security/device_cgroup.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * device_cgroup.c - device cgroup subsystem
   4  *
   5  * Copyright 2007 IBM Corp
   6  */
   7
   8 #include <linux/device_cgroup.h>
   9 #include <linux/cgroup.h>
  10 #include <linux/ctype.h>
  11 #include <linux/list.h>
  12 #include <linux/uaccess.h>
  13 #include <linux/seq_file.h>
  14 #include <linux/slab.h>
  15 #include <linux/rcupdate.h>
  16 #include <linux/mutex.h>
  17
  18 #define ACC_MKNOD 1
  19 #define ACC_READ  2
  20 #define ACC_WRITE 4
  21 #define ACC_MASK (ACC_MKNOD | ACC_READ | ACC_WRITE)
  22
  23 #define DEV_BLOCK 1
  24 #define DEV_CHAR  2
  25 #define DEV_ALL   4  /* this represents all devices */
  26
  27 static DEFINE_MUTEX(devcgroup_mutex);
  28
  29 enum devcg_behavior {
  30         DEVCG_DEFAULT_NONE,
  31         DEVCG_DEFAULT_ALLOW,
  32         DEVCG_DEFAULT_DENY,
  33 };
  34
  35 /*
  36  * exception list locking rules:
  37  * hold devcgroup_mutex for update/read.
  38  * hold rcu_read_lock() for read.
  39  */
  40
  41 struct dev_exception_item {
  42         u32 major, minor;
  43         short type;
  44         short access;
  45         struct list_head list;
  46         struct rcu_head rcu;
  47 };
  48
  49 struct dev_cgroup {
  50         struct cgroup_subsys_state css;
  51         struct list_head exceptions;
  52         enum devcg_behavior behavior;
  53 };
  54
  55 static inline struct dev_cgroup *css_to_devcgroup(struct cgroup_subsys_state *s)
  56 {
  57         return s ? container_of(s, struct dev_cgroup, css) : NULL;
  58 }
  59
  60 static inline struct dev_cgroup *task_devcgroup(struct task_struct *task)
  61 {
  62         return css_to_devcgroup(task_css(task, devices_cgrp_id));
  63 }
  64
  65 /*
  66  * called under devcgroup_mutex
  67  */
  68 static int dev_exceptions_copy(struct list_head *dest, struct list_head *orig)
  69 {
  70         struct dev_exception_item *ex, *tmp, *new;
  71
  72         lockdep_assert_held(&devcgroup_mutex);
  73
  74         list_for_each_entry(ex, orig, list) {
  75                 new = kmemdup(ex, sizeof(*ex), GFP_KERNEL);
  76                 if (!new)
  77                         goto free_and_exit;
  78                 list_add_tail(&new->list, dest);
  79         }
  80
  81         return 0;
  82
  83 free_and_exit:
  84         list_for_each_entry_safe(ex, tmp, dest, list) {
  85                 list_del(&ex->list);
  86                 kfree(ex);
  87         }
  88         return -ENOMEM;
  89 }
  90
  91 /*
  92  * called under devcgroup_mutex
  93  */
  94 static int dev_exception_add(struct dev_cgroup *dev_cgroup,
  95                              struct dev_exception_item *ex)
  96 {
  97         struct dev_exception_item *excopy, *walk;
  98
  99         lockdep_assert_held(&devcgroup_mutex);
 100
 101         excopy = kmemdup(ex, sizeof(*ex), GFP_KERNEL);
 102         if (!excopy)
 103                 return -ENOMEM;
 104
 105         list_for_each_entry(walk, &dev_cgroup->exceptions, list) {
 106                 if (walk->type != ex->type)
 107                         continue;
 108                 if (walk->major != ex->major)
 109                         continue;
 110                 if (walk->minor != ex->minor)
 111                         continue;
 112
 113                 walk->access |= ex->access;
 114                 kfree(excopy);
 115                 excopy = NULL;
 116         }
 117
 118         if (excopy != NULL)
 119                 list_add_tail_rcu(&excopy->list, &dev_cgroup->exceptions);
 120         return 0;
 121 }
 122
 123 /*
 124  * called under devcgroup_mutex
 125  */
 126 static void dev_exception_rm(struct dev_cgroup *dev_cgroup,
 127                              struct dev_exception_item *ex)
 128 {
 129         struct dev_exception_item *walk, *tmp;
 130
 131         lockdep_assert_held(&devcgroup_mutex);
 132
 133         list_for_each_entry_safe(walk, tmp, &dev_cgroup->exceptions, list) {
 134                 if (walk->type != ex->type)
 135                         continue;
 136                 if (walk->major != ex->major)
 137                         continue;
 138                 if (walk->minor != ex->minor)
 139                         continue;
 140
 141                 walk->access &= ~ex->access;
 142                 if (!walk->access) {
 143                         list_del_rcu(&walk->list);
 144                         kfree_rcu(walk, rcu);
 145                 }
 146         }
 147 }
 148
 149 static void __dev_exception_clean(struct dev_cgroup *dev_cgroup)
 150 {
 151         struct dev_exception_item *ex, *tmp;
 152
 153         list_for_each_entry_safe(ex, tmp, &dev_cgroup->exceptions, list) {
 154                 list_del_rcu(&ex->list);
 155                 kfree_rcu(ex, rcu);
 156         }
 157 }
 158
 159 /**
 160  * dev_exception_clean - frees all entries of the exception list
 161  * @dev_cgroup: dev_cgroup with the exception list to be cleaned
 162  *
 163  * called under devcgroup_mutex
 164  */
 165 static void dev_exception_clean(struct dev_cgroup *dev_cgroup)
 166 {
 167         lockdep_assert_held(&devcgroup_mutex);
 168
 169         __dev_exception_clean(dev_cgroup);
 170 }
 171
 172 static inline bool is_devcg_online(const struct dev_cgroup *devcg)
 173 {
 174         return (devcg->behavior != DEVCG_DEFAULT_NONE);
 175 }
 176
 177 /**
 178  * devcgroup_online - initializes devcgroup's behavior and exceptions based on
 179  *                    parent's
 180  * @css: css getting online
 181  * returns 0 in case of success, error code otherwise
 182  */
 183 static int devcgroup_online(struct cgroup_subsys_state *css)
 184 {
 185         struct dev_cgroup *dev_cgroup = css_to_devcgroup(css);
 186         struct dev_cgroup *parent_dev_cgroup = css_to_devcgroup(css->parent);
 187         int ret = 0;
 188
 189         mutex_lock(&devcgroup_mutex);
 190
 191         if (parent_dev_cgroup == NULL)
 192                 dev_cgroup->behavior = DEVCG_DEFAULT_ALLOW;
 193         else {
 194                 ret = dev_exceptions_copy(&dev_cgroup->exceptions,
 195                                           &parent_dev_cgroup->exceptions);
 196                 if (!ret)
 197                         dev_cgroup->behavior = parent_dev_cgroup->behavior;
 198         }
 199         mutex_unlock(&devcgroup_mutex);
 200
 201         return ret;
 202 }
 203
 204 static void devcgroup_offline(struct cgroup_subsys_state *css)
 205 {
 206         struct dev_cgroup *dev_cgroup = css_to_devcgroup(css);
 207
 208         mutex_lock(&devcgroup_mutex);
 209         dev_cgroup->behavior = DEVCG_DEFAULT_NONE;
 210         mutex_unlock(&devcgroup_mutex);
 211 }
 212
 213 /*
 214  * called from kernel/cgroup.c with cgroup_lock() held.
 215  */
 216 static struct cgroup_subsys_state *
 217 devcgroup_css_alloc(struct cgroup_subsys_state *parent_css)
 218 {
 219         struct dev_cgroup *dev_cgroup;
 220
 221         dev_cgroup = kzalloc(sizeof(*dev_cgroup), GFP_KERNEL);
 222         if (!dev_cgroup)
 223                 return ERR_PTR(-ENOMEM);
 224         INIT_LIST_HEAD(&dev_cgroup->exceptions);
 225         dev_cgroup->behavior = DEVCG_DEFAULT_NONE;
 226
 227         return &dev_cgroup->css;
 228 }
 229
 230 static void devcgroup_css_free(struct cgroup_subsys_state *css)
 231 {
 232         struct dev_cgroup *dev_cgroup = css_to_devcgroup(css);
 233
 234         __dev_exception_clean(dev_cgroup);
 235         kfree(dev_cgroup);
 236 }
 237
 238 #define DEVCG_ALLOW 1
 239 #define DEVCG_DENY 2
 240 #define DEVCG_LIST 3
 241
 242 #define MAJMINLEN 13
 243 #define ACCLEN 4
 244
 245 static void set_access(char *acc, short access)
 246 {
 247         int idx = 0;
 248         memset(acc, 0, ACCLEN);
 249         if (access & ACC_READ)
 250                 acc[idx++] = 'r';
 251         if (access & ACC_WRITE)
 252                 acc[idx++] = 'w';
 253         if (access & ACC_MKNOD)
 254                 acc[idx++] = 'm';
 255 }
 256
 257 static char type_to_char(short type)
 258 {
 259         if (type == DEV_ALL)
 260                 return 'a';
 261         if (type == DEV_CHAR)
 262                 return 'c';
 263         if (type == DEV_BLOCK)
 264                 return 'b';
 265         return 'X';
 266 }
 267
 268 static void set_majmin(char *str, unsigned m)
 269 {
 270         if (m == ~0)
 271                 strcpy(str, "*");
 272         else
 273                 sprintf(str, "%u", m);
 274 }
 275
 276 static int devcgroup_seq_show(struct seq_file *m, void *v)
 277 {
 278         struct dev_cgroup *devcgroup = css_to_devcgroup(seq_css(m));
 279         struct dev_exception_item *ex;
 280         char maj[MAJMINLEN], min[MAJMINLEN], acc[ACCLEN];
 281
 282         rcu_read_lock();
 283         /*
 284          * To preserve the compatibility:
 285          * - Only show the "all devices" when the default policy is to allow
 286          * - List the exceptions in case the default policy is to deny
 287          * This way, the file remains as a "whitelist of devices"
 288          */
 289         if (devcgroup->behavior == DEVCG_DEFAULT_ALLOW) {
 290                 set_access(acc, ACC_MASK);
 291                 set_majmin(maj, ~0);
 292                 set_majmin(min, ~0);
 293                 seq_printf(m, "%c %s:%s %s\n", type_to_char(DEV_ALL),
 294                            maj, min, acc);
 295         } else {
 296                 list_for_each_entry_rcu(ex, &devcgroup->exceptions, list) {
 297                         set_access(acc, ex->access);
 298                         set_majmin(maj, ex->major);
 299                         set_majmin(min, ex->minor);
 300                         seq_printf(m, "%c %s:%s %s\n", type_to_char(ex->type),
 301                                    maj, min, acc);
 302                 }
 303         }
 304         rcu_read_unlock();
 305
 306         return 0;
 307 }
 308
 309 /**
 310  * match_exception      - iterates the exception list trying to find a complete match
 311  * @exceptions: list of exceptions
 312  * @type: device type (DEV_BLOCK or DEV_CHAR)
 313  * @major: device file major number, ~0 to match all
 314  * @minor: device file minor number, ~0 to match all
 315  * @access: permission mask (ACC_READ, ACC_WRITE, ACC_MKNOD)
 316  *
 317  * It is considered a complete match if an exception is found that will
 318  * contain the entire range of provided parameters.
 319  *
 320  * Return: true in case it matches an exception completely
 321  */
 322 static bool match_exception(struct list_head *exceptions, short type,
 323                             u32 major, u32 minor, short access)
 324 {
 325         struct dev_exception_item *ex;
 326
 327         list_for_each_entry_rcu(ex, exceptions, list) {
 328                 if ((type & DEV_BLOCK) && !(ex->type & DEV_BLOCK))
 329                         continue;
 330                 if ((type & DEV_CHAR) && !(ex->type & DEV_CHAR))
 331                         continue;
 332                 if (ex->major != ~0 && ex->major != major)
 333                         continue;
 334                 if (ex->minor != ~0 && ex->minor != minor)
 335                         continue;
 336                 /* provided access cannot have more than the exception rule */
 337                 if (access & (~ex->access))
 338                         continue;
 339                 return true;
 340         }
 341         return false;
 342 }
 343
 344 /**
 345  * match_exception_partial - iterates the exception list trying to find a partial match
 346  * @exceptions: list of exceptions
 347  * @type: device type (DEV_BLOCK or DEV_CHAR)
 348  * @major: device file major number, ~0 to match all
 349  * @minor: device file minor number, ~0 to match all
 350  * @access: permission mask (ACC_READ, ACC_WRITE, ACC_MKNOD)
 351  *
 352  * It is considered a partial match if an exception's range is found to
 353  * contain *any* of the devices specified by provided parameters. This is
 354  * used to make sure no extra access is being granted that is forbidden by
 355  * any of the exception list.
 356  *
 357  * Return: true in case the provided range mat matches an exception completely
 358  */
 359 static bool match_exception_partial(struct list_head *exceptions, short type,
 360                                     u32 major, u32 minor, short access)
 361 {
 362         struct dev_exception_item *ex;
 363
 364         list_for_each_entry_rcu(ex, exceptions, list) {
 365                 if ((type & DEV_BLOCK) && !(ex->type & DEV_BLOCK))
 366                         continue;
 367                 if ((type & DEV_CHAR) && !(ex->type & DEV_CHAR))
 368                         continue;
 369                 /*
 370                  * We must be sure that both the exception and the provided
 371                  * range aren't masking all devices
 372                  */
 373                 if (ex->major != ~0 && major != ~0 && ex->major != major)
 374                         continue;
 375                 if (ex->minor != ~0 && minor != ~0 && ex->minor != minor)
 376                         continue;
 377                 /*
 378                  * In order to make sure the provided range isn't matching
 379                  * an exception, all its access bits shouldn't match the
 380                  * exception's access bits
 381                  */
 382                 if (!(access & ex->access))
 383                         continue;
 384                 return true;
 385         }
 386         return false;
 387 }
 388
 389 /**
 390  * verify_new_ex - verifies if a new exception is allowed by parent cgroup's permissions
 391  * @dev_cgroup: dev cgroup to be tested against
 392  * @refex: new exception
 393  * @behavior: behavior of the exception's dev_cgroup
 394  *
 395  * This is used to make sure a child cgroup won't have more privileges
 396  * than its parent
 397  */
 398 static bool verify_new_ex(struct dev_cgroup *dev_cgroup,
 399                           struct dev_exception_item *refex,
 400                           enum devcg_behavior behavior)
 401 {
 402         bool match = false;
 403
 404         RCU_LOCKDEP_WARN(!rcu_read_lock_held() &&
 405                          !lockdep_is_held(&devcgroup_mutex),
 406                          "device_cgroup:verify_new_ex called without proper synchronization");
 407
 408         if (dev_cgroup->behavior == DEVCG_DEFAULT_ALLOW) {
 409                 if (behavior == DEVCG_DEFAULT_ALLOW) {
 410                         /*
 411                          * new exception in the child doesn't matter, only
 412                          * adding extra restrictions
 413                          */
 414                         return true;
 415                 } else {
 416                         /*
 417                          * new exception in the child will add more devices
 418                          * that can be acessed, so it can't match any of
 419                          * parent's exceptions, even slightly
 420                          */
 421                         match = match_exception_partial(&dev_cgroup->exceptions,
 422                                                         refex->type,
 423                                                         refex->major,
 424                                                         refex->minor,
 425                                                         refex->access);
 426
 427                         if (match)
 428                                 return false;
 429                         return true;
 430                 }
 431         } else {
 432                 /*
 433                  * Only behavior == DEVCG_DEFAULT_DENY allowed here, therefore
 434                  * the new exception will add access to more devices and must
 435                  * be contained completely in an parent's exception to be
 436                  * allowed
 437                  */
 438                 match = match_exception(&dev_cgroup->exceptions, refex->type,
 439                                         refex->major, refex->minor,
 440                                         refex->access);
 441
 442                 if (match)
 443                         /* parent has an exception that matches the proposed */
 444                         return true;
 445                 else
 446                         return false;
 447         }
 448         return false;
 449 }
 450
 451 /*
 452  * parent_has_perm:
 453  * when adding a new allow rule to a device exception list, the rule
 454  * must be allowed in the parent device
 455  */
 456 static int parent_has_perm(struct dev_cgroup *childcg,
 457                                   struct dev_exception_item *ex)
 458 {
 459         struct dev_cgroup *parent = css_to_devcgroup(childcg->css.parent);
 460
 461         if (!parent)
 462                 return 1;
 463         return verify_new_ex(parent, ex, childcg->behavior);
 464 }
 465
 466 /**
 467  * parent_allows_removal - verify if it's ok to remove an exception
 468  * @childcg: child cgroup from where the exception will be removed
 469  * @ex: exception being removed
 470  *
 471  * When removing an exception in cgroups with default ALLOW policy, it must
 472  * be checked if removing it will give the child cgroup more access than the
 473  * parent.
 474  *
 475  * Return: true if it's ok to remove exception, false otherwise
 476  */
 477 static bool parent_allows_removal(struct dev_cgroup *childcg,
 478                                   struct dev_exception_item *ex)
 479 {
 480         struct dev_cgroup *parent = css_to_devcgroup(childcg->css.parent);
 481
 482         if (!parent)
 483                 return true;
 484
 485         /* It's always allowed to remove access to devices */
 486         if (childcg->behavior == DEVCG_DEFAULT_DENY)
 487                 return true;
 488
 489         /*
 490          * Make sure you're not removing part or a whole exception existing in
 491          * the parent cgroup
 492          */
 493         return !match_exception_partial(&parent->exceptions, ex->type,
 494                                         ex->major, ex->minor, ex->access);
 495 }
 496
 497 /**
 498  * may_allow_all - checks if it's possible to change the behavior to
 499  *                 allow based on parent's rules.
 500  * @parent: device cgroup's parent
 501  * returns: != 0 in case it's allowed, 0 otherwise
 502  */
 503 static inline int may_allow_all(struct dev_cgroup *parent)
 504 {
 505         if (!parent)
 506                 return 1;
 507         return parent->behavior == DEVCG_DEFAULT_ALLOW;
 508 }
 509
 510 /**
 511  * revalidate_active_exceptions - walks through the active exception list and
 512  *                                revalidates the exceptions based on parent's
 513  *                                behavior and exceptions. The exceptions that
 514  *                                are no longer valid will be removed.
 515  *                                Called with devcgroup_mutex held.
 516  * @devcg: cgroup which exceptions will be checked
 517  *
 518  * This is one of the three key functions for hierarchy implementation.
 519  * This function is responsible for re-evaluating all the cgroup's active
 520  * exceptions due to a parent's exception change.
 521  * Refer to Documentation/cgroups/devices.txt for more details.
 522  */
 523 static void revalidate_active_exceptions(struct dev_cgroup *devcg)
 524 {
 525         struct dev_exception_item *ex;
 526         struct list_head *this, *tmp;
 527
 528         list_for_each_safe(this, tmp, &devcg->exceptions) {
 529                 ex = container_of(this, struct dev_exception_item, list);
 530                 if (!parent_has_perm(devcg, ex))
 531                         dev_exception_rm(devcg, ex);
 532         }
 533 }
 534
 535 /**
 536  * propagate_exception - propagates a new exception to the children
 537  * @devcg_root: device cgroup that added a new exception
 538  * @ex: new exception to be propagated
 539  *
 540  * returns: 0 in case of success, != 0 in case of error
 541  */
 542 static int propagate_exception(struct dev_cgroup *devcg_root,
 543                                struct dev_exception_item *ex)
 544 {
 545         struct cgroup_subsys_state *pos;
 546         int rc = 0;
 547
 548         rcu_read_lock();
 549
 550         css_for_each_descendant_pre(pos, &devcg_root->css) {
 551                 struct dev_cgroup *devcg = css_to_devcgroup(pos);
 552
 553                 /*
 554                  * Because devcgroup_mutex is held, no devcg will become
 555                  * online or offline during the tree walk (see on/offline
 556                  * methods), and online ones are safe to access outside RCU
 557                  * read lock without bumping refcnt.
 558                  */
 559                 if (pos == &devcg_root->css || !is_devcg_online(devcg))
 560                         continue;
 561
 562                 rcu_read_unlock();
 563
 564                 /*
 565                  * in case both root's behavior and devcg is allow, a new
 566                  * restriction means adding to the exception list
 567                  */
 568                 if (devcg_root->behavior == DEVCG_DEFAULT_ALLOW &&
 569                     devcg->behavior == DEVCG_DEFAULT_ALLOW) {
 570                         rc = dev_exception_add(devcg, ex);
 571                         if (rc)
 572                                 break;
 573                 } else {
 574                         /*
 575                          * in the other possible cases:
 576                          * root's behavior: allow, devcg's: deny
 577                          * root's behavior: deny, devcg's: deny
 578                          * the exception will be removed
 579                          */
 580                         dev_exception_rm(devcg, ex);
 581                 }
 582                 revalidate_active_exceptions(devcg);
 583
 584                 rcu_read_lock();
 585         }
 586
 587         rcu_read_unlock();
 588         return rc;
 589 }
 590
 591 /*
 592  * Modify the exception list using allow/deny rules.
 593  * CAP_SYS_ADMIN is needed for this.  It's at least separate from CAP_MKNOD
 594  * so we can give a container CAP_MKNOD to let it create devices but not
 595  * modify the exception list.
 596  * It seems likely we'll want to add a CAP_CONTAINER capability to allow
 597  * us to also grant CAP_SYS_ADMIN to containers without giving away the
 598  * device exception list controls, but for now we'll stick with CAP_SYS_ADMIN
 599  *
 600  * Taking rules away is always allowed (given CAP_SYS_ADMIN).  Granting
 601  * new access is only allowed if you're in the top-level cgroup, or your
 602  * parent cgroup has the access you're asking for.
 603  */
 604 static int devcgroup_update_access(struct dev_cgroup *devcgroup,
 605                                    int filetype, char *buffer)
 606 {
 607         const char *b;
 608         char temp[12];          /* 11 + 1 characters needed for a u32 */
 609         int count, rc = 0;
 610         struct dev_exception_item ex;
 611         struct dev_cgroup *parent = css_to_devcgroup(devcgroup->css.parent);
 612
 613         if (!capable(CAP_SYS_ADMIN))
 614                 return -EPERM;
 615
 616         memset(&ex, 0, sizeof(ex));
 617         b = buffer;
 618
 619         switch (*b) {
 620         case 'a':
 621                 switch (filetype) {
 622                 case DEVCG_ALLOW:
 623                         if (css_has_online_children(&devcgroup->css))
 624                                 return -EINVAL;
 625
 626                         if (!may_allow_all(parent))
 627                                 return -EPERM;
 628                         dev_exception_clean(devcgroup);
 629                         devcgroup->behavior = DEVCG_DEFAULT_ALLOW;
 630                         if (!parent)
 631                                 break;
 632
 633                         rc = dev_exceptions_copy(&devcgroup->exceptions,
 634                                                  &parent->exceptions);
 635                         if (rc)
 636                                 return rc;
 637                         break;
 638                 case DEVCG_DENY:
 639                         if (css_has_online_children(&devcgroup->css))
 640                                 return -EINVAL;
 641
 642                         dev_exception_clean(devcgroup);
 643                         devcgroup->behavior = DEVCG_DEFAULT_DENY;
 644                         break;
 645                 default:
 646                         return -EINVAL;
 647                 }
 648                 return 0;
 649         case 'b':
 650                 ex.type = DEV_BLOCK;
 651                 break;
 652         case 'c':
 653                 ex.type = DEV_CHAR;
 654                 break;
 655         default:
 656                 return -EINVAL;
 657         }
 658         b++;
 659         if (!isspace(*b))
 660                 return -EINVAL;
 661         b++;
 662         if (*b == '*') {
 663                 ex.major = ~0;
 664                 b++;
 665         } else if (isdigit(*b)) {
 666                 memset(temp, 0, sizeof(temp));
 667                 for (count = 0; count < sizeof(temp) - 1; count++) {
 668                         temp[count] = *b;
 669                         b++;
 670                         if (!isdigit(*b))
 671                                 break;
 672                 }
 673                 rc = kstrtou32(temp, 10, &ex.major);
 674                 if (rc)
 675                         return -EINVAL;
 676         } else {
 677                 return -EINVAL;
 678         }
 679         if (*b != ':')
 680                 return -EINVAL;
 681         b++;
 682
 683         /* read minor */
 684         if (*b == '*') {
 685                 ex.minor = ~0;
 686                 b++;
 687         } else if (isdigit(*b)) {
 688                 memset(temp, 0, sizeof(temp));
 689                 for (count = 0; count < sizeof(temp) - 1; count++) {
 690                         temp[count] = *b;
 691                         b++;
 692                         if (!isdigit(*b))
 693                                 break;
 694                 }
 695                 rc = kstrtou32(temp, 10, &ex.minor);
 696                 if (rc)
 697                         return -EINVAL;
 698         } else {
 699                 return -EINVAL;
 700         }
 701         if (!isspace(*b))
 702                 return -EINVAL;
 703         for (b++, count = 0; count < 3; count++, b++) {
 704                 switch (*b) {
 705                 case 'r':
 706                         ex.access |= ACC_READ;
 707                         break;
 708                 case 'w':
 709                         ex.access |= ACC_WRITE;
 710                         break;
 711                 case 'm':
 712                         ex.access |= ACC_MKNOD;
 713                         break;
 714                 case '\n':
 715                 case '\0':
 716                         count = 3;
 717                         break;
 718                 default:
 719                         return -EINVAL;
 720                 }
 721         }
 722
 723         switch (filetype) {
 724         case DEVCG_ALLOW:
 725                 /*
 726                  * If the default policy is to allow by default, try to remove
 727                  * an matching exception instead. And be silent about it: we
 728                  * don't want to break compatibility
 729                  */
 730                 if (devcgroup->behavior == DEVCG_DEFAULT_ALLOW) {
 731                         /* Check if the parent allows removing it first */
 732                         if (!parent_allows_removal(devcgroup, &ex))
 733                                 return -EPERM;
 734                         dev_exception_rm(devcgroup, &ex);
 735                         break;
 736                 }
 737
 738                 if (!parent_has_perm(devcgroup, &ex))
 739                         return -EPERM;
 740                 rc = dev_exception_add(devcgroup, &ex);
 741                 break;
 742         case DEVCG_DENY:
 743                 /*
 744                  * If the default policy is to deny by default, try to remove
 745                  * an matching exception instead. And be silent about it: we
 746                  * don't want to break compatibility
 747                  */
 748                 if (devcgroup->behavior == DEVCG_DEFAULT_DENY)
 749                         dev_exception_rm(devcgroup, &ex);
 750                 else
 751                         rc = dev_exception_add(devcgroup, &ex);
 752
 753                 if (rc)
 754                         break;
 755                 /* we only propagate new restrictions */
 756                 rc = propagate_exception(devcgroup, &ex);
 757                 break;
 758         default:
 759                 rc = -EINVAL;
 760         }
 761         return rc;
 762 }
 763
 764 static ssize_t devcgroup_access_write(struct kernfs_open_file *of,
 765                                       char *buf, size_t nbytes, loff_t off)
 766 {
 767         int retval;
 768
 769         mutex_lock(&devcgroup_mutex);
 770         retval = devcgroup_update_access(css_to_devcgroup(of_css(of)),
 771                                          of_cft(of)->private, strstrip(buf));
 772         mutex_unlock(&devcgroup_mutex);
 773         return retval ?: nbytes;
 774 }
 775
 776 static struct cftype dev_cgroup_files[] = {
 777         {
 778                 .name = "allow",
 779                 .write = devcgroup_access_write,
 780                 .private = DEVCG_ALLOW,
 781         },
 782         {
 783                 .name = "deny",
 784                 .write = devcgroup_access_write,
 785                 .private = DEVCG_DENY,
 786         },
 787         {
 788                 .name = "list",
 789                 .seq_show = devcgroup_seq_show,
 790                 .private = DEVCG_LIST,
 791         },
 792         { }     /* terminate */
 793 };
 794
 795 struct cgroup_subsys devices_cgrp_subsys = {
 796         .css_alloc = devcgroup_css_alloc,
 797         .css_free = devcgroup_css_free,
 798         .css_online = devcgroup_online,
 799         .css_offline = devcgroup_offline,
 800         .legacy_cftypes = dev_cgroup_files,
 801 };
 802
 803 /**
 804  * __devcgroup_check_permission - checks if an inode operation is permitted
 805  * @dev_cgroup: the dev cgroup to be tested against
 806  * @type: device type
 807  * @major: device major number
 808  * @minor: device minor number
 809  * @access: combination of ACC_WRITE, ACC_READ and ACC_MKNOD
 810  *
 811  * returns 0 on success, -EPERM case the operation is not permitted
 812  */
 813 static int __devcgroup_check_permission(short type, u32 major, u32 minor,
 814                                         short access)
 815 {
 816         struct dev_cgroup *dev_cgroup;
 817         bool rc;
 818
 819         rcu_read_lock();
 820         dev_cgroup = task_devcgroup(current);
 821         if (dev_cgroup->behavior == DEVCG_DEFAULT_ALLOW)
 822                 /* Can't match any of the exceptions, even partially */
 823                 rc = !match_exception_partial(&dev_cgroup->exceptions,
 824                                               type, major, minor, access);
 825         else
 826                 /* Need to match completely one exception to be allowed */
 827                 rc = match_exception(&dev_cgroup->exceptions, type, major,
 828                                      minor, access);
 829         rcu_read_unlock();
 830
 831         if (!rc)
 832                 return -EPERM;
 833
 834         return 0;
 835 }
 836
 837 int __devcgroup_inode_permission(struct inode *inode, int mask)
 838 {
 839         short type, access = 0;
 840
 841         if (S_ISBLK(inode->i_mode))
 842                 type = DEV_BLOCK;
 843         if (S_ISCHR(inode->i_mode))
 844                 type = DEV_CHAR;
 845         if (mask & MAY_WRITE)
 846                 access |= ACC_WRITE;
 847         if (mask & MAY_READ)
 848                 access |= ACC_READ;
 849
 850         return __devcgroup_check_permission(type, imajor(inode), iminor(inode),
 851                         access);
 852 }
 853
 854 int devcgroup_inode_mknod(int mode, dev_t dev)
 855 {
 856         short type;
 857
 858         if (!S_ISBLK(mode) && !S_ISCHR(mode))
 859                 return 0;
 860
 861         if (S_ISBLK(mode))
 862                 type = DEV_BLOCK;
 863         else
 864                 type = DEV_CHAR;
 865
 866         return __devcgroup_check_permission(type, MAJOR(dev), MINOR(dev),
 867                         ACC_MKNOD);
 868
 869 }