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 #ifdef CONFIG_CGROUP_DEVICE
  19
  20 static DEFINE_MUTEX(devcgroup_mutex);
  21
  22 enum devcg_behavior {
  23         DEVCG_DEFAULT_NONE,
  24         DEVCG_DEFAULT_ALLOW,
  25         DEVCG_DEFAULT_DENY,
  26 };
  27
  28 /*
  29  * exception list locking rules:
  30  * hold devcgroup_mutex for update/read.
  31  * hold rcu_read_lock() for read.
  32  */
  33
  34 struct dev_exception_item {
  35         u32 major, minor;
  36         short type;
  37         short access;
  38         struct list_head list;
  39         struct rcu_head rcu;
  40 };
  41
  42 struct dev_cgroup {
  43         struct cgroup_subsys_state css;
  44         struct list_head exceptions;
  45         enum devcg_behavior behavior;
  46 };
  47
  48 static inline struct dev_cgroup *css_to_devcgroup(struct cgroup_subsys_state *s)
  49 {
  50         return s ? container_of(s, struct dev_cgroup, css) : NULL;
  51 }
  52
  53 static inline struct dev_cgroup *task_devcgroup(struct task_struct *task)
  54 {
  55         return css_to_devcgroup(task_css(task, devices_cgrp_id));
  56 }
  57
  58 /*
  59  * called under devcgroup_mutex
  60  */
  61 static int dev_exceptions_copy(struct list_head *dest, struct list_head *orig)
  62 {
  63         struct dev_exception_item *ex, *tmp, *new;
  64
  65         lockdep_assert_held(&devcgroup_mutex);
  66
  67         list_for_each_entry(ex, orig, list) {
  68                 new = kmemdup(ex, sizeof(*ex), GFP_KERNEL);
  69                 if (!new)
  70                         goto free_and_exit;
  71                 list_add_tail(&new->list, dest);
  72         }
  73
  74         return 0;
  75
  76 free_and_exit:
  77         list_for_each_entry_safe(ex, tmp, dest, list) {
  78                 list_del(&ex->list);
  79                 kfree(ex);
  80         }
  81         return -ENOMEM;
  82 }
  83
  84 /*
  85  * called under devcgroup_mutex
  86  */
  87 static int dev_exception_add(struct dev_cgroup *dev_cgroup,
  88                              struct dev_exception_item *ex)
  89 {
  90         struct dev_exception_item *excopy, *walk;
  91
  92         lockdep_assert_held(&devcgroup_mutex);
  93
  94         excopy = kmemdup(ex, sizeof(*ex), GFP_KERNEL);
  95         if (!excopy)
  96                 return -ENOMEM;
  97
  98         list_for_each_entry(walk, &dev_cgroup->exceptions, list) {
  99                 if (walk->type != ex->type)
 100                         continue;
 101                 if (walk->major != ex->major)
 102                         continue;
 103                 if (walk->minor != ex->minor)
 104                         continue;
 105
 106                 walk->access |= ex->access;
 107                 kfree(excopy);
 108                 excopy = NULL;
 109         }
 110
 111         if (excopy != NULL)
 112                 list_add_tail_rcu(&excopy->list, &dev_cgroup->exceptions);
 113         return 0;
 114 }
 115
 116 /*
 117  * called under devcgroup_mutex
 118  */
 119 static void dev_exception_rm(struct dev_cgroup *dev_cgroup,
 120                              struct dev_exception_item *ex)
 121 {
 122         struct dev_exception_item *walk, *tmp;
 123
 124         lockdep_assert_held(&devcgroup_mutex);
 125
 126         list_for_each_entry_safe(walk, tmp, &dev_cgroup->exceptions, list) {
 127                 if (walk->type != ex->type)
 128                         continue;
 129                 if (walk->major != ex->major)
 130                         continue;
 131                 if (walk->minor != ex->minor)
 132                         continue;
 133
 134                 walk->access &= ~ex->access;
 135                 if (!walk->access) {
 136                         list_del_rcu(&walk->list);
 137                         kfree_rcu(walk, rcu);
 138                 }
 139         }
 140 }
 141
 142 static void __dev_exception_clean(struct dev_cgroup *dev_cgroup)
 143 {
 144         struct dev_exception_item *ex, *tmp;
 145
 146         list_for_each_entry_safe(ex, tmp, &dev_cgroup->exceptions, list) {
 147                 list_del_rcu(&ex->list);
 148                 kfree_rcu(ex, rcu);
 149         }
 150 }
 151
 152 /**
 153  * dev_exception_clean - frees all entries of the exception list
 154  * @dev_cgroup: dev_cgroup with the exception list to be cleaned
 155  *
 156  * called under devcgroup_mutex
 157  */
 158 static void dev_exception_clean(struct dev_cgroup *dev_cgroup)
 159 {
 160         lockdep_assert_held(&devcgroup_mutex);
 161
 162         __dev_exception_clean(dev_cgroup);
 163 }
 164
 165 static inline bool is_devcg_online(const struct dev_cgroup *devcg)
 166 {
 167         return (devcg->behavior != DEVCG_DEFAULT_NONE);
 168 }
 169
 170 /**
 171  * devcgroup_online - initializes devcgroup's behavior and exceptions based on
 172  *                    parent's
 173  * @css: css getting online
 174  * returns 0 in case of success, error code otherwise
 175  */
 176 static int devcgroup_online(struct cgroup_subsys_state *css)
 177 {
 178         struct dev_cgroup *dev_cgroup = css_to_devcgroup(css);
 179         struct dev_cgroup *parent_dev_cgroup = css_to_devcgroup(css->parent);
 180         int ret = 0;
 181
 182         mutex_lock(&devcgroup_mutex);
 183
 184         if (parent_dev_cgroup == NULL)
 185                 dev_cgroup->behavior = DEVCG_DEFAULT_ALLOW;
 186         else {
 187                 ret = dev_exceptions_copy(&dev_cgroup->exceptions,
 188                                           &parent_dev_cgroup->exceptions);
 189                 if (!ret)
 190                         dev_cgroup->behavior = parent_dev_cgroup->behavior;
 191         }
 192         mutex_unlock(&devcgroup_mutex);
 193
 194         return ret;
 195 }
 196
 197 static void devcgroup_offline(struct cgroup_subsys_state *css)
 198 {
 199         struct dev_cgroup *dev_cgroup = css_to_devcgroup(css);
 200
 201         mutex_lock(&devcgroup_mutex);
 202         dev_cgroup->behavior = DEVCG_DEFAULT_NONE;
 203         mutex_unlock(&devcgroup_mutex);
 204 }
 205
 206 /*
 207  * called from kernel/cgroup.c with cgroup_lock() held.
 208  */
 209 static struct cgroup_subsys_state *
 210 devcgroup_css_alloc(struct cgroup_subsys_state *parent_css)
 211 {
 212         struct dev_cgroup *dev_cgroup;
 213
 214         dev_cgroup = kzalloc(sizeof(*dev_cgroup), GFP_KERNEL);
 215         if (!dev_cgroup)
 216                 return ERR_PTR(-ENOMEM);
 217         INIT_LIST_HEAD(&dev_cgroup->exceptions);
 218         dev_cgroup->behavior = DEVCG_DEFAULT_NONE;
 219
 220         return &dev_cgroup->css;
 221 }
 222
 223 static void devcgroup_css_free(struct cgroup_subsys_state *css)
 224 {
 225         struct dev_cgroup *dev_cgroup = css_to_devcgroup(css);
 226
 227         __dev_exception_clean(dev_cgroup);
 228         kfree(dev_cgroup);
 229 }
 230
 231 #define DEVCG_ALLOW 1
 232 #define DEVCG_DENY 2
 233 #define DEVCG_LIST 3
 234
 235 #define MAJMINLEN 13
 236 #define ACCLEN 4
 237
 238 static void set_access(char *acc, short access)
 239 {
 240         int idx = 0;
 241         memset(acc, 0, ACCLEN);
 242         if (access & DEVCG_ACC_READ)
 243                 acc[idx++] = 'r';
 244         if (access & DEVCG_ACC_WRITE)
 245                 acc[idx++] = 'w';
 246         if (access & DEVCG_ACC_MKNOD)
 247                 acc[idx++] = 'm';
 248 }
 249
 250 static char type_to_char(short type)
 251 {
 252         if (type == DEVCG_DEV_ALL)
 253                 return 'a';
 254         if (type == DEVCG_DEV_CHAR)
 255                 return 'c';
 256         if (type == DEVCG_DEV_BLOCK)
 257                 return 'b';
 258         return 'X';
 259 }
 260
 261 static void set_majmin(char *str, unsigned m)
 262 {
 263         if (m == ~0)
 264                 strcpy(str, "*");
 265         else
 266                 sprintf(str, "%u", m);
 267 }
 268
 269 static int devcgroup_seq_show(struct seq_file *m, void *v)
 270 {
 271         struct dev_cgroup *devcgroup = css_to_devcgroup(seq_css(m));
 272         struct dev_exception_item *ex;
 273         char maj[MAJMINLEN], min[MAJMINLEN], acc[ACCLEN];
 274
 275         rcu_read_lock();
 276         /*
 277          * To preserve the compatibility:
 278          * - Only show the "all devices" when the default policy is to allow
 279          * - List the exceptions in case the default policy is to deny
 280          * This way, the file remains as a "whitelist of devices"
 281          */
 282         if (devcgroup->behavior == DEVCG_DEFAULT_ALLOW) {
 283                 set_access(acc, DEVCG_ACC_MASK);
 284                 set_majmin(maj, ~0);
 285                 set_majmin(min, ~0);
 286                 seq_printf(m, "%c %s:%s %s\n", type_to_char(DEVCG_DEV_ALL),
 287                            maj, min, acc);
 288         } else {
 289                 list_for_each_entry_rcu(ex, &devcgroup->exceptions, list) {
 290                         set_access(acc, ex->access);
 291                         set_majmin(maj, ex->major);
 292                         set_majmin(min, ex->minor);
 293                         seq_printf(m, "%c %s:%s %s\n", type_to_char(ex->type),
 294                                    maj, min, acc);
 295                 }
 296         }
 297         rcu_read_unlock();
 298
 299         return 0;
 300 }
 301
 302 /**
 303  * match_exception      - iterates the exception list trying to find a complete match
 304  * @exceptions: list of exceptions
 305  * @type: device type (DEVCG_DEV_BLOCK or DEVCG_DEV_CHAR)
 306  * @major: device file major number, ~0 to match all
 307  * @minor: device file minor number, ~0 to match all
 308  * @access: permission mask (DEVCG_ACC_READ, DEVCG_ACC_WRITE, DEVCG_ACC_MKNOD)
 309  *
 310  * It is considered a complete match if an exception is found that will
 311  * contain the entire range of provided parameters.
 312  *
 313  * Return: true in case it matches an exception completely
 314  */
 315 static bool match_exception(struct list_head *exceptions, short type,
 316                             u32 major, u32 minor, short access)
 317 {
 318         struct dev_exception_item *ex;
 319
 320         list_for_each_entry_rcu(ex, exceptions, list) {
 321                 if ((type & DEVCG_DEV_BLOCK) && !(ex->type & DEVCG_DEV_BLOCK))
 322                         continue;
 323                 if ((type & DEVCG_DEV_CHAR) && !(ex->type & DEVCG_DEV_CHAR))
 324                         continue;
 325                 if (ex->major != ~0 && ex->major != major)
 326                         continue;
 327                 if (ex->minor != ~0 && ex->minor != minor)
 328                         continue;
 329                 /* provided access cannot have more than the exception rule */
 330                 if (access & (~ex->access))
 331                         continue;
 332                 return true;
 333         }
 334         return false;
 335 }
 336
 337 /**
 338  * match_exception_partial - iterates the exception list trying to find a partial match
 339  * @exceptions: list of exceptions
 340  * @type: device type (DEVCG_DEV_BLOCK or DEVCG_DEV_CHAR)
 341  * @major: device file major number, ~0 to match all
 342  * @minor: device file minor number, ~0 to match all
 343  * @access: permission mask (DEVCG_ACC_READ, DEVCG_ACC_WRITE, DEVCG_ACC_MKNOD)
 344  *
 345  * It is considered a partial match if an exception's range is found to
 346  * contain *any* of the devices specified by provided parameters. This is
 347  * used to make sure no extra access is being granted that is forbidden by
 348  * any of the exception list.
 349  *
 350  * Return: true in case the provided range mat matches an exception completely
 351  */
 352 static bool match_exception_partial(struct list_head *exceptions, short type,
 353                                     u32 major, u32 minor, short access)
 354 {
 355         struct dev_exception_item *ex;
 356
 357         list_for_each_entry_rcu(ex, exceptions, list) {
 358                 if ((type & DEVCG_DEV_BLOCK) && !(ex->type & DEVCG_DEV_BLOCK))
 359                         continue;
 360                 if ((type & DEVCG_DEV_CHAR) && !(ex->type & DEVCG_DEV_CHAR))
 361                         continue;
 362                 /*
 363                  * We must be sure that both the exception and the provided
 364                  * range aren't masking all devices
 365                  */
 366                 if (ex->major != ~0 && major != ~0 && ex->major != major)
 367                         continue;
 368                 if (ex->minor != ~0 && minor != ~0 && ex->minor != minor)
 369                         continue;
 370                 /*
 371                  * In order to make sure the provided range isn't matching
 372                  * an exception, all its access bits shouldn't match the
 373                  * exception's access bits
 374                  */
 375                 if (!(access & ex->access))
 376                         continue;
 377                 return true;
 378         }
 379         return false;
 380 }
 381
 382 /**
 383  * verify_new_ex - verifies if a new exception is allowed by parent cgroup's permissions
 384  * @dev_cgroup: dev cgroup to be tested against
 385  * @refex: new exception
 386  * @behavior: behavior of the exception's dev_cgroup
 387  *
 388  * This is used to make sure a child cgroup won't have more privileges
 389  * than its parent
 390  */
 391 static bool verify_new_ex(struct dev_cgroup *dev_cgroup,
 392                           struct dev_exception_item *refex,
 393                           enum devcg_behavior behavior)
 394 {
 395         bool match = false;
 396
 397         RCU_LOCKDEP_WARN(!rcu_read_lock_held() &&
 398                          !lockdep_is_held(&devcgroup_mutex),
 399                          "device_cgroup:verify_new_ex called without proper synchronization");
 400
 401         if (dev_cgroup->behavior == DEVCG_DEFAULT_ALLOW) {
 402                 if (behavior == DEVCG_DEFAULT_ALLOW) {
 403                         /*
 404                          * new exception in the child doesn't matter, only
 405                          * adding extra restrictions
 406                          */
 407                         return true;
 408                 } else {
 409                         /*
 410                          * new exception in the child will add more devices
 411                          * that can be acessed, so it can't match any of
 412                          * parent's exceptions, even slightly
 413                          */
 414                         match = match_exception_partial(&dev_cgroup->exceptions,
 415                                                         refex->type,
 416                                                         refex->major,
 417                                                         refex->minor,
 418                                                         refex->access);
 419
 420                         if (match)
 421                                 return false;
 422                         return true;
 423                 }
 424         } else {
 425                 /*
 426                  * Only behavior == DEVCG_DEFAULT_DENY allowed here, therefore
 427                  * the new exception will add access to more devices and must
 428                  * be contained completely in an parent's exception to be
 429                  * allowed
 430                  */
 431                 match = match_exception(&dev_cgroup->exceptions, refex->type,
 432                                         refex->major, refex->minor,
 433                                         refex->access);
 434
 435                 if (match)
 436                         /* parent has an exception that matches the proposed */
 437                         return true;
 438                 else
 439                         return false;
 440         }
 441         return false;
 442 }
 443
 444 /*
 445  * parent_has_perm:
 446  * when adding a new allow rule to a device exception list, the rule
 447  * must be allowed in the parent device
 448  */
 449 static int parent_has_perm(struct dev_cgroup *childcg,
 450                                   struct dev_exception_item *ex)
 451 {
 452         struct dev_cgroup *parent = css_to_devcgroup(childcg->css.parent);
 453
 454         if (!parent)
 455                 return 1;
 456         return verify_new_ex(parent, ex, childcg->behavior);
 457 }
 458
 459 /**
 460  * parent_allows_removal - verify if it's ok to remove an exception
 461  * @childcg: child cgroup from where the exception will be removed
 462  * @ex: exception being removed
 463  *
 464  * When removing an exception in cgroups with default ALLOW policy, it must
 465  * be checked if removing it will give the child cgroup more access than the
 466  * parent.
 467  *
 468  * Return: true if it's ok to remove exception, false otherwise
 469  */
 470 static bool parent_allows_removal(struct dev_cgroup *childcg,
 471                                   struct dev_exception_item *ex)
 472 {
 473         struct dev_cgroup *parent = css_to_devcgroup(childcg->css.parent);
 474
 475         if (!parent)
 476                 return true;
 477
 478         /* It's always allowed to remove access to devices */
 479         if (childcg->behavior == DEVCG_DEFAULT_DENY)
 480                 return true;
 481
 482         /*
 483          * Make sure you're not removing part or a whole exception existing in
 484          * the parent cgroup
 485          */
 486         return !match_exception_partial(&parent->exceptions, ex->type,
 487                                         ex->major, ex->minor, ex->access);
 488 }
 489
 490 /**
 491  * may_allow_all - checks if it's possible to change the behavior to
 492  *                 allow based on parent's rules.
 493  * @parent: device cgroup's parent
 494  * returns: != 0 in case it's allowed, 0 otherwise
 495  */
 496 static inline int may_allow_all(struct dev_cgroup *parent)
 497 {
 498         if (!parent)
 499                 return 1;
 500         return parent->behavior == DEVCG_DEFAULT_ALLOW;
 501 }
 502
 503 /**
 504  * revalidate_active_exceptions - walks through the active exception list and
 505  *                                revalidates the exceptions based on parent's
 506  *                                behavior and exceptions. The exceptions that
 507  *                                are no longer valid will be removed.
 508  *                                Called with devcgroup_mutex held.
 509  * @devcg: cgroup which exceptions will be checked
 510  *
 511  * This is one of the three key functions for hierarchy implementation.
 512  * This function is responsible for re-evaluating all the cgroup's active
 513  * exceptions due to a parent's exception change.
 514  * Refer to Documentation/admin-guide/cgroup-v1/devices.rst for more details.
 515  */
 516 static void revalidate_active_exceptions(struct dev_cgroup *devcg)
 517 {
 518         struct dev_exception_item *ex;
 519         struct list_head *this, *tmp;
 520
 521         list_for_each_safe(this, tmp, &devcg->exceptions) {
 522                 ex = container_of(this, struct dev_exception_item, list);
 523                 if (!parent_has_perm(devcg, ex))
 524                         dev_exception_rm(devcg, ex);
 525         }
 526 }
 527
 528 /**
 529  * propagate_exception - propagates a new exception to the children
 530  * @devcg_root: device cgroup that added a new exception
 531  * @ex: new exception to be propagated
 532  *
 533  * returns: 0 in case of success, != 0 in case of error
 534  */
 535 static int propagate_exception(struct dev_cgroup *devcg_root,
 536                                struct dev_exception_item *ex)
 537 {
 538         struct cgroup_subsys_state *pos;
 539         int rc = 0;
 540
 541         rcu_read_lock();
 542
 543         css_for_each_descendant_pre(pos, &devcg_root->css) {
 544                 struct dev_cgroup *devcg = css_to_devcgroup(pos);
 545
 546                 /*
 547                  * Because devcgroup_mutex is held, no devcg will become
 548                  * online or offline during the tree walk (see on/offline
 549                  * methods), and online ones are safe to access outside RCU
 550                  * read lock without bumping refcnt.
 551                  */
 552                 if (pos == &devcg_root->css || !is_devcg_online(devcg))
 553                         continue;
 554
 555                 rcu_read_unlock();
 556
 557                 /*
 558                  * in case both root's behavior and devcg is allow, a new
 559                  * restriction means adding to the exception list
 560                  */
 561                 if (devcg_root->behavior == DEVCG_DEFAULT_ALLOW &&
 562                     devcg->behavior == DEVCG_DEFAULT_ALLOW) {
 563                         rc = dev_exception_add(devcg, ex);
 564                         if (rc)
 565                                 return rc;
 566                 } else {
 567                         /*
 568                          * in the other possible cases:
 569                          * root's behavior: allow, devcg's: deny
 570                          * root's behavior: deny, devcg's: deny
 571                          * the exception will be removed
 572                          */
 573                         dev_exception_rm(devcg, ex);
 574                 }
 575                 revalidate_active_exceptions(devcg);
 576
 577                 rcu_read_lock();
 578         }
 579
 580         rcu_read_unlock();
 581         return rc;
 582 }
 583
 584 /*
 585  * Modify the exception list using allow/deny rules.
 586  * CAP_SYS_ADMIN is needed for this.  It's at least separate from CAP_MKNOD
 587  * so we can give a container CAP_MKNOD to let it create devices but not
 588  * modify the exception list.
 589  * It seems likely we'll want to add a CAP_CONTAINER capability to allow
 590  * us to also grant CAP_SYS_ADMIN to containers without giving away the
 591  * device exception list controls, but for now we'll stick with CAP_SYS_ADMIN
 592  *
 593  * Taking rules away is always allowed (given CAP_SYS_ADMIN).  Granting
 594  * new access is only allowed if you're in the top-level cgroup, or your
 595  * parent cgroup has the access you're asking for.
 596  */
 597 static int devcgroup_update_access(struct dev_cgroup *devcgroup,
 598                                    int filetype, char *buffer)
 599 {
 600         const char *b;
 601         char temp[12];          /* 11 + 1 characters needed for a u32 */
 602         int count, rc = 0;
 603         struct dev_exception_item ex;
 604         struct dev_cgroup *parent = css_to_devcgroup(devcgroup->css.parent);
 605
 606         if (!capable(CAP_SYS_ADMIN))
 607                 return -EPERM;
 608
 609         memset(&ex, 0, sizeof(ex));
 610         b = buffer;
 611
 612         switch (*b) {
 613         case 'a':
 614                 switch (filetype) {
 615                 case DEVCG_ALLOW:
 616                         if (css_has_online_children(&devcgroup->css))
 617                                 return -EINVAL;
 618
 619                         if (!may_allow_all(parent))
 620                                 return -EPERM;
 621                         dev_exception_clean(devcgroup);
 622                         devcgroup->behavior = DEVCG_DEFAULT_ALLOW;
 623                         if (!parent)
 624                                 break;
 625
 626                         rc = dev_exceptions_copy(&devcgroup->exceptions,
 627                                                  &parent->exceptions);
 628                         if (rc)
 629                                 return rc;
 630                         break;
 631                 case DEVCG_DENY:
 632                         if (css_has_online_children(&devcgroup->css))
 633                                 return -EINVAL;
 634
 635                         dev_exception_clean(devcgroup);
 636                         devcgroup->behavior = DEVCG_DEFAULT_DENY;
 637                         break;
 638                 default:
 639                         return -EINVAL;
 640                 }
 641                 return 0;
 642         case 'b':
 643                 ex.type = DEVCG_DEV_BLOCK;
 644                 break;
 645         case 'c':
 646                 ex.type = DEVCG_DEV_CHAR;
 647                 break;
 648         default:
 649                 return -EINVAL;
 650         }
 651         b++;
 652         if (!isspace(*b))
 653                 return -EINVAL;
 654         b++;
 655         if (*b == '*') {
 656                 ex.major = ~0;
 657                 b++;
 658         } else if (isdigit(*b)) {
 659                 memset(temp, 0, sizeof(temp));
 660                 for (count = 0; count < sizeof(temp) - 1; count++) {
 661                         temp[count] = *b;
 662                         b++;
 663                         if (!isdigit(*b))
 664                                 break;
 665                 }
 666                 rc = kstrtou32(temp, 10, &ex.major);
 667                 if (rc)
 668                         return -EINVAL;
 669         } else {
 670                 return -EINVAL;
 671         }
 672         if (*b != ':')
 673                 return -EINVAL;
 674         b++;
 675
 676         /* read minor */
 677         if (*b == '*') {
 678                 ex.minor = ~0;
 679                 b++;
 680         } else if (isdigit(*b)) {
 681                 memset(temp, 0, sizeof(temp));
 682                 for (count = 0; count < sizeof(temp) - 1; count++) {
 683                         temp[count] = *b;
 684                         b++;
 685                         if (!isdigit(*b))
 686                                 break;
 687                 }
 688                 rc = kstrtou32(temp, 10, &ex.minor);
 689                 if (rc)
 690                         return -EINVAL;
 691         } else {
 692                 return -EINVAL;
 693         }
 694         if (!isspace(*b))
 695                 return -EINVAL;
 696         for (b++, count = 0; count < 3; count++, b++) {
 697                 switch (*b) {
 698                 case 'r':
 699                         ex.access |= DEVCG_ACC_READ;
 700                         break;
 701                 case 'w':
 702                         ex.access |= DEVCG_ACC_WRITE;
 703                         break;
 704                 case 'm':
 705                         ex.access |= DEVCG_ACC_MKNOD;
 706                         break;
 707                 case '\n':
 708                 case '\0':
 709                         count = 3;
 710                         break;
 711                 default:
 712                         return -EINVAL;
 713                 }
 714         }
 715
 716         switch (filetype) {
 717         case DEVCG_ALLOW:
 718                 /*
 719                  * If the default policy is to allow by default, try to remove
 720                  * an matching exception instead. And be silent about it: we
 721                  * don't want to break compatibility
 722                  */
 723                 if (devcgroup->behavior == DEVCG_DEFAULT_ALLOW) {
 724                         /* Check if the parent allows removing it first */
 725                         if (!parent_allows_removal(devcgroup, &ex))
 726                                 return -EPERM;
 727                         dev_exception_rm(devcgroup, &ex);
 728                         break;
 729                 }
 730
 731                 if (!parent_has_perm(devcgroup, &ex))
 732                         return -EPERM;
 733                 rc = dev_exception_add(devcgroup, &ex);
 734                 break;
 735         case DEVCG_DENY:
 736                 /*
 737                  * If the default policy is to deny by default, try to remove
 738                  * an matching exception instead. And be silent about it: we
 739                  * don't want to break compatibility
 740                  */
 741                 if (devcgroup->behavior == DEVCG_DEFAULT_DENY)
 742                         dev_exception_rm(devcgroup, &ex);
 743                 else
 744                         rc = dev_exception_add(devcgroup, &ex);
 745
 746                 if (rc)
 747                         break;
 748                 /* we only propagate new restrictions */
 749                 rc = propagate_exception(devcgroup, &ex);
 750                 break;
 751         default:
 752                 rc = -EINVAL;
 753         }
 754         return rc;
 755 }
 756
 757 static ssize_t devcgroup_access_write(struct kernfs_open_file *of,
 758                                       char *buf, size_t nbytes, loff_t off)
 759 {
 760         int retval;
 761
 762         mutex_lock(&devcgroup_mutex);
 763         retval = devcgroup_update_access(css_to_devcgroup(of_css(of)),
 764                                          of_cft(of)->private, strstrip(buf));
 765         mutex_unlock(&devcgroup_mutex);
 766         return retval ?: nbytes;
 767 }
 768
 769 static struct cftype dev_cgroup_files[] = {
 770         {
 771                 .name = "allow",
 772                 .write = devcgroup_access_write,
 773                 .private = DEVCG_ALLOW,
 774         },
 775         {
 776                 .name = "deny",
 777                 .write = devcgroup_access_write,
 778                 .private = DEVCG_DENY,
 779         },
 780         {
 781                 .name = "list",
 782                 .seq_show = devcgroup_seq_show,
 783                 .private = DEVCG_LIST,
 784         },
 785         { }     /* terminate */
 786 };
 787
 788 struct cgroup_subsys devices_cgrp_subsys = {
 789         .css_alloc = devcgroup_css_alloc,
 790         .css_free = devcgroup_css_free,
 791         .css_online = devcgroup_online,
 792         .css_offline = devcgroup_offline,
 793         .legacy_cftypes = dev_cgroup_files,
 794 };
 795
 796 /**
 797  * devcgroup_legacy_check_permission - checks if an inode operation is permitted
 798  * @dev_cgroup: the dev cgroup to be tested against
 799  * @type: device type
 800  * @major: device major number
 801  * @minor: device minor number
 802  * @access: combination of DEVCG_ACC_WRITE, DEVCG_ACC_READ and DEVCG_ACC_MKNOD
 803  *
 804  * returns 0 on success, -EPERM case the operation is not permitted
 805  */
 806 static int devcgroup_legacy_check_permission(short type, u32 major, u32 minor,
 807                                         short access)
 808 {
 809         struct dev_cgroup *dev_cgroup;
 810         bool rc;
 811
 812         rcu_read_lock();
 813         dev_cgroup = task_devcgroup(current);
 814         if (dev_cgroup->behavior == DEVCG_DEFAULT_ALLOW)
 815                 /* Can't match any of the exceptions, even partially */
 816                 rc = !match_exception_partial(&dev_cgroup->exceptions,
 817                                               type, major, minor, access);
 818         else
 819                 /* Need to match completely one exception to be allowed */
 820                 rc = match_exception(&dev_cgroup->exceptions, type, major,
 821                                      minor, access);
 822         rcu_read_unlock();
 823
 824         if (!rc)
 825                 return -EPERM;
 826
 827         return 0;
 828 }
 829
 830 #endif /* CONFIG_CGROUP_DEVICE */
 831
 832 #if defined(CONFIG_CGROUP_DEVICE) || defined(CONFIG_CGROUP_BPF)
 833
 834 int devcgroup_check_permission(short type, u32 major, u32 minor, short access)
 835 {
 836         int rc = BPF_CGROUP_RUN_PROG_DEVICE_CGROUP(type, major, minor, access);
 837
 838         if (rc)
 839                 return -EPERM;
 840
 841         #ifdef CONFIG_CGROUP_DEVICE
 842         return devcgroup_legacy_check_permission(type, major, minor, access);
 843
 844         #else /* CONFIG_CGROUP_DEVICE */
 845         return 0;
 846
 847         #endif /* CONFIG_CGROUP_DEVICE */
 848 }
 849 EXPORT_SYMBOL(devcgroup_check_permission);
 850 #endif /* defined(CONFIG_CGROUP_DEVICE) || defined(CONFIG_CGROUP_BPF) */