1 /*
2 * Copyright (C) 2008 IBM Corporation
3 * Author: Mimi Zohar <zohar@us.ibm.com>
4 *
5 * This program is free software; you can redistribute it and/or modify
6 * it under the terms of the GNU General Public License as published by
7 * the Free Software Foundation, version 2 of the License.
8 *
9 * ima_policy.c
10 * - initialize default measure policy rules
11 *
12 */
13 #include <linux/module.h>
14 #include <linux/list.h>
15 #include <linux/security.h>
16 #include <linux/magic.h>
17 #include <linux/parser.h>
18 #include <linux/slab.h>
19
20 #include "ima.h"
21
22 /* flags definitions */
23 #define IMA_FUNC 0x0001
24 #define IMA_MASK 0x0002
25 #define IMA_FSMAGIC 0x0004
26 #define IMA_UID 0x0008
27
28 enum ima_action { UNKNOWN = -1, DONT_MEASURE = 0, MEASURE };
29
30 #define MAX_LSM_RULES 6
31 enum lsm_rule_types { LSM_OBJ_USER, LSM_OBJ_ROLE, LSM_OBJ_TYPE,
32 LSM_SUBJ_USER, LSM_SUBJ_ROLE, LSM_SUBJ_TYPE
33 };
34
35 struct ima_measure_rule_entry {
36 struct list_head list;
37 enum ima_action action;
38 unsigned int flags;
39 enum ima_hooks func;
40 int mask;
41 unsigned long fsmagic;
42 uid_t uid;
43 struct {
44 void *rule; /* LSM file metadata specific */
45 int type; /* audit type */
46 } lsm[MAX_LSM_RULES];
47 };
48
49 /*
50 * Without LSM specific knowledge, the default policy can only be
51 * written in terms of .action, .func, .mask, .fsmagic, and .uid
52 */
53
54 /*
55 * The minimum rule set to allow for full TCB coverage. Measures all files
56 * opened or mmap for exec and everything read by root. Dangerous because
57 * normal users can easily run the machine out of memory simply building
58 * and running executables.
59 */
60 static struct ima_measure_rule_entry default_rules[] = {
61 {.action = DONT_MEASURE,.fsmagic = PROC_SUPER_MAGIC,.flags = IMA_FSMAGIC},
62 {.action = DONT_MEASURE,.fsmagic = SYSFS_MAGIC,.flags = IMA_FSMAGIC},
63 {.action = DONT_MEASURE,.fsmagic = DEBUGFS_MAGIC,.flags = IMA_FSMAGIC},
64 {.action = DONT_MEASURE,.fsmagic = TMPFS_MAGIC,.flags = IMA_FSMAGIC},
65 {.action = DONT_MEASURE,.fsmagic = SECURITYFS_MAGIC,.flags = IMA_FSMAGIC},
66 {.action = DONT_MEASURE,.fsmagic = SELINUX_MAGIC,.flags = IMA_FSMAGIC},
67 {.action = MEASURE,.func = FILE_MMAP,.mask = MAY_EXEC,
68 .flags = IMA_FUNC | IMA_MASK},
69 {.action = MEASURE,.func = BPRM_CHECK,.mask = MAY_EXEC,
70 .flags = IMA_FUNC | IMA_MASK},
71 {.action = MEASURE,.func = FILE_CHECK,.mask = MAY_READ,.uid = 0,
72 .flags = IMA_FUNC | IMA_MASK | IMA_UID},
73 };
74
75 static LIST_HEAD(measure_default_rules);
76 static LIST_HEAD(measure_policy_rules);
77 static struct list_head *ima_measure;
78
79 static DEFINE_MUTEX(ima_measure_mutex);
80
81 static bool ima_use_tcb __initdata;
default_policy_setup(char * str)82 static int __init default_policy_setup(char *str)
83 {
84 ima_use_tcb = 1;
85 return 1;
86 }
87 __setup("ima_tcb", default_policy_setup);
88
89 /**
90 * ima_match_rules - determine whether an inode matches the measure rule.
91 * @rule: a pointer to a rule
92 * @inode: a pointer to an inode
93 * @func: LIM hook identifier
94 * @mask: requested action (MAY_READ | MAY_WRITE | MAY_APPEND | MAY_EXEC)
95 *
96 * Returns true on rule match, false on failure.
97 */
ima_match_rules(struct ima_measure_rule_entry * rule,struct inode * inode,enum ima_hooks func,int mask)98 static bool ima_match_rules(struct ima_measure_rule_entry *rule,
99 struct inode *inode, enum ima_hooks func, int mask)
100 {
101 struct task_struct *tsk = current;
102 int i;
103
104 if ((rule->flags & IMA_FUNC) && rule->func != func)
105 return false;
106 if ((rule->flags & IMA_MASK) && rule->mask != mask)
107 return false;
108 if ((rule->flags & IMA_FSMAGIC)
109 && rule->fsmagic != inode->i_sb->s_magic)
110 return false;
111 if ((rule->flags & IMA_UID) && rule->uid != tsk->cred->uid)
112 return false;
113 for (i = 0; i < MAX_LSM_RULES; i++) {
114 int rc = 0;
115 u32 osid, sid;
116
117 if (!rule->lsm[i].rule)
118 continue;
119
120 switch (i) {
121 case LSM_OBJ_USER:
122 case LSM_OBJ_ROLE:
123 case LSM_OBJ_TYPE:
124 security_inode_getsecid(inode, &osid);
125 rc = security_filter_rule_match(osid,
126 rule->lsm[i].type,
127 Audit_equal,
128 rule->lsm[i].rule,
129 NULL);
130 break;
131 case LSM_SUBJ_USER:
132 case LSM_SUBJ_ROLE:
133 case LSM_SUBJ_TYPE:
134 security_task_getsecid(tsk, &sid);
135 rc = security_filter_rule_match(sid,
136 rule->lsm[i].type,
137 Audit_equal,
138 rule->lsm[i].rule,
139 NULL);
140 default:
141 break;
142 }
143 if (!rc)
144 return false;
145 }
146 return true;
147 }
148
149 /**
150 * ima_match_policy - decision based on LSM and other conditions
151 * @inode: pointer to an inode for which the policy decision is being made
152 * @func: IMA hook identifier
153 * @mask: requested action (MAY_READ | MAY_WRITE | MAY_APPEND | MAY_EXEC)
154 *
155 * Measure decision based on func/mask/fsmagic and LSM(subj/obj/type)
156 * conditions.
157 *
158 * (There is no need for locking when walking the policy list,
159 * as elements in the list are never deleted, nor does the list
160 * change.)
161 */
ima_match_policy(struct inode * inode,enum ima_hooks func,int mask)162 int ima_match_policy(struct inode *inode, enum ima_hooks func, int mask)
163 {
164 struct ima_measure_rule_entry *entry;
165
166 list_for_each_entry(entry, ima_measure, list) {
167 bool rc;
168
169 rc = ima_match_rules(entry, inode, func, mask);
170 if (rc)
171 return entry->action;
172 }
173 return 0;
174 }
175
176 /**
177 * ima_init_policy - initialize the default measure rules.
178 *
179 * ima_measure points to either the measure_default_rules or the
180 * the new measure_policy_rules.
181 */
ima_init_policy(void)182 void __init ima_init_policy(void)
183 {
184 int i, entries;
185
186 /* if !ima_use_tcb set entries = 0 so we load NO default rules */
187 if (ima_use_tcb)
188 entries = ARRAY_SIZE(default_rules);
189 else
190 entries = 0;
191
192 for (i = 0; i < entries; i++)
193 list_add_tail(&default_rules[i].list, &measure_default_rules);
194 ima_measure = &measure_default_rules;
195 }
196
197 /**
198 * ima_update_policy - update default_rules with new measure rules
199 *
200 * Called on file .release to update the default rules with a complete new
201 * policy. Once updated, the policy is locked, no additional rules can be
202 * added to the policy.
203 */
ima_update_policy(void)204 void ima_update_policy(void)
205 {
206 const char *op = "policy_update";
207 const char *cause = "already exists";
208 int result = 1;
209 int audit_info = 0;
210
211 if (ima_measure == &measure_default_rules) {
212 ima_measure = &measure_policy_rules;
213 cause = "complete";
214 result = 0;
215 }
216 integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL,
217 NULL, op, cause, result, audit_info);
218 }
219
220 enum {
221 Opt_err = -1,
222 Opt_measure = 1, Opt_dont_measure,
223 Opt_obj_user, Opt_obj_role, Opt_obj_type,
224 Opt_subj_user, Opt_subj_role, Opt_subj_type,
225 Opt_func, Opt_mask, Opt_fsmagic, Opt_uid
226 };
227
228 static match_table_t policy_tokens = {
229 {Opt_measure, "measure"},
230 {Opt_dont_measure, "dont_measure"},
231 {Opt_obj_user, "obj_user=%s"},
232 {Opt_obj_role, "obj_role=%s"},
233 {Opt_obj_type, "obj_type=%s"},
234 {Opt_subj_user, "subj_user=%s"},
235 {Opt_subj_role, "subj_role=%s"},
236 {Opt_subj_type, "subj_type=%s"},
237 {Opt_func, "func=%s"},
238 {Opt_mask, "mask=%s"},
239 {Opt_fsmagic, "fsmagic=%s"},
240 {Opt_uid, "uid=%s"},
241 {Opt_err, NULL}
242 };
243
ima_lsm_rule_init(struct ima_measure_rule_entry * entry,char * args,int lsm_rule,int audit_type)244 static int ima_lsm_rule_init(struct ima_measure_rule_entry *entry,
245 char *args, int lsm_rule, int audit_type)
246 {
247 int result;
248
249 if (entry->lsm[lsm_rule].rule)
250 return -EINVAL;
251
252 entry->lsm[lsm_rule].type = audit_type;
253 result = security_filter_rule_init(entry->lsm[lsm_rule].type,
254 Audit_equal, args,
255 &entry->lsm[lsm_rule].rule);
256 if (!entry->lsm[lsm_rule].rule)
257 return -EINVAL;
258 return result;
259 }
260
ima_log_string(struct audit_buffer * ab,char * key,char * value)261 static void ima_log_string(struct audit_buffer *ab, char *key, char *value)
262 {
263 audit_log_format(ab, "%s=", key);
264 audit_log_untrustedstring(ab, value);
265 audit_log_format(ab, " ");
266 }
267
ima_parse_rule(char * rule,struct ima_measure_rule_entry * entry)268 static int ima_parse_rule(char *rule, struct ima_measure_rule_entry *entry)
269 {
270 struct audit_buffer *ab;
271 char *p;
272 int result = 0;
273
274 ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_INTEGRITY_RULE);
275
276 entry->uid = -1;
277 entry->action = UNKNOWN;
278 while ((p = strsep(&rule, " \t")) != NULL) {
279 substring_t args[MAX_OPT_ARGS];
280 int token;
281 unsigned long lnum;
282
283 if (result < 0)
284 break;
285 if ((*p == '\0') || (*p == ' ') || (*p == '\t'))
286 continue;
287 token = match_token(p, policy_tokens, args);
288 switch (token) {
289 case Opt_measure:
290 ima_log_string(ab, "action", "measure");
291
292 if (entry->action != UNKNOWN)
293 result = -EINVAL;
294
295 entry->action = MEASURE;
296 break;
297 case Opt_dont_measure:
298 ima_log_string(ab, "action", "dont_measure");
299
300 if (entry->action != UNKNOWN)
301 result = -EINVAL;
302
303 entry->action = DONT_MEASURE;
304 break;
305 case Opt_func:
306 ima_log_string(ab, "func", args[0].from);
307
308 if (entry->func)
309 result = -EINVAL;
310
311 if (strcmp(args[0].from, "FILE_CHECK") == 0)
312 entry->func = FILE_CHECK;
313 /* PATH_CHECK is for backwards compat */
314 else if (strcmp(args[0].from, "PATH_CHECK") == 0)
315 entry->func = FILE_CHECK;
316 else if (strcmp(args[0].from, "FILE_MMAP") == 0)
317 entry->func = FILE_MMAP;
318 else if (strcmp(args[0].from, "BPRM_CHECK") == 0)
319 entry->func = BPRM_CHECK;
320 else
321 result = -EINVAL;
322 if (!result)
323 entry->flags |= IMA_FUNC;
324 break;
325 case Opt_mask:
326 ima_log_string(ab, "mask", args[0].from);
327
328 if (entry->mask)
329 result = -EINVAL;
330
331 if ((strcmp(args[0].from, "MAY_EXEC")) == 0)
332 entry->mask = MAY_EXEC;
333 else if (strcmp(args[0].from, "MAY_WRITE") == 0)
334 entry->mask = MAY_WRITE;
335 else if (strcmp(args[0].from, "MAY_READ") == 0)
336 entry->mask = MAY_READ;
337 else if (strcmp(args[0].from, "MAY_APPEND") == 0)
338 entry->mask = MAY_APPEND;
339 else
340 result = -EINVAL;
341 if (!result)
342 entry->flags |= IMA_MASK;
343 break;
344 case Opt_fsmagic:
345 ima_log_string(ab, "fsmagic", args[0].from);
346
347 if (entry->fsmagic) {
348 result = -EINVAL;
349 break;
350 }
351
352 result = strict_strtoul(args[0].from, 16,
353 &entry->fsmagic);
354 if (!result)
355 entry->flags |= IMA_FSMAGIC;
356 break;
357 case Opt_uid:
358 ima_log_string(ab, "uid", args[0].from);
359
360 if (entry->uid != -1) {
361 result = -EINVAL;
362 break;
363 }
364
365 result = strict_strtoul(args[0].from, 10, &lnum);
366 if (!result) {
367 entry->uid = (uid_t) lnum;
368 if (entry->uid != lnum)
369 result = -EINVAL;
370 else
371 entry->flags |= IMA_UID;
372 }
373 break;
374 case Opt_obj_user:
375 ima_log_string(ab, "obj_user", args[0].from);
376 result = ima_lsm_rule_init(entry, args[0].from,
377 LSM_OBJ_USER,
378 AUDIT_OBJ_USER);
379 break;
380 case Opt_obj_role:
381 ima_log_string(ab, "obj_role", args[0].from);
382 result = ima_lsm_rule_init(entry, args[0].from,
383 LSM_OBJ_ROLE,
384 AUDIT_OBJ_ROLE);
385 break;
386 case Opt_obj_type:
387 ima_log_string(ab, "obj_type", args[0].from);
388 result = ima_lsm_rule_init(entry, args[0].from,
389 LSM_OBJ_TYPE,
390 AUDIT_OBJ_TYPE);
391 break;
392 case Opt_subj_user:
393 ima_log_string(ab, "subj_user", args[0].from);
394 result = ima_lsm_rule_init(entry, args[0].from,
395 LSM_SUBJ_USER,
396 AUDIT_SUBJ_USER);
397 break;
398 case Opt_subj_role:
399 ima_log_string(ab, "subj_role", args[0].from);
400 result = ima_lsm_rule_init(entry, args[0].from,
401 LSM_SUBJ_ROLE,
402 AUDIT_SUBJ_ROLE);
403 break;
404 case Opt_subj_type:
405 ima_log_string(ab, "subj_type", args[0].from);
406 result = ima_lsm_rule_init(entry, args[0].from,
407 LSM_SUBJ_TYPE,
408 AUDIT_SUBJ_TYPE);
409 break;
410 case Opt_err:
411 ima_log_string(ab, "UNKNOWN", p);
412 result = -EINVAL;
413 break;
414 }
415 }
416 if (!result && (entry->action == UNKNOWN))
417 result = -EINVAL;
418
419 audit_log_format(ab, "res=%d", !!result);
420 audit_log_end(ab);
421 return result;
422 }
423
424 /**
425 * ima_parse_add_rule - add a rule to measure_policy_rules
426 * @rule - ima measurement policy rule
427 *
428 * Uses a mutex to protect the policy list from multiple concurrent writers.
429 * Returns the length of the rule parsed, an error code on failure
430 */
ima_parse_add_rule(char * rule)431 ssize_t ima_parse_add_rule(char *rule)
432 {
433 const char *op = "update_policy";
434 char *p;
435 struct ima_measure_rule_entry *entry;
436 ssize_t result, len;
437 int audit_info = 0;
438
439 /* Prevent installed policy from changing */
440 if (ima_measure != &measure_default_rules) {
441 integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL,
442 NULL, op, "already exists",
443 -EACCES, audit_info);
444 return -EACCES;
445 }
446
447 entry = kzalloc(sizeof(*entry), GFP_KERNEL);
448 if (!entry) {
449 integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL,
450 NULL, op, "-ENOMEM", -ENOMEM, audit_info);
451 return -ENOMEM;
452 }
453
454 INIT_LIST_HEAD(&entry->list);
455
456 p = strsep(&rule, "\n");
457 len = strlen(p) + 1;
458
459 if (*p == '#') {
460 kfree(entry);
461 return len;
462 }
463
464 result = ima_parse_rule(p, entry);
465 if (result) {
466 kfree(entry);
467 integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL,
468 NULL, op, "invalid policy", result,
469 audit_info);
470 return result;
471 }
472
473 mutex_lock(&ima_measure_mutex);
474 list_add_tail(&entry->list, &measure_policy_rules);
475 mutex_unlock(&ima_measure_mutex);
476
477 return len;
478 }
479
480 /* ima_delete_rules called to cleanup invalid policy */
ima_delete_rules(void)481 void ima_delete_rules(void)
482 {
483 struct ima_measure_rule_entry *entry, *tmp;
484
485 mutex_lock(&ima_measure_mutex);
486 list_for_each_entry_safe(entry, tmp, &measure_policy_rules, list) {
487 list_del(&entry->list);
488 kfree(entry);
489 }
490 mutex_unlock(&ima_measure_mutex);
491 }
492