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