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_read(struct cgroup_subsys_state *css,
 278                               struct cftype *cft, struct seq_file *m)
 279 {
 280         struct dev_cgroup *devcgroup = css_to_devcgroup(css);
 281         struct dev_exception_item *ex;
 282         char maj[MAJMINLEN], min[MAJMINLEN], acc[ACCLEN];
 283
 284         rcu_read_lock();
 285         /*
 286          * To preserve the compatibility:
 287          * - Only show the "all devices" when the default policy is to allow
 288          * - List the exceptions in case the default policy is to deny
 289          * This way, the file remains as a "whitelist of devices"
 290          */
 291         if (devcgroup->behavior == DEVCG_DEFAULT_ALLOW) {
 292                 set_access(acc, ACC_MASK);
 293                 set_majmin(maj, ~0);
 294                 set_majmin(min, ~0);
 295                 seq_printf(m, "%c %s:%s %s\n", type_to_char(DEV_ALL),
 296                            maj, min, acc);
 297         } else {
 298                 list_for_each_entry_rcu(ex, &devcgroup->exceptions, list) {
 299                         set_access(acc, ex->access);
 300                         set_majmin(maj, ex->major);
 301                         set_majmin(min, ex->minor);
 302                         seq_printf(m, "%c %s:%s %s\n", type_to_char(ex->type),
 303                                    maj, min, acc);
 304                 }
 305         }
 306         rcu_read_unlock();
 307
 308         return 0;
 309 }
 310
 311 /**
 312  * may_access - verifies if a new exception is part of what is allowed
 313  *              by a dev cgroup based on the default policy +
 314  *              exceptions. This is used to make sure a child cgroup
 315  *              won't have more privileges than its parent or to
 316  *              verify if a certain access is allowed.
 317  * @dev_cgroup: dev cgroup to be tested against
 318  * @refex: new exception
 319  * @behavior: behavior of the exception
 320  */
 321 static bool may_access(struct dev_cgroup *dev_cgroup,
 322                        struct dev_exception_item *refex,
 323                        enum devcg_behavior behavior)
 324 {
 325         struct dev_exception_item *ex;
 326         bool match = false;
 327
 328         rcu_lockdep_assert(rcu_read_lock_held() ||
 329                            lockdep_is_held(&devcgroup_mutex),
 330                            "device_cgroup::may_access() called without proper synchronization");
 331
 332         list_for_each_entry_rcu(ex, &dev_cgroup->exceptions, list) {
 333                 if ((refex->type & DEV_BLOCK) && !(ex->type & DEV_BLOCK))
 334                         continue;
 335                 if ((refex->type & DEV_CHAR) && !(ex->type & DEV_CHAR))
 336                         continue;
 337                 if (ex->major != ~0 && ex->major != refex->major)
 338                         continue;
 339                 if (ex->minor != ~0 && ex->minor != refex->minor)
 340                         continue;
 341                 if (refex->access & (~ex->access))
 342                         continue;
 343                 match = true;
 344                 break;
 345         }
 346
 347         if (dev_cgroup->behavior == DEVCG_DEFAULT_ALLOW) {
 348                 if (behavior == DEVCG_DEFAULT_ALLOW) {
 349                         /* the exception will deny access to certain devices */
 350                         return true;
 351                 } else {
 352                         /* the exception will allow access to certain devices */
 353                         if (match)
 354                                 /*
 355                                  * a new exception allowing access shouldn't
 356                                  * match an parent's exception
 357                                  */
 358                                 return false;
 359                         return true;
 360                 }
 361         } else {
 362                 /* only behavior == DEVCG_DEFAULT_DENY allowed here */
 363                 if (match)
 364                         /* parent has an exception that matches the proposed */
 365                         return true;
 366                 else
 367                         return false;
 368         }
 369         return false;
 370 }
 371
 372 /*
 373  * parent_has_perm:
 374  * when adding a new allow rule to a device exception list, the rule
 375  * must be allowed in the parent device
 376  */
 377 static int parent_has_perm(struct dev_cgroup *childcg,
 378                                   struct dev_exception_item *ex)
 379 {
 380         struct dev_cgroup *parent = css_to_devcgroup(css_parent(&childcg->css));
 381
 382         if (!parent)
 383                 return 1;
 384         return may_access(parent, ex, childcg->behavior);
 385 }
 386
 387 /**
 388  * may_allow_all - checks if it's possible to change the behavior to
 389  *                 allow based on parent's rules.
 390  * @parent: device cgroup's parent
 391  * returns: != 0 in case it's allowed, 0 otherwise
 392  */
 393 static inline int may_allow_all(struct dev_cgroup *parent)
 394 {
 395         if (!parent)
 396                 return 1;
 397         return parent->behavior == DEVCG_DEFAULT_ALLOW;
 398 }
 399
 400 /**
 401  * revalidate_active_exceptions - walks through the active exception list and
 402  *                                revalidates the exceptions based on parent's
 403  *                                behavior and exceptions. The exceptions that
 404  *                                are no longer valid will be removed.
 405  *                                Called with devcgroup_mutex held.
 406  * @devcg: cgroup which exceptions will be checked
 407  *
 408  * This is one of the three key functions for hierarchy implementation.
 409  * This function is responsible for re-evaluating all the cgroup's active
 410  * exceptions due to a parent's exception change.
 411  * Refer to Documentation/cgroups/devices.txt for more details.
 412  */
 413 static void revalidate_active_exceptions(struct dev_cgroup *devcg)
 414 {
 415         struct dev_exception_item *ex;
 416         struct list_head *this, *tmp;
 417
 418         list_for_each_safe(this, tmp, &devcg->exceptions) {
 419                 ex = container_of(this, struct dev_exception_item, list);
 420                 if (!parent_has_perm(devcg, ex))
 421                         dev_exception_rm(devcg, ex);
 422         }
 423 }
 424
 425 /**
 426  * propagate_exception - propagates a new exception to the children
 427  * @devcg_root: device cgroup that added a new exception
 428  * @ex: new exception to be propagated
 429  *
 430  * returns: 0 in case of success, != 0 in case of error
 431  */
 432 static int propagate_exception(struct dev_cgroup *devcg_root,
 433                                struct dev_exception_item *ex)
 434 {
 435         struct cgroup_subsys_state *pos;
 436         int rc = 0;
 437
 438         rcu_read_lock();
 439
 440         css_for_each_descendant_pre(pos, &devcg_root->css) {
 441                 struct dev_cgroup *devcg = css_to_devcgroup(pos);
 442
 443                 /*
 444                  * Because devcgroup_mutex is held, no devcg will become
 445                  * online or offline during the tree walk (see on/offline
 446                  * methods), and online ones are safe to access outside RCU
 447                  * read lock without bumping refcnt.
 448                  */
 449                 if (pos == &devcg_root->css || !is_devcg_online(devcg))
 450                         continue;
 451
 452                 rcu_read_unlock();
 453
 454                 /*
 455                  * in case both root's behavior and devcg is allow, a new
 456                  * restriction means adding to the exception list
 457                  */
 458                 if (devcg_root->behavior == DEVCG_DEFAULT_ALLOW &&
 459                     devcg->behavior == DEVCG_DEFAULT_ALLOW) {
 460                         rc = dev_exception_add(devcg, ex);
 461                         if (rc)
 462                                 break;
 463                 } else {
 464                         /*
 465                          * in the other possible cases:
 466                          * root's behavior: allow, devcg's: deny
 467                          * root's behavior: deny, devcg's: deny
 468                          * the exception will be removed
 469                          */
 470                         dev_exception_rm(devcg, ex);
 471                 }
 472                 revalidate_active_exceptions(devcg);
 473
 474                 rcu_read_lock();
 475         }
 476
 477         rcu_read_unlock();
 478         return rc;
 479 }
 480
 481 static inline bool has_children(struct dev_cgroup *devcgroup)
 482 {
 483         struct cgroup *cgrp = devcgroup->css.cgroup;
 484
 485         return !list_empty(&cgrp->children);
 486 }
 487
 488 /*
 489  * Modify the exception list using allow/deny rules.
 490  * CAP_SYS_ADMIN is needed for this.  It's at least separate from CAP_MKNOD
 491  * so we can give a container CAP_MKNOD to let it create devices but not
 492  * modify the exception list.
 493  * It seems likely we'll want to add a CAP_CONTAINER capability to allow
 494  * us to also grant CAP_SYS_ADMIN to containers without giving away the
 495  * device exception list controls, but for now we'll stick with CAP_SYS_ADMIN
 496  *
 497  * Taking rules away is always allowed (given CAP_SYS_ADMIN).  Granting
 498  * new access is only allowed if you're in the top-level cgroup, or your
 499  * parent cgroup has the access you're asking for.
 500  */
 501 static int devcgroup_update_access(struct dev_cgroup *devcgroup,
 502                                    int filetype, const char *buffer)
 503 {
 504         const char *b;
 505         char temp[12];          /* 11 + 1 characters needed for a u32 */
 506         int count, rc = 0;
 507         struct dev_exception_item ex;
 508         struct dev_cgroup *parent = css_to_devcgroup(css_parent(&devcgroup->css));
 509
 510         if (!capable(CAP_SYS_ADMIN))
 511                 return -EPERM;
 512
 513         memset(&ex, 0, sizeof(ex));
 514         b = buffer;
 515
 516         switch (*b) {
 517         case 'a':
 518                 switch (filetype) {
 519                 case DEVCG_ALLOW:
 520                         if (has_children(devcgroup))
 521                                 return -EINVAL;
 522
 523                         if (!may_allow_all(parent))
 524                                 return -EPERM;
 525                         dev_exception_clean(devcgroup);
 526                         devcgroup->behavior = DEVCG_DEFAULT_ALLOW;
 527                         if (!parent)
 528                                 break;
 529
 530                         rc = dev_exceptions_copy(&devcgroup->exceptions,
 531                                                  &parent->exceptions);
 532                         if (rc)
 533                                 return rc;
 534                         break;
 535                 case DEVCG_DENY:
 536                         if (has_children(devcgroup))
 537                                 return -EINVAL;
 538
 539                         dev_exception_clean(devcgroup);
 540                         devcgroup->behavior = DEVCG_DEFAULT_DENY;
 541                         break;
 542                 default:
 543                         return -EINVAL;
 544                 }
 545                 return 0;
 546         case 'b':
 547                 ex.type = DEV_BLOCK;
 548                 break;
 549         case 'c':
 550                 ex.type = DEV_CHAR;
 551                 break;
 552         default:
 553                 return -EINVAL;
 554         }
 555         b++;
 556         if (!isspace(*b))
 557                 return -EINVAL;
 558         b++;
 559         if (*b == '*') {
 560                 ex.major = ~0;
 561                 b++;
 562         } else if (isdigit(*b)) {
 563                 memset(temp, 0, sizeof(temp));
 564                 for (count = 0; count < sizeof(temp) - 1; count++) {
 565                         temp[count] = *b;
 566                         b++;
 567                         if (!isdigit(*b))
 568                                 break;
 569                 }
 570                 rc = kstrtou32(temp, 10, &ex.major);
 571                 if (rc)
 572                         return -EINVAL;
 573         } else {
 574                 return -EINVAL;
 575         }
 576         if (*b != ':')
 577                 return -EINVAL;
 578         b++;
 579
 580         /* read minor */
 581         if (*b == '*') {
 582                 ex.minor = ~0;
 583                 b++;
 584         } else if (isdigit(*b)) {
 585                 memset(temp, 0, sizeof(temp));
 586                 for (count = 0; count < sizeof(temp) - 1; count++) {
 587                         temp[count] = *b;
 588                         b++;
 589                         if (!isdigit(*b))
 590                                 break;
 591                 }
 592                 rc = kstrtou32(temp, 10, &ex.minor);
 593                 if (rc)
 594                         return -EINVAL;
 595         } else {
 596                 return -EINVAL;
 597         }
 598         if (!isspace(*b))
 599                 return -EINVAL;
 600         for (b++, count = 0; count < 3; count++, b++) {
 601                 switch (*b) {
 602                 case 'r':
 603                         ex.access |= ACC_READ;
 604                         break;
 605                 case 'w':
 606                         ex.access |= ACC_WRITE;
 607                         break;
 608                 case 'm':
 609                         ex.access |= ACC_MKNOD;
 610                         break;
 611                 case '\n':
 612                 case '\0':
 613                         count = 3;
 614                         break;
 615                 default:
 616                         return -EINVAL;
 617                 }
 618         }
 619
 620         switch (filetype) {
 621         case DEVCG_ALLOW:
 622                 if (!parent_has_perm(devcgroup, &ex))
 623                         return -EPERM;
 624                 /*
 625                  * If the default policy is to allow by default, try to remove
 626                  * an matching exception instead. And be silent about it: we
 627                  * don't want to break compatibility
 628                  */
 629                 if (devcgroup->behavior == DEVCG_DEFAULT_ALLOW) {
 630                         dev_exception_rm(devcgroup, &ex);
 631                         return 0;
 632                 }
 633                 rc = dev_exception_add(devcgroup, &ex);
 634                 break;
 635         case DEVCG_DENY:
 636                 /*
 637                  * If the default policy is to deny by default, try to remove
 638                  * an matching exception instead. And be silent about it: we
 639                  * don't want to break compatibility
 640                  */
 641                 if (devcgroup->behavior == DEVCG_DEFAULT_DENY)
 642                         dev_exception_rm(devcgroup, &ex);
 643                 else
 644                         rc = dev_exception_add(devcgroup, &ex);
 645
 646                 if (rc)
 647                         break;
 648                 /* we only propagate new restrictions */
 649                 rc = propagate_exception(devcgroup, &ex);
 650                 break;
 651         default:
 652                 rc = -EINVAL;
 653         }
 654         return rc;
 655 }
 656
 657 static int devcgroup_access_write(struct cgroup_subsys_state *css,
 658                                   struct cftype *cft, const char *buffer)
 659 {
 660         int retval;
 661
 662         mutex_lock(&devcgroup_mutex);
 663         retval = devcgroup_update_access(css_to_devcgroup(css),
 664                                          cft->private, buffer);
 665         mutex_unlock(&devcgroup_mutex);
 666         return retval;
 667 }
 668
 669 static struct cftype dev_cgroup_files[] = {
 670         {
 671                 .name = "allow",
 672                 .write_string  = devcgroup_access_write,
 673                 .private = DEVCG_ALLOW,
 674         },
 675         {
 676                 .name = "deny",
 677                 .write_string = devcgroup_access_write,
 678                 .private = DEVCG_DENY,
 679         },
 680         {
 681                 .name = "list",
 682                 .read_seq_string = devcgroup_seq_read,
 683                 .private = DEVCG_LIST,
 684         },
 685         { }     /* terminate */
 686 };
 687
 688 struct cgroup_subsys devices_subsys = {
 689         .name = "devices",
 690         .css_alloc = devcgroup_css_alloc,
 691         .css_free = devcgroup_css_free,
 692         .css_online = devcgroup_online,
 693         .css_offline = devcgroup_offline,
 694         .subsys_id = devices_subsys_id,
 695         .base_cftypes = dev_cgroup_files,
 696 };
 697
 698 /**
 699  * __devcgroup_check_permission - checks if an inode operation is permitted
 700  * @dev_cgroup: the dev cgroup to be tested against
 701  * @type: device type
 702  * @major: device major number
 703  * @minor: device minor number
 704  * @access: combination of ACC_WRITE, ACC_READ and ACC_MKNOD
 705  *
 706  * returns 0 on success, -EPERM case the operation is not permitted
 707  */
 708 static int __devcgroup_check_permission(short type, u32 major, u32 minor,
 709                                         short access)
 710 {
 711         struct dev_cgroup *dev_cgroup;
 712         struct dev_exception_item ex;
 713         int rc;
 714
 715         memset(&ex, 0, sizeof(ex));
 716         ex.type = type;
 717         ex.major = major;
 718         ex.minor = minor;
 719         ex.access = access;
 720
 721         rcu_read_lock();
 722         dev_cgroup = task_devcgroup(current);
 723         rc = may_access(dev_cgroup, &ex, dev_cgroup->behavior);
 724         rcu_read_unlock();
 725
 726         if (!rc)
 727                 return -EPERM;
 728
 729         return 0;
 730 }
 731
 732 int __devcgroup_inode_permission(struct inode *inode, int mask)
 733 {
 734         short type, access = 0;
 735
 736         if (S_ISBLK(inode->i_mode))
 737                 type = DEV_BLOCK;
 738         if (S_ISCHR(inode->i_mode))
 739                 type = DEV_CHAR;
 740         if (mask & MAY_WRITE)
 741                 access |= ACC_WRITE;
 742         if (mask & MAY_READ)
 743                 access |= ACC_READ;
 744
 745         return __devcgroup_check_permission(type, imajor(inode), iminor(inode),
 746                         access);
 747 }
 748
 749 int devcgroup_inode_mknod(int mode, dev_t dev)
 750 {
 751         short type;
 752
 753         if (!S_ISBLK(mode) && !S_ISCHR(mode))
 754                 return 0;
 755
 756         if (S_ISBLK(mode))
 757                 type = DEV_BLOCK;
 758         else
 759                 type = DEV_CHAR;
 760
 761         return __devcgroup_check_permission(type, MAJOR(dev), MINOR(dev),
 762                         ACC_MKNOD);
 763
 764 }