Version:  2.0.40 2.2.26 2.4.37 3.13 3.14 3.15 3.16 3.17 3.18 3.19 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 4.10

Linux/security/device_cgroup.c

  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);
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 find a complete match
310  * @exceptions: list of exceptions
311  * @type: device type (DEV_BLOCK or DEV_CHAR)
312  * @major: device file major number, ~0 to match all
313  * @minor: device file minor number, ~0 to match all
314  * @access: permission mask (ACC_READ, ACC_WRITE, ACC_MKNOD)
315  *
316  * It is considered a complete match if an exception is found that will
317  * contain the entire range of provided parameters.
318  *
319  * Return: 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 find a partial match
345  * @exceptions: list of exceptions
346  * @type: device type (DEV_BLOCK or DEV_CHAR)
347  * @major: device file major number, ~0 to match all
348  * @minor: device file minor number, ~0 to match all
349  * @access: permission mask (ACC_READ, ACC_WRITE, ACC_MKNOD)
350  *
351  * It is considered a partial match if an exception's range is found to
352  * contain *any* of the devices specified by provided parameters. This is
353  * used to make sure no extra access is being granted that is forbidden by
354  * any of the exception list.
355  *
356  * Return: true in case the provided range mat matches an exception completely
357  */
358 static bool match_exception_partial(struct list_head *exceptions, short type,
359                                     u32 major, u32 minor, short access)
360 {
361         struct dev_exception_item *ex;
362 
363         list_for_each_entry_rcu(ex, exceptions, list) {
364                 if ((type & DEV_BLOCK) && !(ex->type & DEV_BLOCK))
365                         continue;
366                 if ((type & DEV_CHAR) && !(ex->type & DEV_CHAR))
367                         continue;
368                 /*
369                  * We must be sure that both the exception and the provided
370                  * range aren't masking all devices
371                  */
372                 if (ex->major != ~0 && major != ~0 && ex->major != major)
373                         continue;
374                 if (ex->minor != ~0 && minor != ~0 && ex->minor != minor)
375                         continue;
376                 /*
377                  * In order to make sure the provided range isn't matching
378                  * an exception, all its access bits shouldn't match the
379                  * exception's access bits
380                  */
381                 if (!(access & ex->access))
382                         continue;
383                 return true;
384         }
385         return false;
386 }
387 
388 /**
389  * verify_new_ex - verifies if a new exception is allowed by parent cgroup's permissions
390  * @dev_cgroup: dev cgroup to be tested against
391  * @refex: new exception
392  * @behavior: behavior of the exception's dev_cgroup
393  *
394  * This is used to make sure a child cgroup won't have more privileges
395  * than its parent
396  */
397 static bool verify_new_ex(struct dev_cgroup *dev_cgroup,
398                           struct dev_exception_item *refex,
399                           enum devcg_behavior behavior)
400 {
401         bool match = false;
402 
403         RCU_LOCKDEP_WARN(!rcu_read_lock_held() &&
404                          !lockdep_is_held(&devcgroup_mutex),
405                          "device_cgroup:verify_new_ex called without proper synchronization");
406 
407         if (dev_cgroup->behavior == DEVCG_DEFAULT_ALLOW) {
408                 if (behavior == DEVCG_DEFAULT_ALLOW) {
409                         /*
410                          * new exception in the child doesn't matter, only
411                          * adding extra restrictions
412                          */ 
413                         return true;
414                 } else {
415                         /*
416                          * new exception in the child will add more devices
417                          * that can be acessed, so it can't match any of
418                          * parent's exceptions, even slightly
419                          */ 
420                         match = match_exception_partial(&dev_cgroup->exceptions,
421                                                         refex->type,
422                                                         refex->major,
423                                                         refex->minor,
424                                                         refex->access);
425 
426                         if (match)
427                                 return false;
428                         return true;
429                 }
430         } else {
431                 /*
432                  * Only behavior == DEVCG_DEFAULT_DENY allowed here, therefore
433                  * the new exception will add access to more devices and must
434                  * be contained completely in an parent's exception to be
435                  * allowed
436                  */
437                 match = match_exception(&dev_cgroup->exceptions, refex->type,
438                                         refex->major, refex->minor,
439                                         refex->access);
440 
441                 if (match)
442                         /* parent has an exception that matches the proposed */
443                         return true;
444                 else
445                         return false;
446         }
447         return false;
448 }
449 
450 /*
451  * parent_has_perm:
452  * when adding a new allow rule to a device exception list, the rule
453  * must be allowed in the parent device
454  */
455 static int parent_has_perm(struct dev_cgroup *childcg,
456                                   struct dev_exception_item *ex)
457 {
458         struct dev_cgroup *parent = css_to_devcgroup(childcg->css.parent);
459 
460         if (!parent)
461                 return 1;
462         return verify_new_ex(parent, ex, childcg->behavior);
463 }
464 
465 /**
466  * parent_allows_removal - verify if it's ok to remove an exception
467  * @childcg: child cgroup from where the exception will be removed
468  * @ex: exception being removed
469  *
470  * When removing an exception in cgroups with default ALLOW policy, it must
471  * be checked if removing it will give the child cgroup more access than the
472  * parent.
473  *
474  * Return: true if it's ok to remove exception, false otherwise
475  */
476 static bool parent_allows_removal(struct dev_cgroup *childcg,
477                                   struct dev_exception_item *ex)
478 {
479         struct dev_cgroup *parent = css_to_devcgroup(childcg->css.parent);
480 
481         if (!parent)
482                 return true;
483 
484         /* It's always allowed to remove access to devices */
485         if (childcg->behavior == DEVCG_DEFAULT_DENY)
486                 return true;
487 
488         /*
489          * Make sure you're not removing part or a whole exception existing in
490          * the parent cgroup
491          */
492         return !match_exception_partial(&parent->exceptions, ex->type,
493                                         ex->major, ex->minor, ex->access);
494 }
495 
496 /**
497  * may_allow_all - checks if it's possible to change the behavior to
498  *                 allow based on parent's rules.
499  * @parent: device cgroup's parent
500  * returns: != 0 in case it's allowed, 0 otherwise
501  */
502 static inline int may_allow_all(struct dev_cgroup *parent)
503 {
504         if (!parent)
505                 return 1;
506         return parent->behavior == DEVCG_DEFAULT_ALLOW;
507 }
508 
509 /**
510  * revalidate_active_exceptions - walks through the active exception list and
511  *                                revalidates the exceptions based on parent's
512  *                                behavior and exceptions. The exceptions that
513  *                                are no longer valid will be removed.
514  *                                Called with devcgroup_mutex held.
515  * @devcg: cgroup which exceptions will be checked
516  *
517  * This is one of the three key functions for hierarchy implementation.
518  * This function is responsible for re-evaluating all the cgroup's active
519  * exceptions due to a parent's exception change.
520  * Refer to Documentation/cgroups/devices.txt for more details.
521  */
522 static void revalidate_active_exceptions(struct dev_cgroup *devcg)
523 {
524         struct dev_exception_item *ex;
525         struct list_head *this, *tmp;
526 
527         list_for_each_safe(this, tmp, &devcg->exceptions) {
528                 ex = container_of(this, struct dev_exception_item, list);
529                 if (!parent_has_perm(devcg, ex))
530                         dev_exception_rm(devcg, ex);
531         }
532 }
533 
534 /**
535  * propagate_exception - propagates a new exception to the children
536  * @devcg_root: device cgroup that added a new exception
537  * @ex: new exception to be propagated
538  *
539  * returns: 0 in case of success, != 0 in case of error
540  */
541 static int propagate_exception(struct dev_cgroup *devcg_root,
542                                struct dev_exception_item *ex)
543 {
544         struct cgroup_subsys_state *pos;
545         int rc = 0;
546 
547         rcu_read_lock();
548 
549         css_for_each_descendant_pre(pos, &devcg_root->css) {
550                 struct dev_cgroup *devcg = css_to_devcgroup(pos);
551 
552                 /*
553                  * Because devcgroup_mutex is held, no devcg will become
554                  * online or offline during the tree walk (see on/offline
555                  * methods), and online ones are safe to access outside RCU
556                  * read lock without bumping refcnt.
557                  */
558                 if (pos == &devcg_root->css || !is_devcg_online(devcg))
559                         continue;
560 
561                 rcu_read_unlock();
562 
563                 /*
564                  * in case both root's behavior and devcg is allow, a new
565                  * restriction means adding to the exception list
566                  */
567                 if (devcg_root->behavior == DEVCG_DEFAULT_ALLOW &&
568                     devcg->behavior == DEVCG_DEFAULT_ALLOW) {
569                         rc = dev_exception_add(devcg, ex);
570                         if (rc)
571                                 break;
572                 } else {
573                         /*
574                          * in the other possible cases:
575                          * root's behavior: allow, devcg's: deny
576                          * root's behavior: deny, devcg's: deny
577                          * the exception will be removed
578                          */
579                         dev_exception_rm(devcg, ex);
580                 }
581                 revalidate_active_exceptions(devcg);
582 
583                 rcu_read_lock();
584         }
585 
586         rcu_read_unlock();
587         return rc;
588 }
589 
590 /*
591  * Modify the exception list using allow/deny rules.
592  * CAP_SYS_ADMIN is needed for this.  It's at least separate from CAP_MKNOD
593  * so we can give a container CAP_MKNOD to let it create devices but not
594  * modify the exception list.
595  * It seems likely we'll want to add a CAP_CONTAINER capability to allow
596  * us to also grant CAP_SYS_ADMIN to containers without giving away the
597  * device exception list controls, but for now we'll stick with CAP_SYS_ADMIN
598  *
599  * Taking rules away is always allowed (given CAP_SYS_ADMIN).  Granting
600  * new access is only allowed if you're in the top-level cgroup, or your
601  * parent cgroup has the access you're asking for.
602  */
603 static int devcgroup_update_access(struct dev_cgroup *devcgroup,
604                                    int filetype, char *buffer)
605 {
606         const char *b;
607         char temp[12];          /* 11 + 1 characters needed for a u32 */
608         int count, rc = 0;
609         struct dev_exception_item ex;
610         struct dev_cgroup *parent = css_to_devcgroup(devcgroup->css.parent);
611 
612         if (!capable(CAP_SYS_ADMIN))
613                 return -EPERM;
614 
615         memset(&ex, 0, sizeof(ex));
616         b = buffer;
617 
618         switch (*b) {
619         case 'a':
620                 switch (filetype) {
621                 case DEVCG_ALLOW:
622                         if (css_has_online_children(&devcgroup->css))
623                                 return -EINVAL;
624 
625                         if (!may_allow_all(parent))
626                                 return -EPERM;
627                         dev_exception_clean(devcgroup);
628                         devcgroup->behavior = DEVCG_DEFAULT_ALLOW;
629                         if (!parent)
630                                 break;
631 
632                         rc = dev_exceptions_copy(&devcgroup->exceptions,
633                                                  &parent->exceptions);
634                         if (rc)
635                                 return rc;
636                         break;
637                 case DEVCG_DENY:
638                         if (css_has_online_children(&devcgroup->css))
639                                 return -EINVAL;
640 
641                         dev_exception_clean(devcgroup);
642                         devcgroup->behavior = DEVCG_DEFAULT_DENY;
643                         break;
644                 default:
645                         return -EINVAL;
646                 }
647                 return 0;
648         case 'b':
649                 ex.type = DEV_BLOCK;
650                 break;
651         case 'c':
652                 ex.type = DEV_CHAR;
653                 break;
654         default:
655                 return -EINVAL;
656         }
657         b++;
658         if (!isspace(*b))
659                 return -EINVAL;
660         b++;
661         if (*b == '*') {
662                 ex.major = ~0;
663                 b++;
664         } else if (isdigit(*b)) {
665                 memset(temp, 0, sizeof(temp));
666                 for (count = 0; count < sizeof(temp) - 1; count++) {
667                         temp[count] = *b;
668                         b++;
669                         if (!isdigit(*b))
670                                 break;
671                 }
672                 rc = kstrtou32(temp, 10, &ex.major);
673                 if (rc)
674                         return -EINVAL;
675         } else {
676                 return -EINVAL;
677         }
678         if (*b != ':')
679                 return -EINVAL;
680         b++;
681 
682         /* read minor */
683         if (*b == '*') {
684                 ex.minor = ~0;
685                 b++;
686         } else if (isdigit(*b)) {
687                 memset(temp, 0, sizeof(temp));
688                 for (count = 0; count < sizeof(temp) - 1; count++) {
689                         temp[count] = *b;
690                         b++;
691                         if (!isdigit(*b))
692                                 break;
693                 }
694                 rc = kstrtou32(temp, 10, &ex.minor);
695                 if (rc)
696                         return -EINVAL;
697         } else {
698                 return -EINVAL;
699         }
700         if (!isspace(*b))
701                 return -EINVAL;
702         for (b++, count = 0; count < 3; count++, b++) {
703                 switch (*b) {
704                 case 'r':
705                         ex.access |= ACC_READ;
706                         break;
707                 case 'w':
708                         ex.access |= ACC_WRITE;
709                         break;
710                 case 'm':
711                         ex.access |= ACC_MKNOD;
712                         break;
713                 case '\n':
714                 case '\0':
715                         count = 3;
716                         break;
717                 default:
718                         return -EINVAL;
719                 }
720         }
721 
722         switch (filetype) {
723         case DEVCG_ALLOW:
724                 /*
725                  * If the default policy is to allow by default, try to remove
726                  * an matching exception instead. And be silent about it: we
727                  * don't want to break compatibility
728                  */
729                 if (devcgroup->behavior == DEVCG_DEFAULT_ALLOW) {
730                         /* Check if the parent allows removing it first */
731                         if (!parent_allows_removal(devcgroup, &ex))
732                                 return -EPERM;
733                         dev_exception_rm(devcgroup, &ex);
734                         break;
735                 }
736 
737                 if (!parent_has_perm(devcgroup, &ex))
738                         return -EPERM;
739                 rc = dev_exception_add(devcgroup, &ex);
740                 break;
741         case DEVCG_DENY:
742                 /*
743                  * If the default policy is to deny by default, try to remove
744                  * an matching exception instead. And be silent about it: we
745                  * don't want to break compatibility
746                  */
747                 if (devcgroup->behavior == DEVCG_DEFAULT_DENY)
748                         dev_exception_rm(devcgroup, &ex);
749                 else
750                         rc = dev_exception_add(devcgroup, &ex);
751 
752                 if (rc)
753                         break;
754                 /* we only propagate new restrictions */
755                 rc = propagate_exception(devcgroup, &ex);
756                 break;
757         default:
758                 rc = -EINVAL;
759         }
760         return rc;
761 }
762 
763 static ssize_t devcgroup_access_write(struct kernfs_open_file *of,
764                                       char *buf, size_t nbytes, loff_t off)
765 {
766         int retval;
767 
768         mutex_lock(&devcgroup_mutex);
769         retval = devcgroup_update_access(css_to_devcgroup(of_css(of)),
770                                          of_cft(of)->private, strstrip(buf));
771         mutex_unlock(&devcgroup_mutex);
772         return retval ?: nbytes;
773 }
774 
775 static struct cftype dev_cgroup_files[] = {
776         {
777                 .name = "allow",
778                 .write = devcgroup_access_write,
779                 .private = DEVCG_ALLOW,
780         },
781         {
782                 .name = "deny",
783                 .write = devcgroup_access_write,
784                 .private = DEVCG_DENY,
785         },
786         {
787                 .name = "list",
788                 .seq_show = devcgroup_seq_show,
789                 .private = DEVCG_LIST,
790         },
791         { }     /* terminate */
792 };
793 
794 struct cgroup_subsys devices_cgrp_subsys = {
795         .css_alloc = devcgroup_css_alloc,
796         .css_free = devcgroup_css_free,
797         .css_online = devcgroup_online,
798         .css_offline = devcgroup_offline,
799         .legacy_cftypes = dev_cgroup_files,
800 };
801 
802 /**
803  * __devcgroup_check_permission - checks if an inode operation is permitted
804  * @dev_cgroup: the dev cgroup to be tested against
805  * @type: device type
806  * @major: device major number
807  * @minor: device minor number
808  * @access: combination of ACC_WRITE, ACC_READ and ACC_MKNOD
809  *
810  * returns 0 on success, -EPERM case the operation is not permitted
811  */
812 static int __devcgroup_check_permission(short type, u32 major, u32 minor,
813                                         short access)
814 {
815         struct dev_cgroup *dev_cgroup;
816         bool rc;
817 
818         rcu_read_lock();
819         dev_cgroup = task_devcgroup(current);
820         if (dev_cgroup->behavior == DEVCG_DEFAULT_ALLOW)
821                 /* Can't match any of the exceptions, even partially */
822                 rc = !match_exception_partial(&dev_cgroup->exceptions,
823                                               type, major, minor, access);
824         else
825                 /* Need to match completely one exception to be allowed */
826                 rc = match_exception(&dev_cgroup->exceptions, type, major,
827                                      minor, access);
828         rcu_read_unlock();
829 
830         if (!rc)
831                 return -EPERM;
832 
833         return 0;
834 }
835 
836 int __devcgroup_inode_permission(struct inode *inode, int mask)
837 {
838         short type, access = 0;
839 
840         if (S_ISBLK(inode->i_mode))
841                 type = DEV_BLOCK;
842         if (S_ISCHR(inode->i_mode))
843                 type = DEV_CHAR;
844         if (mask & MAY_WRITE)
845                 access |= ACC_WRITE;
846         if (mask & MAY_READ)
847                 access |= ACC_READ;
848 
849         return __devcgroup_check_permission(type, imajor(inode), iminor(inode),
850                         access);
851 }
852 
853 int devcgroup_inode_mknod(int mode, dev_t dev)
854 {
855         short type;
856 
857         if (!S_ISBLK(mode) && !S_ISCHR(mode))
858                 return 0;
859 
860         if (S_ISBLK(mode))
861                 type = DEV_BLOCK;
862         else
863                 type = DEV_CHAR;
864 
865         return __devcgroup_check_permission(type, MAJOR(dev), MINOR(dev),
866                         ACC_MKNOD);
867 
868 }
869 

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