xref: /openbmc/linux/security/smack/smack_access.c (revision 0edbfea5)
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(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(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