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 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 static void dev_exceptions_move(struct list_head *dest, struct list_head *orig)
  83 {
  84         struct dev_exception_item *ex, *tmp;
  85
  86         lockdep_assert_held(&devcgroup_mutex);
  87
  88         list_for_each_entry_safe(ex, tmp, orig, list) {
  89                 list_move_tail(&ex->list, dest);
  90         }
  91 }
  92
  93 /*
  94  * called under devcgroup_mutex
  95  */
  96 static int dev_exception_add(struct dev_cgroup *dev_cgroup,
  97                              struct dev_exception_item *ex)
  98 {
  99         struct dev_exception_item *excopy, *walk;
 100
 101         lockdep_assert_held(&devcgroup_mutex);
 102
 103         excopy = kmemdup(ex, sizeof(*ex), GFP_KERNEL);
 104         if (!excopy)
 105                 return -ENOMEM;
 106
 107         list_for_each_entry(walk, &dev_cgroup->exceptions, list) {
 108                 if (walk->type != ex->type)
 109                         continue;
 110                 if (walk->major != ex->major)
 111                         continue;
 112                 if (walk->minor != ex->minor)
 113                         continue;
 114
 115                 walk->access |= ex->access;
 116                 kfree(excopy);
 117                 excopy = NULL;
 118         }
 119
 120         if (excopy != NULL)
 121                 list_add_tail_rcu(&excopy->list, &dev_cgroup->exceptions);
 122         return 0;
 123 }
 124
 125 /*
 126  * called under devcgroup_mutex
 127  */
 128 static void dev_exception_rm(struct dev_cgroup *dev_cgroup,
 129                              struct dev_exception_item *ex)
 130 {
 131         struct dev_exception_item *walk, *tmp;
 132
 133         lockdep_assert_held(&devcgroup_mutex);
 134
 135         list_for_each_entry_safe(walk, tmp, &dev_cgroup->exceptions, list) {
 136                 if (walk->type != ex->type)
 137                         continue;
 138                 if (walk->major != ex->major)
 139                         continue;
 140                 if (walk->minor != ex->minor)
 141                         continue;
 142
 143                 walk->access &= ~ex->access;
 144                 if (!walk->access) {
 145                         list_del_rcu(&walk->list);
 146                         kfree_rcu(walk, rcu);
 147                 }
 148         }
 149 }
 150
 151 static void __dev_exception_clean(struct dev_cgroup *dev_cgroup)
 152 {
 153         struct dev_exception_item *ex, *tmp;
 154
 155         list_for_each_entry_safe(ex, tmp, &dev_cgroup->exceptions, list) {
 156                 list_del_rcu(&ex->list);
 157                 kfree_rcu(ex, rcu);
 158         }
 159 }
 160
 161 /**
 162  * dev_exception_clean - frees all entries of the exception list
 163  * @dev_cgroup: dev_cgroup with the exception list to be cleaned
 164  *
 165  * called under devcgroup_mutex
 166  */
 167 static void dev_exception_clean(struct dev_cgroup *dev_cgroup)
 168 {
 169         lockdep_assert_held(&devcgroup_mutex);
 170
 171         __dev_exception_clean(dev_cgroup);
 172 }
 173
 174 static inline bool is_devcg_online(const struct dev_cgroup *devcg)
 175 {
 176         return (devcg->behavior != DEVCG_DEFAULT_NONE);
 177 }
 178
 179 /**
 180  * devcgroup_online - initializes devcgroup's behavior and exceptions based on
 181  *                    parent's
 182  * @css: css getting online
 183  * returns 0 in case of success, error code otherwise
 184  */
 185 static int devcgroup_online(struct cgroup_subsys_state *css)
 186 {
 187         struct dev_cgroup *dev_cgroup = css_to_devcgroup(css);
 188         struct dev_cgroup *parent_dev_cgroup = css_to_devcgroup(css->parent);
 189         int ret = 0;
 190
 191         mutex_lock(&devcgroup_mutex);
 192
 193         if (parent_dev_cgroup == NULL)
 194                 dev_cgroup->behavior = DEVCG_DEFAULT_ALLOW;
 195         else {
 196                 ret = dev_exceptions_copy(&dev_cgroup->exceptions,
 197                                           &parent_dev_cgroup->exceptions);
 198                 if (!ret)
 199                         dev_cgroup->behavior = parent_dev_cgroup->behavior;
 200         }
 201         mutex_unlock(&devcgroup_mutex);
 202
 203         return ret;
 204 }
 205
 206 static void devcgroup_offline(struct cgroup_subsys_state *css)
 207 {
 208         struct dev_cgroup *dev_cgroup = css_to_devcgroup(css);
 209
 210         mutex_lock(&devcgroup_mutex);
 211         dev_cgroup->behavior = DEVCG_DEFAULT_NONE;
 212         mutex_unlock(&devcgroup_mutex);
 213 }
 214
 215 /*
 216  * called from kernel/cgroup.c with cgroup_lock() held.
 217  */
 218 static struct cgroup_subsys_state *
 219 devcgroup_css_alloc(struct cgroup_subsys_state *parent_css)
 220 {
 221         struct dev_cgroup *dev_cgroup;
 222
 223         dev_cgroup = kzalloc(sizeof(*dev_cgroup), GFP_KERNEL);
 224         if (!dev_cgroup)
 225                 return ERR_PTR(-ENOMEM);
 226         INIT_LIST_HEAD(&dev_cgroup->exceptions);
 227         dev_cgroup->behavior = DEVCG_DEFAULT_NONE;
 228
 229         return &dev_cgroup->css;
 230 }
 231
 232 static void devcgroup_css_free(struct cgroup_subsys_state *css)
 233 {
 234         struct dev_cgroup *dev_cgroup = css_to_devcgroup(css);
 235
 236         __dev_exception_clean(dev_cgroup);
 237         kfree(dev_cgroup);
 238 }
 239
 240 #define DEVCG_ALLOW 1
 241 #define DEVCG_DENY 2
 242 #define DEVCG_LIST 3
 243
 244 #define MAJMINLEN 13
 245 #define ACCLEN 4
 246
 247 static void set_access(char *acc, short access)
 248 {
 249         int idx = 0;
 250         memset(acc, 0, ACCLEN);
 251         if (access & DEVCG_ACC_READ)
 252                 acc[idx++] = 'r';
 253         if (access & DEVCG_ACC_WRITE)
 254                 acc[idx++] = 'w';
 255         if (access & DEVCG_ACC_MKNOD)
 256                 acc[idx++] = 'm';
 257 }
 258
 259 static char type_to_char(short type)
 260 {
 261         if (type == DEVCG_DEV_ALL)
 262                 return 'a';
 263         if (type == DEVCG_DEV_CHAR)
 264                 return 'c';
 265         if (type == DEVCG_DEV_BLOCK)
 266                 return 'b';
 267         return 'X';
 268 }
 269
 270 static void set_majmin(char *str, unsigned m)
 271 {
 272         if (m == ~0)
 273                 strcpy(str, "*");
 274         else
 275                 sprintf(str, "%u", m);
 276 }
 277
 278 static int devcgroup_seq_show(struct seq_file *m, void *v)
 279 {
 280         struct dev_cgroup *devcgroup = css_to_devcgroup(seq_css(m));
 281         struct dev_exception_item *ex;
 282         char maj[MAJMINLEN], min[MAJMINLEN], acc[ACCLEN];
 283
 284         rcu_read_lock();
 285         /*
 286          * To preserve the compatibility:
 287          * - Only show the "all devices" when the default policy is to allow
 288          * - List the exceptions in case the default policy is to deny
 289          * This way, the file remains as a "whitelist of devices"
 290          */
 291         if (devcgroup->behavior == DEVCG_DEFAULT_ALLOW) {
 292                 set_access(acc, DEVCG_ACC_MASK);
 293                 set_majmin(maj, ~0);
 294                 set_majmin(min, ~0);
 295                 seq_printf(m, "%c %s:%s %s\n", type_to_char(DEVCG_DEV_ALL),
 296                            maj, min, acc);
 297         } else {
 298                 list_for_each_entry_rcu(ex, &devcgroup->exceptions, list) {
 299                         set_access(acc, ex->access);
 300                         set_majmin(maj, ex->major);
 301                         set_majmin(min, ex->minor);
 302                         seq_printf(m, "%c %s:%s %s\n", type_to_char(ex->type),
 303                                    maj, min, acc);
 304                 }
 305         }
 306         rcu_read_unlock();
 307
 308         return 0;
 309 }
 310
 311 /**
 312  * match_exception      - iterates the exception list trying to find a complete match
 313  * @exceptions: list of exceptions
 314  * @type: device type (DEVCG_DEV_BLOCK or DEVCG_DEV_CHAR)
 315  * @major: device file major number, ~0 to match all
 316  * @minor: device file minor number, ~0 to match all
 317  * @access: permission mask (DEVCG_ACC_READ, DEVCG_ACC_WRITE, DEVCG_ACC_MKNOD)
 318  *
 319  * It is considered a complete match if an exception is found that will
 320  * contain the entire range of provided parameters.
 321  *
 322  * Return: true in case it matches an exception completely
 323  */
 324 static bool match_exception(struct list_head *exceptions, short type,
 325                             u32 major, u32 minor, short access)
 326 {
 327         struct dev_exception_item *ex;
 328
 329         list_for_each_entry_rcu(ex, exceptions, list) {
 330                 if ((type & DEVCG_DEV_BLOCK) && !(ex->type & DEVCG_DEV_BLOCK))
 331                         continue;
 332                 if ((type & DEVCG_DEV_CHAR) && !(ex->type & DEVCG_DEV_CHAR))
 333                         continue;
 334                 if (ex->major != ~0 && ex->major != major)
 335                         continue;
 336                 if (ex->minor != ~0 && ex->minor != minor)
 337                         continue;
 338                 /* provided access cannot have more than the exception rule */
 339                 if (access & (~ex->access))
 340                         continue;
 341                 return true;
 342         }
 343         return false;
 344 }
 345
 346 /**
 347  * match_exception_partial - iterates the exception list trying to find a partial match
 348  * @exceptions: list of exceptions
 349  * @type: device type (DEVCG_DEV_BLOCK or DEVCG_DEV_CHAR)
 350  * @major: device file major number, ~0 to match all
 351  * @minor: device file minor number, ~0 to match all
 352  * @access: permission mask (DEVCG_ACC_READ, DEVCG_ACC_WRITE, DEVCG_ACC_MKNOD)
 353  *
 354  * It is considered a partial match if an exception's range is found to
 355  * contain *any* of the devices specified by provided parameters. This is
 356  * used to make sure no extra access is being granted that is forbidden by
 357  * any of the exception list.
 358  *
 359  * Return: true in case the provided range mat matches an exception completely
 360  */
 361 static bool match_exception_partial(struct list_head *exceptions, short type,
 362                                     u32 major, u32 minor, short access)
 363 {
 364         struct dev_exception_item *ex;
 365
 366         list_for_each_entry_rcu(ex, exceptions, list) {
 367                 if ((type & DEVCG_DEV_BLOCK) && !(ex->type & DEVCG_DEV_BLOCK))
 368                         continue;
 369                 if ((type & DEVCG_DEV_CHAR) && !(ex->type & DEVCG_DEV_CHAR))
 370                         continue;
 371                 /*
 372                  * We must be sure that both the exception and the provided
 373                  * range aren't masking all devices
 374                  */
 375                 if (ex->major != ~0 && major != ~0 && ex->major != major)
 376                         continue;
 377                 if (ex->minor != ~0 && minor != ~0 && ex->minor != minor)
 378                         continue;
 379                 /*
 380                  * In order to make sure the provided range isn't matching
 381                  * an exception, all its access bits shouldn't match the
 382                  * exception's access bits
 383                  */
 384                 if (!(access & ex->access))
 385                         continue;
 386                 return true;
 387         }
 388         return false;
 389 }
 390
 391 /**
 392  * verify_new_ex - verifies if a new exception is allowed by parent cgroup's permissions
 393  * @dev_cgroup: dev cgroup to be tested against
 394  * @refex: new exception
 395  * @behavior: behavior of the exception's dev_cgroup
 396  *
 397  * This is used to make sure a child cgroup won't have more privileges
 398  * than its parent
 399  */
 400 static bool verify_new_ex(struct dev_cgroup *dev_cgroup,
 401                           struct dev_exception_item *refex,
 402                           enum devcg_behavior behavior)
 403 {
 404         bool match = false;
 405
 406         RCU_LOCKDEP_WARN(!rcu_read_lock_held() &&
 407                          !lockdep_is_held(&devcgroup_mutex),
 408                          "device_cgroup:verify_new_ex called without proper synchronization");
 409
 410         if (dev_cgroup->behavior == DEVCG_DEFAULT_ALLOW) {
 411                 if (behavior == DEVCG_DEFAULT_ALLOW) {
 412                         /*
 413                          * new exception in the child doesn't matter, only
 414                          * adding extra restrictions
 415                          */
 416                         return true;
 417                 } else {
 418                         /*
 419                          * new exception in the child will add more devices
 420                          * that can be acessed, so it can't match any of
 421                          * parent's exceptions, even slightly
 422                          */
 423                         match = match_exception_partial(&dev_cgroup->exceptions,
 424                                                         refex->type,
 425                                                         refex->major,
 426                                                         refex->minor,
 427                                                         refex->access);
 428
 429                         if (match)
 430                                 return false;
 431                         return true;
 432                 }
 433         } else {
 434                 /*
 435                  * Only behavior == DEVCG_DEFAULT_DENY allowed here, therefore
 436                  * the new exception will add access to more devices and must
 437                  * be contained completely in an parent's exception to be
 438                  * allowed
 439                  */
 440                 match = match_exception(&dev_cgroup->exceptions, refex->type,
 441                                         refex->major, refex->minor,
 442                                         refex->access);
 443
 444                 if (match)
 445                         /* parent has an exception that matches the proposed */
 446                         return true;
 447                 else
 448                         return false;
 449         }
 450         return false;
 451 }
 452
 453 /*
 454  * parent_has_perm:
 455  * when adding a new allow rule to a device exception list, the rule
 456  * must be allowed in the parent device
 457  */
 458 static int parent_has_perm(struct dev_cgroup *childcg,
 459                                   struct dev_exception_item *ex)
 460 {
 461         struct dev_cgroup *parent = css_to_devcgroup(childcg->css.parent);
 462
 463         if (!parent)
 464                 return 1;
 465         return verify_new_ex(parent, ex, childcg->behavior);
 466 }
 467
 468 /**
 469  * parent_allows_removal - verify if it's ok to remove an exception
 470  * @childcg: child cgroup from where the exception will be removed
 471  * @ex: exception being removed
 472  *
 473  * When removing an exception in cgroups with default ALLOW policy, it must
 474  * be checked if removing it will give the child cgroup more access than the
 475  * parent.
 476  *
 477  * Return: true if it's ok to remove exception, false otherwise
 478  */
 479 static bool parent_allows_removal(struct dev_cgroup *childcg,
 480                                   struct dev_exception_item *ex)
 481 {
 482         struct dev_cgroup *parent = css_to_devcgroup(childcg->css.parent);
 483
 484         if (!parent)
 485                 return true;
 486
 487         /* It's always allowed to remove access to devices */
 488         if (childcg->behavior == DEVCG_DEFAULT_DENY)
 489                 return true;
 490
 491         /*
 492          * Make sure you're not removing part or a whole exception existing in
 493          * the parent cgroup
 494          */
 495         return !match_exception_partial(&parent->exceptions, ex->type,
 496                                         ex->major, ex->minor, ex->access);
 497 }
 498
 499 /**
 500  * may_allow_all - checks if it's possible to change the behavior to
 501  *                 allow based on parent's rules.
 502  * @parent: device cgroup's parent
 503  * returns: != 0 in case it's allowed, 0 otherwise
 504  */
 505 static inline int may_allow_all(struct dev_cgroup *parent)
 506 {
 507         if (!parent)
 508                 return 1;
 509         return parent->behavior == DEVCG_DEFAULT_ALLOW;
 510 }
 511
 512 /**
 513  * revalidate_active_exceptions - walks through the active exception list and
 514  *                                revalidates the exceptions based on parent's
 515  *                                behavior and exceptions. The exceptions that
 516  *                                are no longer valid will be removed.
 517  *                                Called with devcgroup_mutex held.
 518  * @devcg: cgroup which exceptions will be checked
 519  *
 520  * This is one of the three key functions for hierarchy implementation.
 521  * This function is responsible for re-evaluating all the cgroup's active
 522  * exceptions due to a parent's exception change.
 523  * Refer to Documentation/cgroup-v1/devices.txt for more details.
 524  */
 525 static void revalidate_active_exceptions(struct dev_cgroup *devcg)
 526 {
 527         struct dev_exception_item *ex;
 528         struct list_head *this, *tmp;
 529
 530         list_for_each_safe(this, tmp, &devcg->exceptions) {
 531                 ex = container_of(this, struct dev_exception_item, list);
 532                 if (!parent_has_perm(devcg, ex))
 533                         dev_exception_rm(devcg, ex);
 534         }
 535 }
 536
 537 /**
 538  * propagate_exception - propagates a new exception to the children
 539  * @devcg_root: device cgroup that added a new exception
 540  * @ex: new exception to be propagated
 541  *
 542  * returns: 0 in case of success, != 0 in case of error
 543  */
 544 static int propagate_exception(struct dev_cgroup *devcg_root,
 545                                struct dev_exception_item *ex)
 546 {
 547         struct cgroup_subsys_state *pos;
 548         int rc = 0;
 549
 550         rcu_read_lock();
 551
 552         css_for_each_descendant_pre(pos, &devcg_root->css) {
 553                 struct dev_cgroup *devcg = css_to_devcgroup(pos);
 554
 555                 /*
 556                  * Because devcgroup_mutex is held, no devcg will become
 557                  * online or offline during the tree walk (see on/offline
 558                  * methods), and online ones are safe to access outside RCU
 559                  * read lock without bumping refcnt.
 560                  */
 561                 if (pos == &devcg_root->css || !is_devcg_online(devcg))
 562                         continue;
 563
 564                 rcu_read_unlock();
 565
 566                 /*
 567                  * in case both root's behavior and devcg is allow, a new
 568                  * restriction means adding to the exception list
 569                  */
 570                 if (devcg_root->behavior == DEVCG_DEFAULT_ALLOW &&
 571                     devcg->behavior == DEVCG_DEFAULT_ALLOW) {
 572                         rc = dev_exception_add(devcg, ex);
 573                         if (rc)
 574                                 return rc;
 575                 } else {
 576                         /*
 577                          * in the other possible cases:
 578                          * root's behavior: allow, devcg's: deny
 579                          * root's behavior: deny, devcg's: deny
 580                          * the exception will be removed
 581                          */
 582                         dev_exception_rm(devcg, ex);
 583                 }
 584                 revalidate_active_exceptions(devcg);
 585
 586                 rcu_read_lock();
 587         }
 588
 589         rcu_read_unlock();
 590         return rc;
 591 }
 592
 593 /*
 594  * Modify the exception list using allow/deny rules.
 595  * CAP_SYS_ADMIN is needed for this.  It's at least separate from CAP_MKNOD
 596  * so we can give a container CAP_MKNOD to let it create devices but not
 597  * modify the exception list.
 598  * It seems likely we'll want to add a CAP_CONTAINER capability to allow
 599  * us to also grant CAP_SYS_ADMIN to containers without giving away the
 600  * device exception list controls, but for now we'll stick with CAP_SYS_ADMIN
 601  *
 602  * Taking rules away is always allowed (given CAP_SYS_ADMIN).  Granting
 603  * new access is only allowed if you're in the top-level cgroup, or your
 604  * parent cgroup has the access you're asking for.
 605  */
 606 static int devcgroup_update_access(struct dev_cgroup *devcgroup,
 607                                    int filetype, char *buffer)
 608 {
 609         const char *b;
 610         char temp[12];          /* 11 + 1 characters needed for a u32 */
 611         int count, rc = 0;
 612         struct dev_exception_item ex;
 613         struct dev_cgroup *parent = css_to_devcgroup(devcgroup->css.parent);
 614         struct dev_cgroup tmp_devcgrp;
 615
 616         if (!capable(CAP_SYS_ADMIN))
 617                 return -EPERM;
 618
 619         memset(&ex, 0, sizeof(ex));
 620         memset(&tmp_devcgrp, 0, sizeof(tmp_devcgrp));
 621         b = buffer;
 622
 623         switch (*b) {
 624         case 'a':
 625                 switch (filetype) {
 626                 case DEVCG_ALLOW:
 627                         if (css_has_online_children(&devcgroup->css))
 628                                 return -EINVAL;
 629
 630                         if (!may_allow_all(parent))
 631                                 return -EPERM;
 632                         if (!parent) {
 633                                 devcgroup->behavior = DEVCG_DEFAULT_ALLOW;
 634                                 dev_exception_clean(devcgroup);
 635                                 break;
 636                         }
 637
 638                         INIT_LIST_HEAD(&tmp_devcgrp.exceptions);
 639                         rc = dev_exceptions_copy(&tmp_devcgrp.exceptions,
 640                                                  &devcgroup->exceptions);
 641                         if (rc)
 642                                 return rc;
 643                         dev_exception_clean(devcgroup);
 644                         rc = dev_exceptions_copy(&devcgroup->exceptions,
 645                                                  &parent->exceptions);
 646                         if (rc) {
 647                                 dev_exceptions_move(&devcgroup->exceptions,
 648                                                     &tmp_devcgrp.exceptions);
 649                                 return rc;
 650                         }
 651                         devcgroup->behavior = DEVCG_DEFAULT_ALLOW;
 652                         dev_exception_clean(&tmp_devcgrp);
 653                         break;
 654                 case DEVCG_DENY:
 655                         if (css_has_online_children(&devcgroup->css))
 656                                 return -EINVAL;
 657
 658                         dev_exception_clean(devcgroup);
 659                         devcgroup->behavior = DEVCG_DEFAULT_DENY;
 660                         break;
 661                 default:
 662                         return -EINVAL;
 663                 }
 664                 return 0;
 665         case 'b':
 666                 ex.type = DEVCG_DEV_BLOCK;
 667                 break;
 668         case 'c':
 669                 ex.type = DEVCG_DEV_CHAR;
 670                 break;
 671         default:
 672                 return -EINVAL;
 673         }
 674         b++;
 675         if (!isspace(*b))
 676                 return -EINVAL;
 677         b++;
 678         if (*b == '*') {
 679                 ex.major = ~0;
 680                 b++;
 681         } else if (isdigit(*b)) {
 682                 memset(temp, 0, sizeof(temp));
 683                 for (count = 0; count < sizeof(temp) - 1; count++) {
 684                         temp[count] = *b;
 685                         b++;
 686                         if (!isdigit(*b))
 687                                 break;
 688                 }
 689                 rc = kstrtou32(temp, 10, &ex.major);
 690                 if (rc)
 691                         return -EINVAL;
 692         } else {
 693                 return -EINVAL;
 694         }
 695         if (*b != ':')
 696                 return -EINVAL;
 697         b++;
 698
 699         /* read minor */
 700         if (*b == '*') {
 701                 ex.minor = ~0;
 702                 b++;
 703         } else if (isdigit(*b)) {
 704                 memset(temp, 0, sizeof(temp));
 705                 for (count = 0; count < sizeof(temp) - 1; count++) {
 706                         temp[count] = *b;
 707                         b++;
 708                         if (!isdigit(*b))
 709                                 break;
 710                 }
 711                 rc = kstrtou32(temp, 10, &ex.minor);
 712                 if (rc)
 713                         return -EINVAL;
 714         } else {
 715                 return -EINVAL;
 716         }
 717         if (!isspace(*b))
 718                 return -EINVAL;
 719         for (b++, count = 0; count < 3; count++, b++) {
 720                 switch (*b) {
 721                 case 'r':
 722                         ex.access |= DEVCG_ACC_READ;
 723                         break;
 724                 case 'w':
 725                         ex.access |= DEVCG_ACC_WRITE;
 726                         break;
 727                 case 'm':
 728                         ex.access |= DEVCG_ACC_MKNOD;
 729                         break;
 730                 case '\n':
 731                 case '\0':
 732                         count = 3;
 733                         break;
 734                 default:
 735                         return -EINVAL;
 736                 }
 737         }
 738
 739         switch (filetype) {
 740         case DEVCG_ALLOW:
 741                 /*
 742                  * If the default policy is to allow by default, try to remove
 743                  * an matching exception instead. And be silent about it: we
 744                  * don't want to break compatibility
 745                  */
 746                 if (devcgroup->behavior == DEVCG_DEFAULT_ALLOW) {
 747                         /* Check if the parent allows removing it first */
 748                         if (!parent_allows_removal(devcgroup, &ex))
 749                                 return -EPERM;
 750                         dev_exception_rm(devcgroup, &ex);
 751                         break;
 752                 }
 753
 754                 if (!parent_has_perm(devcgroup, &ex))
 755                         return -EPERM;
 756                 rc = dev_exception_add(devcgroup, &ex);
 757                 break;
 758         case DEVCG_DENY:
 759                 /*
 760                  * If the default policy is to deny by default, try to remove
 761                  * an matching exception instead. And be silent about it: we
 762                  * don't want to break compatibility
 763                  */
 764                 if (devcgroup->behavior == DEVCG_DEFAULT_DENY)
 765                         dev_exception_rm(devcgroup, &ex);
 766                 else
 767                         rc = dev_exception_add(devcgroup, &ex);
 768
 769                 if (rc)
 770                         break;
 771                 /* we only propagate new restrictions */
 772                 rc = propagate_exception(devcgroup, &ex);
 773                 break;
 774         default:
 775                 rc = -EINVAL;
 776         }
 777         return rc;
 778 }
 779
 780 static ssize_t devcgroup_access_write(struct kernfs_open_file *of,
 781                                       char *buf, size_t nbytes, loff_t off)
 782 {
 783         int retval;
 784
 785         mutex_lock(&devcgroup_mutex);
 786         retval = devcgroup_update_access(css_to_devcgroup(of_css(of)),
 787                                          of_cft(of)->private, strstrip(buf));
 788         mutex_unlock(&devcgroup_mutex);
 789         return retval ?: nbytes;
 790 }
 791
 792 static struct cftype dev_cgroup_files[] = {
 793         {
 794                 .name = "allow",
 795                 .write = devcgroup_access_write,
 796                 .private = DEVCG_ALLOW,
 797         },
 798         {
 799                 .name = "deny",
 800                 .write = devcgroup_access_write,
 801                 .private = DEVCG_DENY,
 802         },
 803         {
 804                 .name = "list",
 805                 .seq_show = devcgroup_seq_show,
 806                 .private = DEVCG_LIST,
 807         },
 808         { }     /* terminate */
 809 };
 810
 811 struct cgroup_subsys devices_cgrp_subsys = {
 812         .css_alloc = devcgroup_css_alloc,
 813         .css_free = devcgroup_css_free,
 814         .css_online = devcgroup_online,
 815         .css_offline = devcgroup_offline,
 816         .legacy_cftypes = dev_cgroup_files,
 817 };
 818
 819 /**
 820  * __devcgroup_check_permission - checks if an inode operation is permitted
 821  * @dev_cgroup: the dev cgroup to be tested against
 822  * @type: device type
 823  * @major: device major number
 824  * @minor: device minor number
 825  * @access: combination of DEVCG_ACC_WRITE, DEVCG_ACC_READ and DEVCG_ACC_MKNOD
 826  *
 827  * returns 0 on success, -EPERM case the operation is not permitted
 828  */
 829 int __devcgroup_check_permission(short type, u32 major, u32 minor,
 830                                  short access)
 831 {
 832         struct dev_cgroup *dev_cgroup;
 833         bool rc;
 834
 835         rcu_read_lock();
 836         dev_cgroup = task_devcgroup(current);
 837         if (dev_cgroup->behavior == DEVCG_DEFAULT_ALLOW)
 838                 /* Can't match any of the exceptions, even partially */
 839                 rc = !match_exception_partial(&dev_cgroup->exceptions,
 840                                               type, major, minor, access);
 841         else
 842                 /* Need to match completely one exception to be allowed */
 843                 rc = match_exception(&dev_cgroup->exceptions, type, major,
 844                                      minor, access);
 845         rcu_read_unlock();
 846
 847         if (!rc)
 848                 return -EPERM;
 849
 850         return 0;
 851 }