| 1 | // SPDX-License-Identifier: GPL-2.0 |
| 2 | /* |
| 3 | * device_cgroup.c - device cgroup subsystem |
| 4 | * |
| 5 | * Copyright 2007 IBM Corp |
| 6 | */ |
| 7 | |
| 8 | #include <linux/device_cgroup.h> |
| 9 | #include <linux/cgroup.h> |
| 10 | #include <linux/ctype.h> |
| 11 | #include <linux/list.h> |
| 12 | #include <linux/uaccess.h> |
| 13 | #include <linux/seq_file.h> |
| 14 | #include <linux/slab.h> |
| 15 | #include <linux/rcupdate.h> |
| 16 | #include <linux/mutex.h> |
| 17 | |
| 18 | static DEFINE_MUTEX(devcgroup_mutex); |
| 19 | |
| 20 | enum devcg_behavior { |
| 21 | DEVCG_DEFAULT_NONE, |
| 22 | DEVCG_DEFAULT_ALLOW, |
| 23 | DEVCG_DEFAULT_DENY, |
| 24 | }; |
| 25 | |
| 26 | /* |
| 27 | * exception list locking rules: |
| 28 | * hold devcgroup_mutex for update/read. |
| 29 | * hold rcu_read_lock() for read. |
| 30 | */ |
| 31 | |
| 32 | struct dev_exception_item { |
| 33 | u32 major, minor; |
| 34 | short type; |
| 35 | short access; |
| 36 | struct list_head list; |
| 37 | struct rcu_head rcu; |
| 38 | }; |
| 39 | |
| 40 | struct dev_cgroup { |
| 41 | struct cgroup_subsys_state css; |
| 42 | struct list_head exceptions; |
| 43 | enum devcg_behavior behavior; |
| 44 | }; |
| 45 | |
| 46 | static inline struct dev_cgroup *css_to_devcgroup(struct cgroup_subsys_state *s) |
| 47 | { |
| 48 | return s ? container_of(s, struct dev_cgroup, css) : NULL; |
| 49 | } |
| 50 | |
| 51 | static inline struct dev_cgroup *task_devcgroup(struct task_struct *task) |
| 52 | { |
| 53 | return css_to_devcgroup(task_css(task, devices_cgrp_id)); |
| 54 | } |
| 55 | |
| 56 | /* |
| 57 | * called under devcgroup_mutex |
| 58 | */ |
| 59 | static int dev_exceptions_copy(struct list_head *dest, struct list_head *orig) |
| 60 | { |
| 61 | struct dev_exception_item *ex, *tmp, *new; |
| 62 | |
| 63 | lockdep_assert_held(&devcgroup_mutex); |
| 64 | |
| 65 | list_for_each_entry(ex, orig, list) { |
| 66 | new = kmemdup(ex, sizeof(*ex), GFP_KERNEL); |
| 67 | if (!new) |
| 68 | goto free_and_exit; |
| 69 | list_add_tail(&new->list, dest); |
| 70 | } |
| 71 | |
| 72 | return 0; |
| 73 | |
| 74 | free_and_exit: |
| 75 | list_for_each_entry_safe(ex, tmp, dest, list) { |
| 76 | list_del(&ex->list); |
| 77 | kfree(ex); |
| 78 | } |
| 79 | return -ENOMEM; |
| 80 | } |
| 81 | |
| 82 | /* |
| 83 | * called under devcgroup_mutex |
| 84 | */ |
| 85 | static int dev_exception_add(struct dev_cgroup *dev_cgroup, |
| 86 | struct dev_exception_item *ex) |
| 87 | { |
| 88 | struct dev_exception_item *excopy, *walk; |
| 89 | |
| 90 | lockdep_assert_held(&devcgroup_mutex); |
| 91 | |
| 92 | excopy = kmemdup(ex, sizeof(*ex), GFP_KERNEL); |
| 93 | if (!excopy) |
| 94 | return -ENOMEM; |
| 95 | |
| 96 | list_for_each_entry(walk, &dev_cgroup->exceptions, list) { |
| 97 | if (walk->type != ex->type) |
| 98 | continue; |
| 99 | if (walk->major != ex->major) |
| 100 | continue; |
| 101 | if (walk->minor != ex->minor) |
| 102 | continue; |
| 103 | |
| 104 | walk->access |= ex->access; |
| 105 | kfree(excopy); |
| 106 | excopy = NULL; |
| 107 | } |
| 108 | |
| 109 | if (excopy != NULL) |
| 110 | list_add_tail_rcu(&excopy->list, &dev_cgroup->exceptions); |
| 111 | return 0; |
| 112 | } |
| 113 | |
| 114 | /* |
| 115 | * called under devcgroup_mutex |
| 116 | */ |
| 117 | static void dev_exception_rm(struct dev_cgroup *dev_cgroup, |
| 118 | struct dev_exception_item *ex) |
| 119 | { |
| 120 | struct dev_exception_item *walk, *tmp; |
| 121 | |
| 122 | lockdep_assert_held(&devcgroup_mutex); |
| 123 | |
| 124 | list_for_each_entry_safe(walk, tmp, &dev_cgroup->exceptions, list) { |
| 125 | if (walk->type != ex->type) |
| 126 | continue; |
| 127 | if (walk->major != ex->major) |
| 128 | continue; |
| 129 | if (walk->minor != ex->minor) |
| 130 | continue; |
| 131 | |
| 132 | walk->access &= ~ex->access; |
| 133 | if (!walk->access) { |
| 134 | list_del_rcu(&walk->list); |
| 135 | kfree_rcu(walk, rcu); |
| 136 | } |
| 137 | } |
| 138 | } |
| 139 | |
| 140 | static void __dev_exception_clean(struct dev_cgroup *dev_cgroup) |
| 141 | { |
| 142 | struct dev_exception_item *ex, *tmp; |
| 143 | |
| 144 | list_for_each_entry_safe(ex, tmp, &dev_cgroup->exceptions, list) { |
| 145 | list_del_rcu(&ex->list); |
| 146 | kfree_rcu(ex, rcu); |
| 147 | } |
| 148 | } |
| 149 | |
| 150 | /** |
| 151 | * dev_exception_clean - frees all entries of the exception list |
| 152 | * @dev_cgroup: dev_cgroup with the exception list to be cleaned |
| 153 | * |
| 154 | * called under devcgroup_mutex |
| 155 | */ |
| 156 | static void dev_exception_clean(struct dev_cgroup *dev_cgroup) |
| 157 | { |
| 158 | lockdep_assert_held(&devcgroup_mutex); |
| 159 | |
| 160 | __dev_exception_clean(dev_cgroup); |
| 161 | } |
| 162 | |
| 163 | static inline bool is_devcg_online(const struct dev_cgroup *devcg) |
| 164 | { |
| 165 | return (devcg->behavior != DEVCG_DEFAULT_NONE); |
| 166 | } |
| 167 | |
| 168 | /** |
| 169 | * devcgroup_online - initializes devcgroup's behavior and exceptions based on |
| 170 | * parent's |
| 171 | * @css: css getting online |
| 172 | * returns 0 in case of success, error code otherwise |
| 173 | */ |
| 174 | static int devcgroup_online(struct cgroup_subsys_state *css) |
| 175 | { |
| 176 | struct dev_cgroup *dev_cgroup = css_to_devcgroup(css); |
| 177 | struct dev_cgroup *parent_dev_cgroup = css_to_devcgroup(css->parent); |
| 178 | int ret = 0; |
| 179 | |
| 180 | mutex_lock(&devcgroup_mutex); |
| 181 | |
| 182 | if (parent_dev_cgroup == NULL) |
| 183 | dev_cgroup->behavior = DEVCG_DEFAULT_ALLOW; |
| 184 | else { |
| 185 | ret = dev_exceptions_copy(&dev_cgroup->exceptions, |
| 186 | &parent_dev_cgroup->exceptions); |
| 187 | if (!ret) |
| 188 | dev_cgroup->behavior = parent_dev_cgroup->behavior; |
| 189 | } |
| 190 | mutex_unlock(&devcgroup_mutex); |
| 191 | |
| 192 | return ret; |
| 193 | } |
| 194 | |
| 195 | static void devcgroup_offline(struct cgroup_subsys_state *css) |
| 196 | { |
| 197 | struct dev_cgroup *dev_cgroup = css_to_devcgroup(css); |
| 198 | |
| 199 | mutex_lock(&devcgroup_mutex); |
| 200 | dev_cgroup->behavior = DEVCG_DEFAULT_NONE; |
| 201 | mutex_unlock(&devcgroup_mutex); |
| 202 | } |
| 203 | |
| 204 | /* |
| 205 | * called from kernel/cgroup.c with cgroup_lock() held. |
| 206 | */ |
| 207 | static struct cgroup_subsys_state * |
| 208 | devcgroup_css_alloc(struct cgroup_subsys_state *parent_css) |
| 209 | { |
| 210 | struct dev_cgroup *dev_cgroup; |
| 211 | |
| 212 | dev_cgroup = kzalloc(sizeof(*dev_cgroup), GFP_KERNEL); |
| 213 | if (!dev_cgroup) |
| 214 | return ERR_PTR(-ENOMEM); |
| 215 | INIT_LIST_HEAD(&dev_cgroup->exceptions); |
| 216 | dev_cgroup->behavior = DEVCG_DEFAULT_NONE; |
| 217 | |
| 218 | return &dev_cgroup->css; |
| 219 | } |
| 220 | |
| 221 | static void devcgroup_css_free(struct cgroup_subsys_state *css) |
| 222 | { |
| 223 | struct dev_cgroup *dev_cgroup = css_to_devcgroup(css); |
| 224 | |
| 225 | __dev_exception_clean(dev_cgroup); |
| 226 | kfree(dev_cgroup); |
| 227 | } |
| 228 | |
| 229 | #define DEVCG_ALLOW 1 |
| 230 | #define DEVCG_DENY 2 |
| 231 | #define DEVCG_LIST 3 |
| 232 | |
| 233 | #define MAJMINLEN 13 |
| 234 | #define ACCLEN 4 |
| 235 | |
| 236 | static void set_access(char *acc, short access) |
| 237 | { |
| 238 | int idx = 0; |
| 239 | memset(acc, 0, ACCLEN); |
| 240 | if (access & DEVCG_ACC_READ) |
| 241 | acc[idx++] = 'r'; |
| 242 | if (access & DEVCG_ACC_WRITE) |
| 243 | acc[idx++] = 'w'; |
| 244 | if (access & DEVCG_ACC_MKNOD) |
| 245 | acc[idx++] = 'm'; |
| 246 | } |
| 247 | |
| 248 | static char type_to_char(short type) |
| 249 | { |
| 250 | if (type == DEVCG_DEV_ALL) |
| 251 | return 'a'; |
| 252 | if (type == DEVCG_DEV_CHAR) |
| 253 | return 'c'; |
| 254 | if (type == DEVCG_DEV_BLOCK) |
| 255 | return 'b'; |
| 256 | return 'X'; |
| 257 | } |
| 258 | |
| 259 | static void set_majmin(char *str, unsigned m) |
| 260 | { |
| 261 | if (m == ~0) |
| 262 | strcpy(str, "*"); |
| 263 | else |
| 264 | sprintf(str, "%u", m); |
| 265 | } |
| 266 | |
| 267 | static int devcgroup_seq_show(struct seq_file *m, void *v) |
| 268 | { |
| 269 | struct dev_cgroup *devcgroup = css_to_devcgroup(seq_css(m)); |
| 270 | struct dev_exception_item *ex; |
| 271 | char maj[MAJMINLEN], min[MAJMINLEN], acc[ACCLEN]; |
| 272 | |
| 273 | rcu_read_lock(); |
| 274 | /* |
| 275 | * To preserve the compatibility: |
| 276 | * - Only show the "all devices" when the default policy is to allow |
| 277 | * - List the exceptions in case the default policy is to deny |
| 278 | * This way, the file remains as a "whitelist of devices" |
| 279 | */ |
| 280 | if (devcgroup->behavior == DEVCG_DEFAULT_ALLOW) { |
| 281 | set_access(acc, DEVCG_ACC_MASK); |
| 282 | set_majmin(maj, ~0); |
| 283 | set_majmin(min, ~0); |
| 284 | seq_printf(m, "%c %s:%s %s\n", type_to_char(DEVCG_DEV_ALL), |
| 285 | maj, min, acc); |
| 286 | } else { |
| 287 | list_for_each_entry_rcu(ex, &devcgroup->exceptions, list) { |
| 288 | set_access(acc, ex->access); |
| 289 | set_majmin(maj, ex->major); |
| 290 | set_majmin(min, ex->minor); |
| 291 | seq_printf(m, "%c %s:%s %s\n", type_to_char(ex->type), |
| 292 | maj, min, acc); |
| 293 | } |
| 294 | } |
| 295 | rcu_read_unlock(); |
| 296 | |
| 297 | return 0; |
| 298 | } |
| 299 | |
| 300 | /** |
| 301 | * match_exception - iterates the exception list trying to find a complete match |
| 302 | * @exceptions: list of exceptions |
| 303 | * @type: device type (DEVCG_DEV_BLOCK or DEVCG_DEV_CHAR) |
| 304 | * @major: device file major number, ~0 to match all |
| 305 | * @minor: device file minor number, ~0 to match all |
| 306 | * @access: permission mask (DEVCG_ACC_READ, DEVCG_ACC_WRITE, DEVCG_ACC_MKNOD) |
| 307 | * |
| 308 | * It is considered a complete match if an exception is found that will |
| 309 | * contain the entire range of provided parameters. |
| 310 | * |
| 311 | * Return: true in case it matches an exception completely |
| 312 | */ |
| 313 | static bool match_exception(struct list_head *exceptions, short type, |
| 314 | u32 major, u32 minor, short access) |
| 315 | { |
| 316 | struct dev_exception_item *ex; |
| 317 | |
| 318 | list_for_each_entry_rcu(ex, exceptions, list) { |
| 319 | if ((type & DEVCG_DEV_BLOCK) && !(ex->type & DEVCG_DEV_BLOCK)) |
| 320 | continue; |
| 321 | if ((type & DEVCG_DEV_CHAR) && !(ex->type & DEVCG_DEV_CHAR)) |
| 322 | continue; |
| 323 | if (ex->major != ~0 && ex->major != major) |
| 324 | continue; |
| 325 | if (ex->minor != ~0 && ex->minor != minor) |
| 326 | continue; |
| 327 | /* provided access cannot have more than the exception rule */ |
| 328 | if (access & (~ex->access)) |
| 329 | continue; |
| 330 | return true; |
| 331 | } |
| 332 | return false; |
| 333 | } |
| 334 | |
| 335 | /** |
| 336 | * match_exception_partial - iterates the exception list trying to find a partial match |
| 337 | * @exceptions: list of exceptions |
| 338 | * @type: device type (DEVCG_DEV_BLOCK or DEVCG_DEV_CHAR) |
| 339 | * @major: device file major number, ~0 to match all |
| 340 | * @minor: device file minor number, ~0 to match all |
| 341 | * @access: permission mask (DEVCG_ACC_READ, DEVCG_ACC_WRITE, DEVCG_ACC_MKNOD) |
| 342 | * |
| 343 | * It is considered a partial match if an exception's range is found to |
| 344 | * contain *any* of the devices specified by provided parameters. This is |
| 345 | * used to make sure no extra access is being granted that is forbidden by |
| 346 | * any of the exception list. |
| 347 | * |
| 348 | * Return: true in case the provided range mat matches an exception completely |
| 349 | */ |
| 350 | static bool match_exception_partial(struct list_head *exceptions, short type, |
| 351 | u32 major, u32 minor, short access) |
| 352 | { |
| 353 | struct dev_exception_item *ex; |
| 354 | |
| 355 | list_for_each_entry_rcu(ex, exceptions, list) { |
| 356 | if ((type & DEVCG_DEV_BLOCK) && !(ex->type & DEVCG_DEV_BLOCK)) |
| 357 | continue; |
| 358 | if ((type & DEVCG_DEV_CHAR) && !(ex->type & DEVCG_DEV_CHAR)) |
| 359 | continue; |
| 360 | /* |
| 361 | * We must be sure that both the exception and the provided |
| 362 | * range aren't masking all devices |
| 363 | */ |
| 364 | if (ex->major != ~0 && major != ~0 && ex->major != major) |
| 365 | continue; |
| 366 | if (ex->minor != ~0 && minor != ~0 && ex->minor != minor) |
| 367 | continue; |
| 368 | /* |
| 369 | * In order to make sure the provided range isn't matching |
| 370 | * an exception, all its access bits shouldn't match the |
| 371 | * exception's access bits |
| 372 | */ |
| 373 | if (!(access & ex->access)) |
| 374 | continue; |
| 375 | return true; |
| 376 | } |
| 377 | return false; |
| 378 | } |
| 379 | |
| 380 | /** |
| 381 | * verify_new_ex - verifies if a new exception is allowed by parent cgroup's permissions |
| 382 | * @dev_cgroup: dev cgroup to be tested against |
| 383 | * @refex: new exception |
| 384 | * @behavior: behavior of the exception's dev_cgroup |
| 385 | * |
| 386 | * This is used to make sure a child cgroup won't have more privileges |
| 387 | * than its parent |
| 388 | */ |
| 389 | static bool verify_new_ex(struct dev_cgroup *dev_cgroup, |
| 390 | struct dev_exception_item *refex, |
| 391 | enum devcg_behavior behavior) |
| 392 | { |
| 393 | bool match = false; |
| 394 | |
| 395 | RCU_LOCKDEP_WARN(!rcu_read_lock_held() && |
| 396 | !lockdep_is_held(&devcgroup_mutex), |
| 397 | "device_cgroup:verify_new_ex called without proper synchronization"); |
| 398 | |
| 399 | if (dev_cgroup->behavior == DEVCG_DEFAULT_ALLOW) { |
| 400 | if (behavior == DEVCG_DEFAULT_ALLOW) { |
| 401 | /* |
| 402 | * new exception in the child doesn't matter, only |
| 403 | * adding extra restrictions |
| 404 | */ |
| 405 | return true; |
| 406 | } else { |
| 407 | /* |
| 408 | * new exception in the child will add more devices |
| 409 | * that can be acessed, so it can't match any of |
| 410 | * parent's exceptions, even slightly |
| 411 | */ |
| 412 | match = match_exception_partial(&dev_cgroup->exceptions, |
| 413 | refex->type, |
| 414 | refex->major, |
| 415 | refex->minor, |
| 416 | refex->access); |
| 417 | |
| 418 | if (match) |
| 419 | return false; |
| 420 | return true; |
| 421 | } |
| 422 | } else { |
| 423 | /* |
| 424 | * Only behavior == DEVCG_DEFAULT_DENY allowed here, therefore |
| 425 | * the new exception will add access to more devices and must |
| 426 | * be contained completely in an parent's exception to be |
| 427 | * allowed |
| 428 | */ |
| 429 | match = match_exception(&dev_cgroup->exceptions, refex->type, |
| 430 | refex->major, refex->minor, |
| 431 | refex->access); |
| 432 | |
| 433 | if (match) |
| 434 | /* parent has an exception that matches the proposed */ |
| 435 | return true; |
| 436 | else |
| 437 | return false; |
| 438 | } |
| 439 | return false; |
| 440 | } |
| 441 | |
| 442 | /* |
| 443 | * parent_has_perm: |
| 444 | * when adding a new allow rule to a device exception list, the rule |
| 445 | * must be allowed in the parent device |
| 446 | */ |
| 447 | static int parent_has_perm(struct dev_cgroup *childcg, |
| 448 | struct dev_exception_item *ex) |
| 449 | { |
| 450 | struct dev_cgroup *parent = css_to_devcgroup(childcg->css.parent); |
| 451 | |
| 452 | if (!parent) |
| 453 | return 1; |
| 454 | return verify_new_ex(parent, ex, childcg->behavior); |
| 455 | } |
| 456 | |
| 457 | /** |
| 458 | * parent_allows_removal - verify if it's ok to remove an exception |
| 459 | * @childcg: child cgroup from where the exception will be removed |
| 460 | * @ex: exception being removed |
| 461 | * |
| 462 | * When removing an exception in cgroups with default ALLOW policy, it must |
| 463 | * be checked if removing it will give the child cgroup more access than the |
| 464 | * parent. |
| 465 | * |
| 466 | * Return: true if it's ok to remove exception, false otherwise |
| 467 | */ |
| 468 | static bool parent_allows_removal(struct dev_cgroup *childcg, |
| 469 | struct dev_exception_item *ex) |
| 470 | { |
| 471 | struct dev_cgroup *parent = css_to_devcgroup(childcg->css.parent); |
| 472 | |
| 473 | if (!parent) |
| 474 | return true; |
| 475 | |
| 476 | /* It's always allowed to remove access to devices */ |
| 477 | if (childcg->behavior == DEVCG_DEFAULT_DENY) |
| 478 | return true; |
| 479 | |
| 480 | /* |
| 481 | * Make sure you're not removing part or a whole exception existing in |
| 482 | * the parent cgroup |
| 483 | */ |
| 484 | return !match_exception_partial(&parent->exceptions, ex->type, |
| 485 | ex->major, ex->minor, ex->access); |
| 486 | } |
| 487 | |
| 488 | /** |
| 489 | * may_allow_all - checks if it's possible to change the behavior to |
| 490 | * allow based on parent's rules. |
| 491 | * @parent: device cgroup's parent |
| 492 | * returns: != 0 in case it's allowed, 0 otherwise |
| 493 | */ |
| 494 | static inline int may_allow_all(struct dev_cgroup *parent) |
| 495 | { |
| 496 | if (!parent) |
| 497 | return 1; |
| 498 | return parent->behavior == DEVCG_DEFAULT_ALLOW; |
| 499 | } |
| 500 | |
| 501 | /** |
| 502 | * revalidate_active_exceptions - walks through the active exception list and |
| 503 | * revalidates the exceptions based on parent's |
| 504 | * behavior and exceptions. The exceptions that |
| 505 | * are no longer valid will be removed. |
| 506 | * Called with devcgroup_mutex held. |
| 507 | * @devcg: cgroup which exceptions will be checked |
| 508 | * |
| 509 | * This is one of the three key functions for hierarchy implementation. |
| 510 | * This function is responsible for re-evaluating all the cgroup's active |
| 511 | * exceptions due to a parent's exception change. |
| 512 | * Refer to Documentation/cgroup-v1/devices.txt for more details. |
| 513 | */ |
| 514 | static void revalidate_active_exceptions(struct dev_cgroup *devcg) |
| 515 | { |
| 516 | struct dev_exception_item *ex; |
| 517 | struct list_head *this, *tmp; |
| 518 | |
| 519 | list_for_each_safe(this, tmp, &devcg->exceptions) { |
| 520 | ex = container_of(this, struct dev_exception_item, list); |
| 521 | if (!parent_has_perm(devcg, ex)) |
| 522 | dev_exception_rm(devcg, ex); |
| 523 | } |
| 524 | } |
| 525 | |
| 526 | /** |
| 527 | * propagate_exception - propagates a new exception to the children |
| 528 | * @devcg_root: device cgroup that added a new exception |
| 529 | * @ex: new exception to be propagated |
| 530 | * |
| 531 | * returns: 0 in case of success, != 0 in case of error |
| 532 | */ |
| 533 | static int propagate_exception(struct dev_cgroup *devcg_root, |
| 534 | struct dev_exception_item *ex) |
| 535 | { |
| 536 | struct cgroup_subsys_state *pos; |
| 537 | int rc = 0; |
| 538 | |
| 539 | rcu_read_lock(); |
| 540 | |
| 541 | css_for_each_descendant_pre(pos, &devcg_root->css) { |
| 542 | struct dev_cgroup *devcg = css_to_devcgroup(pos); |
| 543 | |
| 544 | /* |
| 545 | * Because devcgroup_mutex is held, no devcg will become |
| 546 | * online or offline during the tree walk (see on/offline |
| 547 | * methods), and online ones are safe to access outside RCU |
| 548 | * read lock without bumping refcnt. |
| 549 | */ |
| 550 | if (pos == &devcg_root->css || !is_devcg_online(devcg)) |
| 551 | continue; |
| 552 | |
| 553 | rcu_read_unlock(); |
| 554 | |
| 555 | /* |
| 556 | * in case both root's behavior and devcg is allow, a new |
| 557 | * restriction means adding to the exception list |
| 558 | */ |
| 559 | if (devcg_root->behavior == DEVCG_DEFAULT_ALLOW && |
| 560 | devcg->behavior == DEVCG_DEFAULT_ALLOW) { |
| 561 | rc = dev_exception_add(devcg, ex); |
| 562 | if (rc) |
| 563 | break; |
| 564 | } else { |
| 565 | /* |
| 566 | * in the other possible cases: |
| 567 | * root's behavior: allow, devcg's: deny |
| 568 | * root's behavior: deny, devcg's: deny |
| 569 | * the exception will be removed |
| 570 | */ |
| 571 | dev_exception_rm(devcg, ex); |
| 572 | } |
| 573 | revalidate_active_exceptions(devcg); |
| 574 | |
| 575 | rcu_read_lock(); |
| 576 | } |
| 577 | |
| 578 | rcu_read_unlock(); |
| 579 | return rc; |
| 580 | } |
| 581 | |
| 582 | /* |
| 583 | * Modify the exception list using allow/deny rules. |
| 584 | * CAP_SYS_ADMIN is needed for this. It's at least separate from CAP_MKNOD |
| 585 | * so we can give a container CAP_MKNOD to let it create devices but not |
| 586 | * modify the exception list. |
| 587 | * It seems likely we'll want to add a CAP_CONTAINER capability to allow |
| 588 | * us to also grant CAP_SYS_ADMIN to containers without giving away the |
| 589 | * device exception list controls, but for now we'll stick with CAP_SYS_ADMIN |
| 590 | * |
| 591 | * Taking rules away is always allowed (given CAP_SYS_ADMIN). Granting |
| 592 | * new access is only allowed if you're in the top-level cgroup, or your |
| 593 | * parent cgroup has the access you're asking for. |
| 594 | */ |
| 595 | static int devcgroup_update_access(struct dev_cgroup *devcgroup, |
| 596 | int filetype, char *buffer) |
| 597 | { |
| 598 | const char *b; |
| 599 | char temp[12]; /* 11 + 1 characters needed for a u32 */ |
| 600 | int count, rc = 0; |
| 601 | struct dev_exception_item ex; |
| 602 | struct dev_cgroup *parent = css_to_devcgroup(devcgroup->css.parent); |
| 603 | |
| 604 | if (!capable(CAP_SYS_ADMIN)) |
| 605 | return -EPERM; |
| 606 | |
| 607 | memset(&ex, 0, sizeof(ex)); |
| 608 | b = buffer; |
| 609 | |
| 610 | switch (*b) { |
| 611 | case 'a': |
| 612 | switch (filetype) { |
| 613 | case DEVCG_ALLOW: |
| 614 | if (css_has_online_children(&devcgroup->css)) |
| 615 | return -EINVAL; |
| 616 | |
| 617 | if (!may_allow_all(parent)) |
| 618 | return -EPERM; |
| 619 | dev_exception_clean(devcgroup); |
| 620 | devcgroup->behavior = DEVCG_DEFAULT_ALLOW; |
| 621 | if (!parent) |
| 622 | break; |
| 623 | |
| 624 | rc = dev_exceptions_copy(&devcgroup->exceptions, |
| 625 | &parent->exceptions); |
| 626 | if (rc) |
| 627 | return rc; |
| 628 | break; |
| 629 | case DEVCG_DENY: |
| 630 | if (css_has_online_children(&devcgroup->css)) |
| 631 | return -EINVAL; |
| 632 | |
| 633 | dev_exception_clean(devcgroup); |
| 634 | devcgroup->behavior = DEVCG_DEFAULT_DENY; |
| 635 | break; |
| 636 | default: |
| 637 | return -EINVAL; |
| 638 | } |
| 639 | return 0; |
| 640 | case 'b': |
| 641 | ex.type = DEVCG_DEV_BLOCK; |
| 642 | break; |
| 643 | case 'c': |
| 644 | ex.type = DEVCG_DEV_CHAR; |
| 645 | break; |
| 646 | default: |
| 647 | return -EINVAL; |
| 648 | } |
| 649 | b++; |
| 650 | if (!isspace(*b)) |
| 651 | return -EINVAL; |
| 652 | b++; |
| 653 | if (*b == '*') { |
| 654 | ex.major = ~0; |
| 655 | b++; |
| 656 | } else if (isdigit(*b)) { |
| 657 | memset(temp, 0, sizeof(temp)); |
| 658 | for (count = 0; count < sizeof(temp) - 1; count++) { |
| 659 | temp[count] = *b; |
| 660 | b++; |
| 661 | if (!isdigit(*b)) |
| 662 | break; |
| 663 | } |
| 664 | rc = kstrtou32(temp, 10, &ex.major); |
| 665 | if (rc) |
| 666 | return -EINVAL; |
| 667 | } else { |
| 668 | return -EINVAL; |
| 669 | } |
| 670 | if (*b != ':') |
| 671 | return -EINVAL; |
| 672 | b++; |
| 673 | |
| 674 | /* read minor */ |
| 675 | if (*b == '*') { |
| 676 | ex.minor = ~0; |
| 677 | b++; |
| 678 | } else if (isdigit(*b)) { |
| 679 | memset(temp, 0, sizeof(temp)); |
| 680 | for (count = 0; count < sizeof(temp) - 1; count++) { |
| 681 | temp[count] = *b; |
| 682 | b++; |
| 683 | if (!isdigit(*b)) |
| 684 | break; |
| 685 | } |
| 686 | rc = kstrtou32(temp, 10, &ex.minor); |
| 687 | if (rc) |
| 688 | return -EINVAL; |
| 689 | } else { |
| 690 | return -EINVAL; |
| 691 | } |
| 692 | if (!isspace(*b)) |
| 693 | return -EINVAL; |
| 694 | for (b++, count = 0; count < 3; count++, b++) { |
| 695 | switch (*b) { |
| 696 | case 'r': |
| 697 | ex.access |= DEVCG_ACC_READ; |
| 698 | break; |
| 699 | case 'w': |
| 700 | ex.access |= DEVCG_ACC_WRITE; |
| 701 | break; |
| 702 | case 'm': |
| 703 | ex.access |= DEVCG_ACC_MKNOD; |
| 704 | break; |
| 705 | case '\n': |
| 706 | case '\0': |
| 707 | count = 3; |
| 708 | break; |
| 709 | default: |
| 710 | return -EINVAL; |
| 711 | } |
| 712 | } |
| 713 | |
| 714 | switch (filetype) { |
| 715 | case DEVCG_ALLOW: |
| 716 | /* |
| 717 | * If the default policy is to allow by default, try to remove |
| 718 | * an matching exception instead. And be silent about it: we |
| 719 | * don't want to break compatibility |
| 720 | */ |
| 721 | if (devcgroup->behavior == DEVCG_DEFAULT_ALLOW) { |
| 722 | /* Check if the parent allows removing it first */ |
| 723 | if (!parent_allows_removal(devcgroup, &ex)) |
| 724 | return -EPERM; |
| 725 | dev_exception_rm(devcgroup, &ex); |
| 726 | break; |
| 727 | } |
| 728 | |
| 729 | if (!parent_has_perm(devcgroup, &ex)) |
| 730 | return -EPERM; |
| 731 | rc = dev_exception_add(devcgroup, &ex); |
| 732 | break; |
| 733 | case DEVCG_DENY: |
| 734 | /* |
| 735 | * If the default policy is to deny by default, try to remove |
| 736 | * an matching exception instead. And be silent about it: we |
| 737 | * don't want to break compatibility |
| 738 | */ |
| 739 | if (devcgroup->behavior == DEVCG_DEFAULT_DENY) |
| 740 | dev_exception_rm(devcgroup, &ex); |
| 741 | else |
| 742 | rc = dev_exception_add(devcgroup, &ex); |
| 743 | |
| 744 | if (rc) |
| 745 | break; |
| 746 | /* we only propagate new restrictions */ |
| 747 | rc = propagate_exception(devcgroup, &ex); |
| 748 | break; |
| 749 | default: |
| 750 | rc = -EINVAL; |
| 751 | } |
| 752 | return rc; |
| 753 | } |
| 754 | |
| 755 | static ssize_t devcgroup_access_write(struct kernfs_open_file *of, |
| 756 | char *buf, size_t nbytes, loff_t off) |
| 757 | { |
| 758 | int retval; |
| 759 | |
| 760 | mutex_lock(&devcgroup_mutex); |
| 761 | retval = devcgroup_update_access(css_to_devcgroup(of_css(of)), |
| 762 | of_cft(of)->private, strstrip(buf)); |
| 763 | mutex_unlock(&devcgroup_mutex); |
| 764 | return retval ?: nbytes; |
| 765 | } |
| 766 | |
| 767 | static struct cftype dev_cgroup_files[] = { |
| 768 | { |
| 769 | .name = "allow", |
| 770 | .write = devcgroup_access_write, |
| 771 | .private = DEVCG_ALLOW, |
| 772 | }, |
| 773 | { |
| 774 | .name = "deny", |
| 775 | .write = devcgroup_access_write, |
| 776 | .private = DEVCG_DENY, |
| 777 | }, |
| 778 | { |
| 779 | .name = "list", |
| 780 | .seq_show = devcgroup_seq_show, |
| 781 | .private = DEVCG_LIST, |
| 782 | }, |
| 783 | { } /* terminate */ |
| 784 | }; |
| 785 | |
| 786 | struct cgroup_subsys devices_cgrp_subsys = { |
| 787 | .css_alloc = devcgroup_css_alloc, |
| 788 | .css_free = devcgroup_css_free, |
| 789 | .css_online = devcgroup_online, |
| 790 | .css_offline = devcgroup_offline, |
| 791 | .legacy_cftypes = dev_cgroup_files, |
| 792 | }; |
| 793 | |
| 794 | /** |
| 795 | * __devcgroup_check_permission - checks if an inode operation is permitted |
| 796 | * @dev_cgroup: the dev cgroup to be tested against |
| 797 | * @type: device type |
| 798 | * @major: device major number |
| 799 | * @minor: device minor number |
| 800 | * @access: combination of DEVCG_ACC_WRITE, DEVCG_ACC_READ and DEVCG_ACC_MKNOD |
| 801 | * |
| 802 | * returns 0 on success, -EPERM case the operation is not permitted |
| 803 | */ |
| 804 | int __devcgroup_check_permission(short type, u32 major, u32 minor, |
| 805 | short access) |
| 806 | { |
| 807 | struct dev_cgroup *dev_cgroup; |
| 808 | bool rc; |
| 809 | |
| 810 | rcu_read_lock(); |
| 811 | dev_cgroup = task_devcgroup(current); |
| 812 | if (dev_cgroup->behavior == DEVCG_DEFAULT_ALLOW) |
| 813 | /* Can't match any of the exceptions, even partially */ |
| 814 | rc = !match_exception_partial(&dev_cgroup->exceptions, |
| 815 | type, major, minor, access); |
| 816 | else |
| 817 | /* Need to match completely one exception to be allowed */ |
| 818 | rc = match_exception(&dev_cgroup->exceptions, type, major, |
| 819 | minor, access); |
| 820 | rcu_read_unlock(); |
| 821 | |
| 822 | if (!rc) |
| 823 | return -EPERM; |
| 824 | |
| 825 | return 0; |
| 826 | } |