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; 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 */ 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 const struct cred *cred = current_cred(); 103 int i; 104 105 if ((rule->flags & IMA_FUNC) && rule->func != func) 106 return false; 107 if ((rule->flags & IMA_MASK) && rule->mask != mask) 108 return false; 109 if ((rule->flags & IMA_FSMAGIC) 110 && rule->fsmagic != inode->i_sb->s_magic) 111 return false; 112 if ((rule->flags & IMA_UID) && rule->uid != cred->uid) 113 return false; 114 for (i = 0; i < MAX_LSM_RULES; i++) { 115 int rc = 0; 116 u32 osid, sid; 117 118 if (!rule->lsm[i].rule) 119 continue; 120 121 switch (i) { 122 case LSM_OBJ_USER: 123 case LSM_OBJ_ROLE: 124 case LSM_OBJ_TYPE: 125 security_inode_getsecid(inode, &osid); 126 rc = security_filter_rule_match(osid, 127 rule->lsm[i].type, 128 Audit_equal, 129 rule->lsm[i].rule, 130 NULL); 131 break; 132 case LSM_SUBJ_USER: 133 case LSM_SUBJ_ROLE: 134 case LSM_SUBJ_TYPE: 135 security_task_getsecid(tsk, &sid); 136 rc = security_filter_rule_match(sid, 137 rule->lsm[i].type, 138 Audit_equal, 139 rule->lsm[i].rule, 140 NULL); 141 default: 142 break; 143 } 144 if (!rc) 145 return false; 146 } 147 return true; 148 } 149 150 /** 151 * ima_match_policy - decision based on LSM and other conditions 152 * @inode: pointer to an inode for which the policy decision is being made 153 * @func: IMA hook identifier 154 * @mask: requested action (MAY_READ | MAY_WRITE | MAY_APPEND | MAY_EXEC) 155 * 156 * Measure decision based on func/mask/fsmagic and LSM(subj/obj/type) 157 * conditions. 158 * 159 * (There is no need for locking when walking the policy list, 160 * as elements in the list are never deleted, nor does the list 161 * change.) 162 */ 163 int ima_match_policy(struct inode *inode, enum ima_hooks func, int mask) 164 { 165 struct ima_measure_rule_entry *entry; 166 167 list_for_each_entry(entry, ima_measure, list) { 168 bool rc; 169 170 rc = ima_match_rules(entry, inode, func, mask); 171 if (rc) 172 return entry->action; 173 } 174 return 0; 175 } 176 177 /** 178 * ima_init_policy - initialize the default measure rules. 179 * 180 * ima_measure points to either the measure_default_rules or the 181 * the new measure_policy_rules. 182 */ 183 void __init ima_init_policy(void) 184 { 185 int i, entries; 186 187 /* if !ima_use_tcb set entries = 0 so we load NO default rules */ 188 if (ima_use_tcb) 189 entries = ARRAY_SIZE(default_rules); 190 else 191 entries = 0; 192 193 for (i = 0; i < entries; i++) 194 list_add_tail(&default_rules[i].list, &measure_default_rules); 195 ima_measure = &measure_default_rules; 196 } 197 198 /** 199 * ima_update_policy - update default_rules with new measure rules 200 * 201 * Called on file .release to update the default rules with a complete new 202 * policy. Once updated, the policy is locked, no additional rules can be 203 * added to the policy. 204 */ 205 void ima_update_policy(void) 206 { 207 const char *op = "policy_update"; 208 const char *cause = "already exists"; 209 int result = 1; 210 int audit_info = 0; 211 212 if (ima_measure == &measure_default_rules) { 213 ima_measure = &measure_policy_rules; 214 cause = "complete"; 215 result = 0; 216 } 217 integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL, 218 NULL, op, cause, result, audit_info); 219 } 220 221 enum { 222 Opt_err = -1, 223 Opt_measure = 1, Opt_dont_measure, 224 Opt_obj_user, Opt_obj_role, Opt_obj_type, 225 Opt_subj_user, Opt_subj_role, Opt_subj_type, 226 Opt_func, Opt_mask, Opt_fsmagic, Opt_uid 227 }; 228 229 static match_table_t policy_tokens = { 230 {Opt_measure, "measure"}, 231 {Opt_dont_measure, "dont_measure"}, 232 {Opt_obj_user, "obj_user=%s"}, 233 {Opt_obj_role, "obj_role=%s"}, 234 {Opt_obj_type, "obj_type=%s"}, 235 {Opt_subj_user, "subj_user=%s"}, 236 {Opt_subj_role, "subj_role=%s"}, 237 {Opt_subj_type, "subj_type=%s"}, 238 {Opt_func, "func=%s"}, 239 {Opt_mask, "mask=%s"}, 240 {Opt_fsmagic, "fsmagic=%s"}, 241 {Opt_uid, "uid=%s"}, 242 {Opt_err, NULL} 243 }; 244 245 static int ima_lsm_rule_init(struct ima_measure_rule_entry *entry, 246 char *args, int lsm_rule, int audit_type) 247 { 248 int result; 249 250 if (entry->lsm[lsm_rule].rule) 251 return -EINVAL; 252 253 entry->lsm[lsm_rule].type = audit_type; 254 result = security_filter_rule_init(entry->lsm[lsm_rule].type, 255 Audit_equal, args, 256 &entry->lsm[lsm_rule].rule); 257 if (!entry->lsm[lsm_rule].rule) 258 return -EINVAL; 259 return result; 260 } 261 262 static void ima_log_string(struct audit_buffer *ab, char *key, char *value) 263 { 264 audit_log_format(ab, "%s=", key); 265 audit_log_untrustedstring(ab, value); 266 audit_log_format(ab, " "); 267 } 268 269 static int ima_parse_rule(char *rule, struct ima_measure_rule_entry *entry) 270 { 271 struct audit_buffer *ab; 272 char *p; 273 int result = 0; 274 275 ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_INTEGRITY_RULE); 276 277 entry->uid = -1; 278 entry->action = UNKNOWN; 279 while ((p = strsep(&rule, " \t")) != NULL) { 280 substring_t args[MAX_OPT_ARGS]; 281 int token; 282 unsigned long lnum; 283 284 if (result < 0) 285 break; 286 if ((*p == '\0') || (*p == ' ') || (*p == '\t')) 287 continue; 288 token = match_token(p, policy_tokens, args); 289 switch (token) { 290 case Opt_measure: 291 ima_log_string(ab, "action", "measure"); 292 293 if (entry->action != UNKNOWN) 294 result = -EINVAL; 295 296 entry->action = MEASURE; 297 break; 298 case Opt_dont_measure: 299 ima_log_string(ab, "action", "dont_measure"); 300 301 if (entry->action != UNKNOWN) 302 result = -EINVAL; 303 304 entry->action = DONT_MEASURE; 305 break; 306 case Opt_func: 307 ima_log_string(ab, "func", args[0].from); 308 309 if (entry->func) 310 result = -EINVAL; 311 312 if (strcmp(args[0].from, "FILE_CHECK") == 0) 313 entry->func = FILE_CHECK; 314 /* PATH_CHECK is for backwards compat */ 315 else if (strcmp(args[0].from, "PATH_CHECK") == 0) 316 entry->func = FILE_CHECK; 317 else if (strcmp(args[0].from, "FILE_MMAP") == 0) 318 entry->func = FILE_MMAP; 319 else if (strcmp(args[0].from, "BPRM_CHECK") == 0) 320 entry->func = BPRM_CHECK; 321 else 322 result = -EINVAL; 323 if (!result) 324 entry->flags |= IMA_FUNC; 325 break; 326 case Opt_mask: 327 ima_log_string(ab, "mask", args[0].from); 328 329 if (entry->mask) 330 result = -EINVAL; 331 332 if ((strcmp(args[0].from, "MAY_EXEC")) == 0) 333 entry->mask = MAY_EXEC; 334 else if (strcmp(args[0].from, "MAY_WRITE") == 0) 335 entry->mask = MAY_WRITE; 336 else if (strcmp(args[0].from, "MAY_READ") == 0) 337 entry->mask = MAY_READ; 338 else if (strcmp(args[0].from, "MAY_APPEND") == 0) 339 entry->mask = MAY_APPEND; 340 else 341 result = -EINVAL; 342 if (!result) 343 entry->flags |= IMA_MASK; 344 break; 345 case Opt_fsmagic: 346 ima_log_string(ab, "fsmagic", args[0].from); 347 348 if (entry->fsmagic) { 349 result = -EINVAL; 350 break; 351 } 352 353 result = strict_strtoul(args[0].from, 16, 354 &entry->fsmagic); 355 if (!result) 356 entry->flags |= IMA_FSMAGIC; 357 break; 358 case Opt_uid: 359 ima_log_string(ab, "uid", args[0].from); 360 361 if (entry->uid != -1) { 362 result = -EINVAL; 363 break; 364 } 365 366 result = strict_strtoul(args[0].from, 10, &lnum); 367 if (!result) { 368 entry->uid = (uid_t) lnum; 369 if (entry->uid != lnum) 370 result = -EINVAL; 371 else 372 entry->flags |= IMA_UID; 373 } 374 break; 375 case Opt_obj_user: 376 ima_log_string(ab, "obj_user", args[0].from); 377 result = ima_lsm_rule_init(entry, args[0].from, 378 LSM_OBJ_USER, 379 AUDIT_OBJ_USER); 380 break; 381 case Opt_obj_role: 382 ima_log_string(ab, "obj_role", args[0].from); 383 result = ima_lsm_rule_init(entry, args[0].from, 384 LSM_OBJ_ROLE, 385 AUDIT_OBJ_ROLE); 386 break; 387 case Opt_obj_type: 388 ima_log_string(ab, "obj_type", args[0].from); 389 result = ima_lsm_rule_init(entry, args[0].from, 390 LSM_OBJ_TYPE, 391 AUDIT_OBJ_TYPE); 392 break; 393 case Opt_subj_user: 394 ima_log_string(ab, "subj_user", args[0].from); 395 result = ima_lsm_rule_init(entry, args[0].from, 396 LSM_SUBJ_USER, 397 AUDIT_SUBJ_USER); 398 break; 399 case Opt_subj_role: 400 ima_log_string(ab, "subj_role", args[0].from); 401 result = ima_lsm_rule_init(entry, args[0].from, 402 LSM_SUBJ_ROLE, 403 AUDIT_SUBJ_ROLE); 404 break; 405 case Opt_subj_type: 406 ima_log_string(ab, "subj_type", args[0].from); 407 result = ima_lsm_rule_init(entry, args[0].from, 408 LSM_SUBJ_TYPE, 409 AUDIT_SUBJ_TYPE); 410 break; 411 case Opt_err: 412 ima_log_string(ab, "UNKNOWN", p); 413 result = -EINVAL; 414 break; 415 } 416 } 417 if (!result && (entry->action == UNKNOWN)) 418 result = -EINVAL; 419 420 audit_log_format(ab, "res=%d", !!result); 421 audit_log_end(ab); 422 return result; 423 } 424 425 /** 426 * ima_parse_add_rule - add a rule to measure_policy_rules 427 * @rule - ima measurement policy rule 428 * 429 * Uses a mutex to protect the policy list from multiple concurrent writers. 430 * Returns the length of the rule parsed, an error code on failure 431 */ 432 ssize_t ima_parse_add_rule(char *rule) 433 { 434 const char *op = "update_policy"; 435 char *p; 436 struct ima_measure_rule_entry *entry; 437 ssize_t result, len; 438 int audit_info = 0; 439 440 /* Prevent installed policy from changing */ 441 if (ima_measure != &measure_default_rules) { 442 integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL, 443 NULL, op, "already exists", 444 -EACCES, audit_info); 445 return -EACCES; 446 } 447 448 entry = kzalloc(sizeof(*entry), GFP_KERNEL); 449 if (!entry) { 450 integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL, 451 NULL, op, "-ENOMEM", -ENOMEM, audit_info); 452 return -ENOMEM; 453 } 454 455 INIT_LIST_HEAD(&entry->list); 456 457 p = strsep(&rule, "\n"); 458 len = strlen(p) + 1; 459 460 if (*p == '#') { 461 kfree(entry); 462 return len; 463 } 464 465 result = ima_parse_rule(p, entry); 466 if (result) { 467 kfree(entry); 468 integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL, 469 NULL, op, "invalid policy", result, 470 audit_info); 471 return result; 472 } 473 474 mutex_lock(&ima_measure_mutex); 475 list_add_tail(&entry->list, &measure_policy_rules); 476 mutex_unlock(&ima_measure_mutex); 477 478 return len; 479 } 480 481 /* ima_delete_rules called to cleanup invalid policy */ 482 void ima_delete_rules(void) 483 { 484 struct ima_measure_rule_entry *entry, *tmp; 485 486 mutex_lock(&ima_measure_mutex); 487 list_for_each_entry_safe(entry, tmp, &measure_policy_rules, list) { 488 list_del(&entry->list); 489 kfree(entry); 490 } 491 mutex_unlock(&ima_measure_mutex); 492 } 493