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 = RAMFS_MAGIC,.flags = IMA_FSMAGIC}, 66 {.action = DONT_MEASURE,.fsmagic = SECURITYFS_MAGIC,.flags = IMA_FSMAGIC}, 67 {.action = DONT_MEASURE,.fsmagic = SELINUX_MAGIC,.flags = IMA_FSMAGIC}, 68 {.action = MEASURE,.func = FILE_MMAP,.mask = MAY_EXEC, 69 .flags = IMA_FUNC | IMA_MASK}, 70 {.action = MEASURE,.func = BPRM_CHECK,.mask = MAY_EXEC, 71 .flags = IMA_FUNC | IMA_MASK}, 72 {.action = MEASURE,.func = FILE_CHECK,.mask = MAY_READ,.uid = 0, 73 .flags = IMA_FUNC | IMA_MASK | IMA_UID}, 74 }; 75 76 static LIST_HEAD(measure_default_rules); 77 static LIST_HEAD(measure_policy_rules); 78 static struct list_head *ima_measure; 79 80 static DEFINE_MUTEX(ima_measure_mutex); 81 82 static bool ima_use_tcb __initdata; 83 static int __init default_policy_setup(char *str) 84 { 85 ima_use_tcb = 1; 86 return 1; 87 } 88 __setup("ima_tcb", default_policy_setup); 89 90 /** 91 * ima_match_rules - determine whether an inode matches the measure rule. 92 * @rule: a pointer to a rule 93 * @inode: a pointer to an inode 94 * @func: LIM hook identifier 95 * @mask: requested action (MAY_READ | MAY_WRITE | MAY_APPEND | MAY_EXEC) 96 * 97 * Returns true on rule match, false on failure. 98 */ 99 static bool ima_match_rules(struct ima_measure_rule_entry *rule, 100 struct inode *inode, enum ima_hooks func, int mask) 101 { 102 struct task_struct *tsk = current; 103 const struct cred *cred = current_cred(); 104 int i; 105 106 if ((rule->flags & IMA_FUNC) && rule->func != func) 107 return false; 108 if ((rule->flags & IMA_MASK) && rule->mask != mask) 109 return false; 110 if ((rule->flags & IMA_FSMAGIC) 111 && rule->fsmagic != inode->i_sb->s_magic) 112 return false; 113 if ((rule->flags & IMA_UID) && rule->uid != cred->uid) 114 return false; 115 for (i = 0; i < MAX_LSM_RULES; i++) { 116 int rc = 0; 117 u32 osid, sid; 118 119 if (!rule->lsm[i].rule) 120 continue; 121 122 switch (i) { 123 case LSM_OBJ_USER: 124 case LSM_OBJ_ROLE: 125 case LSM_OBJ_TYPE: 126 security_inode_getsecid(inode, &osid); 127 rc = security_filter_rule_match(osid, 128 rule->lsm[i].type, 129 Audit_equal, 130 rule->lsm[i].rule, 131 NULL); 132 break; 133 case LSM_SUBJ_USER: 134 case LSM_SUBJ_ROLE: 135 case LSM_SUBJ_TYPE: 136 security_task_getsecid(tsk, &sid); 137 rc = security_filter_rule_match(sid, 138 rule->lsm[i].type, 139 Audit_equal, 140 rule->lsm[i].rule, 141 NULL); 142 default: 143 break; 144 } 145 if (!rc) 146 return false; 147 } 148 return true; 149 } 150 151 /** 152 * ima_match_policy - decision based on LSM and other conditions 153 * @inode: pointer to an inode for which the policy decision is being made 154 * @func: IMA hook identifier 155 * @mask: requested action (MAY_READ | MAY_WRITE | MAY_APPEND | MAY_EXEC) 156 * 157 * Measure decision based on func/mask/fsmagic and LSM(subj/obj/type) 158 * conditions. 159 * 160 * (There is no need for locking when walking the policy list, 161 * as elements in the list are never deleted, nor does the list 162 * change.) 163 */ 164 int ima_match_policy(struct inode *inode, enum ima_hooks func, int mask) 165 { 166 struct ima_measure_rule_entry *entry; 167 168 list_for_each_entry(entry, ima_measure, list) { 169 bool rc; 170 171 rc = ima_match_rules(entry, inode, func, mask); 172 if (rc) 173 return entry->action; 174 } 175 return 0; 176 } 177 178 /** 179 * ima_init_policy - initialize the default measure rules. 180 * 181 * ima_measure points to either the measure_default_rules or the 182 * the new measure_policy_rules. 183 */ 184 void __init ima_init_policy(void) 185 { 186 int i, entries; 187 188 /* if !ima_use_tcb set entries = 0 so we load NO default rules */ 189 if (ima_use_tcb) 190 entries = ARRAY_SIZE(default_rules); 191 else 192 entries = 0; 193 194 for (i = 0; i < entries; i++) 195 list_add_tail(&default_rules[i].list, &measure_default_rules); 196 ima_measure = &measure_default_rules; 197 } 198 199 /** 200 * ima_update_policy - update default_rules with new measure rules 201 * 202 * Called on file .release to update the default rules with a complete new 203 * policy. Once updated, the policy is locked, no additional rules can be 204 * added to the policy. 205 */ 206 void ima_update_policy(void) 207 { 208 const char *op = "policy_update"; 209 const char *cause = "already exists"; 210 int result = 1; 211 int audit_info = 0; 212 213 if (ima_measure == &measure_default_rules) { 214 ima_measure = &measure_policy_rules; 215 cause = "complete"; 216 result = 0; 217 } 218 integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL, 219 NULL, op, cause, result, audit_info); 220 } 221 222 enum { 223 Opt_err = -1, 224 Opt_measure = 1, Opt_dont_measure, 225 Opt_obj_user, Opt_obj_role, Opt_obj_type, 226 Opt_subj_user, Opt_subj_role, Opt_subj_type, 227 Opt_func, Opt_mask, Opt_fsmagic, Opt_uid 228 }; 229 230 static match_table_t policy_tokens = { 231 {Opt_measure, "measure"}, 232 {Opt_dont_measure, "dont_measure"}, 233 {Opt_obj_user, "obj_user=%s"}, 234 {Opt_obj_role, "obj_role=%s"}, 235 {Opt_obj_type, "obj_type=%s"}, 236 {Opt_subj_user, "subj_user=%s"}, 237 {Opt_subj_role, "subj_role=%s"}, 238 {Opt_subj_type, "subj_type=%s"}, 239 {Opt_func, "func=%s"}, 240 {Opt_mask, "mask=%s"}, 241 {Opt_fsmagic, "fsmagic=%s"}, 242 {Opt_uid, "uid=%s"}, 243 {Opt_err, NULL} 244 }; 245 246 static int ima_lsm_rule_init(struct ima_measure_rule_entry *entry, 247 char *args, int lsm_rule, int audit_type) 248 { 249 int result; 250 251 if (entry->lsm[lsm_rule].rule) 252 return -EINVAL; 253 254 entry->lsm[lsm_rule].type = audit_type; 255 result = security_filter_rule_init(entry->lsm[lsm_rule].type, 256 Audit_equal, args, 257 &entry->lsm[lsm_rule].rule); 258 if (!entry->lsm[lsm_rule].rule) 259 return -EINVAL; 260 return result; 261 } 262 263 static void ima_log_string(struct audit_buffer *ab, char *key, char *value) 264 { 265 audit_log_format(ab, "%s=", key); 266 audit_log_untrustedstring(ab, value); 267 audit_log_format(ab, " "); 268 } 269 270 static int ima_parse_rule(char *rule, struct ima_measure_rule_entry *entry) 271 { 272 struct audit_buffer *ab; 273 char *p; 274 int result = 0; 275 276 ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_INTEGRITY_RULE); 277 278 entry->uid = -1; 279 entry->action = UNKNOWN; 280 while ((p = strsep(&rule, " \t")) != NULL) { 281 substring_t args[MAX_OPT_ARGS]; 282 int token; 283 unsigned long lnum; 284 285 if (result < 0) 286 break; 287 if ((*p == '\0') || (*p == ' ') || (*p == '\t')) 288 continue; 289 token = match_token(p, policy_tokens, args); 290 switch (token) { 291 case Opt_measure: 292 ima_log_string(ab, "action", "measure"); 293 294 if (entry->action != UNKNOWN) 295 result = -EINVAL; 296 297 entry->action = MEASURE; 298 break; 299 case Opt_dont_measure: 300 ima_log_string(ab, "action", "dont_measure"); 301 302 if (entry->action != UNKNOWN) 303 result = -EINVAL; 304 305 entry->action = DONT_MEASURE; 306 break; 307 case Opt_func: 308 ima_log_string(ab, "func", args[0].from); 309 310 if (entry->func) 311 result = -EINVAL; 312 313 if (strcmp(args[0].from, "FILE_CHECK") == 0) 314 entry->func = FILE_CHECK; 315 /* PATH_CHECK is for backwards compat */ 316 else if (strcmp(args[0].from, "PATH_CHECK") == 0) 317 entry->func = FILE_CHECK; 318 else if (strcmp(args[0].from, "FILE_MMAP") == 0) 319 entry->func = FILE_MMAP; 320 else if (strcmp(args[0].from, "BPRM_CHECK") == 0) 321 entry->func = BPRM_CHECK; 322 else 323 result = -EINVAL; 324 if (!result) 325 entry->flags |= IMA_FUNC; 326 break; 327 case Opt_mask: 328 ima_log_string(ab, "mask", args[0].from); 329 330 if (entry->mask) 331 result = -EINVAL; 332 333 if ((strcmp(args[0].from, "MAY_EXEC")) == 0) 334 entry->mask = MAY_EXEC; 335 else if (strcmp(args[0].from, "MAY_WRITE") == 0) 336 entry->mask = MAY_WRITE; 337 else if (strcmp(args[0].from, "MAY_READ") == 0) 338 entry->mask = MAY_READ; 339 else if (strcmp(args[0].from, "MAY_APPEND") == 0) 340 entry->mask = MAY_APPEND; 341 else 342 result = -EINVAL; 343 if (!result) 344 entry->flags |= IMA_MASK; 345 break; 346 case Opt_fsmagic: 347 ima_log_string(ab, "fsmagic", args[0].from); 348 349 if (entry->fsmagic) { 350 result = -EINVAL; 351 break; 352 } 353 354 result = strict_strtoul(args[0].from, 16, 355 &entry->fsmagic); 356 if (!result) 357 entry->flags |= IMA_FSMAGIC; 358 break; 359 case Opt_uid: 360 ima_log_string(ab, "uid", args[0].from); 361 362 if (entry->uid != -1) { 363 result = -EINVAL; 364 break; 365 } 366 367 result = strict_strtoul(args[0].from, 10, &lnum); 368 if (!result) { 369 entry->uid = (uid_t) lnum; 370 if (entry->uid != lnum) 371 result = -EINVAL; 372 else 373 entry->flags |= IMA_UID; 374 } 375 break; 376 case Opt_obj_user: 377 ima_log_string(ab, "obj_user", args[0].from); 378 result = ima_lsm_rule_init(entry, args[0].from, 379 LSM_OBJ_USER, 380 AUDIT_OBJ_USER); 381 break; 382 case Opt_obj_role: 383 ima_log_string(ab, "obj_role", args[0].from); 384 result = ima_lsm_rule_init(entry, args[0].from, 385 LSM_OBJ_ROLE, 386 AUDIT_OBJ_ROLE); 387 break; 388 case Opt_obj_type: 389 ima_log_string(ab, "obj_type", args[0].from); 390 result = ima_lsm_rule_init(entry, args[0].from, 391 LSM_OBJ_TYPE, 392 AUDIT_OBJ_TYPE); 393 break; 394 case Opt_subj_user: 395 ima_log_string(ab, "subj_user", args[0].from); 396 result = ima_lsm_rule_init(entry, args[0].from, 397 LSM_SUBJ_USER, 398 AUDIT_SUBJ_USER); 399 break; 400 case Opt_subj_role: 401 ima_log_string(ab, "subj_role", args[0].from); 402 result = ima_lsm_rule_init(entry, args[0].from, 403 LSM_SUBJ_ROLE, 404 AUDIT_SUBJ_ROLE); 405 break; 406 case Opt_subj_type: 407 ima_log_string(ab, "subj_type", args[0].from); 408 result = ima_lsm_rule_init(entry, args[0].from, 409 LSM_SUBJ_TYPE, 410 AUDIT_SUBJ_TYPE); 411 break; 412 case Opt_err: 413 ima_log_string(ab, "UNKNOWN", p); 414 result = -EINVAL; 415 break; 416 } 417 } 418 if (!result && (entry->action == UNKNOWN)) 419 result = -EINVAL; 420 421 audit_log_format(ab, "res=%d", !result); 422 audit_log_end(ab); 423 return result; 424 } 425 426 /** 427 * ima_parse_add_rule - add a rule to measure_policy_rules 428 * @rule - ima measurement policy rule 429 * 430 * Uses a mutex to protect the policy list from multiple concurrent writers. 431 * Returns the length of the rule parsed, an error code on failure 432 */ 433 ssize_t ima_parse_add_rule(char *rule) 434 { 435 const char *op = "update_policy"; 436 char *p; 437 struct ima_measure_rule_entry *entry; 438 ssize_t result, len; 439 int audit_info = 0; 440 441 /* Prevent installed policy from changing */ 442 if (ima_measure != &measure_default_rules) { 443 integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL, 444 NULL, op, "already exists", 445 -EACCES, audit_info); 446 return -EACCES; 447 } 448 449 entry = kzalloc(sizeof(*entry), GFP_KERNEL); 450 if (!entry) { 451 integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL, 452 NULL, op, "-ENOMEM", -ENOMEM, audit_info); 453 return -ENOMEM; 454 } 455 456 INIT_LIST_HEAD(&entry->list); 457 458 p = strsep(&rule, "\n"); 459 len = strlen(p) + 1; 460 461 if (*p == '#') { 462 kfree(entry); 463 return len; 464 } 465 466 result = ima_parse_rule(p, entry); 467 if (result) { 468 kfree(entry); 469 integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL, 470 NULL, op, "invalid policy", result, 471 audit_info); 472 return result; 473 } 474 475 mutex_lock(&ima_measure_mutex); 476 list_add_tail(&entry->list, &measure_policy_rules); 477 mutex_unlock(&ima_measure_mutex); 478 479 return len; 480 } 481 482 /* ima_delete_rules called to cleanup invalid policy */ 483 void ima_delete_rules(void) 484 { 485 struct ima_measure_rule_entry *entry, *tmp; 486 487 mutex_lock(&ima_measure_mutex); 488 list_for_each_entry_safe(entry, tmp, &measure_policy_rules, list) { 489 list_del(&entry->list); 490 kfree(entry); 491 } 492 mutex_unlock(&ima_measure_mutex); 493 } 494