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Linux/security/smack/smack_access.c

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  1 /*
  2  * Copyright (C) 2007 Casey Schaufler <casey@schaufler-ca.com>
  3  *
  4  *      This program is free software; you can redistribute it and/or modify
  5  *      it under the terms of the GNU General Public License as published by
  6  *      the Free Software Foundation, version 2.
  7  *
  8  * Author:
  9  *      Casey Schaufler <casey@schaufler-ca.com>
 10  *
 11  */
 12 
 13 #include <linux/types.h>
 14 #include <linux/slab.h>
 15 #include <linux/fs.h>
 16 #include <linux/sched.h>
 17 #include "smack.h"
 18 
 19 struct smack_known smack_known_huh = {
 20         .smk_known      = "?",
 21         .smk_secid      = 2,
 22 };
 23 
 24 struct smack_known smack_known_hat = {
 25         .smk_known      = "^",
 26         .smk_secid      = 3,
 27 };
 28 
 29 struct smack_known smack_known_star = {
 30         .smk_known      = "*",
 31         .smk_secid      = 4,
 32 };
 33 
 34 struct smack_known smack_known_floor = {
 35         .smk_known      = "_",
 36         .smk_secid      = 5,
 37 };
 38 
 39 struct smack_known smack_known_invalid = {
 40         .smk_known      = "",
 41         .smk_secid      = 6,
 42 };
 43 
 44 struct smack_known smack_known_web = {
 45         .smk_known      = "@",
 46         .smk_secid      = 7,
 47 };
 48 
 49 LIST_HEAD(smack_known_list);
 50 
 51 /*
 52  * The initial value needs to be bigger than any of the
 53  * known values above.
 54  */
 55 static u32 smack_next_secid = 10;
 56 
 57 /*
 58  * what events do we log
 59  * can be overwritten at run-time by /smack/logging
 60  */
 61 int log_policy = SMACK_AUDIT_DENIED;
 62 
 63 /**
 64  * smk_access_entry - look up matching access rule
 65  * @subject_label: a pointer to the subject's Smack label
 66  * @object_label: a pointer to the object's Smack label
 67  * @rule_list: the list of rules to search
 68  *
 69  * This function looks up the subject/object pair in the
 70  * access rule list and returns the access mode. If no
 71  * entry is found returns -ENOENT.
 72  *
 73  * NOTE:
 74  *
 75  * Earlier versions of this function allowed for labels that
 76  * were not on the label list. This was done to allow for
 77  * labels to come over the network that had never been seen
 78  * before on this host. Unless the receiving socket has the
 79  * star label this will always result in a failure check. The
 80  * star labeled socket case is now handled in the networking
 81  * hooks so there is no case where the label is not on the
 82  * label list. Checking to see if the address of two labels
 83  * is the same is now a reliable test.
 84  *
 85  * Do the object check first because that is more
 86  * likely to differ.
 87  *
 88  * Allowing write access implies allowing locking.
 89  */
 90 int smk_access_entry(char *subject_label, char *object_label,
 91                         struct list_head *rule_list)
 92 {
 93         int may = -ENOENT;
 94         struct smack_rule *srp;
 95 
 96         list_for_each_entry_rcu(srp, rule_list, list) {
 97                 if (srp->smk_object->smk_known == object_label &&
 98                     srp->smk_subject->smk_known == subject_label) {
 99                         may = srp->smk_access;
100                         break;
101                 }
102         }
103 
104         /*
105          * MAY_WRITE implies MAY_LOCK.
106          */
107         if ((may & MAY_WRITE) == MAY_WRITE)
108                 may |= MAY_LOCK;
109         return may;
110 }
111 
112 /**
113  * smk_access - determine if a subject has a specific access to an object
114  * @subject: a pointer to the subject's Smack label entry
115  * @object: a pointer to the object's Smack label entry
116  * @request: the access requested, in "MAY" format
117  * @a : a pointer to the audit data
118  *
119  * This function looks up the subject/object pair in the
120  * access rule list and returns 0 if the access is permitted,
121  * non zero otherwise.
122  *
123  * Smack labels are shared on smack_list
124  */
125 int smk_access(struct smack_known *subject, struct smack_known *object,
126                int request, struct smk_audit_info *a)
127 {
128         int may = MAY_NOT;
129         int rc = 0;
130 
131         /*
132          * Hardcoded comparisons.
133          */
134         /*
135          * A star subject can't access any object.
136          */
137         if (subject == &smack_known_star) {
138                 rc = -EACCES;
139                 goto out_audit;
140         }
141         /*
142          * An internet object can be accessed by any subject.
143          * Tasks cannot be assigned the internet label.
144          * An internet subject can access any object.
145          */
146         if (object == &smack_known_web || subject == &smack_known_web)
147                 goto out_audit;
148         /*
149          * A star object can be accessed by any subject.
150          */
151         if (object == &smack_known_star)
152                 goto out_audit;
153         /*
154          * An object can be accessed in any way by a subject
155          * with the same label.
156          */
157         if (subject->smk_known == object->smk_known)
158                 goto out_audit;
159         /*
160          * A hat subject can read or lock any object.
161          * A floor object can be read or locked by any subject.
162          */
163         if ((request & MAY_ANYREAD) == request ||
164             (request & MAY_LOCK) == request) {
165                 if (object == &smack_known_floor)
166                         goto out_audit;
167                 if (subject == &smack_known_hat)
168                         goto out_audit;
169         }
170         /*
171          * Beyond here an explicit relationship is required.
172          * If the requested access is contained in the available
173          * access (e.g. read is included in readwrite) it's
174          * good. A negative response from smk_access_entry()
175          * indicates there is no entry for this pair.
176          */
177         rcu_read_lock();
178         may = smk_access_entry(subject->smk_known, object->smk_known,
179                                &subject->smk_rules);
180         rcu_read_unlock();
181 
182         if (may <= 0 || (request & may) != request) {
183                 rc = -EACCES;
184                 goto out_audit;
185         }
186 #ifdef CONFIG_SECURITY_SMACK_BRINGUP
187         /*
188          * Return a positive value if using bringup mode.
189          * This allows the hooks to identify checks that
190          * succeed because of "b" rules.
191          */
192         if (may & MAY_BRINGUP)
193                 rc = SMACK_BRINGUP_ALLOW;
194 #endif
195 
196 out_audit:
197 
198 #ifdef CONFIG_SECURITY_SMACK_BRINGUP
199         if (rc < 0) {
200                 if (object == smack_unconfined)
201                         rc = SMACK_UNCONFINED_OBJECT;
202                 if (subject == smack_unconfined)
203                         rc = SMACK_UNCONFINED_SUBJECT;
204         }
205 #endif
206 
207 #ifdef CONFIG_AUDIT
208         if (a)
209                 smack_log(subject->smk_known, object->smk_known,
210                           request, rc, a);
211 #endif
212 
213         return rc;
214 }
215 
216 /**
217  * smk_tskacc - determine if a task has a specific access to an object
218  * @tsp: a pointer to the subject's task
219  * @obj_known: a pointer to the object's label entry
220  * @mode: the access requested, in "MAY" format
221  * @a : common audit data
222  *
223  * This function checks the subject task's label/object label pair
224  * in the access rule list and returns 0 if the access is permitted,
225  * non zero otherwise. It allows that the task may have the capability
226  * to override the rules.
227  */
228 int smk_tskacc(struct task_smack *tsp, struct smack_known *obj_known,
229                u32 mode, struct smk_audit_info *a)
230 {
231         struct smack_known *sbj_known = smk_of_task(tsp);
232         int may;
233         int rc;
234 
235         /*
236          * Check the global rule list
237          */
238         rc = smk_access(sbj_known, obj_known, mode, NULL);
239         if (rc >= 0) {
240                 /*
241                  * If there is an entry in the task's rule list
242                  * it can further restrict access.
243                  */
244                 may = smk_access_entry(sbj_known->smk_known,
245                                        obj_known->smk_known,
246                                        &tsp->smk_rules);
247                 if (may < 0)
248                         goto out_audit;
249                 if ((mode & may) == mode)
250                         goto out_audit;
251                 rc = -EACCES;
252         }
253 
254         /*
255          * Allow for priviliged to override policy.
256          */
257         if (rc != 0 && smack_privileged(CAP_MAC_OVERRIDE))
258                 rc = 0;
259 
260 out_audit:
261 #ifdef CONFIG_AUDIT
262         if (a)
263                 smack_log(sbj_known->smk_known, obj_known->smk_known,
264                           mode, rc, a);
265 #endif
266         return rc;
267 }
268 
269 /**
270  * smk_curacc - determine if current has a specific access to an object
271  * @obj_known: a pointer to the object's Smack label entry
272  * @mode: the access requested, in "MAY" format
273  * @a : common audit data
274  *
275  * This function checks the current subject label/object label pair
276  * in the access rule list and returns 0 if the access is permitted,
277  * non zero otherwise. It allows that current may have the capability
278  * to override the rules.
279  */
280 int smk_curacc(struct smack_known *obj_known,
281                u32 mode, struct smk_audit_info *a)
282 {
283         struct task_smack *tsp = current_security();
284 
285         return smk_tskacc(tsp, obj_known, mode, a);
286 }
287 
288 #ifdef CONFIG_AUDIT
289 /**
290  * smack_str_from_perm : helper to transalate an int to a
291  * readable string
292  * @string : the string to fill
293  * @access : the int
294  *
295  */
296 static inline void smack_str_from_perm(char *string, int access)
297 {
298         int i = 0;
299 
300         if (access & MAY_READ)
301                 string[i++] = 'r';
302         if (access & MAY_WRITE)
303                 string[i++] = 'w';
304         if (access & MAY_EXEC)
305                 string[i++] = 'x';
306         if (access & MAY_APPEND)
307                 string[i++] = 'a';
308         if (access & MAY_TRANSMUTE)
309                 string[i++] = 't';
310         if (access & MAY_LOCK)
311                 string[i++] = 'l';
312         string[i] = '\0';
313 }
314 /**
315  * smack_log_callback - SMACK specific information
316  * will be called by generic audit code
317  * @ab : the audit_buffer
318  * @a  : audit_data
319  *
320  */
321 static void smack_log_callback(struct audit_buffer *ab, void *a)
322 {
323         struct common_audit_data *ad = a;
324         struct smack_audit_data *sad = ad->smack_audit_data;
325         audit_log_format(ab, "lsm=SMACK fn=%s action=%s",
326                          ad->smack_audit_data->function,
327                          sad->result ? "denied" : "granted");
328         audit_log_format(ab, " subject=");
329         audit_log_untrustedstring(ab, sad->subject);
330         audit_log_format(ab, " object=");
331         audit_log_untrustedstring(ab, sad->object);
332         if (sad->request[0] == '\0')
333                 audit_log_format(ab, " labels_differ");
334         else
335                 audit_log_format(ab, " requested=%s", sad->request);
336 }
337 
338 /**
339  *  smack_log - Audit the granting or denial of permissions.
340  *  @subject_label : smack label of the requester
341  *  @object_label  : smack label of the object being accessed
342  *  @request: requested permissions
343  *  @result: result from smk_access
344  *  @a:  auxiliary audit data
345  *
346  * Audit the granting or denial of permissions in accordance
347  * with the policy.
348  */
349 void smack_log(char *subject_label, char *object_label, int request,
350                int result, struct smk_audit_info *ad)
351 {
352 #ifdef CONFIG_SECURITY_SMACK_BRINGUP
353         char request_buffer[SMK_NUM_ACCESS_TYPE + 5];
354 #else
355         char request_buffer[SMK_NUM_ACCESS_TYPE + 1];
356 #endif
357         struct smack_audit_data *sad;
358         struct common_audit_data *a = &ad->a;
359 
360         /* check if we have to log the current event */
361         if (result < 0 && (log_policy & SMACK_AUDIT_DENIED) == 0)
362                 return;
363         if (result == 0 && (log_policy & SMACK_AUDIT_ACCEPT) == 0)
364                 return;
365 
366         sad = a->smack_audit_data;
367 
368         if (sad->function == NULL)
369                 sad->function = "unknown";
370 
371         /* end preparing the audit data */
372         smack_str_from_perm(request_buffer, request);
373         sad->subject = subject_label;
374         sad->object  = object_label;
375 #ifdef CONFIG_SECURITY_SMACK_BRINGUP
376         /*
377          * The result may be positive in bringup mode.
378          * A positive result is an allow, but not for normal reasons.
379          * Mark it as successful, but don't filter it out even if
380          * the logging policy says to do so.
381          */
382         if (result == SMACK_UNCONFINED_SUBJECT)
383                 strcat(request_buffer, "(US)");
384         else if (result == SMACK_UNCONFINED_OBJECT)
385                 strcat(request_buffer, "(UO)");
386 
387         if (result > 0)
388                 result = 0;
389 #endif
390         sad->request = request_buffer;
391         sad->result  = result;
392 
393         common_lsm_audit(a, smack_log_callback, NULL);
394 }
395 #else /* #ifdef CONFIG_AUDIT */
396 void smack_log(char *subject_label, char *object_label, int request,
397                int result, struct smk_audit_info *ad)
398 {
399 }
400 #endif
401 
402 DEFINE_MUTEX(smack_known_lock);
403 
404 struct hlist_head smack_known_hash[SMACK_HASH_SLOTS];
405 
406 /**
407  * smk_insert_entry - insert a smack label into a hash map,
408  *
409  * this function must be called under smack_known_lock
410  */
411 void smk_insert_entry(struct smack_known *skp)
412 {
413         unsigned int hash;
414         struct hlist_head *head;
415 
416         hash = full_name_hash(NULL, skp->smk_known, strlen(skp->smk_known));
417         head = &smack_known_hash[hash & (SMACK_HASH_SLOTS - 1)];
418 
419         hlist_add_head_rcu(&skp->smk_hashed, head);
420         list_add_rcu(&skp->list, &smack_known_list);
421 }
422 
423 /**
424  * smk_find_entry - find a label on the list, return the list entry
425  * @string: a text string that might be a Smack label
426  *
427  * Returns a pointer to the entry in the label list that
428  * matches the passed string or NULL if not found.
429  */
430 struct smack_known *smk_find_entry(const char *string)
431 {
432         unsigned int hash;
433         struct hlist_head *head;
434         struct smack_known *skp;
435 
436         hash = full_name_hash(NULL, string, strlen(string));
437         head = &smack_known_hash[hash & (SMACK_HASH_SLOTS - 1)];
438 
439         hlist_for_each_entry_rcu(skp, head, smk_hashed)
440                 if (strcmp(skp->smk_known, string) == 0)
441                         return skp;
442 
443         return NULL;
444 }
445 
446 /**
447  * smk_parse_smack - parse smack label from a text string
448  * @string: a text string that might contain a Smack label
449  * @len: the maximum size, or zero if it is NULL terminated.
450  *
451  * Returns a pointer to the clean label or an error code.
452  */
453 char *smk_parse_smack(const char *string, int len)
454 {
455         char *smack;
456         int i;
457 
458         if (len <= 0)
459                 len = strlen(string) + 1;
460 
461         /*
462          * Reserve a leading '-' as an indicator that
463          * this isn't a label, but an option to interfaces
464          * including /smack/cipso and /smack/cipso2
465          */
466         if (string[0] == '-')
467                 return ERR_PTR(-EINVAL);
468 
469         for (i = 0; i < len; i++)
470                 if (string[i] > '~' || string[i] <= ' ' || string[i] == '/' ||
471                     string[i] == '"' || string[i] == '\\' || string[i] == '\'')
472                         break;
473 
474         if (i == 0 || i >= SMK_LONGLABEL)
475                 return ERR_PTR(-EINVAL);
476 
477         smack = kzalloc(i + 1, GFP_KERNEL);
478         if (smack == NULL)
479                 return ERR_PTR(-ENOMEM);
480 
481         strncpy(smack, string, i);
482 
483         return smack;
484 }
485 
486 /**
487  * smk_netlbl_mls - convert a catset to netlabel mls categories
488  * @catset: the Smack categories
489  * @sap: where to put the netlabel categories
490  *
491  * Allocates and fills attr.mls
492  * Returns 0 on success, error code on failure.
493  */
494 int smk_netlbl_mls(int level, char *catset, struct netlbl_lsm_secattr *sap,
495                         int len)
496 {
497         unsigned char *cp;
498         unsigned char m;
499         int cat;
500         int rc;
501         int byte;
502 
503         sap->flags |= NETLBL_SECATTR_MLS_CAT;
504         sap->attr.mls.lvl = level;
505         sap->attr.mls.cat = NULL;
506 
507         for (cat = 1, cp = catset, byte = 0; byte < len; cp++, byte++)
508                 for (m = 0x80; m != 0; m >>= 1, cat++) {
509                         if ((m & *cp) == 0)
510                                 continue;
511                         rc = netlbl_catmap_setbit(&sap->attr.mls.cat,
512                                                   cat, GFP_ATOMIC);
513                         if (rc < 0) {
514                                 netlbl_catmap_free(sap->attr.mls.cat);
515                                 return rc;
516                         }
517                 }
518 
519         return 0;
520 }
521 
522 /**
523  * smk_import_entry - import a label, return the list entry
524  * @string: a text string that might be a Smack label
525  * @len: the maximum size, or zero if it is NULL terminated.
526  *
527  * Returns a pointer to the entry in the label list that
528  * matches the passed string, adding it if necessary,
529  * or an error code.
530  */
531 struct smack_known *smk_import_entry(const char *string, int len)
532 {
533         struct smack_known *skp;
534         char *smack;
535         int slen;
536         int rc;
537 
538         smack = smk_parse_smack(string, len);
539         if (IS_ERR(smack))
540                 return ERR_CAST(smack);
541 
542         mutex_lock(&smack_known_lock);
543 
544         skp = smk_find_entry(smack);
545         if (skp != NULL)
546                 goto freeout;
547 
548         skp = kzalloc(sizeof(*skp), GFP_KERNEL);
549         if (skp == NULL) {
550                 skp = ERR_PTR(-ENOMEM);
551                 goto freeout;
552         }
553 
554         skp->smk_known = smack;
555         skp->smk_secid = smack_next_secid++;
556         skp->smk_netlabel.domain = skp->smk_known;
557         skp->smk_netlabel.flags =
558                 NETLBL_SECATTR_DOMAIN | NETLBL_SECATTR_MLS_LVL;
559         /*
560          * If direct labeling works use it.
561          * Otherwise use mapped labeling.
562          */
563         slen = strlen(smack);
564         if (slen < SMK_CIPSOLEN)
565                 rc = smk_netlbl_mls(smack_cipso_direct, skp->smk_known,
566                                &skp->smk_netlabel, slen);
567         else
568                 rc = smk_netlbl_mls(smack_cipso_mapped, (char *)&skp->smk_secid,
569                                &skp->smk_netlabel, sizeof(skp->smk_secid));
570 
571         if (rc >= 0) {
572                 INIT_LIST_HEAD(&skp->smk_rules);
573                 mutex_init(&skp->smk_rules_lock);
574                 /*
575                  * Make sure that the entry is actually
576                  * filled before putting it on the list.
577                  */
578                 smk_insert_entry(skp);
579                 goto unlockout;
580         }
581         /*
582          * smk_netlbl_mls failed.
583          */
584         kfree(skp);
585         skp = ERR_PTR(rc);
586 freeout:
587         kfree(smack);
588 unlockout:
589         mutex_unlock(&smack_known_lock);
590 
591         return skp;
592 }
593 
594 /**
595  * smack_from_secid - find the Smack label associated with a secid
596  * @secid: an integer that might be associated with a Smack label
597  *
598  * Returns a pointer to the appropriate Smack label entry if there is one,
599  * otherwise a pointer to the invalid Smack label.
600  */
601 struct smack_known *smack_from_secid(const u32 secid)
602 {
603         struct smack_known *skp;
604 
605         rcu_read_lock();
606         list_for_each_entry_rcu(skp, &smack_known_list, list) {
607                 if (skp->smk_secid == secid) {
608                         rcu_read_unlock();
609                         return skp;
610                 }
611         }
612 
613         /*
614          * If we got this far someone asked for the translation
615          * of a secid that is not on the list.
616          */
617         rcu_read_unlock();
618         return &smack_known_invalid;
619 }
620 
621 /*
622  * Unless a process is running with one of these labels
623  * even having CAP_MAC_OVERRIDE isn't enough to grant
624  * privilege to violate MAC policy. If no labels are
625  * designated (the empty list case) capabilities apply to
626  * everyone.
627  */
628 LIST_HEAD(smack_onlycap_list);
629 DEFINE_MUTEX(smack_onlycap_lock);
630 
631 /*
632  * Is the task privileged and allowed to be privileged
633  * by the onlycap rule.
634  *
635  * Returns 1 if the task is allowed to be privileged, 0 if it's not.
636  */
637 int smack_privileged(int cap)
638 {
639         struct smack_known *skp = smk_of_current();
640         struct smack_known_list_elem *sklep;
641 
642         /*
643          * All kernel tasks are privileged
644          */
645         if (unlikely(current->flags & PF_KTHREAD))
646                 return 1;
647 
648         if (!capable(cap))
649                 return 0;
650 
651         rcu_read_lock();
652         if (list_empty(&smack_onlycap_list)) {
653                 rcu_read_unlock();
654                 return 1;
655         }
656 
657         list_for_each_entry_rcu(sklep, &smack_onlycap_list, list) {
658                 if (sklep->smk_label == skp) {
659                         rcu_read_unlock();
660                         return 1;
661                 }
662         }
663         rcu_read_unlock();
664 
665         return 0;
666 }
667 

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