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 = DEVPTS_SUPER_MAGIC,.flags = IMA_FSMAGIC}, 67 {.action = DONT_MEASURE,.fsmagic = BINFMTFS_MAGIC,.flags = IMA_FSMAGIC}, 68 {.action = DONT_MEASURE,.fsmagic = SECURITYFS_MAGIC,.flags = IMA_FSMAGIC}, 69 {.action = DONT_MEASURE,.fsmagic = SELINUX_MAGIC,.flags = IMA_FSMAGIC}, 70 {.action = MEASURE,.func = FILE_MMAP,.mask = MAY_EXEC, 71 .flags = IMA_FUNC | IMA_MASK}, 72 {.action = MEASURE,.func = BPRM_CHECK,.mask = MAY_EXEC, 73 .flags = IMA_FUNC | IMA_MASK}, 74 {.action = MEASURE,.func = FILE_CHECK,.mask = MAY_READ,.uid = 0, 75 .flags = IMA_FUNC | IMA_MASK | IMA_UID}, 76 }; 77 78 static LIST_HEAD(measure_default_rules); 79 static LIST_HEAD(measure_policy_rules); 80 static struct list_head *ima_measure; 81 82 static DEFINE_MUTEX(ima_measure_mutex); 83 84 static bool ima_use_tcb __initdata; 85 static int __init default_policy_setup(char *str) 86 { 87 ima_use_tcb = 1; 88 return 1; 89 } 90 __setup("ima_tcb", default_policy_setup); 91 92 /** 93 * ima_match_rules - determine whether an inode matches the measure rule. 94 * @rule: a pointer to a rule 95 * @inode: a pointer to an inode 96 * @func: LIM hook identifier 97 * @mask: requested action (MAY_READ | MAY_WRITE | MAY_APPEND | MAY_EXEC) 98 * 99 * Returns true on rule match, false on failure. 100 */ 101 static bool ima_match_rules(struct ima_measure_rule_entry *rule, 102 struct inode *inode, enum ima_hooks func, int mask) 103 { 104 struct task_struct *tsk = current; 105 const struct cred *cred = current_cred(); 106 int i; 107 108 if ((rule->flags & IMA_FUNC) && rule->func != func) 109 return false; 110 if ((rule->flags & IMA_MASK) && rule->mask != mask) 111 return false; 112 if ((rule->flags & IMA_FSMAGIC) 113 && rule->fsmagic != inode->i_sb->s_magic) 114 return false; 115 if ((rule->flags & IMA_UID) && rule->uid != cred->uid) 116 return false; 117 for (i = 0; i < MAX_LSM_RULES; i++) { 118 int rc = 0; 119 u32 osid, sid; 120 121 if (!rule->lsm[i].rule) 122 continue; 123 124 switch (i) { 125 case LSM_OBJ_USER: 126 case LSM_OBJ_ROLE: 127 case LSM_OBJ_TYPE: 128 security_inode_getsecid(inode, &osid); 129 rc = security_filter_rule_match(osid, 130 rule->lsm[i].type, 131 Audit_equal, 132 rule->lsm[i].rule, 133 NULL); 134 break; 135 case LSM_SUBJ_USER: 136 case LSM_SUBJ_ROLE: 137 case LSM_SUBJ_TYPE: 138 security_task_getsecid(tsk, &sid); 139 rc = security_filter_rule_match(sid, 140 rule->lsm[i].type, 141 Audit_equal, 142 rule->lsm[i].rule, 143 NULL); 144 default: 145 break; 146 } 147 if (!rc) 148 return false; 149 } 150 return true; 151 } 152 153 /** 154 * ima_match_policy - decision based on LSM and other conditions 155 * @inode: pointer to an inode for which the policy decision is being made 156 * @func: IMA hook identifier 157 * @mask: requested action (MAY_READ | MAY_WRITE | MAY_APPEND | MAY_EXEC) 158 * 159 * Measure decision based on func/mask/fsmagic and LSM(subj/obj/type) 160 * conditions. 161 * 162 * (There is no need for locking when walking the policy list, 163 * as elements in the list are never deleted, nor does the list 164 * change.) 165 */ 166 int ima_match_policy(struct inode *inode, enum ima_hooks func, int mask) 167 { 168 struct ima_measure_rule_entry *entry; 169 170 list_for_each_entry(entry, ima_measure, list) { 171 bool rc; 172 173 rc = ima_match_rules(entry, inode, func, mask); 174 if (rc) 175 return entry->action; 176 } 177 return 0; 178 } 179 180 /** 181 * ima_init_policy - initialize the default measure rules. 182 * 183 * ima_measure points to either the measure_default_rules or the 184 * the new measure_policy_rules. 185 */ 186 void __init ima_init_policy(void) 187 { 188 int i, entries; 189 190 /* if !ima_use_tcb set entries = 0 so we load NO default rules */ 191 if (ima_use_tcb) 192 entries = ARRAY_SIZE(default_rules); 193 else 194 entries = 0; 195 196 for (i = 0; i < entries; i++) 197 list_add_tail(&default_rules[i].list, &measure_default_rules); 198 ima_measure = &measure_default_rules; 199 } 200 201 /** 202 * ima_update_policy - update default_rules with new measure rules 203 * 204 * Called on file .release to update the default rules with a complete new 205 * policy. Once updated, the policy is locked, no additional rules can be 206 * added to the policy. 207 */ 208 void ima_update_policy(void) 209 { 210 const char *op = "policy_update"; 211 const char *cause = "already exists"; 212 int result = 1; 213 int audit_info = 0; 214 215 if (ima_measure == &measure_default_rules) { 216 ima_measure = &measure_policy_rules; 217 cause = "complete"; 218 result = 0; 219 } 220 integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL, 221 NULL, op, cause, result, audit_info); 222 } 223 224 enum { 225 Opt_err = -1, 226 Opt_measure = 1, Opt_dont_measure, 227 Opt_obj_user, Opt_obj_role, Opt_obj_type, 228 Opt_subj_user, Opt_subj_role, Opt_subj_type, 229 Opt_func, Opt_mask, Opt_fsmagic, Opt_uid 230 }; 231 232 static match_table_t policy_tokens = { 233 {Opt_measure, "measure"}, 234 {Opt_dont_measure, "dont_measure"}, 235 {Opt_obj_user, "obj_user=%s"}, 236 {Opt_obj_role, "obj_role=%s"}, 237 {Opt_obj_type, "obj_type=%s"}, 238 {Opt_subj_user, "subj_user=%s"}, 239 {Opt_subj_role, "subj_role=%s"}, 240 {Opt_subj_type, "subj_type=%s"}, 241 {Opt_func, "func=%s"}, 242 {Opt_mask, "mask=%s"}, 243 {Opt_fsmagic, "fsmagic=%s"}, 244 {Opt_uid, "uid=%s"}, 245 {Opt_err, NULL} 246 }; 247 248 static int ima_lsm_rule_init(struct ima_measure_rule_entry *entry, 249 char *args, int lsm_rule, int audit_type) 250 { 251 int result; 252 253 if (entry->lsm[lsm_rule].rule) 254 return -EINVAL; 255 256 entry->lsm[lsm_rule].type = audit_type; 257 result = security_filter_rule_init(entry->lsm[lsm_rule].type, 258 Audit_equal, args, 259 &entry->lsm[lsm_rule].rule); 260 if (!entry->lsm[lsm_rule].rule) 261 return -EINVAL; 262 return result; 263 } 264 265 static void ima_log_string(struct audit_buffer *ab, char *key, char *value) 266 { 267 audit_log_format(ab, "%s=", key); 268 audit_log_untrustedstring(ab, value); 269 audit_log_format(ab, " "); 270 } 271 272 static int ima_parse_rule(char *rule, struct ima_measure_rule_entry *entry) 273 { 274 struct audit_buffer *ab; 275 char *p; 276 int result = 0; 277 278 ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_INTEGRITY_RULE); 279 280 entry->uid = -1; 281 entry->action = UNKNOWN; 282 while ((p = strsep(&rule, " \t")) != NULL) { 283 substring_t args[MAX_OPT_ARGS]; 284 int token; 285 unsigned long lnum; 286 287 if (result < 0) 288 break; 289 if ((*p == '\0') || (*p == ' ') || (*p == '\t')) 290 continue; 291 token = match_token(p, policy_tokens, args); 292 switch (token) { 293 case Opt_measure: 294 ima_log_string(ab, "action", "measure"); 295 296 if (entry->action != UNKNOWN) 297 result = -EINVAL; 298 299 entry->action = MEASURE; 300 break; 301 case Opt_dont_measure: 302 ima_log_string(ab, "action", "dont_measure"); 303 304 if (entry->action != UNKNOWN) 305 result = -EINVAL; 306 307 entry->action = DONT_MEASURE; 308 break; 309 case Opt_func: 310 ima_log_string(ab, "func", args[0].from); 311 312 if (entry->func) 313 result = -EINVAL; 314 315 if (strcmp(args[0].from, "FILE_CHECK") == 0) 316 entry->func = FILE_CHECK; 317 /* PATH_CHECK is for backwards compat */ 318 else if (strcmp(args[0].from, "PATH_CHECK") == 0) 319 entry->func = FILE_CHECK; 320 else if (strcmp(args[0].from, "FILE_MMAP") == 0) 321 entry->func = FILE_MMAP; 322 else if (strcmp(args[0].from, "BPRM_CHECK") == 0) 323 entry->func = BPRM_CHECK; 324 else 325 result = -EINVAL; 326 if (!result) 327 entry->flags |= IMA_FUNC; 328 break; 329 case Opt_mask: 330 ima_log_string(ab, "mask", args[0].from); 331 332 if (entry->mask) 333 result = -EINVAL; 334 335 if ((strcmp(args[0].from, "MAY_EXEC")) == 0) 336 entry->mask = MAY_EXEC; 337 else if (strcmp(args[0].from, "MAY_WRITE") == 0) 338 entry->mask = MAY_WRITE; 339 else if (strcmp(args[0].from, "MAY_READ") == 0) 340 entry->mask = MAY_READ; 341 else if (strcmp(args[0].from, "MAY_APPEND") == 0) 342 entry->mask = MAY_APPEND; 343 else 344 result = -EINVAL; 345 if (!result) 346 entry->flags |= IMA_MASK; 347 break; 348 case Opt_fsmagic: 349 ima_log_string(ab, "fsmagic", args[0].from); 350 351 if (entry->fsmagic) { 352 result = -EINVAL; 353 break; 354 } 355 356 result = strict_strtoul(args[0].from, 16, 357 &entry->fsmagic); 358 if (!result) 359 entry->flags |= IMA_FSMAGIC; 360 break; 361 case Opt_uid: 362 ima_log_string(ab, "uid", args[0].from); 363 364 if (entry->uid != -1) { 365 result = -EINVAL; 366 break; 367 } 368 369 result = strict_strtoul(args[0].from, 10, &lnum); 370 if (!result) { 371 entry->uid = (uid_t) lnum; 372 if (entry->uid != lnum) 373 result = -EINVAL; 374 else 375 entry->flags |= IMA_UID; 376 } 377 break; 378 case Opt_obj_user: 379 ima_log_string(ab, "obj_user", args[0].from); 380 result = ima_lsm_rule_init(entry, args[0].from, 381 LSM_OBJ_USER, 382 AUDIT_OBJ_USER); 383 break; 384 case Opt_obj_role: 385 ima_log_string(ab, "obj_role", args[0].from); 386 result = ima_lsm_rule_init(entry, args[0].from, 387 LSM_OBJ_ROLE, 388 AUDIT_OBJ_ROLE); 389 break; 390 case Opt_obj_type: 391 ima_log_string(ab, "obj_type", args[0].from); 392 result = ima_lsm_rule_init(entry, args[0].from, 393 LSM_OBJ_TYPE, 394 AUDIT_OBJ_TYPE); 395 break; 396 case Opt_subj_user: 397 ima_log_string(ab, "subj_user", args[0].from); 398 result = ima_lsm_rule_init(entry, args[0].from, 399 LSM_SUBJ_USER, 400 AUDIT_SUBJ_USER); 401 break; 402 case Opt_subj_role: 403 ima_log_string(ab, "subj_role", args[0].from); 404 result = ima_lsm_rule_init(entry, args[0].from, 405 LSM_SUBJ_ROLE, 406 AUDIT_SUBJ_ROLE); 407 break; 408 case Opt_subj_type: 409 ima_log_string(ab, "subj_type", args[0].from); 410 result = ima_lsm_rule_init(entry, args[0].from, 411 LSM_SUBJ_TYPE, 412 AUDIT_SUBJ_TYPE); 413 break; 414 case Opt_err: 415 ima_log_string(ab, "UNKNOWN", p); 416 result = -EINVAL; 417 break; 418 } 419 } 420 if (!result && (entry->action == UNKNOWN)) 421 result = -EINVAL; 422 423 audit_log_format(ab, "res=%d", !result); 424 audit_log_end(ab); 425 return result; 426 } 427 428 /** 429 * ima_parse_add_rule - add a rule to measure_policy_rules 430 * @rule - ima measurement policy rule 431 * 432 * Uses a mutex to protect the policy list from multiple concurrent writers. 433 * Returns the length of the rule parsed, an error code on failure 434 */ 435 ssize_t ima_parse_add_rule(char *rule) 436 { 437 const char *op = "update_policy"; 438 char *p; 439 struct ima_measure_rule_entry *entry; 440 ssize_t result, len; 441 int audit_info = 0; 442 443 /* Prevent installed policy from changing */ 444 if (ima_measure != &measure_default_rules) { 445 integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL, 446 NULL, op, "already exists", 447 -EACCES, audit_info); 448 return -EACCES; 449 } 450 451 entry = kzalloc(sizeof(*entry), GFP_KERNEL); 452 if (!entry) { 453 integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL, 454 NULL, op, "-ENOMEM", -ENOMEM, audit_info); 455 return -ENOMEM; 456 } 457 458 INIT_LIST_HEAD(&entry->list); 459 460 p = strsep(&rule, "\n"); 461 len = strlen(p) + 1; 462 463 if (*p == '#') { 464 kfree(entry); 465 return len; 466 } 467 468 result = ima_parse_rule(p, entry); 469 if (result) { 470 kfree(entry); 471 integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL, 472 NULL, op, "invalid policy", result, 473 audit_info); 474 return result; 475 } 476 477 mutex_lock(&ima_measure_mutex); 478 list_add_tail(&entry->list, &measure_policy_rules); 479 mutex_unlock(&ima_measure_mutex); 480 481 return len; 482 } 483 484 /* ima_delete_rules called to cleanup invalid policy */ 485 void ima_delete_rules(void) 486 { 487 struct ima_measure_rule_entry *entry, *tmp; 488 489 mutex_lock(&ima_measure_mutex); 490 list_for_each_entry_safe(entry, tmp, &measure_policy_rules, list) { 491 list_del(&entry->list); 492 kfree(entry); 493 } 494 mutex_unlock(&ima_measure_mutex); 495 } 496