xref: /linux/security/device_cgroup.c (revision cdd5b5a9761fd66d17586e4f4ba6588c70e640ea)
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 
css_to_devcgroup(struct cgroup_subsys_state * s)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 
task_devcgroup(struct task_struct * task)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  */
dev_exceptions_copy(struct list_head * dest,struct list_head * orig)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 
dev_exceptions_move(struct list_head * dest,struct list_head * orig)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  */
dev_exception_add(struct dev_cgroup * dev_cgroup,struct dev_exception_item * ex)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  */
dev_exception_rm(struct dev_cgroup * dev_cgroup,struct dev_exception_item * ex)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 
__dev_exception_clean(struct dev_cgroup * dev_cgroup)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  */
dev_exception_clean(struct dev_cgroup * dev_cgroup)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 
is_devcg_online(const struct dev_cgroup * devcg)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  */
devcgroup_online(struct cgroup_subsys_state * css)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 
devcgroup_offline(struct cgroup_subsys_state * css)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 *
devcgroup_css_alloc(struct cgroup_subsys_state * parent_css)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 
devcgroup_css_free(struct cgroup_subsys_state * css)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 
set_access(char * acc,short access)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 
type_to_char(short type)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 
set_majmin(char * str,unsigned m)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 
devcgroup_seq_show(struct seq_file * m,void * v)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  */
match_exception(struct list_head * exceptions,short type,u32 major,u32 minor,short access)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  */
match_exception_partial(struct list_head * exceptions,short type,u32 major,u32 minor,short access)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  */
verify_new_ex(struct dev_cgroup * dev_cgroup,struct dev_exception_item * refex,enum devcg_behavior behavior)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  */
parent_has_perm(struct dev_cgroup * childcg,struct dev_exception_item * ex)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  */
parent_allows_removal(struct dev_cgroup * childcg,struct dev_exception_item * ex)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  */
may_allow_all(struct dev_cgroup * parent)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  */
revalidate_active_exceptions(struct dev_cgroup * devcg)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  */
propagate_exception(struct dev_cgroup * devcg_root,struct dev_exception_item * ex)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  */
devcgroup_update_access(struct dev_cgroup * devcgroup,int filetype,char * buffer)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 
devcgroup_access_write(struct kernfs_open_file * of,char * buf,size_t nbytes,loff_t off)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  */
devcgroup_legacy_check_permission(short type,u32 major,u32 minor,short access)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 
devcgroup_check_permission(short type,u32 major,u32 minor,short access)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) */
877