root/security/device_cgroup.c

DEFINITIONS

1. css_to_devcgroup
2. task_devcgroup
3. dev_exceptions_copy
4. dev_exception_add
5. dev_exception_rm
6. __dev_exception_clean
7. dev_exception_clean
8. is_devcg_online
9. devcgroup_online
10. devcgroup_offline
11. devcgroup_css_alloc
12. devcgroup_css_free
13. set_access
14. type_to_char
15. set_majmin
16. devcgroup_seq_show
17. match_exception
18. match_exception_partial
19. verify_new_ex
20. parent_has_perm
21. parent_allows_removal
22. may_allow_all
23. revalidate_active_exceptions
24. propagate_exception
25. devcgroup_update_access
26. devcgroup_access_write
27. __devcgroup_check_permission

   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 static DEFINE_MUTEX(devcgroup_mutex);
  19 
  20 enum devcg_behavior {
  21         DEVCG_DEFAULT_NONE,
  22         DEVCG_DEFAULT_ALLOW,
  23         DEVCG_DEFAULT_DENY,
  24 };
  25 
  26 /*
  27  * exception list locking rules:
  28  * hold devcgroup_mutex for update/read.
  29  * hold rcu_read_lock() for read.
  30  */
  31 
  32 struct dev_exception_item {
  33         u32 major, minor;
  34         short type;
  35         short access;
  36         struct list_head list;
  37         struct rcu_head rcu;
  38 };
  39 
  40 struct dev_cgroup {
  41         struct cgroup_subsys_state css;
  42         struct list_head exceptions;
  43         enum devcg_behavior behavior;
  44 };
  45 
  46 static inline struct dev_cgroup *css_to_devcgroup(struct cgroup_subsys_state *s)
  47 {
  48         return s ? container_of(s, struct dev_cgroup, css) : NULL;
  49 }
  50 
  51 static inline struct dev_cgroup *task_devcgroup(struct task_struct *task)
  52 {
  53         return css_to_devcgroup(task_css(task, devices_cgrp_id));
  54 }
  55 
  56 /*
  57  * called under devcgroup_mutex
  58  */
  59 static int dev_exceptions_copy(struct list_head *dest, struct list_head *orig)
  60 {
  61         struct dev_exception_item *ex, *tmp, *new;
  62 
  63         lockdep_assert_held(&devcgroup_mutex);
  64 
  65         list_for_each_entry(ex, orig, list) {
  66                 new = kmemdup(ex, sizeof(*ex), GFP_KERNEL);
  67                 if (!new)
  68                         goto free_and_exit;
  69                 list_add_tail(&new->list, dest);
  70         }
  71 
  72         return 0;
  73 
  74 free_and_exit:
  75         list_for_each_entry_safe(ex, tmp, dest, list) {
  76                 list_del(&ex->list);
  77                 kfree(ex);
  78         }
  79         return -ENOMEM;
  80 }
  81 
  82 /*
  83  * called under devcgroup_mutex
  84  */
  85 static int dev_exception_add(struct dev_cgroup *dev_cgroup,
  86                              struct dev_exception_item *ex)
  87 {
  88         struct dev_exception_item *excopy, *walk;
  89 
  90         lockdep_assert_held(&devcgroup_mutex);
  91 
  92         excopy = kmemdup(ex, sizeof(*ex), GFP_KERNEL);
  93         if (!excopy)
  94                 return -ENOMEM;
  95 
  96         list_for_each_entry(walk, &dev_cgroup->exceptions, list) {
  97                 if (walk->type != ex->type)
  98                         continue;
  99                 if (walk->major != ex->major)
 100                         continue;
 101                 if (walk->minor != ex->minor)
 102                         continue;
 103 
 104                 walk->access |= ex->access;
 105                 kfree(excopy);
 106                 excopy = NULL;
 107         }
 108 
 109         if (excopy != NULL)
 110                 list_add_tail_rcu(&excopy->list, &dev_cgroup->exceptions);
 111         return 0;
 112 }
 113 
 114 /*
 115  * called under devcgroup_mutex
 116  */
 117 static void dev_exception_rm(struct dev_cgroup *dev_cgroup,
 118                              struct dev_exception_item *ex)
 119 {
 120         struct dev_exception_item *walk, *tmp;
 121 
 122         lockdep_assert_held(&devcgroup_mutex);
 123 
 124         list_for_each_entry_safe(walk, tmp, &dev_cgroup->exceptions, list) {
 125                 if (walk->type != ex->type)
 126                         continue;
 127                 if (walk->major != ex->major)
 128                         continue;
 129                 if (walk->minor != ex->minor)
 130                         continue;
 131 
 132                 walk->access &= ~ex->access;
 133                 if (!walk->access) {
 134                         list_del_rcu(&walk->list);
 135                         kfree_rcu(walk, rcu);
 136                 }
 137         }
 138 }
 139 
 140 static void __dev_exception_clean(struct dev_cgroup *dev_cgroup)
 141 {
 142         struct dev_exception_item *ex, *tmp;
 143 
 144         list_for_each_entry_safe(ex, tmp, &dev_cgroup->exceptions, list) {
 145                 list_del_rcu(&ex->list);
 146                 kfree_rcu(ex, rcu);
 147         }
 148 }
 149 
 150 /**
 151  * dev_exception_clean - frees all entries of the exception list
 152  * @dev_cgroup: dev_cgroup with the exception list to be cleaned
 153  *
 154  * called under devcgroup_mutex
 155  */
 156 static void dev_exception_clean(struct dev_cgroup *dev_cgroup)
 157 {
 158         lockdep_assert_held(&devcgroup_mutex);
 159 
 160         __dev_exception_clean(dev_cgroup);
 161 }
 162 
 163 static inline bool is_devcg_online(const struct dev_cgroup *devcg)
 164 {
 165         return (devcg->behavior != DEVCG_DEFAULT_NONE);
 166 }
 167 
 168 /**
 169  * devcgroup_online - initializes devcgroup's behavior and exceptions based on
 170  *                    parent's
 171  * @css: css getting online
 172  * returns 0 in case of success, error code otherwise
 173  */
 174 static int devcgroup_online(struct cgroup_subsys_state *css)
 175 {
 176         struct dev_cgroup *dev_cgroup = css_to_devcgroup(css);
 177         struct dev_cgroup *parent_dev_cgroup = css_to_devcgroup(css->parent);
 178         int ret = 0;
 179 
 180         mutex_lock(&devcgroup_mutex);
 181 
 182         if (parent_dev_cgroup == NULL)
 183                 dev_cgroup->behavior = DEVCG_DEFAULT_ALLOW;
 184         else {
 185                 ret = dev_exceptions_copy(&dev_cgroup->exceptions,
 186                                           &parent_dev_cgroup->exceptions);
 187                 if (!ret)
 188                         dev_cgroup->behavior = parent_dev_cgroup->behavior;
 189         }
 190         mutex_unlock(&devcgroup_mutex);
 191 
 192         return ret;
 193 }
 194 
 195 static void devcgroup_offline(struct cgroup_subsys_state *css)
 196 {
 197         struct dev_cgroup *dev_cgroup = css_to_devcgroup(css);
 198 
 199         mutex_lock(&devcgroup_mutex);
 200         dev_cgroup->behavior = DEVCG_DEFAULT_NONE;
 201         mutex_unlock(&devcgroup_mutex);
 202 }
 203 
 204 /*
 205  * called from kernel/cgroup.c with cgroup_lock() held.
 206  */
 207 static struct cgroup_subsys_state *
 208 devcgroup_css_alloc(struct cgroup_subsys_state *parent_css)
 209 {
 210         struct dev_cgroup *dev_cgroup;
 211 
 212         dev_cgroup = kzalloc(sizeof(*dev_cgroup), GFP_KERNEL);
 213         if (!dev_cgroup)
 214                 return ERR_PTR(-ENOMEM);
 215         INIT_LIST_HEAD(&dev_cgroup->exceptions);
 216         dev_cgroup->behavior = DEVCG_DEFAULT_NONE;
 217 
 218         return &dev_cgroup->css;
 219 }
 220 
 221 static void devcgroup_css_free(struct cgroup_subsys_state *css)
 222 {
 223         struct dev_cgroup *dev_cgroup = css_to_devcgroup(css);
 224 
 225         __dev_exception_clean(dev_cgroup);
 226         kfree(dev_cgroup);
 227 }
 228 
 229 #define DEVCG_ALLOW 1
 230 #define DEVCG_DENY 2
 231 #define DEVCG_LIST 3
 232 
 233 #define MAJMINLEN 13
 234 #define ACCLEN 4
 235 
 236 static void set_access(char *acc, short access)
 237 {
 238         int idx = 0;
 239         memset(acc, 0, ACCLEN);
 240         if (access & DEVCG_ACC_READ)
 241                 acc[idx++] = 'r';
 242         if (access & DEVCG_ACC_WRITE)
 243                 acc[idx++] = 'w';
 244         if (access & DEVCG_ACC_MKNOD)
 245                 acc[idx++] = 'm';
 246 }
 247 
 248 static char type_to_char(short type)
 249 {
 250         if (type == DEVCG_DEV_ALL)
 251                 return 'a';
 252         if (type == DEVCG_DEV_CHAR)
 253                 return 'c';
 254         if (type == DEVCG_DEV_BLOCK)
 255                 return 'b';
 256         return 'X';
 257 }
 258 
 259 static void set_majmin(char *str, unsigned m)
 260 {
 261         if (m == ~0)
 262                 strcpy(str, "*");
 263         else
 264                 sprintf(str, "%u", m);
 265 }
 266 
 267 static int devcgroup_seq_show(struct seq_file *m, void *v)
 268 {
 269         struct dev_cgroup *devcgroup = css_to_devcgroup(seq_css(m));
 270         struct dev_exception_item *ex;
 271         char maj[MAJMINLEN], min[MAJMINLEN], acc[ACCLEN];
 272 
 273         rcu_read_lock();
 274         /*
 275          * To preserve the compatibility:
 276          * - Only show the "all devices" when the default policy is to allow
 277          * - List the exceptions in case the default policy is to deny
 278          * This way, the file remains as a "whitelist of devices"
 279          */
 280         if (devcgroup->behavior == DEVCG_DEFAULT_ALLOW) {
 281                 set_access(acc, DEVCG_ACC_MASK);
 282                 set_majmin(maj, ~0);
 283                 set_majmin(min, ~0);
 284                 seq_printf(m, "%c %s:%s %s\n", type_to_char(DEVCG_DEV_ALL),
 285                            maj, min, acc);
 286         } else {
 287                 list_for_each_entry_rcu(ex, &devcgroup->exceptions, list) {
 288                         set_access(acc, ex->access);
 289                         set_majmin(maj, ex->major);
 290                         set_majmin(min, ex->minor);
 291                         seq_printf(m, "%c %s:%s %s\n", type_to_char(ex->type),
 292                                    maj, min, acc);
 293                 }
 294         }
 295         rcu_read_unlock();
 296 
 297         return 0;
 298 }
 299 
 300 /**
 301  * match_exception      - iterates the exception list trying to find a complete match
 302  * @exceptions: list of exceptions
 303  * @type: device type (DEVCG_DEV_BLOCK or DEVCG_DEV_CHAR)
 304  * @major: device file major number, ~0 to match all
 305  * @minor: device file minor number, ~0 to match all
 306  * @access: permission mask (DEVCG_ACC_READ, DEVCG_ACC_WRITE, DEVCG_ACC_MKNOD)
 307  *
 308  * It is considered a complete match if an exception is found that will
 309  * contain the entire range of provided parameters.
 310  *
 311  * Return: true in case it matches an exception completely
 312  */
 313 static bool match_exception(struct list_head *exceptions, short type,
 314                             u32 major, u32 minor, short access)
 315 {
 316         struct dev_exception_item *ex;
 317 
 318         list_for_each_entry_rcu(ex, exceptions, list) {
 319                 if ((type & DEVCG_DEV_BLOCK) && !(ex->type & DEVCG_DEV_BLOCK))
 320                         continue;
 321                 if ((type & DEVCG_DEV_CHAR) && !(ex->type & DEVCG_DEV_CHAR))
 322                         continue;
 323                 if (ex->major != ~0 && ex->major != major)
 324                         continue;
 325                 if (ex->minor != ~0 && ex->minor != minor)
 326                         continue;
 327                 /* provided access cannot have more than the exception rule */
 328                 if (access & (~ex->access))
 329                         continue;
 330                 return true;
 331         }
 332         return false;
 333 }
 334 
 335 /**
 336  * match_exception_partial - iterates the exception list trying to find a partial match
 337  * @exceptions: list of exceptions
 338  * @type: device type (DEVCG_DEV_BLOCK or DEVCG_DEV_CHAR)
 339  * @major: device file major number, ~0 to match all
 340  * @minor: device file minor number, ~0 to match all
 341  * @access: permission mask (DEVCG_ACC_READ, DEVCG_ACC_WRITE, DEVCG_ACC_MKNOD)
 342  *
 343  * It is considered a partial match if an exception's range is found to
 344  * contain *any* of the devices specified by provided parameters. This is
 345  * used to make sure no extra access is being granted that is forbidden by
 346  * any of the exception list.
 347  *
 348  * Return: true in case the provided range mat matches an exception completely
 349  */
 350 static bool match_exception_partial(struct list_head *exceptions, short type,
 351                                     u32 major, u32 minor, short access)
 352 {
 353         struct dev_exception_item *ex;
 354 
 355         list_for_each_entry_rcu(ex, exceptions, list) {
 356                 if ((type & DEVCG_DEV_BLOCK) && !(ex->type & DEVCG_DEV_BLOCK))
 357                         continue;
 358                 if ((type & DEVCG_DEV_CHAR) && !(ex->type & DEVCG_DEV_CHAR))
 359                         continue;
 360                 /*
 361                  * We must be sure that both the exception and the provided
 362                  * range aren't masking all devices
 363                  */
 364                 if (ex->major != ~0 && major != ~0 && ex->major != major)
 365                         continue;
 366                 if (ex->minor != ~0 && minor != ~0 && ex->minor != minor)
 367                         continue;
 368                 /*
 369                  * In order to make sure the provided range isn't matching
 370                  * an exception, all its access bits shouldn't match the
 371                  * exception's access bits
 372                  */
 373                 if (!(access & ex->access))
 374                         continue;
 375                 return true;
 376         }
 377         return false;
 378 }
 379 
 380 /**
 381  * verify_new_ex - verifies if a new exception is allowed by parent cgroup's permissions
 382  * @dev_cgroup: dev cgroup to be tested against
 383  * @refex: new exception
 384  * @behavior: behavior of the exception's dev_cgroup
 385  *
 386  * This is used to make sure a child cgroup won't have more privileges
 387  * than its parent
 388  */
 389 static bool verify_new_ex(struct dev_cgroup *dev_cgroup,
 390                           struct dev_exception_item *refex,
 391                           enum devcg_behavior behavior)
 392 {
 393         bool match = false;
 394 
 395         RCU_LOCKDEP_WARN(!rcu_read_lock_held() &&
 396                          !lockdep_is_held(&devcgroup_mutex),
 397                          "device_cgroup:verify_new_ex called without proper synchronization");
 398 
 399         if (dev_cgroup->behavior == DEVCG_DEFAULT_ALLOW) {
 400                 if (behavior == DEVCG_DEFAULT_ALLOW) {
 401                         /*
 402                          * new exception in the child doesn't matter, only
 403                          * adding extra restrictions
 404                          */ 
 405                         return true;
 406                 } else {
 407                         /*
 408                          * new exception in the child will add more devices
 409                          * that can be acessed, so it can't match any of
 410                          * parent's exceptions, even slightly
 411                          */ 
 412                         match = match_exception_partial(&dev_cgroup->exceptions,
 413                                                         refex->type,
 414                                                         refex->major,
 415                                                         refex->minor,
 416                                                         refex->access);
 417 
 418                         if (match)
 419                                 return false;
 420                         return true;
 421                 }
 422         } else {
 423                 /*
 424                  * Only behavior == DEVCG_DEFAULT_DENY allowed here, therefore
 425                  * the new exception will add access to more devices and must
 426                  * be contained completely in an parent's exception to be
 427                  * allowed
 428                  */
 429                 match = match_exception(&dev_cgroup->exceptions, refex->type,
 430                                         refex->major, refex->minor,
 431                                         refex->access);
 432 
 433                 if (match)
 434                         /* parent has an exception that matches the proposed */
 435                         return true;
 436                 else
 437                         return false;
 438         }
 439         return false;
 440 }
 441 
 442 /*
 443  * parent_has_perm:
 444  * when adding a new allow rule to a device exception list, the rule
 445  * must be allowed in the parent device
 446  */
 447 static int parent_has_perm(struct dev_cgroup *childcg,
 448                                   struct dev_exception_item *ex)
 449 {
 450         struct dev_cgroup *parent = css_to_devcgroup(childcg->css.parent);
 451 
 452         if (!parent)
 453                 return 1;
 454         return verify_new_ex(parent, ex, childcg->behavior);
 455 }
 456 
 457 /**
 458  * parent_allows_removal - verify if it's ok to remove an exception
 459  * @childcg: child cgroup from where the exception will be removed
 460  * @ex: exception being removed
 461  *
 462  * When removing an exception in cgroups with default ALLOW policy, it must
 463  * be checked if removing it will give the child cgroup more access than the
 464  * parent.
 465  *
 466  * Return: true if it's ok to remove exception, false otherwise
 467  */
 468 static bool parent_allows_removal(struct dev_cgroup *childcg,
 469                                   struct dev_exception_item *ex)
 470 {
 471         struct dev_cgroup *parent = css_to_devcgroup(childcg->css.parent);
 472 
 473         if (!parent)
 474                 return true;
 475 
 476         /* It's always allowed to remove access to devices */
 477         if (childcg->behavior == DEVCG_DEFAULT_DENY)
 478                 return true;
 479 
 480         /*
 481          * Make sure you're not removing part or a whole exception existing in
 482          * the parent cgroup
 483          */
 484         return !match_exception_partial(&parent->exceptions, ex->type,
 485                                         ex->major, ex->minor, ex->access);
 486 }
 487 
 488 /**
 489  * may_allow_all - checks if it's possible to change the behavior to
 490  *                 allow based on parent's rules.
 491  * @parent: device cgroup's parent
 492  * returns: != 0 in case it's allowed, 0 otherwise
 493  */
 494 static inline int may_allow_all(struct dev_cgroup *parent)
 495 {
 496         if (!parent)
 497                 return 1;
 498         return parent->behavior == DEVCG_DEFAULT_ALLOW;
 499 }
 500 
 501 /**
 502  * revalidate_active_exceptions - walks through the active exception list and
 503  *                                revalidates the exceptions based on parent's
 504  *                                behavior and exceptions. The exceptions that
 505  *                                are no longer valid will be removed.
 506  *                                Called with devcgroup_mutex held.
 507  * @devcg: cgroup which exceptions will be checked
 508  *
 509  * This is one of the three key functions for hierarchy implementation.
 510  * This function is responsible for re-evaluating all the cgroup's active
 511  * exceptions due to a parent's exception change.
 512  * Refer to Documentation/admin-guide/cgroup-v1/devices.rst for more details.
 513  */
 514 static void revalidate_active_exceptions(struct dev_cgroup *devcg)
 515 {
 516         struct dev_exception_item *ex;
 517         struct list_head *this, *tmp;
 518 
 519         list_for_each_safe(this, tmp, &devcg->exceptions) {
 520                 ex = container_of(this, struct dev_exception_item, list);
 521                 if (!parent_has_perm(devcg, ex))
 522                         dev_exception_rm(devcg, ex);
 523         }
 524 }
 525 
 526 /**
 527  * propagate_exception - propagates a new exception to the children
 528  * @devcg_root: device cgroup that added a new exception
 529  * @ex: new exception to be propagated
 530  *
 531  * returns: 0 in case of success, != 0 in case of error
 532  */
 533 static int propagate_exception(struct dev_cgroup *devcg_root,
 534                                struct dev_exception_item *ex)
 535 {
 536         struct cgroup_subsys_state *pos;
 537         int rc = 0;
 538 
 539         rcu_read_lock();
 540 
 541         css_for_each_descendant_pre(pos, &devcg_root->css) {
 542                 struct dev_cgroup *devcg = css_to_devcgroup(pos);
 543 
 544                 /*
 545                  * Because devcgroup_mutex is held, no devcg will become
 546                  * online or offline during the tree walk (see on/offline
 547                  * methods), and online ones are safe to access outside RCU
 548                  * read lock without bumping refcnt.
 549                  */
 550                 if (pos == &devcg_root->css || !is_devcg_online(devcg))
 551                         continue;
 552 
 553                 rcu_read_unlock();
 554 
 555                 /*
 556                  * in case both root's behavior and devcg is allow, a new
 557                  * restriction means adding to the exception list
 558                  */
 559                 if (devcg_root->behavior == DEVCG_DEFAULT_ALLOW &&
 560                     devcg->behavior == DEVCG_DEFAULT_ALLOW) {
 561                         rc = dev_exception_add(devcg, ex);
 562                         if (rc)
 563                                 return rc;
 564                 } else {
 565                         /*
 566                          * in the other possible cases:
 567                          * root's behavior: allow, devcg's: deny
 568                          * root's behavior: deny, devcg's: deny
 569                          * the exception will be removed
 570                          */
 571                         dev_exception_rm(devcg, ex);
 572                 }
 573                 revalidate_active_exceptions(devcg);
 574 
 575                 rcu_read_lock();
 576         }
 577 
 578         rcu_read_unlock();
 579         return rc;
 580 }
 581 
 582 /*
 583  * Modify the exception list using allow/deny rules.
 584  * CAP_SYS_ADMIN is needed for this.  It's at least separate from CAP_MKNOD
 585  * so we can give a container CAP_MKNOD to let it create devices but not
 586  * modify the exception list.
 587  * It seems likely we'll want to add a CAP_CONTAINER capability to allow
 588  * us to also grant CAP_SYS_ADMIN to containers without giving away the
 589  * device exception list controls, but for now we'll stick with CAP_SYS_ADMIN
 590  *
 591  * Taking rules away is always allowed (given CAP_SYS_ADMIN).  Granting
 592  * new access is only allowed if you're in the top-level cgroup, or your
 593  * parent cgroup has the access you're asking for.
 594  */
 595 static int devcgroup_update_access(struct dev_cgroup *devcgroup,
 596                                    int filetype, char *buffer)
 597 {
 598         const char *b;
 599         char temp[12];          /* 11 + 1 characters needed for a u32 */
 600         int count, rc = 0;
 601         struct dev_exception_item ex;
 602         struct dev_cgroup *parent = css_to_devcgroup(devcgroup->css.parent);
 603 
 604         if (!capable(CAP_SYS_ADMIN))
 605                 return -EPERM;
 606 
 607         memset(&ex, 0, sizeof(ex));
 608         b = buffer;
 609 
 610         switch (*b) {
 611         case 'a':
 612                 switch (filetype) {
 613                 case DEVCG_ALLOW:
 614                         if (css_has_online_children(&devcgroup->css))
 615                                 return -EINVAL;
 616 
 617                         if (!may_allow_all(parent))
 618                                 return -EPERM;
 619                         dev_exception_clean(devcgroup);
 620                         devcgroup->behavior = DEVCG_DEFAULT_ALLOW;
 621                         if (!parent)
 622                                 break;
 623 
 624                         rc = dev_exceptions_copy(&devcgroup->exceptions,
 625                                                  &parent->exceptions);
 626                         if (rc)
 627                                 return rc;
 628                         break;
 629                 case DEVCG_DENY:
 630                         if (css_has_online_children(&devcgroup->css))
 631                                 return -EINVAL;
 632 
 633                         dev_exception_clean(devcgroup);
 634                         devcgroup->behavior = DEVCG_DEFAULT_DENY;
 635                         break;
 636                 default:
 637                         return -EINVAL;
 638                 }
 639                 return 0;
 640         case 'b':
 641                 ex.type = DEVCG_DEV_BLOCK;
 642                 break;
 643         case 'c':
 644                 ex.type = DEVCG_DEV_CHAR;
 645                 break;
 646         default:
 647                 return -EINVAL;
 648         }
 649         b++;
 650         if (!isspace(*b))
 651                 return -EINVAL;
 652         b++;
 653         if (*b == '*') {
 654                 ex.major = ~0;
 655                 b++;
 656         } else if (isdigit(*b)) {
 657                 memset(temp, 0, sizeof(temp));
 658                 for (count = 0; count < sizeof(temp) - 1; count++) {
 659                         temp[count] = *b;
 660                         b++;
 661                         if (!isdigit(*b))
 662                                 break;
 663                 }
 664                 rc = kstrtou32(temp, 10, &ex.major);
 665                 if (rc)
 666                         return -EINVAL;
 667         } else {
 668                 return -EINVAL;
 669         }
 670         if (*b != ':')
 671                 return -EINVAL;
 672         b++;
 673 
 674         /* read minor */
 675         if (*b == '*') {
 676                 ex.minor = ~0;
 677                 b++;
 678         } else if (isdigit(*b)) {
 679                 memset(temp, 0, sizeof(temp));
 680                 for (count = 0; count < sizeof(temp) - 1; count++) {
 681                         temp[count] = *b;
 682                         b++;
 683                         if (!isdigit(*b))
 684                                 break;
 685                 }
 686                 rc = kstrtou32(temp, 10, &ex.minor);
 687                 if (rc)
 688                         return -EINVAL;
 689         } else {
 690                 return -EINVAL;
 691         }
 692         if (!isspace(*b))
 693                 return -EINVAL;
 694         for (b++, count = 0; count < 3; count++, b++) {
 695                 switch (*b) {
 696                 case 'r':
 697                         ex.access |= DEVCG_ACC_READ;
 698                         break;
 699                 case 'w':
 700                         ex.access |= DEVCG_ACC_WRITE;
 701                         break;
 702                 case 'm':
 703                         ex.access |= DEVCG_ACC_MKNOD;
 704                         break;
 705                 case '\n':
 706                 case '\0':
 707                         count = 3;
 708                         break;
 709                 default:
 710                         return -EINVAL;
 711                 }
 712         }
 713 
 714         switch (filetype) {
 715         case DEVCG_ALLOW:
 716                 /*
 717                  * If the default policy is to allow by default, try to remove
 718                  * an matching exception instead. And be silent about it: we
 719                  * don't want to break compatibility
 720                  */
 721                 if (devcgroup->behavior == DEVCG_DEFAULT_ALLOW) {
 722                         /* Check if the parent allows removing it first */
 723                         if (!parent_allows_removal(devcgroup, &ex))
 724                                 return -EPERM;
 725                         dev_exception_rm(devcgroup, &ex);
 726                         break;
 727                 }
 728 
 729                 if (!parent_has_perm(devcgroup, &ex))
 730                         return -EPERM;
 731                 rc = dev_exception_add(devcgroup, &ex);
 732                 break;
 733         case DEVCG_DENY:
 734                 /*
 735                  * If the default policy is to deny by default, try to remove
 736                  * an matching exception instead. And be silent about it: we
 737                  * don't want to break compatibility
 738                  */
 739                 if (devcgroup->behavior == DEVCG_DEFAULT_DENY)
 740                         dev_exception_rm(devcgroup, &ex);
 741                 else
 742                         rc = dev_exception_add(devcgroup, &ex);
 743 
 744                 if (rc)
 745                         break;
 746                 /* we only propagate new restrictions */
 747                 rc = propagate_exception(devcgroup, &ex);
 748                 break;
 749         default:
 750                 rc = -EINVAL;
 751         }
 752         return rc;
 753 }
 754 
 755 static ssize_t devcgroup_access_write(struct kernfs_open_file *of,
 756                                       char *buf, size_t nbytes, loff_t off)
 757 {
 758         int retval;
 759 
 760         mutex_lock(&devcgroup_mutex);
 761         retval = devcgroup_update_access(css_to_devcgroup(of_css(of)),
 762                                          of_cft(of)->private, strstrip(buf));
 763         mutex_unlock(&devcgroup_mutex);
 764         return retval ?: nbytes;
 765 }
 766 
 767 static struct cftype dev_cgroup_files[] = {
 768         {
 769                 .name = "allow",
 770                 .write = devcgroup_access_write,
 771                 .private = DEVCG_ALLOW,
 772         },
 773         {
 774                 .name = "deny",
 775                 .write = devcgroup_access_write,
 776                 .private = DEVCG_DENY,
 777         },
 778         {
 779                 .name = "list",
 780                 .seq_show = devcgroup_seq_show,
 781                 .private = DEVCG_LIST,
 782         },
 783         { }     /* terminate */
 784 };
 785 
 786 struct cgroup_subsys devices_cgrp_subsys = {
 787         .css_alloc = devcgroup_css_alloc,
 788         .css_free = devcgroup_css_free,
 789         .css_online = devcgroup_online,
 790         .css_offline = devcgroup_offline,
 791         .legacy_cftypes = dev_cgroup_files,
 792 };
 793 
 794 /**
 795  * __devcgroup_check_permission - checks if an inode operation is permitted
 796  * @dev_cgroup: the dev cgroup to be tested against
 797  * @type: device type
 798  * @major: device major number
 799  * @minor: device minor number
 800  * @access: combination of DEVCG_ACC_WRITE, DEVCG_ACC_READ and DEVCG_ACC_MKNOD
 801  *
 802  * returns 0 on success, -EPERM case the operation is not permitted
 803  */
 804 int __devcgroup_check_permission(short type, u32 major, u32 minor,
 805                                  short access)
 806 {
 807         struct dev_cgroup *dev_cgroup;
 808         bool rc;
 809 
 810         rcu_read_lock();
 811         dev_cgroup = task_devcgroup(current);
 812         if (dev_cgroup->behavior == DEVCG_DEFAULT_ALLOW)
 813                 /* Can't match any of the exceptions, even partially */
 814                 rc = !match_exception_partial(&dev_cgroup->exceptions,
 815                                               type, major, minor, access);
 816         else
 817                 /* Need to match completely one exception to be allowed */
 818                 rc = match_exception(&dev_cgroup->exceptions, type, major,
 819                                      minor, access);
 820         rcu_read_unlock();
 821 
 822         if (!rc)
 823                 return -EPERM;
 824 
 825         return 0;
 826 }