Merge tag 'for-6.2-rc2-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/kdave...
[platform/kernel/linux-starfive.git] / 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.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 acessed, 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  * @dev_cgroup: the dev cgroup to be tested against
826  * @type: device type
827  * @major: device major number
828  * @minor: device minor number
829  * @access: combination of DEVCG_ACC_WRITE, DEVCG_ACC_READ and DEVCG_ACC_MKNOD
830  *
831  * returns 0 on success, -EPERM case the operation is not permitted
832  */
833 static int devcgroup_legacy_check_permission(short type, u32 major, u32 minor,
834                                         short access)
835 {
836         struct dev_cgroup *dev_cgroup;
837         bool rc;
838
839         rcu_read_lock();
840         dev_cgroup = task_devcgroup(current);
841         if (dev_cgroup->behavior == DEVCG_DEFAULT_ALLOW)
842                 /* Can't match any of the exceptions, even partially */
843                 rc = !match_exception_partial(&dev_cgroup->exceptions,
844                                               type, major, minor, access);
845         else
846                 /* Need to match completely one exception to be allowed */
847                 rc = match_exception(&dev_cgroup->exceptions, type, major,
848                                      minor, access);
849         rcu_read_unlock();
850
851         if (!rc)
852                 return -EPERM;
853
854         return 0;
855 }
856
857 #endif /* CONFIG_CGROUP_DEVICE */
858
859 #if defined(CONFIG_CGROUP_DEVICE) || defined(CONFIG_CGROUP_BPF)
860
861 int devcgroup_check_permission(short type, u32 major, u32 minor, short access)
862 {
863         int rc = BPF_CGROUP_RUN_PROG_DEVICE_CGROUP(type, major, minor, access);
864
865         if (rc)
866                 return rc;
867
868         #ifdef CONFIG_CGROUP_DEVICE
869         return devcgroup_legacy_check_permission(type, major, minor, access);
870
871         #else /* CONFIG_CGROUP_DEVICE */
872         return 0;
873
874         #endif /* CONFIG_CGROUP_DEVICE */
875 }
876 EXPORT_SYMBOL(devcgroup_check_permission);
877 #endif /* defined(CONFIG_CGROUP_DEVICE) || defined(CONFIG_CGROUP_BPF) */