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                                 lockdep_is_held(&devcgroup_mutex)) {
 359                 if ((type & DEVCG_DEV_BLOCK) && !(ex->type & DEVCG_DEV_BLOCK))
 360                         continue;
 361                 if ((type & DEVCG_DEV_CHAR) && !(ex->type & DEVCG_DEV_CHAR))
 362                         continue;
 363                 /*
 364                  * We must be sure that both the exception and the provided
 365                  * range aren't masking all devices
 366                  */
 367                 if (ex->major != ~0 && major != ~0 && ex->major != major)
 368                         continue;
 369                 if (ex->minor != ~0 && minor != ~0 && ex->minor != minor)
 370                         continue;
 371                 /*
 372                  * In order to make sure the provided range isn't matching
 373                  * an exception, all its access bits shouldn't match the
 374                  * exception's access bits
 375                  */
 376                 if (!(access & ex->access))
 377                         continue;
 378                 return true;
 379         }
 380         return false;
 381 }
 382
 383 /**
 384  * verify_new_ex - verifies if a new exception is allowed by parent cgroup's permissions
 385  * @dev_cgroup: dev cgroup to be tested against
 386  * @refex: new exception
 387  * @behavior: behavior of the exception's dev_cgroup
 388  *
 389  * This is used to make sure a child cgroup won't have more privileges
 390  * than its parent
 391  */
 392 static bool verify_new_ex(struct dev_cgroup *dev_cgroup,
 393                           struct dev_exception_item *refex,
 394                           enum devcg_behavior behavior)
 395 {
 396         bool match = false;
 397
 398         RCU_LOCKDEP_WARN(!rcu_read_lock_held() &&
 399                          !lockdep_is_held(&devcgroup_mutex),
 400                          "device_cgroup:verify_new_ex called without proper synchronization");
 401
 402         if (dev_cgroup->behavior == DEVCG_DEFAULT_ALLOW) {
 403                 if (behavior == DEVCG_DEFAULT_ALLOW) {
 404                         /*
 405                          * new exception in the child doesn't matter, only
 406                          * adding extra restrictions
 407                          */
 408                         return true;
 409                 } else {
 410                         /*
 411                          * new exception in the child will add more devices
 412                          * that can be acessed, so it can't match any of
 413                          * parent's exceptions, even slightly
 414                          */
 415                         match = match_exception_partial(&dev_cgroup->exceptions,
 416                                                         refex->type,
 417                                                         refex->major,
 418                                                         refex->minor,
 419                                                         refex->access);
 420
 421                         if (match)
 422                                 return false;
 423                         return true;
 424                 }
 425         } else {
 426                 /*
 427                  * Only behavior == DEVCG_DEFAULT_DENY allowed here, therefore
 428                  * the new exception will add access to more devices and must
 429                  * be contained completely in an parent's exception to be
 430                  * allowed
 431                  */
 432                 match = match_exception(&dev_cgroup->exceptions, refex->type,
 433                                         refex->major, refex->minor,
 434                                         refex->access);
 435
 436                 if (match)
 437                         /* parent has an exception that matches the proposed */
 438                         return true;
 439                 else
 440                         return false;
 441         }
 442         return false;
 443 }
 444
 445 /*
 446  * parent_has_perm:
 447  * when adding a new allow rule to a device exception list, the rule
 448  * must be allowed in the parent device
 449  */
 450 static int parent_has_perm(struct dev_cgroup *childcg,
 451                                   struct dev_exception_item *ex)
 452 {
 453         struct dev_cgroup *parent = css_to_devcgroup(childcg->css.parent);
 454
 455         if (!parent)
 456                 return 1;
 457         return verify_new_ex(parent, ex, childcg->behavior);
 458 }
 459
 460 /**
 461  * parent_allows_removal - verify if it's ok to remove an exception
 462  * @childcg: child cgroup from where the exception will be removed
 463  * @ex: exception being removed
 464  *
 465  * When removing an exception in cgroups with default ALLOW policy, it must
 466  * be checked if removing it will give the child cgroup more access than the
 467  * parent.
 468  *
 469  * Return: true if it's ok to remove exception, false otherwise
 470  */
 471 static bool parent_allows_removal(struct dev_cgroup *childcg,
 472                                   struct dev_exception_item *ex)
 473 {
 474         struct dev_cgroup *parent = css_to_devcgroup(childcg->css.parent);
 475
 476         if (!parent)
 477                 return true;
 478
 479         /* It's always allowed to remove access to devices */
 480         if (childcg->behavior == DEVCG_DEFAULT_DENY)
 481                 return true;
 482
 483         /*
 484          * Make sure you're not removing part or a whole exception existing in
 485          * the parent cgroup
 486          */
 487         return !match_exception_partial(&parent->exceptions, ex->type,
 488                                         ex->major, ex->minor, ex->access);
 489 }
 490
 491 /**
 492  * may_allow_all - checks if it's possible to change the behavior to
 493  *                 allow based on parent's rules.
 494  * @parent: device cgroup's parent
 495  * returns: != 0 in case it's allowed, 0 otherwise
 496  */
 497 static inline int may_allow_all(struct dev_cgroup *parent)
 498 {
 499         if (!parent)
 500                 return 1;
 501         return parent->behavior == DEVCG_DEFAULT_ALLOW;
 502 }
 503
 504 /**
 505  * revalidate_active_exceptions - walks through the active exception list and
 506  *                                revalidates the exceptions based on parent's
 507  *                                behavior and exceptions. The exceptions that
 508  *                                are no longer valid will be removed.
 509  *                                Called with devcgroup_mutex held.
 510  * @devcg: cgroup which exceptions will be checked
 511  *
 512  * This is one of the three key functions for hierarchy implementation.
 513  * This function is responsible for re-evaluating all the cgroup's active
 514  * exceptions due to a parent's exception change.
 515  * Refer to Documentation/admin-guide/cgroup-v1/devices.rst for more details.
 516  */
 517 static void revalidate_active_exceptions(struct dev_cgroup *devcg)
 518 {
 519         struct dev_exception_item *ex;
 520         struct list_head *this, *tmp;
 521
 522         list_for_each_safe(this, tmp, &devcg->exceptions) {
 523                 ex = container_of(this, struct dev_exception_item, list);
 524                 if (!parent_has_perm(devcg, ex))
 525                         dev_exception_rm(devcg, ex);
 526         }
 527 }
 528
 529 /**
 530  * propagate_exception - propagates a new exception to the children
 531  * @devcg_root: device cgroup that added a new exception
 532  * @ex: new exception to be propagated
 533  *
 534  * returns: 0 in case of success, != 0 in case of error
 535  */
 536 static int propagate_exception(struct dev_cgroup *devcg_root,
 537                                struct dev_exception_item *ex)
 538 {
 539         struct cgroup_subsys_state *pos;
 540         int rc = 0;
 541
 542         rcu_read_lock();
 543
 544         css_for_each_descendant_pre(pos, &devcg_root->css) {
 545                 struct dev_cgroup *devcg = css_to_devcgroup(pos);
 546
 547                 /*
 548                  * Because devcgroup_mutex is held, no devcg will become
 549                  * online or offline during the tree walk (see on/offline
 550                  * methods), and online ones are safe to access outside RCU
 551                  * read lock without bumping refcnt.
 552                  */
 553                 if (pos == &devcg_root->css || !is_devcg_online(devcg))
 554                         continue;
 555
 556                 rcu_read_unlock();
 557
 558                 /*
 559                  * in case both root's behavior and devcg is allow, a new
 560                  * restriction means adding to the exception list
 561                  */
 562                 if (devcg_root->behavior == DEVCG_DEFAULT_ALLOW &&
 563                     devcg->behavior == DEVCG_DEFAULT_ALLOW) {
 564                         rc = dev_exception_add(devcg, ex);
 565                         if (rc)
 566                                 return rc;
 567                 } else {
 568                         /*
 569                          * in the other possible cases:
 570                          * root's behavior: allow, devcg's: deny
 571                          * root's behavior: deny, devcg's: deny
 572                          * the exception will be removed
 573                          */
 574                         dev_exception_rm(devcg, ex);
 575                 }
 576                 revalidate_active_exceptions(devcg);
 577
 578                 rcu_read_lock();
 579         }
 580
 581         rcu_read_unlock();
 582         return rc;
 583 }
 584
 585 /*
 586  * Modify the exception list using allow/deny rules.
 587  * CAP_SYS_ADMIN is needed for this.  It's at least separate from CAP_MKNOD
 588  * so we can give a container CAP_MKNOD to let it create devices but not
 589  * modify the exception list.
 590  * It seems likely we'll want to add a CAP_CONTAINER capability to allow
 591  * us to also grant CAP_SYS_ADMIN to containers without giving away the
 592  * device exception list controls, but for now we'll stick with CAP_SYS_ADMIN
 593  *
 594  * Taking rules away is always allowed (given CAP_SYS_ADMIN).  Granting
 595  * new access is only allowed if you're in the top-level cgroup, or your
 596  * parent cgroup has the access you're asking for.
 597  */
 598 static int devcgroup_update_access(struct dev_cgroup *devcgroup,
 599                                    int filetype, char *buffer)
 600 {
 601         const char *b;
 602         char temp[12];          /* 11 + 1 characters needed for a u32 */
 603         int count, rc = 0;
 604         struct dev_exception_item ex;
 605         struct dev_cgroup *parent = css_to_devcgroup(devcgroup->css.parent);
 606
 607         if (!capable(CAP_SYS_ADMIN))
 608                 return -EPERM;
 609
 610         memset(&ex, 0, sizeof(ex));
 611         b = buffer;
 612
 613         switch (*b) {
 614         case 'a':
 615                 switch (filetype) {
 616                 case DEVCG_ALLOW:
 617                         if (css_has_online_children(&devcgroup->css))
 618                                 return -EINVAL;
 619
 620                         if (!may_allow_all(parent))
 621                                 return -EPERM;
 622                         dev_exception_clean(devcgroup);
 623                         devcgroup->behavior = DEVCG_DEFAULT_ALLOW;
 624                         if (!parent)
 625                                 break;
 626
 627                         rc = dev_exceptions_copy(&devcgroup->exceptions,
 628                                                  &parent->exceptions);
 629                         if (rc)
 630                                 return rc;
 631                         break;
 632                 case DEVCG_DENY:
 633                         if (css_has_online_children(&devcgroup->css))
 634                                 return -EINVAL;
 635
 636                         dev_exception_clean(devcgroup);
 637                         devcgroup->behavior = DEVCG_DEFAULT_DENY;
 638                         break;
 639                 default:
 640                         return -EINVAL;
 641                 }
 642                 return 0;
 643         case 'b':
 644                 ex.type = DEVCG_DEV_BLOCK;
 645                 break;
 646         case 'c':
 647                 ex.type = DEVCG_DEV_CHAR;
 648                 break;
 649         default:
 650                 return -EINVAL;
 651         }
 652         b++;
 653         if (!isspace(*b))
 654                 return -EINVAL;
 655         b++;
 656         if (*b == '*') {
 657                 ex.major = ~0;
 658                 b++;
 659         } else if (isdigit(*b)) {
 660                 memset(temp, 0, sizeof(temp));
 661                 for (count = 0; count < sizeof(temp) - 1; count++) {
 662                         temp[count] = *b;
 663                         b++;
 664                         if (!isdigit(*b))
 665                                 break;
 666                 }
 667                 rc = kstrtou32(temp, 10, &ex.major);
 668                 if (rc)
 669                         return -EINVAL;
 670         } else {
 671                 return -EINVAL;
 672         }
 673         if (*b != ':')
 674                 return -EINVAL;
 675         b++;
 676
 677         /* read minor */
 678         if (*b == '*') {
 679                 ex.minor = ~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.minor);
 690                 if (rc)
 691                         return -EINVAL;
 692         } else {
 693                 return -EINVAL;
 694         }
 695         if (!isspace(*b))
 696                 return -EINVAL;
 697         for (b++, count = 0; count < 3; count++, b++) {
 698                 switch (*b) {
 699                 case 'r':
 700                         ex.access |= DEVCG_ACC_READ;
 701                         break;
 702                 case 'w':
 703                         ex.access |= DEVCG_ACC_WRITE;
 704                         break;
 705                 case 'm':
 706                         ex.access |= DEVCG_ACC_MKNOD;
 707                         break;
 708                 case '\n':
 709                 case '\0':
 710                         count = 3;
 711                         break;
 712                 default:
 713                         return -EINVAL;
 714                 }
 715         }
 716
 717         switch (filetype) {
 718         case DEVCG_ALLOW:
 719                 /*
 720                  * If the default policy is to allow by default, try to remove
 721                  * an matching exception instead. And be silent about it: we
 722                  * don't want to break compatibility
 723                  */
 724                 if (devcgroup->behavior == DEVCG_DEFAULT_ALLOW) {
 725                         /* Check if the parent allows removing it first */
 726                         if (!parent_allows_removal(devcgroup, &ex))
 727                                 return -EPERM;
 728                         dev_exception_rm(devcgroup, &ex);
 729                         break;
 730                 }
 731
 732                 if (!parent_has_perm(devcgroup, &ex))
 733                         return -EPERM;
 734                 rc = dev_exception_add(devcgroup, &ex);
 735                 break;
 736         case DEVCG_DENY:
 737                 /*
 738                  * If the default policy is to deny by default, try to remove
 739                  * an matching exception instead. And be silent about it: we
 740                  * don't want to break compatibility
 741                  */
 742                 if (devcgroup->behavior == DEVCG_DEFAULT_DENY)
 743                         dev_exception_rm(devcgroup, &ex);
 744                 else
 745                         rc = dev_exception_add(devcgroup, &ex);
 746
 747                 if (rc)
 748                         break;
 749                 /* we only propagate new restrictions */
 750                 rc = propagate_exception(devcgroup, &ex);
 751                 break;
 752         default:
 753                 rc = -EINVAL;
 754         }
 755         return rc;
 756 }
 757
 758 static ssize_t devcgroup_access_write(struct kernfs_open_file *of,
 759                                       char *buf, size_t nbytes, loff_t off)
 760 {
 761         int retval;
 762
 763         mutex_lock(&devcgroup_mutex);
 764         retval = devcgroup_update_access(css_to_devcgroup(of_css(of)),
 765                                          of_cft(of)->private, strstrip(buf));
 766         mutex_unlock(&devcgroup_mutex);
 767         return retval ?: nbytes;
 768 }
 769
 770 static struct cftype dev_cgroup_files[] = {
 771         {
 772                 .name = "allow",
 773                 .write = devcgroup_access_write,
 774                 .private = DEVCG_ALLOW,
 775         },
 776         {
 777                 .name = "deny",
 778                 .write = devcgroup_access_write,
 779                 .private = DEVCG_DENY,
 780         },
 781         {
 782                 .name = "list",
 783                 .seq_show = devcgroup_seq_show,
 784                 .private = DEVCG_LIST,
 785         },
 786         { }     /* terminate */
 787 };
 788
 789 struct cgroup_subsys devices_cgrp_subsys = {
 790         .css_alloc = devcgroup_css_alloc,
 791         .css_free = devcgroup_css_free,
 792         .css_online = devcgroup_online,
 793         .css_offline = devcgroup_offline,
 794         .legacy_cftypes = dev_cgroup_files,
 795 };
 796
 797 /**
 798  * devcgroup_legacy_check_permission - checks if an inode operation is permitted
 799  * @dev_cgroup: the dev cgroup to be tested against
 800  * @type: device type
 801  * @major: device major number
 802  * @minor: device minor number
 803  * @access: combination of DEVCG_ACC_WRITE, DEVCG_ACC_READ and DEVCG_ACC_MKNOD
 804  *
 805  * returns 0 on success, -EPERM case the operation is not permitted
 806  */
 807 static int devcgroup_legacy_check_permission(short type, u32 major, u32 minor,
 808                                         short access)
 809 {
 810         struct dev_cgroup *dev_cgroup;
 811         bool rc;
 812
 813         rcu_read_lock();
 814         dev_cgroup = task_devcgroup(current);
 815         if (dev_cgroup->behavior == DEVCG_DEFAULT_ALLOW)
 816                 /* Can't match any of the exceptions, even partially */
 817                 rc = !match_exception_partial(&dev_cgroup->exceptions,
 818                                               type, major, minor, access);
 819         else
 820                 /* Need to match completely one exception to be allowed */
 821                 rc = match_exception(&dev_cgroup->exceptions, type, major,
 822                                      minor, access);
 823         rcu_read_unlock();
 824
 825         if (!rc)
 826                 return -EPERM;
 827
 828         return 0;
 829 }
 830
 831 #endif /* CONFIG_CGROUP_DEVICE */
 832
 833 #if defined(CONFIG_CGROUP_DEVICE) || defined(CONFIG_CGROUP_BPF)
 834
 835 int devcgroup_check_permission(short type, u32 major, u32 minor, short access)
 836 {
 837         int rc = BPF_CGROUP_RUN_PROG_DEVICE_CGROUP(type, major, minor, access);
 838
 839         if (rc)
 840                 return -EPERM;
 841
 842         #ifdef CONFIG_CGROUP_DEVICE
 843         return devcgroup_legacy_check_permission(type, major, minor, access);
 844
 845         #else /* CONFIG_CGROUP_DEVICE */
 846         return 0;
 847
 848         #endif /* CONFIG_CGROUP_DEVICE */
 849 }
 850 EXPORT_SYMBOL(devcgroup_check_permission);
 851 #endif /* defined(CONFIG_CGROUP_DEVICE) || defined(CONFIG_CGROUP_BPF) */