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/bpf-cgroup.h>
   9 #include <linux/device_cgroup.h>
  10 #include <linux/cgroup.h>
  11 #include <linux/ctype.h>
  12 #include <linux/list.h>
  13 #include <linux/uaccess.h>
  14 #include <linux/seq_file.h>
  15 #include <linux/slab.h>
  16 #include <linux/rcupdate.h>
  17 #include <linux/mutex.h>
  18
  19 #ifdef CONFIG_CGROUP_DEVICE
  20
  21 static DEFINE_MUTEX(devcgroup_mutex);
  22
  23 enum devcg_behavior {
  24         DEVCG_DEFAULT_NONE,
  25         DEVCG_DEFAULT_ALLOW,
  26         DEVCG_DEFAULT_DENY,
  27 };
  28
  29 /*
  30  * exception list locking rules:
  31  * hold devcgroup_mutex for update/read.
  32  * hold rcu_read_lock() for read.
  33  */
  34
  35 struct dev_exception_item {
  36         u32 major, minor;
  37         short type;
  38         short access;
  39         struct list_head list;
  40         struct rcu_head rcu;
  41 };
  42
  43 struct dev_cgroup {
  44         struct cgroup_subsys_state css;
  45         struct list_head exceptions;
  46         enum devcg_behavior behavior;
  47 };
  48
  49 static inline struct dev_cgroup *css_to_devcgroup(struct cgroup_subsys_state *s)
  50 {
  51         return s ? container_of(s, struct dev_cgroup, css) : NULL;
  52 }
  53
  54 static inline struct dev_cgroup *task_devcgroup(struct task_struct *task)
  55 {
  56         return css_to_devcgroup(task_css(task, devices_cgrp_id));
  57 }
  58
  59 /*
  60  * called under devcgroup_mutex
  61  */
  62 static int dev_exceptions_copy(struct list_head *dest, struct list_head *orig)
  63 {
  64         struct dev_exception_item *ex, *tmp, *new;
  65
  66         lockdep_assert_held(&devcgroup_mutex);
  67
  68         list_for_each_entry(ex, orig, list) {
  69                 new = kmemdup(ex, sizeof(*ex), GFP_KERNEL);
  70                 if (!new)
  71                         goto free_and_exit;
  72                 list_add_tail(&new->list, dest);
  73         }
  74
  75         return 0;
  76
  77 free_and_exit:
  78         list_for_each_entry_safe(ex, tmp, dest, list) {
  79                 list_del(&ex->list);
  80                 kfree(ex);
  81         }
  82         return -ENOMEM;
  83 }
  84
  85 static void dev_exceptions_move(struct list_head *dest, struct list_head *orig)
  86 {
  87         struct dev_exception_item *ex, *tmp;
  88
  89         lockdep_assert_held(&devcgroup_mutex);
  90
  91         list_for_each_entry_safe(ex, tmp, orig, list) {
  92                 list_move_tail(&ex->list, dest);
  93         }
  94 }
  95
  96 /*
  97  * called under devcgroup_mutex
  98  */
  99 static int dev_exception_add(struct dev_cgroup *dev_cgroup,
 100                              struct dev_exception_item *ex)
 101 {
 102         struct dev_exception_item *excopy, *walk;
 103
 104         lockdep_assert_held(&devcgroup_mutex);
 105
 106         excopy = kmemdup(ex, sizeof(*ex), GFP_KERNEL);
 107         if (!excopy)
 108                 return -ENOMEM;
 109
 110         list_for_each_entry(walk, &dev_cgroup->exceptions, list) {
 111                 if (walk->type != ex->type)
 112                         continue;
 113                 if (walk->major != ex->major)
 114                         continue;
 115                 if (walk->minor != ex->minor)
 116                         continue;
 117
 118                 walk->access |= ex->access;
 119                 kfree(excopy);
 120                 excopy = NULL;
 121         }
 122
 123         if (excopy != NULL)
 124                 list_add_tail_rcu(&excopy->list, &dev_cgroup->exceptions);
 125         return 0;
 126 }
 127
 128 /*
 129  * called under devcgroup_mutex
 130  */
 131 static void dev_exception_rm(struct dev_cgroup *dev_cgroup,
 132                              struct dev_exception_item *ex)
 133 {
 134         struct dev_exception_item *walk, *tmp;
 135
 136         lockdep_assert_held(&devcgroup_mutex);
 137
 138         list_for_each_entry_safe(walk, tmp, &dev_cgroup->exceptions, list) {
 139                 if (walk->type != ex->type)
 140                         continue;
 141                 if (walk->major != ex->major)
 142                         continue;
 143                 if (walk->minor != ex->minor)
 144                         continue;
 145
 146                 walk->access &= ~ex->access;
 147                 if (!walk->access) {
 148                         list_del_rcu(&walk->list);
 149                         kfree_rcu(walk, rcu);
 150                 }
 151         }
 152 }
 153
 154 static void __dev_exception_clean(struct dev_cgroup *dev_cgroup)
 155 {
 156         struct dev_exception_item *ex, *tmp;
 157
 158         list_for_each_entry_safe(ex, tmp, &dev_cgroup->exceptions, list) {
 159                 list_del_rcu(&ex->list);
 160                 kfree_rcu(ex, rcu);
 161         }
 162 }
 163
 164 /**
 165  * dev_exception_clean - frees all entries of the exception list
 166  * @dev_cgroup: dev_cgroup with the exception list to be cleaned
 167  *
 168  * called under devcgroup_mutex
 169  */
 170 static void dev_exception_clean(struct dev_cgroup *dev_cgroup)
 171 {
 172         lockdep_assert_held(&devcgroup_mutex);
 173
 174         __dev_exception_clean(dev_cgroup);
 175 }
 176
 177 static inline bool is_devcg_online(const struct dev_cgroup *devcg)
 178 {
 179         return (devcg->behavior != DEVCG_DEFAULT_NONE);
 180 }
 181
 182 /**
 183  * devcgroup_online - initializes devcgroup's behavior and exceptions based on
 184  *                    parent's
 185  * @css: css getting online
 186  * returns 0 in case of success, error code otherwise
 187  */
 188 static int devcgroup_online(struct cgroup_subsys_state *css)
 189 {
 190         struct dev_cgroup *dev_cgroup = css_to_devcgroup(css);
 191         struct dev_cgroup *parent_dev_cgroup = css_to_devcgroup(css->parent);
 192         int ret = 0;
 193
 194         mutex_lock(&devcgroup_mutex);
 195
 196         if (parent_dev_cgroup == NULL)
 197                 dev_cgroup->behavior = DEVCG_DEFAULT_ALLOW;
 198         else {
 199                 ret = dev_exceptions_copy(&dev_cgroup->exceptions,
 200                                           &parent_dev_cgroup->exceptions);
 201                 if (!ret)
 202                         dev_cgroup->behavior = parent_dev_cgroup->behavior;
 203         }
 204         mutex_unlock(&devcgroup_mutex);
 205
 206         return ret;
 207 }
 208
 209 static void devcgroup_offline(struct cgroup_subsys_state *css)
 210 {
 211         struct dev_cgroup *dev_cgroup = css_to_devcgroup(css);
 212
 213         mutex_lock(&devcgroup_mutex);
 214         dev_cgroup->behavior = DEVCG_DEFAULT_NONE;
 215         mutex_unlock(&devcgroup_mutex);
 216 }
 217
 218 /*
 219  * called from kernel/cgroup/cgroup.c with cgroup_lock() held.
 220  */
 221 static struct cgroup_subsys_state *
 222 devcgroup_css_alloc(struct cgroup_subsys_state *parent_css)
 223 {
 224         struct dev_cgroup *dev_cgroup;
 225
 226         dev_cgroup = kzalloc(sizeof(*dev_cgroup), GFP_KERNEL);
 227         if (!dev_cgroup)
 228                 return ERR_PTR(-ENOMEM);
 229         INIT_LIST_HEAD(&dev_cgroup->exceptions);
 230         dev_cgroup->behavior = DEVCG_DEFAULT_NONE;
 231
 232         return &dev_cgroup->css;
 233 }
 234
 235 static void devcgroup_css_free(struct cgroup_subsys_state *css)
 236 {
 237         struct dev_cgroup *dev_cgroup = css_to_devcgroup(css);
 238
 239         __dev_exception_clean(dev_cgroup);
 240         kfree(dev_cgroup);
 241 }
 242
 243 #define DEVCG_ALLOW 1
 244 #define DEVCG_DENY 2
 245 #define DEVCG_LIST 3
 246
 247 #define MAJMINLEN 13
 248 #define ACCLEN 4
 249
 250 static void set_access(char *acc, short access)
 251 {
 252         int idx = 0;
 253         memset(acc, 0, ACCLEN);
 254         if (access & DEVCG_ACC_READ)
 255                 acc[idx++] = 'r';
 256         if (access & DEVCG_ACC_WRITE)
 257                 acc[idx++] = 'w';
 258         if (access & DEVCG_ACC_MKNOD)
 259                 acc[idx++] = 'm';
 260 }
 261
 262 static char type_to_char(short type)
 263 {
 264         if (type == DEVCG_DEV_ALL)
 265                 return 'a';
 266         if (type == DEVCG_DEV_CHAR)
 267                 return 'c';
 268         if (type == DEVCG_DEV_BLOCK)
 269                 return 'b';
 270         return 'X';
 271 }
 272
 273 static void set_majmin(char *str, unsigned m)
 274 {
 275         if (m == ~0)
 276                 strcpy(str, "*");
 277         else
 278                 sprintf(str, "%u", m);
 279 }
 280
 281 static int devcgroup_seq_show(struct seq_file *m, void *v)
 282 {
 283         struct dev_cgroup *devcgroup = css_to_devcgroup(seq_css(m));
 284         struct dev_exception_item *ex;
 285         char maj[MAJMINLEN], min[MAJMINLEN], acc[ACCLEN];
 286
 287         rcu_read_lock();
 288         /*
 289          * To preserve the compatibility:
 290          * - Only show the "all devices" when the default policy is to allow
 291          * - List the exceptions in case the default policy is to deny
 292          * This way, the file remains as a "whitelist of devices"
 293          */
 294         if (devcgroup->behavior == DEVCG_DEFAULT_ALLOW) {
 295                 set_access(acc, DEVCG_ACC_MASK);
 296                 set_majmin(maj, ~0);
 297                 set_majmin(min, ~0);
 298                 seq_printf(m, "%c %s:%s %s\n", type_to_char(DEVCG_DEV_ALL),
 299                            maj, min, acc);
 300         } else {
 301                 list_for_each_entry_rcu(ex, &devcgroup->exceptions, list) {
 302                         set_access(acc, ex->access);
 303                         set_majmin(maj, ex->major);
 304                         set_majmin(min, ex->minor);
 305                         seq_printf(m, "%c %s:%s %s\n", type_to_char(ex->type),
 306                                    maj, min, acc);
 307                 }
 308         }
 309         rcu_read_unlock();
 310
 311         return 0;
 312 }
 313
 314 /**
 315  * match_exception      - iterates the exception list trying to find a complete match
 316  * @exceptions: list of exceptions
 317  * @type: device type (DEVCG_DEV_BLOCK or DEVCG_DEV_CHAR)
 318  * @major: device file major number, ~0 to match all
 319  * @minor: device file minor number, ~0 to match all
 320  * @access: permission mask (DEVCG_ACC_READ, DEVCG_ACC_WRITE, DEVCG_ACC_MKNOD)
 321  *
 322  * It is considered a complete match if an exception is found that will
 323  * contain the entire range of provided parameters.
 324  *
 325  * Return: true in case it matches an exception completely
 326  */
 327 static bool match_exception(struct list_head *exceptions, short type,
 328                             u32 major, u32 minor, short access)
 329 {
 330         struct dev_exception_item *ex;
 331
 332         list_for_each_entry_rcu(ex, exceptions, list) {
 333                 if ((type & DEVCG_DEV_BLOCK) && !(ex->type & DEVCG_DEV_BLOCK))
 334                         continue;
 335                 if ((type & DEVCG_DEV_CHAR) && !(ex->type & DEVCG_DEV_CHAR))
 336                         continue;
 337                 if (ex->major != ~0 && ex->major != major)
 338                         continue;
 339                 if (ex->minor != ~0 && ex->minor != minor)
 340                         continue;
 341                 /* provided access cannot have more than the exception rule */
 342                 if (access & (~ex->access))
 343                         continue;
 344                 return true;
 345         }
 346         return false;
 347 }
 348
 349 /**
 350  * match_exception_partial - iterates the exception list trying to find a partial match
 351  * @exceptions: list of exceptions
 352  * @type: device type (DEVCG_DEV_BLOCK or DEVCG_DEV_CHAR)
 353  * @major: device file major number, ~0 to match all
 354  * @minor: device file minor number, ~0 to match all
 355  * @access: permission mask (DEVCG_ACC_READ, DEVCG_ACC_WRITE, DEVCG_ACC_MKNOD)
 356  *
 357  * It is considered a partial match if an exception's range is found to
 358  * contain *any* of the devices specified by provided parameters. This is
 359  * used to make sure no extra access is being granted that is forbidden by
 360  * any of the exception list.
 361  *
 362  * Return: true in case the provided range mat matches an exception completely
 363  */
 364 static bool match_exception_partial(struct list_head *exceptions, short type,
 365                                     u32 major, u32 minor, short access)
 366 {
 367         struct dev_exception_item *ex;
 368
 369         list_for_each_entry_rcu(ex, exceptions, list,
 370                                 lockdep_is_held(&devcgroup_mutex)) {
 371                 if ((type & DEVCG_DEV_BLOCK) && !(ex->type & DEVCG_DEV_BLOCK))
 372                         continue;
 373                 if ((type & DEVCG_DEV_CHAR) && !(ex->type & DEVCG_DEV_CHAR))
 374                         continue;
 375                 /*
 376                  * We must be sure that both the exception and the provided
 377                  * range aren't masking all devices
 378                  */
 379                 if (ex->major != ~0 && major != ~0 && ex->major != major)
 380                         continue;
 381                 if (ex->minor != ~0 && minor != ~0 && ex->minor != minor)
 382                         continue;
 383                 /*
 384                  * In order to make sure the provided range isn't matching
 385                  * an exception, all its access bits shouldn't match the
 386                  * exception's access bits
 387                  */
 388                 if (!(access & ex->access))
 389                         continue;
 390                 return true;
 391         }
 392         return false;
 393 }
 394
 395 /**
 396  * verify_new_ex - verifies if a new exception is allowed by parent cgroup's permissions
 397  * @dev_cgroup: dev cgroup to be tested against
 398  * @refex: new exception
 399  * @behavior: behavior of the exception's dev_cgroup
 400  *
 401  * This is used to make sure a child cgroup won't have more privileges
 402  * than its parent
 403  */
 404 static bool verify_new_ex(struct dev_cgroup *dev_cgroup,
 405                           struct dev_exception_item *refex,
 406                           enum devcg_behavior behavior)
 407 {
 408         bool match = false;
 409
 410         RCU_LOCKDEP_WARN(!rcu_read_lock_held() &&
 411                          !lockdep_is_held(&devcgroup_mutex),
 412                          "device_cgroup:verify_new_ex called without proper synchronization");
 413
 414         if (dev_cgroup->behavior == DEVCG_DEFAULT_ALLOW) {
 415                 if (behavior == DEVCG_DEFAULT_ALLOW) {
 416                         /*
 417                          * new exception in the child doesn't matter, only
 418                          * adding extra restrictions
 419                          */
 420                         return true;
 421                 } else {
 422                         /*
 423                          * new exception in the child will add more devices
 424                          * that can be accessed, so it can't match any of
 425                          * parent's exceptions, even slightly
 426                          */
 427                         match = match_exception_partial(&dev_cgroup->exceptions,
 428                                                         refex->type,
 429                                                         refex->major,
 430                                                         refex->minor,
 431                                                         refex->access);
 432
 433                         if (match)
 434                                 return false;
 435                         return true;
 436                 }
 437         } else {
 438                 /*
 439                  * Only behavior == DEVCG_DEFAULT_DENY allowed here, therefore
 440                  * the new exception will add access to more devices and must
 441                  * be contained completely in an parent's exception to be
 442                  * allowed
 443                  */
 444                 match = match_exception(&dev_cgroup->exceptions, refex->type,
 445                                         refex->major, refex->minor,
 446                                         refex->access);
 447
 448                 if (match)
 449                         /* parent has an exception that matches the proposed */
 450                         return true;
 451                 else
 452                         return false;
 453         }
 454         return false;
 455 }
 456
 457 /*
 458  * parent_has_perm:
 459  * when adding a new allow rule to a device exception list, the rule
 460  * must be allowed in the parent device
 461  */
 462 static int parent_has_perm(struct dev_cgroup *childcg,
 463                                   struct dev_exception_item *ex)
 464 {
 465         struct dev_cgroup *parent = css_to_devcgroup(childcg->css.parent);
 466
 467         if (!parent)
 468                 return 1;
 469         return verify_new_ex(parent, ex, childcg->behavior);
 470 }
 471
 472 /**
 473  * parent_allows_removal - verify if it's ok to remove an exception
 474  * @childcg: child cgroup from where the exception will be removed
 475  * @ex: exception being removed
 476  *
 477  * When removing an exception in cgroups with default ALLOW policy, it must
 478  * be checked if removing it will give the child cgroup more access than the
 479  * parent.
 480  *
 481  * Return: true if it's ok to remove exception, false otherwise
 482  */
 483 static bool parent_allows_removal(struct dev_cgroup *childcg,
 484                                   struct dev_exception_item *ex)
 485 {
 486         struct dev_cgroup *parent = css_to_devcgroup(childcg->css.parent);
 487
 488         if (!parent)
 489                 return true;
 490
 491         /* It's always allowed to remove access to devices */
 492         if (childcg->behavior == DEVCG_DEFAULT_DENY)
 493                 return true;
 494
 495         /*
 496          * Make sure you're not removing part or a whole exception existing in
 497          * the parent cgroup
 498          */
 499         return !match_exception_partial(&parent->exceptions, ex->type,
 500                                         ex->major, ex->minor, ex->access);
 501 }
 502
 503 /**
 504  * may_allow_all - checks if it's possible to change the behavior to
 505  *                 allow based on parent's rules.
 506  * @parent: device cgroup's parent
 507  * returns: != 0 in case it's allowed, 0 otherwise
 508  */
 509 static inline int may_allow_all(struct dev_cgroup *parent)
 510 {
 511         if (!parent)
 512                 return 1;
 513         return parent->behavior == DEVCG_DEFAULT_ALLOW;
 514 }
 515
 516 /**
 517  * revalidate_active_exceptions - walks through the active exception list and
 518  *                                revalidates the exceptions based on parent's
 519  *                                behavior and exceptions. The exceptions that
 520  *                                are no longer valid will be removed.
 521  *                                Called with devcgroup_mutex held.
 522  * @devcg: cgroup which exceptions will be checked
 523  *
 524  * This is one of the three key functions for hierarchy implementation.
 525  * This function is responsible for re-evaluating all the cgroup's active
 526  * exceptions due to a parent's exception change.
 527  * Refer to Documentation/admin-guide/cgroup-v1/devices.rst for more details.
 528  */
 529 static void revalidate_active_exceptions(struct dev_cgroup *devcg)
 530 {
 531         struct dev_exception_item *ex;
 532         struct list_head *this, *tmp;
 533
 534         list_for_each_safe(this, tmp, &devcg->exceptions) {
 535                 ex = container_of(this, struct dev_exception_item, list);
 536                 if (!parent_has_perm(devcg, ex))
 537                         dev_exception_rm(devcg, ex);
 538         }
 539 }
 540
 541 /**
 542  * propagate_exception - propagates a new exception to the children
 543  * @devcg_root: device cgroup that added a new exception
 544  * @ex: new exception to be propagated
 545  *
 546  * returns: 0 in case of success, != 0 in case of error
 547  */
 548 static int propagate_exception(struct dev_cgroup *devcg_root,
 549                                struct dev_exception_item *ex)
 550 {
 551         struct cgroup_subsys_state *pos;
 552         int rc = 0;
 553
 554         rcu_read_lock();
 555
 556         css_for_each_descendant_pre(pos, &devcg_root->css) {
 557                 struct dev_cgroup *devcg = css_to_devcgroup(pos);
 558
 559                 /*
 560                  * Because devcgroup_mutex is held, no devcg will become
 561                  * online or offline during the tree walk (see on/offline
 562                  * methods), and online ones are safe to access outside RCU
 563                  * read lock without bumping refcnt.
 564                  */
 565                 if (pos == &devcg_root->css || !is_devcg_online(devcg))
 566                         continue;
 567
 568                 rcu_read_unlock();
 569
 570                 /*
 571                  * in case both root's behavior and devcg is allow, a new
 572                  * restriction means adding to the exception list
 573                  */
 574                 if (devcg_root->behavior == DEVCG_DEFAULT_ALLOW &&
 575                     devcg->behavior == DEVCG_DEFAULT_ALLOW) {
 576                         rc = dev_exception_add(devcg, ex);
 577                         if (rc)
 578                                 return rc;
 579                 } else {
 580                         /*
 581                          * in the other possible cases:
 582                          * root's behavior: allow, devcg's: deny
 583                          * root's behavior: deny, devcg's: deny
 584                          * the exception will be removed
 585                          */
 586                         dev_exception_rm(devcg, ex);
 587                 }
 588                 revalidate_active_exceptions(devcg);
 589
 590                 rcu_read_lock();
 591         }
 592
 593         rcu_read_unlock();
 594         return rc;
 595 }
 596
 597 /*
 598  * Modify the exception list using allow/deny rules.
 599  * CAP_SYS_ADMIN is needed for this.  It's at least separate from CAP_MKNOD
 600  * so we can give a container CAP_MKNOD to let it create devices but not
 601  * modify the exception list.
 602  * It seems likely we'll want to add a CAP_CONTAINER capability to allow
 603  * us to also grant CAP_SYS_ADMIN to containers without giving away the
 604  * device exception list controls, but for now we'll stick with CAP_SYS_ADMIN
 605  *
 606  * Taking rules away is always allowed (given CAP_SYS_ADMIN).  Granting
 607  * new access is only allowed if you're in the top-level cgroup, or your
 608  * parent cgroup has the access you're asking for.
 609  */
 610 static int devcgroup_update_access(struct dev_cgroup *devcgroup,
 611                                    int filetype, char *buffer)
 612 {
 613         const char *b;
 614         char temp[12];          /* 11 + 1 characters needed for a u32 */
 615         int count, rc = 0;
 616         struct dev_exception_item ex;
 617         struct dev_cgroup *parent = css_to_devcgroup(devcgroup->css.parent);
 618         struct dev_cgroup tmp_devcgrp;
 619
 620         if (!capable(CAP_SYS_ADMIN))
 621                 return -EPERM;
 622
 623         memset(&ex, 0, sizeof(ex));
 624         memset(&tmp_devcgrp, 0, sizeof(tmp_devcgrp));
 625         b = buffer;
 626
 627         switch (*b) {
 628         case 'a':
 629                 switch (filetype) {
 630                 case DEVCG_ALLOW:
 631                         if (css_has_online_children(&devcgroup->css))
 632                                 return -EINVAL;
 633
 634                         if (!may_allow_all(parent))
 635                                 return -EPERM;
 636                         if (!parent) {
 637                                 devcgroup->behavior = DEVCG_DEFAULT_ALLOW;
 638                                 dev_exception_clean(devcgroup);
 639                                 break;
 640                         }
 641
 642                         INIT_LIST_HEAD(&tmp_devcgrp.exceptions);
 643                         rc = dev_exceptions_copy(&tmp_devcgrp.exceptions,
 644                                                  &devcgroup->exceptions);
 645                         if (rc)
 646                                 return rc;
 647                         dev_exception_clean(devcgroup);
 648                         rc = dev_exceptions_copy(&devcgroup->exceptions,
 649                                                  &parent->exceptions);
 650                         if (rc) {
 651                                 dev_exceptions_move(&devcgroup->exceptions,
 652                                                     &tmp_devcgrp.exceptions);
 653                                 return rc;
 654                         }
 655                         devcgroup->behavior = DEVCG_DEFAULT_ALLOW;
 656                         dev_exception_clean(&tmp_devcgrp);
 657                         break;
 658                 case DEVCG_DENY:
 659                         if (css_has_online_children(&devcgroup->css))
 660                                 return -EINVAL;
 661
 662                         dev_exception_clean(devcgroup);
 663                         devcgroup->behavior = DEVCG_DEFAULT_DENY;
 664                         break;
 665                 default:
 666                         return -EINVAL;
 667                 }
 668                 return 0;
 669         case 'b':
 670                 ex.type = DEVCG_DEV_BLOCK;
 671                 break;
 672         case 'c':
 673                 ex.type = DEVCG_DEV_CHAR;
 674                 break;
 675         default:
 676                 return -EINVAL;
 677         }
 678         b++;
 679         if (!isspace(*b))
 680                 return -EINVAL;
 681         b++;
 682         if (*b == '*') {
 683                 ex.major = ~0;
 684                 b++;
 685         } else if (isdigit(*b)) {
 686                 memset(temp, 0, sizeof(temp));
 687                 for (count = 0; count < sizeof(temp) - 1; count++) {
 688                         temp[count] = *b;
 689                         b++;
 690                         if (!isdigit(*b))
 691                                 break;
 692                 }
 693                 rc = kstrtou32(temp, 10, &ex.major);
 694                 if (rc)
 695                         return -EINVAL;
 696         } else {
 697                 return -EINVAL;
 698         }
 699         if (*b != ':')
 700                 return -EINVAL;
 701         b++;
 702
 703         /* read minor */
 704         if (*b == '*') {
 705                 ex.minor = ~0;
 706                 b++;
 707         } else if (isdigit(*b)) {
 708                 memset(temp, 0, sizeof(temp));
 709                 for (count = 0; count < sizeof(temp) - 1; count++) {
 710                         temp[count] = *b;
 711                         b++;
 712                         if (!isdigit(*b))
 713                                 break;
 714                 }
 715                 rc = kstrtou32(temp, 10, &ex.minor);
 716                 if (rc)
 717                         return -EINVAL;
 718         } else {
 719                 return -EINVAL;
 720         }
 721         if (!isspace(*b))
 722                 return -EINVAL;
 723         for (b++, count = 0; count < 3; count++, b++) {
 724                 switch (*b) {
 725                 case 'r':
 726                         ex.access |= DEVCG_ACC_READ;
 727                         break;
 728                 case 'w':
 729                         ex.access |= DEVCG_ACC_WRITE;
 730                         break;
 731                 case 'm':
 732                         ex.access |= DEVCG_ACC_MKNOD;
 733                         break;
 734                 case '\n':
 735                 case '\0':
 736                         count = 3;
 737                         break;
 738                 default:
 739                         return -EINVAL;
 740                 }
 741         }
 742
 743         switch (filetype) {
 744         case DEVCG_ALLOW:
 745                 /*
 746                  * If the default policy is to allow by default, try to remove
 747                  * an matching exception instead. And be silent about it: we
 748                  * don't want to break compatibility
 749                  */
 750                 if (devcgroup->behavior == DEVCG_DEFAULT_ALLOW) {
 751                         /* Check if the parent allows removing it first */
 752                         if (!parent_allows_removal(devcgroup, &ex))
 753                                 return -EPERM;
 754                         dev_exception_rm(devcgroup, &ex);
 755                         break;
 756                 }
 757
 758                 if (!parent_has_perm(devcgroup, &ex))
 759                         return -EPERM;
 760                 rc = dev_exception_add(devcgroup, &ex);
 761                 break;
 762         case DEVCG_DENY:
 763                 /*
 764                  * If the default policy is to deny by default, try to remove
 765                  * an matching exception instead. And be silent about it: we
 766                  * don't want to break compatibility
 767                  */
 768                 if (devcgroup->behavior == DEVCG_DEFAULT_DENY)
 769                         dev_exception_rm(devcgroup, &ex);
 770                 else
 771                         rc = dev_exception_add(devcgroup, &ex);
 772
 773                 if (rc)
 774                         break;
 775                 /* we only propagate new restrictions */
 776                 rc = propagate_exception(devcgroup, &ex);
 777                 break;
 778         default:
 779                 rc = -EINVAL;
 780         }
 781         return rc;
 782 }
 783
 784 static ssize_t devcgroup_access_write(struct kernfs_open_file *of,
 785                                       char *buf, size_t nbytes, loff_t off)
 786 {
 787         int retval;
 788
 789         mutex_lock(&devcgroup_mutex);
 790         retval = devcgroup_update_access(css_to_devcgroup(of_css(of)),
 791                                          of_cft(of)->private, strstrip(buf));
 792         mutex_unlock(&devcgroup_mutex);
 793         return retval ?: nbytes;
 794 }
 795
 796 static struct cftype dev_cgroup_files[] = {
 797         {
 798                 .name = "allow",
 799                 .write = devcgroup_access_write,
 800                 .private = DEVCG_ALLOW,
 801         },
 802         {
 803                 .name = "deny",
 804                 .write = devcgroup_access_write,
 805                 .private = DEVCG_DENY,
 806         },
 807         {
 808                 .name = "list",
 809                 .seq_show = devcgroup_seq_show,
 810                 .private = DEVCG_LIST,
 811         },
 812         { }     /* terminate */
 813 };
 814
 815 struct cgroup_subsys devices_cgrp_subsys = {
 816         .css_alloc = devcgroup_css_alloc,
 817         .css_free = devcgroup_css_free,
 818         .css_online = devcgroup_online,
 819         .css_offline = devcgroup_offline,
 820         .legacy_cftypes = dev_cgroup_files,
 821 };
 822
 823 /**
 824  * devcgroup_legacy_check_permission - checks if an inode operation is permitted
 825  * @type: device type
 826  * @major: device major number
 827  * @minor: device minor number
 828  * @access: combination of DEVCG_ACC_WRITE, DEVCG_ACC_READ and DEVCG_ACC_MKNOD
 829  *
 830  * returns 0 on success, -EPERM case the operation is not permitted
 831  */
 832 static int devcgroup_legacy_check_permission(short type, u32 major, u32 minor,
 833                                         short access)
 834 {
 835         struct dev_cgroup *dev_cgroup;
 836         bool rc;
 837
 838         rcu_read_lock();
 839         dev_cgroup = task_devcgroup(current);
 840         if (dev_cgroup->behavior == DEVCG_DEFAULT_ALLOW)
 841                 /* Can't match any of the exceptions, even partially */
 842                 rc = !match_exception_partial(&dev_cgroup->exceptions,
 843                                               type, major, minor, access);
 844         else
 845                 /* Need to match completely one exception to be allowed */
 846                 rc = match_exception(&dev_cgroup->exceptions, type, major,
 847                                      minor, access);
 848         rcu_read_unlock();
 849
 850         if (!rc)
 851                 return -EPERM;
 852
 853         return 0;
 854 }
 855
 856 #endif /* CONFIG_CGROUP_DEVICE */
 857
 858 #if defined(CONFIG_CGROUP_DEVICE) || defined(CONFIG_CGROUP_BPF)
 859
 860 int devcgroup_check_permission(short type, u32 major, u32 minor, short access)
 861 {
 862         int rc = BPF_CGROUP_RUN_PROG_DEVICE_CGROUP(type, major, minor, access);
 863
 864         if (rc)
 865                 return rc;
 866
 867         #ifdef CONFIG_CGROUP_DEVICE
 868         return devcgroup_legacy_check_permission(type, major, minor, access);
 869
 870         #else /* CONFIG_CGROUP_DEVICE */
 871         return 0;
 872
 873         #endif /* CONFIG_CGROUP_DEVICE */
 874 }
 875 EXPORT_SYMBOL(devcgroup_check_permission);
 876 #endif /* defined(CONFIG_CGROUP_DEVICE) || defined(CONFIG_CGROUP_BPF) */