xref: /openbmc/linux/security/smack/smack_access.c (revision d2999e1b)
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 == 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_known: a pointer to the subject's Smack label entry
115  * @object_label: a pointer to the object's Smack label
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_known, char *object_label,
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 	 * A star subject can't access any object.
135 	 */
136 	if (subject_known == &smack_known_star) {
137 		rc = -EACCES;
138 		goto out_audit;
139 	}
140 	/*
141 	 * An internet object can be accessed by any subject.
142 	 * Tasks cannot be assigned the internet label.
143 	 * An internet subject can access any object.
144 	 */
145 	if (object_label == smack_known_web.smk_known ||
146 	    subject_known == &smack_known_web)
147 		goto out_audit;
148 	/*
149 	 * A star object can be accessed by any subject.
150 	 */
151 	if (object_label == smack_known_star.smk_known)
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_known->smk_known == object_label)
158 		goto out_audit;
159 	/*
160 	 * A hat subject can read any object.
161 	 * A floor object can be read by any subject.
162 	 */
163 	if ((request & MAY_ANYREAD) == request) {
164 		if (object_label == smack_known_floor.smk_known)
165 			goto out_audit;
166 		if (subject_known == &smack_known_hat)
167 			goto out_audit;
168 	}
169 	/*
170 	 * Beyond here an explicit relationship is required.
171 	 * If the requested access is contained in the available
172 	 * access (e.g. read is included in readwrite) it's
173 	 * good. A negative response from smk_access_entry()
174 	 * indicates there is no entry for this pair.
175 	 */
176 	rcu_read_lock();
177 	may = smk_access_entry(subject_known->smk_known, object_label,
178 				&subject_known->smk_rules);
179 	rcu_read_unlock();
180 
181 	if (may > 0 && (request & may) == request)
182 		goto out_audit;
183 
184 	rc = -EACCES;
185 out_audit:
186 #ifdef CONFIG_AUDIT
187 	if (a)
188 		smack_log(subject_known->smk_known, object_label, request,
189 				rc, a);
190 #endif
191 	return rc;
192 }
193 
194 /**
195  * smk_tskacc - determine if a task has a specific access to an object
196  * @tsp: a pointer to the subject task
197  * @obj_label: a pointer to the object's Smack label
198  * @mode: the access requested, in "MAY" format
199  * @a : common audit data
200  *
201  * This function checks the subject task's label/object label pair
202  * in the access rule list and returns 0 if the access is permitted,
203  * non zero otherwise. It allows that the task may have the capability
204  * to override the rules.
205  */
206 int smk_tskacc(struct task_smack *subject, char *obj_label,
207 	       u32 mode, struct smk_audit_info *a)
208 {
209 	struct smack_known *skp = smk_of_task(subject);
210 	int may;
211 	int rc;
212 
213 	/*
214 	 * Check the global rule list
215 	 */
216 	rc = smk_access(skp, obj_label, mode, NULL);
217 	if (rc == 0) {
218 		/*
219 		 * If there is an entry in the task's rule list
220 		 * it can further restrict access.
221 		 */
222 		may = smk_access_entry(skp->smk_known, obj_label,
223 					&subject->smk_rules);
224 		if (may < 0)
225 			goto out_audit;
226 		if ((mode & may) == mode)
227 			goto out_audit;
228 		rc = -EACCES;
229 	}
230 
231 	/*
232 	 * Allow for priviliged to override policy.
233 	 */
234 	if (rc != 0 && smack_privileged(CAP_MAC_OVERRIDE))
235 		rc = 0;
236 
237 out_audit:
238 #ifdef CONFIG_AUDIT
239 	if (a)
240 		smack_log(skp->smk_known, obj_label, mode, rc, a);
241 #endif
242 	return rc;
243 }
244 
245 /**
246  * smk_curacc - determine if current has a specific access to an object
247  * @obj_label: a pointer to the object's Smack label
248  * @mode: the access requested, in "MAY" format
249  * @a : common audit data
250  *
251  * This function checks the current subject label/object label pair
252  * in the access rule list and returns 0 if the access is permitted,
253  * non zero otherwise. It allows that current may have the capability
254  * to override the rules.
255  */
256 int smk_curacc(char *obj_label, u32 mode, struct smk_audit_info *a)
257 {
258 	struct task_smack *tsp = current_security();
259 
260 	return smk_tskacc(tsp, obj_label, mode, a);
261 }
262 
263 #ifdef CONFIG_AUDIT
264 /**
265  * smack_str_from_perm : helper to transalate an int to a
266  * readable string
267  * @string : the string to fill
268  * @access : the int
269  *
270  */
271 static inline void smack_str_from_perm(char *string, int access)
272 {
273 	int i = 0;
274 
275 	if (access & MAY_READ)
276 		string[i++] = 'r';
277 	if (access & MAY_WRITE)
278 		string[i++] = 'w';
279 	if (access & MAY_EXEC)
280 		string[i++] = 'x';
281 	if (access & MAY_APPEND)
282 		string[i++] = 'a';
283 	if (access & MAY_TRANSMUTE)
284 		string[i++] = 't';
285 	if (access & MAY_LOCK)
286 		string[i++] = 'l';
287 	string[i] = '\0';
288 }
289 /**
290  * smack_log_callback - SMACK specific information
291  * will be called by generic audit code
292  * @ab : the audit_buffer
293  * @a  : audit_data
294  *
295  */
296 static void smack_log_callback(struct audit_buffer *ab, void *a)
297 {
298 	struct common_audit_data *ad = a;
299 	struct smack_audit_data *sad = ad->smack_audit_data;
300 	audit_log_format(ab, "lsm=SMACK fn=%s action=%s",
301 			 ad->smack_audit_data->function,
302 			 sad->result ? "denied" : "granted");
303 	audit_log_format(ab, " subject=");
304 	audit_log_untrustedstring(ab, sad->subject);
305 	audit_log_format(ab, " object=");
306 	audit_log_untrustedstring(ab, sad->object);
307 	if (sad->request[0] == '\0')
308 		audit_log_format(ab, " labels_differ");
309 	else
310 		audit_log_format(ab, " requested=%s", sad->request);
311 }
312 
313 /**
314  *  smack_log - Audit the granting or denial of permissions.
315  *  @subject_label : smack label of the requester
316  *  @object_label  : smack label of the object being accessed
317  *  @request: requested permissions
318  *  @result: result from smk_access
319  *  @a:  auxiliary audit data
320  *
321  * Audit the granting or denial of permissions in accordance
322  * with the policy.
323  */
324 void smack_log(char *subject_label, char *object_label, int request,
325 	       int result, struct smk_audit_info *ad)
326 {
327 	char request_buffer[SMK_NUM_ACCESS_TYPE + 1];
328 	struct smack_audit_data *sad;
329 	struct common_audit_data *a = &ad->a;
330 
331 	/* check if we have to log the current event */
332 	if (result != 0 && (log_policy & SMACK_AUDIT_DENIED) == 0)
333 		return;
334 	if (result == 0 && (log_policy & SMACK_AUDIT_ACCEPT) == 0)
335 		return;
336 
337 	sad = a->smack_audit_data;
338 
339 	if (sad->function == NULL)
340 		sad->function = "unknown";
341 
342 	/* end preparing the audit data */
343 	smack_str_from_perm(request_buffer, request);
344 	sad->subject = subject_label;
345 	sad->object  = object_label;
346 	sad->request = request_buffer;
347 	sad->result  = result;
348 
349 	common_lsm_audit(a, smack_log_callback, NULL);
350 }
351 #else /* #ifdef CONFIG_AUDIT */
352 void smack_log(char *subject_label, char *object_label, int request,
353                int result, struct smk_audit_info *ad)
354 {
355 }
356 #endif
357 
358 DEFINE_MUTEX(smack_known_lock);
359 
360 struct hlist_head smack_known_hash[SMACK_HASH_SLOTS];
361 
362 /**
363  * smk_insert_entry - insert a smack label into a hash map,
364  *
365  * this function must be called under smack_known_lock
366  */
367 void smk_insert_entry(struct smack_known *skp)
368 {
369 	unsigned int hash;
370 	struct hlist_head *head;
371 
372 	hash = full_name_hash(skp->smk_known, strlen(skp->smk_known));
373 	head = &smack_known_hash[hash & (SMACK_HASH_SLOTS - 1)];
374 
375 	hlist_add_head_rcu(&skp->smk_hashed, head);
376 	list_add_rcu(&skp->list, &smack_known_list);
377 }
378 
379 /**
380  * smk_find_entry - find a label on the list, return the list entry
381  * @string: a text string that might be a Smack label
382  *
383  * Returns a pointer to the entry in the label list that
384  * matches the passed string.
385  */
386 struct smack_known *smk_find_entry(const char *string)
387 {
388 	unsigned int hash;
389 	struct hlist_head *head;
390 	struct smack_known *skp;
391 
392 	hash = full_name_hash(string, strlen(string));
393 	head = &smack_known_hash[hash & (SMACK_HASH_SLOTS - 1)];
394 
395 	hlist_for_each_entry_rcu(skp, head, smk_hashed)
396 		if (strcmp(skp->smk_known, string) == 0)
397 			return skp;
398 
399 	return NULL;
400 }
401 
402 /**
403  * smk_parse_smack - parse smack label from a text string
404  * @string: a text string that might contain a Smack label
405  * @len: the maximum size, or zero if it is NULL terminated.
406  *
407  * Returns a pointer to the clean label, or NULL
408  */
409 char *smk_parse_smack(const char *string, int len)
410 {
411 	char *smack;
412 	int i;
413 
414 	if (len <= 0)
415 		len = strlen(string) + 1;
416 
417 	/*
418 	 * Reserve a leading '-' as an indicator that
419 	 * this isn't a label, but an option to interfaces
420 	 * including /smack/cipso and /smack/cipso2
421 	 */
422 	if (string[0] == '-')
423 		return NULL;
424 
425 	for (i = 0; i < len; i++)
426 		if (string[i] > '~' || string[i] <= ' ' || string[i] == '/' ||
427 		    string[i] == '"' || string[i] == '\\' || string[i] == '\'')
428 			break;
429 
430 	if (i == 0 || i >= SMK_LONGLABEL)
431 		return NULL;
432 
433 	smack = kzalloc(i + 1, GFP_KERNEL);
434 	if (smack != NULL) {
435 		strncpy(smack, string, i + 1);
436 		smack[i] = '\0';
437 	}
438 	return smack;
439 }
440 
441 /**
442  * smk_netlbl_mls - convert a catset to netlabel mls categories
443  * @catset: the Smack categories
444  * @sap: where to put the netlabel categories
445  *
446  * Allocates and fills attr.mls
447  * Returns 0 on success, error code on failure.
448  */
449 int smk_netlbl_mls(int level, char *catset, struct netlbl_lsm_secattr *sap,
450 			int len)
451 {
452 	unsigned char *cp;
453 	unsigned char m;
454 	int cat;
455 	int rc;
456 	int byte;
457 
458 	sap->flags |= NETLBL_SECATTR_MLS_CAT;
459 	sap->attr.mls.lvl = level;
460 	sap->attr.mls.cat = netlbl_secattr_catmap_alloc(GFP_ATOMIC);
461 	if (!sap->attr.mls.cat)
462 		return -ENOMEM;
463 	sap->attr.mls.cat->startbit = 0;
464 
465 	for (cat = 1, cp = catset, byte = 0; byte < len; cp++, byte++)
466 		for (m = 0x80; m != 0; m >>= 1, cat++) {
467 			if ((m & *cp) == 0)
468 				continue;
469 			rc = netlbl_secattr_catmap_setbit(sap->attr.mls.cat,
470 							  cat, GFP_ATOMIC);
471 			if (rc < 0) {
472 				netlbl_secattr_catmap_free(sap->attr.mls.cat);
473 				return rc;
474 			}
475 		}
476 
477 	return 0;
478 }
479 
480 /**
481  * smk_import_entry - import a label, return the list entry
482  * @string: a text string that might be a Smack label
483  * @len: the maximum size, or zero if it is NULL terminated.
484  *
485  * Returns a pointer to the entry in the label list that
486  * matches the passed string, adding it if necessary.
487  */
488 struct smack_known *smk_import_entry(const char *string, int len)
489 {
490 	struct smack_known *skp;
491 	char *smack;
492 	int slen;
493 	int rc;
494 
495 	smack = smk_parse_smack(string, len);
496 	if (smack == NULL)
497 		return NULL;
498 
499 	mutex_lock(&smack_known_lock);
500 
501 	skp = smk_find_entry(smack);
502 	if (skp != NULL)
503 		goto freeout;
504 
505 	skp = kzalloc(sizeof(*skp), GFP_KERNEL);
506 	if (skp == NULL)
507 		goto freeout;
508 
509 	skp->smk_known = smack;
510 	skp->smk_secid = smack_next_secid++;
511 	skp->smk_netlabel.domain = skp->smk_known;
512 	skp->smk_netlabel.flags =
513 		NETLBL_SECATTR_DOMAIN | NETLBL_SECATTR_MLS_LVL;
514 	/*
515 	 * If direct labeling works use it.
516 	 * Otherwise use mapped labeling.
517 	 */
518 	slen = strlen(smack);
519 	if (slen < SMK_CIPSOLEN)
520 		rc = smk_netlbl_mls(smack_cipso_direct, skp->smk_known,
521 			       &skp->smk_netlabel, slen);
522 	else
523 		rc = smk_netlbl_mls(smack_cipso_mapped, (char *)&skp->smk_secid,
524 			       &skp->smk_netlabel, sizeof(skp->smk_secid));
525 
526 	if (rc >= 0) {
527 		INIT_LIST_HEAD(&skp->smk_rules);
528 		mutex_init(&skp->smk_rules_lock);
529 		/*
530 		 * Make sure that the entry is actually
531 		 * filled before putting it on the list.
532 		 */
533 		smk_insert_entry(skp);
534 		goto unlockout;
535 	}
536 	/*
537 	 * smk_netlbl_mls failed.
538 	 */
539 	kfree(skp);
540 	skp = NULL;
541 freeout:
542 	kfree(smack);
543 unlockout:
544 	mutex_unlock(&smack_known_lock);
545 
546 	return skp;
547 }
548 
549 /**
550  * smk_import - import a smack label
551  * @string: a text string that might be a Smack label
552  * @len: the maximum size, or zero if it is NULL terminated.
553  *
554  * Returns a pointer to the label in the label list that
555  * matches the passed string, adding it if necessary.
556  */
557 char *smk_import(const char *string, int len)
558 {
559 	struct smack_known *skp;
560 
561 	/* labels cannot begin with a '-' */
562 	if (string[0] == '-')
563 		return NULL;
564 	skp = smk_import_entry(string, len);
565 	if (skp == NULL)
566 		return NULL;
567 	return skp->smk_known;
568 }
569 
570 /**
571  * smack_from_secid - find the Smack label associated with a secid
572  * @secid: an integer that might be associated with a Smack label
573  *
574  * Returns a pointer to the appropriate Smack label entry if there is one,
575  * otherwise a pointer to the invalid Smack label.
576  */
577 struct smack_known *smack_from_secid(const u32 secid)
578 {
579 	struct smack_known *skp;
580 
581 	rcu_read_lock();
582 	list_for_each_entry_rcu(skp, &smack_known_list, list) {
583 		if (skp->smk_secid == secid) {
584 			rcu_read_unlock();
585 			return skp;
586 		}
587 	}
588 
589 	/*
590 	 * If we got this far someone asked for the translation
591 	 * of a secid that is not on the list.
592 	 */
593 	rcu_read_unlock();
594 	return &smack_known_invalid;
595 }
596 
597 /**
598  * smack_to_secid - find the secid associated with a Smack label
599  * @smack: the Smack label
600  *
601  * Returns the appropriate secid if there is one,
602  * otherwise 0
603  */
604 u32 smack_to_secid(const char *smack)
605 {
606 	struct smack_known *skp = smk_find_entry(smack);
607 
608 	if (skp == NULL)
609 		return 0;
610 	return skp->smk_secid;
611 }
612