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 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 */ 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 */ 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 */ 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 }; 243 244 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 return result; 257 } 258 259 static void ima_log_string(struct audit_buffer *ab, char *key, char *value) 260 { 261 audit_log_format(ab, "%s=", key); 262 audit_log_untrustedstring(ab, value); 263 audit_log_format(ab, " "); 264 } 265 266 static int ima_parse_rule(char *rule, struct ima_measure_rule_entry *entry) 267 { 268 struct audit_buffer *ab; 269 char *p; 270 int result = 0; 271 272 ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_INTEGRITY_RULE); 273 274 entry->uid = -1; 275 entry->action = UNKNOWN; 276 while ((p = strsep(&rule, " \t")) != NULL) { 277 substring_t args[MAX_OPT_ARGS]; 278 int token; 279 unsigned long lnum; 280 281 if (result < 0) 282 break; 283 if ((*p == '\0') || (*p == ' ') || (*p == '\t')) 284 continue; 285 token = match_token(p, policy_tokens, args); 286 switch (token) { 287 case Opt_measure: 288 ima_log_string(ab, "action", "measure"); 289 290 if (entry->action != UNKNOWN) 291 result = -EINVAL; 292 293 entry->action = MEASURE; 294 break; 295 case Opt_dont_measure: 296 ima_log_string(ab, "action", "dont_measure"); 297 298 if (entry->action != UNKNOWN) 299 result = -EINVAL; 300 301 entry->action = DONT_MEASURE; 302 break; 303 case Opt_func: 304 ima_log_string(ab, "func", args[0].from); 305 306 if (entry->func) 307 result = -EINVAL; 308 309 if (strcmp(args[0].from, "FILE_CHECK") == 0) 310 entry->func = FILE_CHECK; 311 /* PATH_CHECK is for backwards compat */ 312 else if (strcmp(args[0].from, "PATH_CHECK") == 0) 313 entry->func = FILE_CHECK; 314 else if (strcmp(args[0].from, "FILE_MMAP") == 0) 315 entry->func = FILE_MMAP; 316 else if (strcmp(args[0].from, "BPRM_CHECK") == 0) 317 entry->func = BPRM_CHECK; 318 else 319 result = -EINVAL; 320 if (!result) 321 entry->flags |= IMA_FUNC; 322 break; 323 case Opt_mask: 324 ima_log_string(ab, "mask", args[0].from); 325 326 if (entry->mask) 327 result = -EINVAL; 328 329 if ((strcmp(args[0].from, "MAY_EXEC")) == 0) 330 entry->mask = MAY_EXEC; 331 else if (strcmp(args[0].from, "MAY_WRITE") == 0) 332 entry->mask = MAY_WRITE; 333 else if (strcmp(args[0].from, "MAY_READ") == 0) 334 entry->mask = MAY_READ; 335 else if (strcmp(args[0].from, "MAY_APPEND") == 0) 336 entry->mask = MAY_APPEND; 337 else 338 result = -EINVAL; 339 if (!result) 340 entry->flags |= IMA_MASK; 341 break; 342 case Opt_fsmagic: 343 ima_log_string(ab, "fsmagic", args[0].from); 344 345 if (entry->fsmagic) { 346 result = -EINVAL; 347 break; 348 } 349 350 result = strict_strtoul(args[0].from, 16, 351 &entry->fsmagic); 352 if (!result) 353 entry->flags |= IMA_FSMAGIC; 354 break; 355 case Opt_uid: 356 ima_log_string(ab, "uid", args[0].from); 357 358 if (entry->uid != -1) { 359 result = -EINVAL; 360 break; 361 } 362 363 result = strict_strtoul(args[0].from, 10, &lnum); 364 if (!result) { 365 entry->uid = (uid_t) lnum; 366 if (entry->uid != lnum) 367 result = -EINVAL; 368 else 369 entry->flags |= IMA_UID; 370 } 371 break; 372 case Opt_obj_user: 373 ima_log_string(ab, "obj_user", args[0].from); 374 result = ima_lsm_rule_init(entry, args[0].from, 375 LSM_OBJ_USER, 376 AUDIT_OBJ_USER); 377 break; 378 case Opt_obj_role: 379 ima_log_string(ab, "obj_role", args[0].from); 380 result = ima_lsm_rule_init(entry, args[0].from, 381 LSM_OBJ_ROLE, 382 AUDIT_OBJ_ROLE); 383 break; 384 case Opt_obj_type: 385 ima_log_string(ab, "obj_type", args[0].from); 386 result = ima_lsm_rule_init(entry, args[0].from, 387 LSM_OBJ_TYPE, 388 AUDIT_OBJ_TYPE); 389 break; 390 case Opt_subj_user: 391 ima_log_string(ab, "subj_user", args[0].from); 392 result = ima_lsm_rule_init(entry, args[0].from, 393 LSM_SUBJ_USER, 394 AUDIT_SUBJ_USER); 395 break; 396 case Opt_subj_role: 397 ima_log_string(ab, "subj_role", args[0].from); 398 result = ima_lsm_rule_init(entry, args[0].from, 399 LSM_SUBJ_ROLE, 400 AUDIT_SUBJ_ROLE); 401 break; 402 case Opt_subj_type: 403 ima_log_string(ab, "subj_type", args[0].from); 404 result = ima_lsm_rule_init(entry, args[0].from, 405 LSM_SUBJ_TYPE, 406 AUDIT_SUBJ_TYPE); 407 break; 408 case Opt_err: 409 ima_log_string(ab, "UNKNOWN", p); 410 result = -EINVAL; 411 break; 412 } 413 } 414 if (!result && (entry->action == UNKNOWN)) 415 result = -EINVAL; 416 417 audit_log_format(ab, "res=%d", !!result); 418 audit_log_end(ab); 419 return result; 420 } 421 422 /** 423 * ima_parse_add_rule - add a rule to measure_policy_rules 424 * @rule - ima measurement policy rule 425 * 426 * Uses a mutex to protect the policy list from multiple concurrent writers. 427 * Returns the length of the rule parsed, an error code on failure 428 */ 429 ssize_t ima_parse_add_rule(char *rule) 430 { 431 const char *op = "update_policy"; 432 char *p; 433 struct ima_measure_rule_entry *entry; 434 ssize_t result, len; 435 int audit_info = 0; 436 437 /* Prevent installed policy from changing */ 438 if (ima_measure != &measure_default_rules) { 439 integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL, 440 NULL, op, "already exists", 441 -EACCES, audit_info); 442 return -EACCES; 443 } 444 445 entry = kzalloc(sizeof(*entry), GFP_KERNEL); 446 if (!entry) { 447 integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL, 448 NULL, op, "-ENOMEM", -ENOMEM, audit_info); 449 return -ENOMEM; 450 } 451 452 INIT_LIST_HEAD(&entry->list); 453 454 p = strsep(&rule, "\n"); 455 len = strlen(p) + 1; 456 457 if (*p == '#') { 458 kfree(entry); 459 return len; 460 } 461 462 result = ima_parse_rule(p, entry); 463 if (result) { 464 kfree(entry); 465 integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL, 466 NULL, op, "invalid policy", result, 467 audit_info); 468 return result; 469 } 470 471 mutex_lock(&ima_measure_mutex); 472 list_add_tail(&entry->list, &measure_policy_rules); 473 mutex_unlock(&ima_measure_mutex); 474 475 return len; 476 } 477 478 /* ima_delete_rules called to cleanup invalid policy */ 479 void ima_delete_rules(void) 480 { 481 struct ima_measure_rule_entry *entry, *tmp; 482 483 mutex_lock(&ima_measure_mutex); 484 list_for_each_entry_safe(entry, tmp, &measure_policy_rules, list) { 485 list_del(&entry->list); 486 kfree(entry); 487 } 488 mutex_unlock(&ima_measure_mutex); 489 } 490