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