inline bool is_devcg_online(const struct dev_cgroup *devcg)
 174 {
 175         return (devcg->behavior != DEVCG_DEFAULT_NONE);
 176 }
 177
 178 /**
 179  * devcgroup_online - initializes devcgroup's behavior and exceptions based on
 180  *                    parent's
 181  * @css: css getting online
 182  * returns 0 in case of success, error code otherwise
 183  */
 184 static int devcgroup_online(struct cgroup_subsys_state *css)
 185 {
 186         struct dev_cgroup *dev_cgroup = css_to_devcgroup(css);
 187         struct dev_cgroup *parent_dev_cgroup = css_to_devcgroup(css_parent(css));
 188         int ret = 0;
 189
 190         mutex_lock(&devcgroup_mutex);
 191
 192         if (parent_dev_cgroup == NULL)
 193                 dev_cgroup->behavior = DEVCG_DEFAULT_ALLOW;
 194         else {
 195                 ret = dev_exceptions_copy(&dev_cgroup->exceptions,
 196                                           &parent_dev_cgroup->exceptions);
 197                 if (!ret)
 198                         dev_cgroup->behavior = parent_dev_cgroup->behavior;
 199         }
 200         mutex_unlock(&devcgroup_mutex);
 201
 202         return ret;
 203 }
 204
 205 static void devcgroup_offline(struct cgroup_subsys_state *css)
 206 {
 207         struct dev_cgroup *dev_cgroup = css_to_devcgroup(css);
 208
 209         mutex_lock(&devcgroup_mutex);
 210         dev_cgroup->behavior = DEVCG_DEFAULT_NONE;
 211         mutex_unlock(&devcgroup_mutex);
 212 }
 213
 214 /*
 215  * called from kernel/cgroup.c with cgroup_lock() held.
 216  */
 217 static struct cgroup_subsys_state *
 218 devcgroup_css_alloc(struct cgroup_subsys_state *parent_css)
 219 {
 220         struct dev_cgroup *dev_cgroup;
 221
 222         dev_cgroup = kzalloc(sizeof(*dev_cgroup), GFP_KERNEL);
 223         if (!dev_cgroup)
 224                 return ERR_PTR(-ENOMEM);
 225         INIT_LIST_HEAD(&dev_cgroup->exceptions);
 226         dev_cgroup->behavior = DEVCG_DEFAULT_NONE;
 227
 228         return &dev_cgroup->css;
 229 }
 230
 231 static void devcgroup_css_free(struct cgroup_subsys_state *css)
 232 {
 233         struct dev_cgroup *dev_cgroup = css_to_devcgroup(css);
 234
 235         __dev_exception_clean(dev_cgroup);
 236         kfree(dev_cgroup);
 237 }
 238
 239 #define DEVCG_ALLOW 1
 240 #define DEVCG_DENY 2
 241 #define DEVCG_LIST 3
 242
 243 #define MAJMINLEN 13
 244 #define ACCLEN 4
 245
 246 static void set_access(char *acc, short access)
 247 {
 248         int idx = 0;
 249         memset(acc, 0, ACCLEN);
 250         if (access & ACC_READ)
 251                 acc[idx++] = 'r';
 252         if (access & ACC_WRITE)
 253                 acc[idx++] = 'w';
 254         if (access & ACC_MKNOD)
 255                 acc[idx++] = 'm';
 256 }
 257
 258 static char type_to_char(short type)
 259 {
 260         if (type == DEV_ALL)
 261                 return 'a';
 262         if (type == DEV_CHAR)
 263                 return 'c';
 264         if (type == DEV_BLOCK)
 265                 return 'b';
 266         return 'X';
 267 }
 268
 269 static void set_majmin(char *str, unsigned m)
 270 {
 271         if (m == ~0)
 272                 strcpy(str, "*");
 273         else
 274                 sprintf(str, "%u", m);
 275 }
 276
 277 static int devcgroup_seq_show(struct seq_file *m, void *v)
 278 {
 279         struct dev_cgroup *devcgroup = css_to_devcgroup(seq_css(m));
 280         struct dev_exception_item *ex;
 281         char maj[MAJMINLEN], min[MAJMINLEN], acc[ACCLEN];
 282
 283         rcu_read_lock();
 284         /*
 285          * To preserve the compatibility:
 286          * - Only show the "all devices" when the default policy is to allow
 287          * - List the exceptions in case the default policy is to deny
 288          * This way, the file remains as a "whitelist of devices"
 289          */
 290         if (devcgroup->behavior == DEVCG_DEFAULT_ALLOW) {
 291                 set_access(acc, ACC_MASK);
 292                 set_majmin(maj, ~0);
 293                 set_majmin(min, ~0);
 294                 seq_printf(m, "%c %s:%s %s\n", type_to_char(DEV_ALL),
 295                            maj, min, acc);
 296         } else {
 297                 list_for_each_entry_rcu(ex, &devcgroup->exceptions, list) {
 298                         set_access(acc, ex->access);
 299                         set_majmin(maj, ex->major);
 300                         set_majmin(min, ex->minor);
 301                         seq_printf(m, "%c %s:%s %s\n", type_to_char(ex->type),
 302                                    maj, min, acc);
 303                 }
 304         }
 305         rcu_read_unlock();
 306
 307         return 0;
 308 }
 309
 310 /**
 311  * may_access - verifies if a new exception is part of what is allowed
 312  *              by a dev cgroup based on the default policy +
 313  *              exceptions. This is used to make sure a child cgroup
 314  *              won't have more privileges than its parent or to
 315  *              verify if a certain access is allowed.
 316  * @dev_cgroup: dev cgroup to be tested against
 317  * @refex: new exception
 318  * @behavior: behavior of the exception
 319  */
 320 static bool may_access(struct dev_cgroup *dev_cgroup,
 321                        struct dev_exception_item *refex,
 322                        enum devcg_behavior behavior)
 323 {
 324         struct dev_exception_item *ex;
 325         bool match = false;
 326
 327         rcu_lockdep_assert(rcu_read_lock_held() ||
 328                            lockdep_is_held(&devcgroup_mutex),
 329                            "device_cgroup::may_access() called without proper synchronization");
 330
 331         list_for_each_entry_rcu(ex, &dev_cgroup->exceptions, list) {
 332                 if ((refex->type & DEV_BLOCK) && !(ex->type & DEV_BLOCK))
 333                         continue;
 334                 if ((refex->type & DEV_CHAR) && !(ex->type & DEV_CHAR))
 335                         continue;
 336                 if (ex->major != ~0 && ex->major != refex->major)
 337                         continue;
 338                 if (ex->minor != ~0 && ex->minor != refex->minor)
 339                         continue;
 340                 if (refex->access & (~ex->access))
 341                         continue;
 342                 match = true;
 343                 break;
 344         }
 345
 346         if (dev_cgroup->behavior == DEVCG_DEFAULT_ALLOW) {
 347                 if (behavior == DEVCG_DEFAULT_ALLOW) {
 348                         /* the exception will deny access to certain devices */
 349                         return true;
 350                 } else {
 351                         /* the exception will allow access to certain devices */
 352                         if (match)
 353                                 /*
 354                                  * a new exception allowing access shouldn't
 355                                  * match an parent's exception
 356                                  */
 357                                 return false;
 358                         return true;
 359                 }
 360         } else {
 361                 /* only behavior == DEVCG_DEFAULT_DENY allowed here */
 362                 if (match)
 363                         /* parent has an exception that matches the proposed */
 364                         return true;
 365                 else
 366                         return false;
 367         }
 368         return false;
 369 }
 370
 371 /*
 372  * parent_has_perm:
 373  * when adding a new allow rule to a device exception list, the rule
 374  * must be allowed in the parent device
 375  */
 376 static int parent_has_perm(struct dev_cgroup *childcg,
 377                                   struct dev_exception_item *ex)
 378 {
 379         struct dev_cgroup *parent = css_to_devcgroup(css_parent(&childcg->css));
 380
 381         if (!parent)
 382                 return 1;
 383         return may_access(parent, ex, childcg->behavior);
 384 }
 385
 386 /**
 387  * may_allow_all - checks if it's possible to change the behavior to
 388  *                 allow based on parent's rules.
 389  * @parent: device cgroup's parent
 390  * returns: != 0 in case it's allowed, 0 otherwise
 391  */
 392 static inline int may_allow_all(struct dev_cgroup *parent)
 393 {
 394         if (!parent)
 395                 return 1;
 396         return parent->behavior == DEVCG_DEFAULT_ALLOW;
 397 }
 398
 399 /**
 400  * revalidate_active_exceptions - walks through the active exception list and
 401  *                                revalidates the exceptions based on parent's
 402  *                                behavior and exceptions. The exceptions that
 403  *                                are no longer valid will be removed.
 404  *                                Called with devcgroup_mutex held.
 405  * @devcg: cgroup which exceptions will be checked
 406  *
 407  * This is one of the three key functions for hierarchy implementation.
 408  * This function is responsible for re-evaluating all the cgroup's active
 409  * exceptions due to a parent's exception change.
 410  * Refer to Documentation/cgroups/devices.txt for more details.
 411  */
 412 static void revalidate_active_exceptions(struct dev_cgroup *devcg)
 413 {
 414         struct dev_exception_item *ex;
 415         struct list_head *this, *tmp;
 416
 417         list_for_each_safe(this, tmp, &devcg->exceptions) {
 418                 ex = container_of(this, struct dev_exception_item, list);
 419                 if (!parent_has_perm(devcg, ex))
 420                         dev_exception_rm(devcg, ex);
 421         }
 422 }
 423
 424 /**
 425  * propagate_exception - propagates a new exception to the children
 426  * @devcg_root: device cgroup that added a new exception
 427  * @ex: new exception to be propagated
 428  *
 429  * returns: 0 in case of success, != 0 in case of error
 430  */
 431 static int propagate_exception(struct dev_cgroup *devcg_root,
 432                                struct dev_exception_item *ex)
 433 {
 434         struct cgroup_subsys_state *pos;
 435         int rc = 0;
 436
 437         rcu_read_lock();
 438
 439         css_for_each_descendant_pre(pos, &devcg_root->css) {
 440                 struct dev_cgroup *devcg = css_to_devcgroup(pos);
 441
 442                 /*
 443                  * Because devcgroup_mutex is held, no devcg will become
 444                  * online or offline during the tree walk (see on/offline
 445                  * methods), and online ones are safe to access outside RCU
 446                  * read lock without bumping refcnt.
 447                  */
 448                 if (pos == &devcg_root->css || !is_devcg_online(devcg))
 449                         continue;
 450
 451                 rcu_read_unlock();
 452
 453                 /*
 454                  * in case both root's behavior and devcg is allow, a new
 455                  * restriction means adding to the exception list
 456                  */
 457                 if (devcg_root->behavior == DEVCG_DEFAULT_ALLOW &&
 458                     devcg->behavior == DEVCG_DEFAULT_ALLOW) {
 459                         rc = dev_exception_add(devcg, ex);
 460                         if (rc)
 461                                 break;
 462                 } else {
 463                         /*
 464                          * in the other possible cases:
 465                          * root's behavior: allow, devcg's: deny
 466                          * root's behavior: deny, devcg's: deny
 467                          * the exception will be removed
 468                          */
 469                         dev_exception_rm(devcg, ex);
 470                 }
 471                 revalidate_active_exceptions(devcg);
 472
 473                 rcu_read_lock();
 474         }
 475
 476         rcu_read_unlock();
 477         return rc;
 478 }
 479
 480 static inline bool has_children(struct dev_cgroup *devcgroup)
 481 {
 482         struct cgroup *cgrp = devcgroup->css.cgroup;
 483
 484         return !list_empty(&cgrp->children);
 485 }
 486
 487 /*
 488  * Modify the exception list using allow/deny rules.
 489  * CAP_SYS_ADMIN is needed for this.  It's at least separate from CAP_MKNOD
 490  * so we can give a container CAP_MKNOD to let it create devices but not
 491  * modify the exception list.
 492  * It seems likely we'll want to add a CAP_CONTAINER capability to allow
 493  * us to also grant CAP_SYS_ADMIN to containers without giving away the
 494  * device exception list controls, but for now we'll stick with CAP_SYS_ADMIN
 495  *
 496  * Taking rules away is always allowed (given CAP_SYS_ADMIN).  Granting
 497  * new access is only allowed if you're in the top-level cgroup, or your
 498  * parent cgroup has the access you're asking for.
 499  */
 500 static int devcgroup_update_access(struct dev_cgroup *devcgroup,
 501                                    int filetype, const char *buffer)
 502 {
 503         const char *b;
 504         char temp[12];          /* 11 + 1 characters needed for a u32 */
 505         int count, rc = 0;
 506         struct dev_exception_item ex;
 507         struct dev_cgroup *parent = css_to_devcgroup(css_parent(&devcgroup->css));
 508
 509         if (!capable(CAP_SYS_ADMIN))
 510                 return -EPERM;
 511
 512         memset(&ex, 0, sizeof(ex));
 513         b = buffer;
 514
 515         switch (*b) {
 516         case 'a':
 517                 switch (filetype) {
 518                 case DEVCG_ALLOW:
 519                         if (has_children(devcgroup))
 520                                 return -EINVAL;
 521
 522                         if (!may_allow_all(parent))
 523                                 return -EPERM;
 524                         dev_exception_clean(devcgroup);
 525                         devcgroup->behavior = DEVCG_DEFAULT_ALLOW;
 526                         if (!parent)
 527                                 break;
 528
 529                         rc = dev_exceptions_copy(&devcgroup->exceptions,
 530                                                  &parent->exceptions);
 531                         if (rc)
 532                                 return rc;
 533                         break;
 534                 case DEVCG_DENY:
 535                         if (has_children(devcgroup))
 536                                 return -EINVAL;
 537
 538                         dev_exception_clean(devcgroup);
 539                         devcgroup->behavior = DEVCG_DEFAULT_DENY;
 540                         break;
 541                 default:
 542                         return -EINVAL;
 543                 }
 544                 return 0;
 545         case 'b':
 546                 ex.type = DEV_BLOCK;
 547                 break;
 548         case 'c':
 549                 ex.type = DEV_CHAR;
 550                 break;
 551         default:
 552                 return -EINVAL;
 553         }
 554         b++;
 555         if (!isspace(*b))
 556                 return -EINVAL;
 557         b++;
 558         if (*b == '*') {
 559                 ex.major = ~0;
 560                 b++;
 561         } else if (isdigit(*b)) {
 562                 memset(temp, 0, sizeof(temp));
 563                 for (count = 0; count < sizeof(temp) - 1; count++) {
 564                         temp[count] = *b;
 565                         b++;
 566                         if (!isdigit(*b))
 567                                 break;
 568                 }
 569                 rc = kstrtou32(temp, 10, &ex.major);
 570                 if (rc)
 571                         return -EINVAL;
 572         } else {
 573                 return -EINVAL;
 574         }
 575         if (*b != ':')
 576                 return -EINVAL;
 577         b++;
 578
 579         /* read minor */
 580         if (*b == '*') {
 581                 ex.minor = ~0;
 582                 b++;
 583         } else if (isdigit(*b)) {
 584                 memset(temp, 0, sizeof(temp));
 585                 for (count = 0; count < sizeof(temp) - 1; count++) {
 586                         temp[count] = *b;
 587                         b++;
 588                         if (!isdigit(*b))
 589                                 break;
 590                 }
 591                 rc = kstrtou32(temp, 10, &ex.minor);
 592                 if (rc)
 593                         return -EINVAL;
 594         } else {
 595                 return -EINVAL;
 596         }
 597         if (!isspace(*b))
 598                 return -EINVAL;
 599         for (b++, count = 0; count < 3; count++, b++) {
 600                 switch (*b) {
 601                 case 'r':
 602                         ex.access |= ACC_READ;
 603                         break;
 604                 case 'w':
 605                         ex.access |= ACC_WRITE;
 606                         break;
 607                 case 'm':
 608                         ex.access |= ACC_MKNOD;
 609                         break;
 610                 case '\n':
 611                 case '\0':
 612                         count = 3;
 613                         break;
 614                 default:
 615                         return -EINVAL;
 616                 }
 617         }
 618
 619         switch (filetype) {
 620         case DEVCG_ALLOW:
 621                 if (!parent_has_perm(devcgroup, &ex))
 622                         return -EPERM;
 623                 /*
 624                  * If the default policy is to allow by default, try to remove
 625                  * an matching exception instead. And be silent about it: we
 626                  * don't want to break compatibility
 627                  */
 628                 if (devcgroup->behavior == DEVCG_DEFAULT_ALLOW) {
 629                         dev_exception_rm(devcgroup, &ex);
 630                         return 0;
 631                 }
 632                 rc = dev_exception_add(devcgroup, &ex);
 633                 break;
 634         case DEVCG_DENY:
 635                 /*
 636                  * If the default policy is to deny by default, try to remove
 637                  * an matching exception instead. And be silent about it: we
 638                  * don't want to break compatibility
 639                  */
 640                 if (devcgroup->behavior == DEVCG_DEFAULT_DENY)
 641                         dev_exception_rm(devcgroup, &ex);
 642                 else
 643                         rc = dev_exception_add(devcgroup, &ex);
 644
 645                 if (rc)
 646                         break;
 647                 /* we only propagate new restrictions */
 648                 rc = propagate_exception(devcgroup, &ex);
 649                 break;
 650         default:
 651                 rc = -EINVAL;
 652         }
 653         return rc;
 654 }
 655
 656 static int devcgroup_access_write(struct cgroup_subsys_state *css,
 657                                   struct cftype *cft, const char *buffer)
 658 {
 659         int retval;
 660
 661         mutex_lock(&devcgroup_mutex);
 662         retval = devcgroup_update_access(css_to_devcgroup(css),
 663                                          cft->private, buffer);
 664         mutex_unlock(&devcgroup_mutex);
 665         return retval;
 666 }
 667
 668 static struct cftype dev_cgroup_files[] = {
 669         {
 670                 .name = "allow",
 671                 .write_string  = devcgroup_access_write,
 672                 .private = DEVCG_ALLOW,
 673         },
 674         {
 675                 .name = "deny",
 676                 .write_string = devcgroup_access_write,
 677                 .private = DEVCG_DENY,
 678         },
 679         {
 680                 .name = "list",
 681                 .seq_show = devcgroup_seq_show,
 682                 .private = DEVCG_LIST,
 683         },
 684         { }     /* terminate */
 685 };
 686
 687 struct cgroup_subsys devices_subsys = {
 688         .name = "devices",
 689         .css_alloc = devcgroup_css_alloc,
 690         .css_free = devcgroup_css_free,
 691         .css_online = devcgroup_online,
 692         .css_offline = devcgroup_offline,
 693         .subsys_id = devices_subsys_id,
 694         .base_cftypes = dev_cgroup_files,
 695 };
 696
 697 /**
 698  * __devcgroup_check_permission - checks if an inode operation is permitted
 699  * @dev_cgroup: the dev cgroup to be tested against
 700  * @type: device type
 701  * @major: device major number
 702  * @minor: device minor number
 703  * @access: combination of ACC_WRITE, ACC_READ and ACC_MKNOD
 704  *
 705  * returns 0 on success, -EPERM case the operation is not permitted
 706  */
 707 static int __devcgroup_check_permission(short type, u32 major, u32 minor,
 708                                         short access)
 709 {
 710         struct dev_cgroup *dev_cgroup;
 711         struct dev_exception_item ex;
 712         int rc;
 713
 714         memset(&ex, 0, sizeof(ex));
 715         ex.type = type;
 716         ex.major = major;
 717         ex.minor = minor;
 718         ex.access = access;
 719
 720         rcu_read_lock();
 721         dev_cgroup = task_devcgroup(current);
 722         rc = may_access(dev_cgroup, &ex, dev_cgroup->behavior);
 723         rcu_read_unlock();
 724
 725         if (!rc)
 726                 return -EPERM;
 727
 728         return 0;
 729 }
 730
 731 int __devcgroup_inode_permission(struct inode *inode, int mask)
 732 {
 733         short type, access = 0;
 734
 735         if (S_ISBLK(inode->i_mode))
 736                 type = DEV_BLOCK;
 737         if (S_ISCHR(inode->i_mode))
 738                 type = DEV_CHAR;
 739         if (mask & MAY_WRITE)
 740                 access |= ACC_WRITE;
 741         if (mask & MAY_READ)
 742                 access |= ACC_READ;
 743
 744         return __devcgroup_check_permission(type, imajor(inode), iminor(inode),
 745                         access);
 746 }
 747
 748 int devcgroup_inode_mknod(int mode, dev_t dev)
 749 {
 750         short type;
 751
 752         if (!S_ISBLK(mode) && !S_ISCHR(mode))
 753                 return 0;
 754
 755         if (S_ISBLK(mode))
 756                 type = DEV_BLOCK;
 757         else
 758                 type = DEV_CHAR;
 759
 760         return __devcgroup_check_permission(type, MAJOR(dev), MINOR(dev),
 761                         ACC_MKNOD);
 762
 763 }