1 /* 2 * device_cgroup.c - device cgroup subsystem 3 * 4 * Copyright 2007 IBM Corp 5 */ 6 7 #include <linux/device_cgroup.h> 8 #include <linux/cgroup.h> 9 #include <linux/ctype.h> 10 #include <linux/list.h> 11 #include <linux/uaccess.h> 12 #include <linux/seq_file.h> 13 #include <linux/slab.h> 14 #include <linux/rcupdate.h> 15 #include <linux/mutex.h> 16 17 #define ACC_MKNOD 1 18 #define ACC_READ 2 19 #define ACC_WRITE 4 20 #define ACC_MASK (ACC_MKNOD | ACC_READ | ACC_WRITE) 21 22 #define DEV_BLOCK 1 23 #define DEV_CHAR 2 24 #define DEV_ALL 4 /* this represents all devices */ 25 26 static DEFINE_MUTEX(devcgroup_mutex); 27 28 enum devcg_behavior { 29 DEVCG_DEFAULT_NONE, 30 DEVCG_DEFAULT_ALLOW, 31 DEVCG_DEFAULT_DENY, 32 }; 33 34 /* 35 * exception list locking rules: 36 * hold devcgroup_mutex for update/read. 37 * hold rcu_read_lock() for read. 38 */ 39 40 struct dev_exception_item { 41 u32 major, minor; 42 short type; 43 short access; 44 struct list_head list; 45 struct rcu_head rcu; 46 }; 47 48 struct dev_cgroup { 49 struct cgroup_subsys_state css; 50 struct list_head exceptions; 51 enum devcg_behavior behavior; 52 }; 53 54 static inline struct dev_cgroup *css_to_devcgroup(struct cgroup_subsys_state *s) 55 { 56 return s ? container_of(s, struct dev_cgroup, css) : NULL; 57 } 58 59 static inline struct dev_cgroup *task_devcgroup(struct task_struct *task) 60 { 61 return css_to_devcgroup(task_css(task, devices_cgrp_id)); 62 } 63 64 /* 65 * called under devcgroup_mutex 66 */ 67 static int dev_exceptions_copy(struct list_head *dest, struct list_head *orig) 68 { 69 struct dev_exception_item *ex, *tmp, *new; 70 71 lockdep_assert_held(&devcgroup_mutex); 72 73 list_for_each_entry(ex, orig, list) { 74 new = kmemdup(ex, sizeof(*ex), GFP_KERNEL); 75 if (!new) 76 goto free_and_exit; 77 list_add_tail(&new->list, dest); 78 } 79 80 return 0; 81 82 free_and_exit: 83 list_for_each_entry_safe(ex, tmp, dest, list) { 84 list_del(&ex->list); 85 kfree(ex); 86 } 87 return -ENOMEM; 88 } 89 90 /* 91 * called under devcgroup_mutex 92 */ 93 static int dev_exception_add(struct dev_cgroup *dev_cgroup, 94 struct dev_exception_item *ex) 95 { 96 struct dev_exception_item *excopy, *walk; 97 98 lockdep_assert_held(&devcgroup_mutex); 99 100 excopy = kmemdup(ex, sizeof(*ex), GFP_KERNEL); 101 if (!excopy) 102 return -ENOMEM; 103 104 list_for_each_entry(walk, &dev_cgroup->exceptions, list) { 105 if (walk->type != ex->type) 106 continue; 107 if (walk->major != ex->major) 108 continue; 109 if (walk->minor != ex->minor) 110 continue; 111 112 walk->access |= ex->access; 113 kfree(excopy); 114 excopy = NULL; 115 } 116 117 if (excopy != NULL) 118 list_add_tail_rcu(&excopy->list, &dev_cgroup->exceptions); 119 return 0; 120 } 121 122 /* 123 * called under devcgroup_mutex 124 */ 125 static void dev_exception_rm(struct dev_cgroup *dev_cgroup, 126 struct dev_exception_item *ex) 127 { 128 struct dev_exception_item *walk, *tmp; 129 130 lockdep_assert_held(&devcgroup_mutex); 131 132 list_for_each_entry_safe(walk, tmp, &dev_cgroup->exceptions, list) { 133 if (walk->type != ex->type) 134 continue; 135 if (walk->major != ex->major) 136 continue; 137 if (walk->minor != ex->minor) 138 continue; 139 140 walk->access &= ~ex->access; 141 if (!walk->access) { 142 list_del_rcu(&walk->list); 143 kfree_rcu(walk, rcu); 144 } 145 } 146 } 147 148 static void __dev_exception_clean(struct dev_cgroup *dev_cgroup) 149 { 150 struct dev_exception_item *ex, *tmp; 151 152 list_for_each_entry_safe(ex, tmp, &dev_cgroup->exceptions, list) { 153 list_del_rcu(&ex->list); 154 kfree_rcu(ex, rcu); 155 } 156 } 157 158 /** 159 * dev_exception_clean - frees all entries of the exception list 160 * @dev_cgroup: dev_cgroup with the exception list to be cleaned 161 * 162 * called under devcgroup_mutex 163 */ 164 static void dev_exception_clean(struct dev_cgroup *dev_cgroup) 165 { 166 lockdep_assert_held(&devcgroup_mutex); 167 168 __dev_exception_clean(dev_cgroup); 169 } 170 171 static inline bool is_devcg_online(const struct dev_cgroup *devcg) 172 { 173 return (devcg->behavior != DEVCG_DEFAULT_NONE); 174 } 175 176 /** 177 * devcgroup_online - initializes devcgroup's behavior and exceptions based on 178 * parent's 179 * @css: css getting online 180 * returns 0 in case of success, error code otherwise 181 */ 182 static int devcgroup_online(struct cgroup_subsys_state *css) 183 { 184 struct dev_cgroup *dev_cgroup = css_to_devcgroup(css); 185 struct dev_cgroup *parent_dev_cgroup = css_to_devcgroup(css_parent(css)); 186 int ret = 0; 187 188 mutex_lock(&devcgroup_mutex); 189 190 if (parent_dev_cgroup == NULL) 191 dev_cgroup->behavior = DEVCG_DEFAULT_ALLOW; 192 else { 193 ret = dev_exceptions_copy(&dev_cgroup->exceptions, 194 &parent_dev_cgroup->exceptions); 195 if (!ret) 196 dev_cgroup->behavior = parent_dev_cgroup->behavior; 197 } 198 mutex_unlock(&devcgroup_mutex); 199 200 return ret; 201 } 202 203 static void devcgroup_offline(struct cgroup_subsys_state *css) 204 { 205 struct dev_cgroup *dev_cgroup = css_to_devcgroup(css); 206 207 mutex_lock(&devcgroup_mutex); 208 dev_cgroup->behavior = DEVCG_DEFAULT_NONE; 209 mutex_unlock(&devcgroup_mutex); 210 } 211 212 /* 213 * called from kernel/cgroup.c with cgroup_lock() held. 214 */ 215 static struct cgroup_subsys_state * 216 devcgroup_css_alloc(struct cgroup_subsys_state *parent_css) 217 { 218 struct dev_cgroup *dev_cgroup; 219 220 dev_cgroup = kzalloc(sizeof(*dev_cgroup), GFP_KERNEL); 221 if (!dev_cgroup) 222 return ERR_PTR(-ENOMEM); 223 INIT_LIST_HEAD(&dev_cgroup->exceptions); 224 dev_cgroup->behavior = DEVCG_DEFAULT_NONE; 225 226 return &dev_cgroup->css; 227 } 228 229 static void devcgroup_css_free(struct cgroup_subsys_state *css) 230 { 231 struct dev_cgroup *dev_cgroup = css_to_devcgroup(css); 232 233 __dev_exception_clean(dev_cgroup); 234 kfree(dev_cgroup); 235 } 236 237 #define DEVCG_ALLOW 1 238 #define DEVCG_DENY 2 239 #define DEVCG_LIST 3 240 241 #define MAJMINLEN 13 242 #define ACCLEN 4 243 244 static void set_access(char *acc, short access) 245 { 246 int idx = 0; 247 memset(acc, 0, ACCLEN); 248 if (access & ACC_READ) 249 acc[idx++] = 'r'; 250 if (access & ACC_WRITE) 251 acc[idx++] = 'w'; 252 if (access & ACC_MKNOD) 253 acc[idx++] = 'm'; 254 } 255 256 static char type_to_char(short type) 257 { 258 if (type == DEV_ALL) 259 return 'a'; 260 if (type == DEV_CHAR) 261 return 'c'; 262 if (type == DEV_BLOCK) 263 return 'b'; 264 return 'X'; 265 } 266 267 static void set_majmin(char *str, unsigned m) 268 { 269 if (m == ~0) 270 strcpy(str, "*"); 271 else 272 sprintf(str, "%u", m); 273 } 274 275 static int devcgroup_seq_show(struct seq_file *m, void *v) 276 { 277 struct dev_cgroup *devcgroup = css_to_devcgroup(seq_css(m)); 278 struct dev_exception_item *ex; 279 char maj[MAJMINLEN], min[MAJMINLEN], acc[ACCLEN]; 280 281 rcu_read_lock(); 282 /* 283 * To preserve the compatibility: 284 * - Only show the "all devices" when the default policy is to allow 285 * - List the exceptions in case the default policy is to deny 286 * This way, the file remains as a "whitelist of devices" 287 */ 288 if (devcgroup->behavior == DEVCG_DEFAULT_ALLOW) { 289 set_access(acc, ACC_MASK); 290 set_majmin(maj, ~0); 291 set_majmin(min, ~0); 292 seq_printf(m, "%c %s:%s %s\n", type_to_char(DEV_ALL), 293 maj, min, acc); 294 } else { 295 list_for_each_entry_rcu(ex, &devcgroup->exceptions, list) { 296 set_access(acc, ex->access); 297 set_majmin(maj, ex->major); 298 set_majmin(min, ex->minor); 299 seq_printf(m, "%c %s:%s %s\n", type_to_char(ex->type), 300 maj, min, acc); 301 } 302 } 303 rcu_read_unlock(); 304 305 return 0; 306 } 307 308 /** 309 * match_exception - iterates the exception list trying to match a rule 310 * based on type, major, minor and access type. It is 311 * considered a match if an exception is found that 312 * will contain the entire range of provided parameters. 313 * @exceptions: list of exceptions 314 * @type: device type (DEV_BLOCK or DEV_CHAR) 315 * @major: device file major number, ~0 to match all 316 * @minor: device file minor number, ~0 to match all 317 * @access: permission mask (ACC_READ, ACC_WRITE, ACC_MKNOD) 318 * 319 * returns: true in case it matches an exception completely 320 */ 321 static bool match_exception(struct list_head *exceptions, short type, 322 u32 major, u32 minor, short access) 323 { 324 struct dev_exception_item *ex; 325 326 list_for_each_entry_rcu(ex, exceptions, list) { 327 if ((type & DEV_BLOCK) && !(ex->type & DEV_BLOCK)) 328 continue; 329 if ((type & DEV_CHAR) && !(ex->type & DEV_CHAR)) 330 continue; 331 if (ex->major != ~0 && ex->major != major) 332 continue; 333 if (ex->minor != ~0 && ex->minor != minor) 334 continue; 335 /* provided access cannot have more than the exception rule */ 336 if (access & (~ex->access)) 337 continue; 338 return true; 339 } 340 return false; 341 } 342 343 /** 344 * match_exception_partial - iterates the exception list trying to match a rule 345 * based on type, major, minor and access type. It is 346 * considered a match if an exception's range is 347 * found to contain *any* of the devices specified by 348 * provided parameters. This is used to make sure no 349 * extra access is being granted that is forbidden by 350 * any of the exception list. 351 * @exceptions: list of exceptions 352 * @type: device type (DEV_BLOCK or 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 (ACC_READ, ACC_WRITE, ACC_MKNOD) 356 * 357 * returns: true in case the provided range mat matches an exception completely 358 */ 359 static bool match_exception_partial(struct list_head *exceptions, short type, 360 u32 major, u32 minor, short access) 361 { 362 struct dev_exception_item *ex; 363 364 list_for_each_entry_rcu(ex, exceptions, list) { 365 if ((type & DEV_BLOCK) && !(ex->type & DEV_BLOCK)) 366 continue; 367 if ((type & DEV_CHAR) && !(ex->type & DEV_CHAR)) 368 continue; 369 /* 370 * We must be sure that both the exception and the provided 371 * range aren't masking all devices 372 */ 373 if (ex->major != ~0 && major != ~0 && ex->major != major) 374 continue; 375 if (ex->minor != ~0 && minor != ~0 && ex->minor != minor) 376 continue; 377 /* 378 * In order to make sure the provided range isn't matching 379 * an exception, all its access bits shouldn't match the 380 * exception's access bits 381 */ 382 if (!(access & ex->access)) 383 continue; 384 return true; 385 } 386 return false; 387 } 388 389 /** 390 * verify_new_ex - verifies if a new exception is part of what is allowed 391 * by a dev cgroup based on the default policy + 392 * exceptions. This is used to make sure a child cgroup 393 * won't have more privileges than its parent 394 * @dev_cgroup: dev cgroup to be tested against 395 * @refex: new exception 396 * @behavior: behavior of the exception's dev_cgroup 397 */ 398 static bool verify_new_ex(struct dev_cgroup *dev_cgroup, 399 struct dev_exception_item *refex, 400 enum devcg_behavior behavior) 401 { 402 bool match = false; 403 404 rcu_lockdep_assert(rcu_read_lock_held() || 405 lockdep_is_held(&devcgroup_mutex), 406 "device_cgroup:verify_new_ex called without proper synchronization"); 407 408 if (dev_cgroup->behavior == DEVCG_DEFAULT_ALLOW) { 409 if (behavior == DEVCG_DEFAULT_ALLOW) { 410 /* 411 * new exception in the child doesn't matter, only 412 * adding extra restrictions 413 */ 414 return true; 415 } else { 416 /* 417 * new exception in the child will add more devices 418 * that can be acessed, so it can't match any of 419 * parent's exceptions, even slightly 420 */ 421 match = match_exception_partial(&dev_cgroup->exceptions, 422 refex->type, 423 refex->major, 424 refex->minor, 425 refex->access); 426 427 if (match) 428 return false; 429 return true; 430 } 431 } else { 432 /* 433 * Only behavior == DEVCG_DEFAULT_DENY allowed here, therefore 434 * the new exception will add access to more devices and must 435 * be contained completely in an parent's exception to be 436 * allowed 437 */ 438 match = match_exception(&dev_cgroup->exceptions, refex->type, 439 refex->major, refex->minor, 440 refex->access); 441 442 if (match) 443 /* parent has an exception that matches the proposed */ 444 return true; 445 else 446 return false; 447 } 448 return false; 449 } 450 451 /* 452 * parent_has_perm: 453 * when adding a new allow rule to a device exception list, the rule 454 * must be allowed in the parent device 455 */ 456 static int parent_has_perm(struct dev_cgroup *childcg, 457 struct dev_exception_item *ex) 458 { 459 struct dev_cgroup *parent = css_to_devcgroup(css_parent(&childcg->css)); 460 461 if (!parent) 462 return 1; 463 return verify_new_ex(parent, ex, childcg->behavior); 464 } 465 466 /** 467 * may_allow_all - checks if it's possible to change the behavior to 468 * allow based on parent's rules. 469 * @parent: device cgroup's parent 470 * returns: != 0 in case it's allowed, 0 otherwise 471 */ 472 static inline int may_allow_all(struct dev_cgroup *parent) 473 { 474 if (!parent) 475 return 1; 476 return parent->behavior == DEVCG_DEFAULT_ALLOW; 477 } 478 479 /** 480 * revalidate_active_exceptions - walks through the active exception list and 481 * revalidates the exceptions based on parent's 482 * behavior and exceptions. The exceptions that 483 * are no longer valid will be removed. 484 * Called with devcgroup_mutex held. 485 * @devcg: cgroup which exceptions will be checked 486 * 487 * This is one of the three key functions for hierarchy implementation. 488 * This function is responsible for re-evaluating all the cgroup's active 489 * exceptions due to a parent's exception change. 490 * Refer to Documentation/cgroups/devices.txt for more details. 491 */ 492 static void revalidate_active_exceptions(struct dev_cgroup *devcg) 493 { 494 struct dev_exception_item *ex; 495 struct list_head *this, *tmp; 496 497 list_for_each_safe(this, tmp, &devcg->exceptions) { 498 ex = container_of(this, struct dev_exception_item, list); 499 if (!parent_has_perm(devcg, ex)) 500 dev_exception_rm(devcg, ex); 501 } 502 } 503 504 /** 505 * propagate_exception - propagates a new exception to the children 506 * @devcg_root: device cgroup that added a new exception 507 * @ex: new exception to be propagated 508 * 509 * returns: 0 in case of success, != 0 in case of error 510 */ 511 static int propagate_exception(struct dev_cgroup *devcg_root, 512 struct dev_exception_item *ex) 513 { 514 struct cgroup_subsys_state *pos; 515 int rc = 0; 516 517 rcu_read_lock(); 518 519 css_for_each_descendant_pre(pos, &devcg_root->css) { 520 struct dev_cgroup *devcg = css_to_devcgroup(pos); 521 522 /* 523 * Because devcgroup_mutex is held, no devcg will become 524 * online or offline during the tree walk (see on/offline 525 * methods), and online ones are safe to access outside RCU 526 * read lock without bumping refcnt. 527 */ 528 if (pos == &devcg_root->css || !is_devcg_online(devcg)) 529 continue; 530 531 rcu_read_unlock(); 532 533 /* 534 * in case both root's behavior and devcg is allow, a new 535 * restriction means adding to the exception list 536 */ 537 if (devcg_root->behavior == DEVCG_DEFAULT_ALLOW && 538 devcg->behavior == DEVCG_DEFAULT_ALLOW) { 539 rc = dev_exception_add(devcg, ex); 540 if (rc) 541 break; 542 } else { 543 /* 544 * in the other possible cases: 545 * root's behavior: allow, devcg's: deny 546 * root's behavior: deny, devcg's: deny 547 * the exception will be removed 548 */ 549 dev_exception_rm(devcg, ex); 550 } 551 revalidate_active_exceptions(devcg); 552 553 rcu_read_lock(); 554 } 555 556 rcu_read_unlock(); 557 return rc; 558 } 559 560 static inline bool has_children(struct dev_cgroup *devcgroup) 561 { 562 struct cgroup *cgrp = devcgroup->css.cgroup; 563 564 return !list_empty(&cgrp->children); 565 } 566 567 /* 568 * Modify the exception list using allow/deny rules. 569 * CAP_SYS_ADMIN is needed for this. It's at least separate from CAP_MKNOD 570 * so we can give a container CAP_MKNOD to let it create devices but not 571 * modify the exception list. 572 * It seems likely we'll want to add a CAP_CONTAINER capability to allow 573 * us to also grant CAP_SYS_ADMIN to containers without giving away the 574 * device exception list controls, but for now we'll stick with CAP_SYS_ADMIN 575 * 576 * Taking rules away is always allowed (given CAP_SYS_ADMIN). Granting 577 * new access is only allowed if you're in the top-level cgroup, or your 578 * parent cgroup has the access you're asking for. 579 */ 580 static int devcgroup_update_access(struct dev_cgroup *devcgroup, 581 int filetype, char *buffer) 582 { 583 const char *b; 584 char temp[12]; /* 11 + 1 characters needed for a u32 */ 585 int count, rc = 0; 586 struct dev_exception_item ex; 587 struct dev_cgroup *parent = css_to_devcgroup(css_parent(&devcgroup->css)); 588 589 if (!capable(CAP_SYS_ADMIN)) 590 return -EPERM; 591 592 memset(&ex, 0, sizeof(ex)); 593 b = buffer; 594 595 switch (*b) { 596 case 'a': 597 switch (filetype) { 598 case DEVCG_ALLOW: 599 if (has_children(devcgroup)) 600 return -EINVAL; 601 602 if (!may_allow_all(parent)) 603 return -EPERM; 604 dev_exception_clean(devcgroup); 605 devcgroup->behavior = DEVCG_DEFAULT_ALLOW; 606 if (!parent) 607 break; 608 609 rc = dev_exceptions_copy(&devcgroup->exceptions, 610 &parent->exceptions); 611 if (rc) 612 return rc; 613 break; 614 case DEVCG_DENY: 615 if (has_children(devcgroup)) 616 return -EINVAL; 617 618 dev_exception_clean(devcgroup); 619 devcgroup->behavior = DEVCG_DEFAULT_DENY; 620 break; 621 default: 622 return -EINVAL; 623 } 624 return 0; 625 case 'b': 626 ex.type = DEV_BLOCK; 627 break; 628 case 'c': 629 ex.type = DEV_CHAR; 630 break; 631 default: 632 return -EINVAL; 633 } 634 b++; 635 if (!isspace(*b)) 636 return -EINVAL; 637 b++; 638 if (*b == '*') { 639 ex.major = ~0; 640 b++; 641 } else if (isdigit(*b)) { 642 memset(temp, 0, sizeof(temp)); 643 for (count = 0; count < sizeof(temp) - 1; count++) { 644 temp[count] = *b; 645 b++; 646 if (!isdigit(*b)) 647 break; 648 } 649 rc = kstrtou32(temp, 10, &ex.major); 650 if (rc) 651 return -EINVAL; 652 } else { 653 return -EINVAL; 654 } 655 if (*b != ':') 656 return -EINVAL; 657 b++; 658 659 /* read minor */ 660 if (*b == '*') { 661 ex.minor = ~0; 662 b++; 663 } else if (isdigit(*b)) { 664 memset(temp, 0, sizeof(temp)); 665 for (count = 0; count < sizeof(temp) - 1; count++) { 666 temp[count] = *b; 667 b++; 668 if (!isdigit(*b)) 669 break; 670 } 671 rc = kstrtou32(temp, 10, &ex.minor); 672 if (rc) 673 return -EINVAL; 674 } else { 675 return -EINVAL; 676 } 677 if (!isspace(*b)) 678 return -EINVAL; 679 for (b++, count = 0; count < 3; count++, b++) { 680 switch (*b) { 681 case 'r': 682 ex.access |= ACC_READ; 683 break; 684 case 'w': 685 ex.access |= ACC_WRITE; 686 break; 687 case 'm': 688 ex.access |= ACC_MKNOD; 689 break; 690 case '\n': 691 case '\0': 692 count = 3; 693 break; 694 default: 695 return -EINVAL; 696 } 697 } 698 699 switch (filetype) { 700 case DEVCG_ALLOW: 701 if (!parent_has_perm(devcgroup, &ex)) 702 return -EPERM; 703 /* 704 * If the default policy is to allow by default, try to remove 705 * an matching exception instead. And be silent about it: we 706 * don't want to break compatibility 707 */ 708 if (devcgroup->behavior == DEVCG_DEFAULT_ALLOW) { 709 dev_exception_rm(devcgroup, &ex); 710 return 0; 711 } 712 rc = dev_exception_add(devcgroup, &ex); 713 break; 714 case DEVCG_DENY: 715 /* 716 * If the default policy is to deny by default, try to remove 717 * an matching exception instead. And be silent about it: we 718 * don't want to break compatibility 719 */ 720 if (devcgroup->behavior == DEVCG_DEFAULT_DENY) 721 dev_exception_rm(devcgroup, &ex); 722 else 723 rc = dev_exception_add(devcgroup, &ex); 724 725 if (rc) 726 break; 727 /* we only propagate new restrictions */ 728 rc = propagate_exception(devcgroup, &ex); 729 break; 730 default: 731 rc = -EINVAL; 732 } 733 return rc; 734 } 735 736 static int devcgroup_access_write(struct cgroup_subsys_state *css, 737 struct cftype *cft, char *buffer) 738 { 739 int retval; 740 741 mutex_lock(&devcgroup_mutex); 742 retval = devcgroup_update_access(css_to_devcgroup(css), 743 cft->private, buffer); 744 mutex_unlock(&devcgroup_mutex); 745 return retval; 746 } 747 748 static struct cftype dev_cgroup_files[] = { 749 { 750 .name = "allow", 751 .write_string = devcgroup_access_write, 752 .private = DEVCG_ALLOW, 753 }, 754 { 755 .name = "deny", 756 .write_string = devcgroup_access_write, 757 .private = DEVCG_DENY, 758 }, 759 { 760 .name = "list", 761 .seq_show = devcgroup_seq_show, 762 .private = DEVCG_LIST, 763 }, 764 { } /* terminate */ 765 }; 766 767 struct cgroup_subsys devices_cgrp_subsys = { 768 .css_alloc = devcgroup_css_alloc, 769 .css_free = devcgroup_css_free, 770 .css_online = devcgroup_online, 771 .css_offline = devcgroup_offline, 772 .base_cftypes = dev_cgroup_files, 773 }; 774 775 /** 776 * __devcgroup_check_permission - checks if an inode operation is permitted 777 * @dev_cgroup: the dev cgroup to be tested against 778 * @type: device type 779 * @major: device major number 780 * @minor: device minor number 781 * @access: combination of ACC_WRITE, ACC_READ and ACC_MKNOD 782 * 783 * returns 0 on success, -EPERM case the operation is not permitted 784 */ 785 static int __devcgroup_check_permission(short type, u32 major, u32 minor, 786 short access) 787 { 788 struct dev_cgroup *dev_cgroup; 789 bool rc; 790 791 rcu_read_lock(); 792 dev_cgroup = task_devcgroup(current); 793 if (dev_cgroup->behavior == DEVCG_DEFAULT_ALLOW) 794 /* Can't match any of the exceptions, even partially */ 795 rc = !match_exception_partial(&dev_cgroup->exceptions, 796 type, major, minor, access); 797 else 798 /* Need to match completely one exception to be allowed */ 799 rc = match_exception(&dev_cgroup->exceptions, type, major, 800 minor, access); 801 rcu_read_unlock(); 802 803 if (!rc) 804 return -EPERM; 805 806 return 0; 807 } 808 809 int __devcgroup_inode_permission(struct inode *inode, int mask) 810 { 811 short type, access = 0; 812 813 if (S_ISBLK(inode->i_mode)) 814 type = DEV_BLOCK; 815 if (S_ISCHR(inode->i_mode)) 816 type = DEV_CHAR; 817 if (mask & MAY_WRITE) 818 access |= ACC_WRITE; 819 if (mask & MAY_READ) 820 access |= ACC_READ; 821 822 return __devcgroup_check_permission(type, imajor(inode), iminor(inode), 823 access); 824 } 825 826 int devcgroup_inode_mknod(int mode, dev_t dev) 827 { 828 short type; 829 830 if (!S_ISBLK(mode) && !S_ISCHR(mode)) 831 return 0; 832 833 if (S_ISBLK(mode)) 834 type = DEV_BLOCK; 835 else 836 type = DEV_CHAR; 837 838 return __devcgroup_check_permission(type, MAJOR(dev), MINOR(dev), 839 ACC_MKNOD); 840 841 } 842