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 container_of(s, struct dev_cgroup, css);
  57 }
  58
  59 static inline struct dev_cgroup *cgroup_to_devcgroup(struct cgroup *cgroup)
  60 {
  61         return css_to_devcgroup(cgroup_subsys_state(cgroup, devices_subsys_id));
  62 }
  63
  64 static inline struct dev_cgroup *task_devcgroup(struct task_struct *task)
  65 {
  66         return css_to_devcgroup(task_subsys_state(task, devices_subsys_id));
  67 }
  68
  69 struct cgroup_subsys devices_subsys;
  70
  71 static int devcgroup_can_attach(struct cgroup *new_cgrp,
  72                                 struct cgroup_taskset *set)
  73 {
  74         struct task_struct *task = cgroup_taskset_first(set);
  75
  76         if (current != task && !capable(CAP_SYS_ADMIN))
  77                 return -EPERM;
  78         return 0;
  79 }
  80
  81 /*
  82  * called under devcgroup_mutex
  83  */
  84 static int dev_exceptions_copy(struct list_head *dest, struct list_head *orig)
  85 {
  86         struct dev_exception_item *ex, *tmp, *new;
  87
  88         lockdep_assert_held(&devcgroup_mutex);
  89
  90         list_for_each_entry(ex, orig, list) {
  91                 new = kmemdup(ex, sizeof(*ex), GFP_KERNEL);
  92                 if (!new)
  93                         goto free_and_exit;
  94                 list_add_tail(&new->list, dest);
  95         }
  96
  97         return 0;
  98
  99 free_and_exit:
 100         list_for_each_entry_safe(ex, tmp, dest, list) {
 101                 list_del(&ex->list);
 102                 kfree(ex);
 103         }
 104         return -ENOMEM;
 105 }
 106
 107 /*
 108  * called under devcgroup_mutex
 109  */
 110 static int dev_exception_add(struct dev_cgroup *dev_cgroup,
 111                              struct dev_exception_item *ex)
 112 {
 113         struct dev_exception_item *excopy, *walk;
 114
 115         lockdep_assert_held(&devcgroup_mutex);
 116
 117         excopy = kmemdup(ex, sizeof(*ex), GFP_KERNEL);
 118         if (!excopy)
 119                 return -ENOMEM;
 120
 121         list_for_each_entry(walk, &dev_cgroup->exceptions, list) {
 122                 if (walk->type != ex->type)
 123                         continue;
 124                 if (walk->major != ex->major)
 125                         continue;
 126                 if (walk->minor != ex->minor)
 127                         continue;
 128
 129                 walk->access |= ex->access;
 130                 kfree(excopy);
 131                 excopy = NULL;
 132         }
 133
 134         if (excopy != NULL)
 135                 list_add_tail_rcu(&excopy->list, &dev_cgroup->exceptions);
 136         return 0;
 137 }
 138
 139 /*
 140  * called under devcgroup_mutex
 141  */
 142 static void dev_exception_rm(struct dev_cgroup *dev_cgroup,
 143                              struct dev_exception_item *ex)
 144 {
 145         struct dev_exception_item *walk, *tmp;
 146
 147         lockdep_assert_held(&devcgroup_mutex);
 148
 149         list_for_each_entry_safe(walk, tmp, &dev_cgroup->exceptions, list) {
 150                 if (walk->type != ex->type)
 151                         continue;
 152                 if (walk->major != ex->major)
 153                         continue;
 154                 if (walk->minor != ex->minor)
 155                         continue;
 156
 157                 walk->access &= ~ex->access;
 158                 if (!walk->access) {
 159                         list_del_rcu(&walk->list);
 160                         kfree_rcu(walk, rcu);
 161                 }
 162         }
 163 }
 164
 165 static void __dev_exception_clean(struct dev_cgroup *dev_cgroup)
 166 {
 167         struct dev_exception_item *ex, *tmp;
 168
 169         list_for_each_entry_safe(ex, tmp, &dev_cgroup->exceptions, list) {
 170                 list_del_rcu(&ex->list);
 171                 kfree_rcu(ex, rcu);
 172         }
 173 }
 174
 175 /**
 176  * dev_exception_clean - frees all entries of the exception list
 177  * @dev_cgroup: dev_cgroup with the exception list to be cleaned
 178  *
 179  * called under devcgroup_mutex
 180  */
 181 static void dev_exception_clean(struct dev_cgroup *dev_cgroup)
 182 {
 183         lockdep_assert_held(&devcgroup_mutex);
 184
 185         __dev_exception_clean(dev_cgroup);
 186 }
 187
 188 static inline bool is_devcg_online(const struct dev_cgroup *devcg)
 189 {
 190         return (devcg->behavior != DEVCG_DEFAULT_NONE);
 191 }
 192
 193 /**
 194  * devcgroup_online - initializes devcgroup's behavior and exceptions based on
 195  *                    parent's
 196  * @cgroup: cgroup getting online
 197  * returns 0 in case of success, error code otherwise
 198  */
 199 static int devcgroup_online(struct cgroup *cgroup)
 200 {
 201         struct dev_cgroup *dev_cgroup, *parent_dev_cgroup = NULL;
 202         int ret = 0;
 203
 204         mutex_lock(&devcgroup_mutex);
 205         dev_cgroup = cgroup_to_devcgroup(cgroup);
 206         if (cgroup->parent)
 207                 parent_dev_cgroup = cgroup_to_devcgroup(cgroup->parent);
 208
 209         if (parent_dev_cgroup == NULL)
 210                 dev_cgroup->behavior = DEVCG_DEFAULT_ALLOW;
 211         else {
 212                 ret = dev_exceptions_copy(&dev_cgroup->exceptions,
 213                                           &parent_dev_cgroup->exceptions);
 214                 if (!ret)
 215                         dev_cgroup->behavior = parent_dev_cgroup->behavior;
 216         }
 217         mutex_unlock(&devcgroup_mutex);
 218
 219         return ret;
 220 }
 221
 222 static void devcgroup_offline(struct cgroup *cgroup)
 223 {
 224         struct dev_cgroup *dev_cgroup = cgroup_to_devcgroup(cgroup);
 225
 226         mutex_lock(&devcgroup_mutex);
 227         dev_cgroup->behavior = DEVCG_DEFAULT_NONE;
 228         mutex_unlock(&devcgroup_mutex);
 229 }
 230
 231 /*
 232  * called from kernel/cgroup.c with cgroup_lock() held.
 233  */
 234 static struct cgroup_subsys_state *devcgroup_css_alloc(struct cgroup *cgroup)
 235 {
 236         struct dev_cgroup *dev_cgroup;
 237
 238         dev_cgroup = kzalloc(sizeof(*dev_cgroup), GFP_KERNEL);
 239         if (!dev_cgroup)
 240                 return ERR_PTR(-ENOMEM);
 241         INIT_LIST_HEAD(&dev_cgroup->exceptions);
 242         dev_cgroup->behavior = DEVCG_DEFAULT_NONE;
 243
 244         return &dev_cgroup->css;
 245 }
 246
 247 static void devcgroup_css_free(struct cgroup *cgroup)
 248 {
 249         struct dev_cgroup *dev_cgroup;
 250
 251         dev_cgroup = cgroup_to_devcgroup(cgroup);
 252         __dev_exception_clean(dev_cgroup);
 253         kfree(dev_cgroup);
 254 }
 255
 256 #define DEVCG_ALLOW 1
 257 #define DEVCG_DENY 2
 258 #define DEVCG_LIST 3
 259
 260 #define MAJMINLEN 13
 261 #define ACCLEN 4
 262
 263 static void set_access(char *acc, short access)
 264 {
 265         int idx = 0;
 266         memset(acc, 0, ACCLEN);
 267         if (access & ACC_READ)
 268                 acc[idx++] = 'r';
 269         if (access & ACC_WRITE)
 270                 acc[idx++] = 'w';
 271         if (access & ACC_MKNOD)
 272                 acc[idx++] = 'm';
 273 }
 274
 275 static char type_to_char(short type)
 276 {
 277         if (type == DEV_ALL)
 278                 return 'a';
 279         if (type == DEV_CHAR)
 280                 return 'c';
 281         if (type == DEV_BLOCK)
 282                 return 'b';
 283         return 'X';
 284 }
 285
 286 static void set_majmin(char *str, unsigned m)
 287 {
 288         if (m == ~0)
 289                 strcpy(str, "*");
 290         else
 291                 sprintf(str, "%u", m);
 292 }
 293
 294 static int devcgroup_seq_read(struct cgroup *cgroup, struct cftype *cft,
 295                                 struct seq_file *m)
 296 {
 297         struct dev_cgroup *devcgroup = cgroup_to_devcgroup(cgroup);
 298         struct dev_exception_item *ex;
 299         char maj[MAJMINLEN], min[MAJMINLEN], acc[ACCLEN];
 300
 301         rcu_read_lock();
 302         /*
 303          * To preserve the compatibility:
 304          * - Only show the "all devices" when the default policy is to allow
 305          * - List the exceptions in case the default policy is to deny
 306          * This way, the file remains as a "whitelist of devices"
 307          */
 308         if (devcgroup->behavior == DEVCG_DEFAULT_ALLOW) {
 309                 set_access(acc, ACC_MASK);
 310                 set_majmin(maj, ~0);
 311                 set_majmin(min, ~0);
 312                 seq_printf(m, "%c %s:%s %s\n", type_to_char(DEV_ALL),
 313                            maj, min, acc);
 314         } else {
 315                 list_for_each_entry_rcu(ex, &devcgroup->exceptions, list) {
 316                         set_access(acc, ex->access);
 317                         set_majmin(maj, ex->major);
 318                         set_majmin(min, ex->minor);
 319                         seq_printf(m, "%c %s:%s %s\n", type_to_char(ex->type),
 320                                    maj, min, acc);
 321                 }
 322         }
 323         rcu_read_unlock();
 324
 325         return 0;
 326 }
 327
 328 /**
 329  * may_access - verifies if a new exception is part of what is allowed
 330  *              by a dev cgroup based on the default policy +
 331  *              exceptions. This is used to make sure a child cgroup
 332  *              won't have more privileges than its parent or to
 333  *              verify if a certain access is allowed.
 334  * @dev_cgroup: dev cgroup to be tested against
 335  * @refex: new exception
 336  * @behavior: behavior of the exception
 337  */
 338 static bool may_access(struct dev_cgroup *dev_cgroup,
 339                        struct dev_exception_item *refex,
 340                        enum devcg_behavior behavior)
 341 {
 342         struct dev_exception_item *ex;
 343         bool match = false;
 344
 345         rcu_lockdep_assert(rcu_read_lock_held() ||
 346                            lockdep_is_held(&devcgroup_mutex),
 347                            "device_cgroup::may_access() called without proper synchronization");
 348
 349         list_for_each_entry_rcu(ex, &dev_cgroup->exceptions, list) {
 350                 if ((refex->type & DEV_BLOCK) && !(ex->type & DEV_BLOCK))
 351                         continue;
 352                 if ((refex->type & DEV_CHAR) && !(ex->type & DEV_CHAR))
 353                         continue;
 354                 if (ex->major != ~0 && ex->major != refex->major)
 355                         continue;
 356                 if (ex->minor != ~0 && ex->minor != refex->minor)
 357                         continue;
 358                 if (refex->access & (~ex->access))
 359                         continue;
 360                 match = true;
 361                 break;
 362         }
 363
 364         if (dev_cgroup->behavior == DEVCG_DEFAULT_ALLOW) {
 365                 if (behavior == DEVCG_DEFAULT_ALLOW) {
 366                         /* the exception will deny access to certain devices */
 367                         return true;
 368                 } else {
 369                         /* the exception will allow access to certain devices */
 370                         if (match)
 371                                 /*
 372                                  * a new exception allowing access shouldn't
 373                                  * match an parent's exception
 374                                  */
 375                                 return false;
 376                         return true;
 377                 }
 378         } else {
 379                 /* only behavior == DEVCG_DEFAULT_DENY allowed here */
 380                 if (match)
 381                         /* parent has an exception that matches the proposed */
 382                         return true;
 383                 else
 384                         return false;
 385         }
 386         return false;
 387 }
 388
 389 /*
 390  * parent_has_perm:
 391  * when adding a new allow rule to a device exception list, the rule
 392  * must be allowed in the parent device
 393  */
 394 static int parent_has_perm(struct dev_cgroup *childcg,
 395                                   struct dev_exception_item *ex)
 396 {
 397         struct cgroup *pcg = childcg->css.cgroup->parent;
 398         struct dev_cgroup *parent;
 399
 400         if (!pcg)
 401                 return 1;
 402         parent = cgroup_to_devcgroup(pcg);
 403         return may_access(parent, ex, childcg->behavior);
 404 }
 405
 406 /**
 407  * may_allow_all - checks if it's possible to change the behavior to
 408  *                 allow based on parent's rules.
 409  * @parent: device cgroup's parent
 410  * returns: != 0 in case it's allowed, 0 otherwise
 411  */
 412 static inline int may_allow_all(struct dev_cgroup *parent)
 413 {
 414         if (!parent)
 415                 return 1;
 416         return parent->behavior == DEVCG_DEFAULT_ALLOW;
 417 }
 418
 419 /**
 420  * revalidate_active_exceptions - walks through the active exception list and
 421  *                                revalidates the exceptions based on parent's
 422  *                                behavior and exceptions. The exceptions that
 423  *                                are no longer valid will be removed.
 424  *                                Called with devcgroup_mutex held.
 425  * @devcg: cgroup which exceptions will be checked
 426  *
 427  * This is one of the three key functions for hierarchy implementation.
 428  * This function is responsible for re-evaluating all the cgroup's active
 429  * exceptions due to a parent's exception change.
 430  * Refer to Documentation/cgroups/devices.txt for more details.
 431  */
 432 static void revalidate_active_exceptions(struct dev_cgroup *devcg)
 433 {
 434         struct dev_exception_item *ex;
 435         struct list_head *this, *tmp;
 436
 437         list_for_each_safe(this, tmp, &devcg->exceptions) {
 438                 ex = container_of(this, struct dev_exception_item, list);
 439                 if (!parent_has_perm(devcg, ex))
 440                         dev_exception_rm(devcg, ex);
 441         }
 442 }
 443
 444 /**
 445  * propagate_exception - propagates a new exception to the children
 446  * @devcg_root: device cgroup that added a new exception
 447  * @ex: new exception to be propagated
 448  *
 449  * returns: 0 in case of success, != 0 in case of error
 450  */
 451 static int propagate_exception(struct dev_cgroup *devcg_root,
 452                                struct dev_exception_item *ex)
 453 {
 454         struct cgroup *root = devcg_root->css.cgroup, *pos;
 455         int rc = 0;
 456
 457         rcu_read_lock();
 458
 459         cgroup_for_each_descendant_pre(pos, root) {
 460                 struct dev_cgroup *devcg = cgroup_to_devcgroup(pos);
 461
 462                 /*
 463                  * Because devcgroup_mutex is held, no devcg will become
 464                  * online or offline during the tree walk (see on/offline
 465                  * methods), and online ones are safe to access outside RCU
 466                  * read lock without bumping refcnt.
 467                  */
 468                 if (!is_devcg_online(devcg))
 469                         continue;
 470
 471                 rcu_read_unlock();
 472
 473                 /*
 474                  * in case both root's behavior and devcg is allow, a new
 475                  * restriction means adding to the exception list
 476                  */
 477                 if (devcg_root->behavior == DEVCG_DEFAULT_ALLOW &&
 478                     devcg->behavior == DEVCG_DEFAULT_ALLOW) {
 479                         rc = dev_exception_add(devcg, ex);
 480                         if (rc)
 481                                 break;
 482                 } else {
 483                         /*
 484                          * in the other possible cases:
 485                          * root's behavior: allow, devcg's: deny
 486                          * root's behavior: deny, devcg's: deny
 487                          * the exception will be removed
 488                          */
 489                         dev_exception_rm(devcg, ex);
 490                 }
 491                 revalidate_active_exceptions(devcg);
 492
 493                 rcu_read_lock();
 494         }
 495
 496         rcu_read_unlock();
 497         return rc;
 498 }
 499
 500 static inline bool has_children(struct dev_cgroup *devcgroup)
 501 {
 502         struct cgroup *cgrp = devcgroup->css.cgroup;
 503
 504         return !list_empty(&cgrp->children);
 505 }
 506
 507 /*
 508  * Modify the exception list using allow/deny rules.
 509  * CAP_SYS_ADMIN is needed for this.  It's at least separate from CAP_MKNOD
 510  * so we can give a container CAP_MKNOD to let it create devices but not
 511  * modify the exception list.
 512  * It seems likely we'll want to add a CAP_CONTAINER capability to allow
 513  * us to also grant CAP_SYS_ADMIN to containers without giving away the
 514  * device exception list controls, but for now we'll stick with CAP_SYS_ADMIN
 515  *
 516  * Taking rules away is always allowed (given CAP_SYS_ADMIN).  Granting
 517  * new access is only allowed if you're in the top-level cgroup, or your
 518  * parent cgroup has the access you're asking for.
 519  */
 520 static int devcgroup_update_access(struct dev_cgroup *devcgroup,
 521                                    int filetype, const char *buffer)
 522 {
 523         const char *b;
 524         char temp[12];          /* 11 + 1 characters needed for a u32 */
 525         int count, rc = 0;
 526         struct dev_exception_item ex;
 527         struct cgroup *p = devcgroup->css.cgroup;
 528         struct dev_cgroup *parent = NULL;
 529
 530         if (!capable(CAP_SYS_ADMIN))
 531                 return -EPERM;
 532
 533         if (p->parent)
 534                 parent = cgroup_to_devcgroup(p->parent);
 535
 536         memset(&ex, 0, sizeof(ex));
 537         b = buffer;
 538
 539         switch (*b) {
 540         case 'a':
 541                 switch (filetype) {
 542                 case DEVCG_ALLOW:
 543                         if (has_children(devcgroup))
 544                                 return -EINVAL;
 545
 546                         if (!may_allow_all(parent))
 547                                 return -EPERM;
 548                         dev_exception_clean(devcgroup);
 549                         devcgroup->behavior = DEVCG_DEFAULT_ALLOW;
 550                         if (!parent)
 551                                 break;
 552
 553                         rc = dev_exceptions_copy(&devcgroup->exceptions,
 554                                                  &parent->exceptions);
 555                         if (rc)
 556                                 return rc;
 557                         break;
 558                 case DEVCG_DENY:
 559                         if (has_children(devcgroup))
 560                                 return -EINVAL;
 561
 562                         dev_exception_clean(devcgroup);
 563                         devcgroup->behavior = DEVCG_DEFAULT_DENY;
 564                         break;
 565                 default:
 566                         return -EINVAL;
 567                 }
 568                 return 0;
 569         case 'b':
 570                 ex.type = DEV_BLOCK;
 571                 break;
 572         case 'c':
 573                 ex.type = DEV_CHAR;
 574                 break;
 575         default:
 576                 return -EINVAL;
 577         }
 578         b++;
 579         if (!isspace(*b))
 580                 return -EINVAL;
 581         b++;
 582         if (*b == '*') {
 583                 ex.major = ~0;
 584                 b++;
 585         } else if (isdigit(*b)) {
 586                 memset(temp, 0, sizeof(temp));
 587                 for (count = 0; count < sizeof(temp) - 1; count++) {
 588                         temp[count] = *b;
 589                         b++;
 590                         if (!isdigit(*b))
 591                                 break;
 592                 }
 593                 rc = kstrtou32(temp, 10, &ex.major);
 594                 if (rc)
 595                         return -EINVAL;
 596         } else {
 597                 return -EINVAL;
 598         }
 599         if (*b != ':')
 600                 return -EINVAL;
 601         b++;
 602
 603         /* read minor */
 604         if (*b == '*') {
 605                 ex.minor = ~0;
 606                 b++;
 607         } else if (isdigit(*b)) {
 608                 memset(temp, 0, sizeof(temp));
 609                 for (count = 0; count < sizeof(temp) - 1; count++) {
 610                         temp[count] = *b;
 611                         b++;
 612                         if (!isdigit(*b))
 613                                 break;
 614                 }
 615                 rc = kstrtou32(temp, 10, &ex.minor);
 616                 if (rc)
 617                         return -EINVAL;
 618         } else {
 619                 return -EINVAL;
 620         }
 621         if (!isspace(*b))
 622                 return -EINVAL;
 623         for (b++, count = 0; count < 3; count++, b++) {
 624                 switch (*b) {
 625                 case 'r':
 626                         ex.access |= ACC_READ;
 627                         break;
 628                 case 'w':
 629                         ex.access |= ACC_WRITE;
 630                         break;
 631                 case 'm':
 632                         ex.access |= ACC_MKNOD;
 633                         break;
 634                 case '\n':
 635                 case '\0':
 636                         count = 3;
 637                         break;
 638                 default:
 639                         return -EINVAL;
 640                 }
 641         }
 642
 643         switch (filetype) {
 644         case DEVCG_ALLOW:
 645                 if (!parent_has_perm(devcgroup, &ex))
 646                         return -EPERM;
 647                 /*
 648                  * If the default policy is to allow by default, try to remove
 649                  * an matching exception instead. And be silent about it: we
 650                  * don't want to break compatibility
 651                  */
 652                 if (devcgroup->behavior == DEVCG_DEFAULT_ALLOW) {
 653                         dev_exception_rm(devcgroup, &ex);
 654                         return 0;
 655                 }
 656                 rc = dev_exception_add(devcgroup, &ex);
 657                 break;
 658         case DEVCG_DENY:
 659                 /*
 660                  * If the default policy is to deny by default, try to remove
 661                  * an matching exception instead. And be silent about it: we
 662                  * don't want to break compatibility
 663                  */
 664                 if (devcgroup->behavior == DEVCG_DEFAULT_DENY)
 665                         dev_exception_rm(devcgroup, &ex);
 666                 else
 667                         rc = dev_exception_add(devcgroup, &ex);
 668
 669                 if (rc)
 670                         break;
 671                 /* we only propagate new restrictions */
 672                 rc = propagate_exception(devcgroup, &ex);
 673                 break;
 674         default:
 675                 rc = -EINVAL;
 676         }
 677         return rc;
 678 }
 679
 680 static int devcgroup_access_write(struct cgroup *cgrp, struct cftype *cft,
 681                                   const char *buffer)
 682 {
 683         int retval;
 684
 685         mutex_lock(&devcgroup_mutex);
 686         retval = devcgroup_update_access(cgroup_to_devcgroup(cgrp),
 687                                          cft->private, buffer);
 688         mutex_unlock(&devcgroup_mutex);
 689         return retval;
 690 }
 691
 692 static struct cftype dev_cgroup_files[] = {
 693         {
 694                 .name = "allow",
 695                 .write_string  = devcgroup_access_write,
 696                 .private = DEVCG_ALLOW,
 697         },
 698         {
 699                 .name = "deny",
 700                 .write_string = devcgroup_access_write,
 701                 .private = DEVCG_DENY,
 702         },
 703         {
 704                 .name = "list",
 705                 .read_seq_string = devcgroup_seq_read,
 706                 .private = DEVCG_LIST,
 707         },
 708         { }     /* terminate */
 709 };
 710
 711 struct cgroup_subsys devices_subsys = {
 712         .name = "devices",
 713         .can_attach = devcgroup_can_attach,
 714         .css_alloc = devcgroup_css_alloc,
 715         .css_free = devcgroup_css_free,
 716         .css_online = devcgroup_online,
 717         .css_offline = devcgroup_offline,
 718         .subsys_id = devices_subsys_id,
 719         .base_cftypes = dev_cgroup_files,
 720 };
 721
 722 /**
 723  * __devcgroup_check_permission - checks if an inode operation is permitted
 724  * @dev_cgroup: the dev cgroup to be tested against
 725  * @type: device type
 726  * @major: device major number
 727  * @minor: device minor number
 728  * @access: combination of ACC_WRITE, ACC_READ and ACC_MKNOD
 729  *
 730  * returns 0 on success, -EPERM case the operation is not permitted
 731  */
 732 static int __devcgroup_check_permission(short type, u32 major, u32 minor,
 733                                         short access)
 734 {
 735         struct dev_cgroup *dev_cgroup;
 736         struct dev_exception_item ex;
 737         int rc;
 738
 739         memset(&ex, 0, sizeof(ex));
 740         ex.type = type;
 741         ex.major = major;
 742         ex.minor = minor;
 743         ex.access = access;
 744
 745         rcu_read_lock();
 746         dev_cgroup = task_devcgroup(current);
 747         rc = may_access(dev_cgroup, &ex, dev_cgroup->behavior);
 748         rcu_read_unlock();
 749
 750         if (!rc)
 751                 return -EPERM;
 752
 753         return 0;
 754 }
 755
 756 int __devcgroup_inode_permission(struct inode *inode, int mask)
 757 {
 758         short type, access = 0;
 759
 760         if (S_ISBLK(inode->i_mode))
 761                 type = DEV_BLOCK;
 762         if (S_ISCHR(inode->i_mode))
 763                 type = DEV_CHAR;
 764         if (mask & MAY_WRITE)
 765                 access |= ACC_WRITE;
 766         if (mask & MAY_READ)
 767                 access |= ACC_READ;
 768
 769         return __devcgroup_check_permission(type, imajor(inode), iminor(inode),
 770                         access);
 771 }
 772
 773 int devcgroup_inode_mknod(int mode, dev_t dev)
 774 {
 775         short type;
 776
 777         if (!S_ISBLK(mode) && !S_ISCHR(mode))
 778                 return 0;
 779
 780         if (S_ISBLK(mode))
 781                 type = DEV_BLOCK;
 782         else
 783                 type = DEV_CHAR;
 784
 785         return __devcgroup_check_permission(type, MAJOR(dev), MINOR(dev),
 786                         ACC_MKNOD);
 787
 788 }