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 entry->lsm[lsm_rule].type = audit_type; 250 result = security_filter_rule_init(entry->lsm[lsm_rule].type, 251 Audit_equal, args, 252 &entry->lsm[lsm_rule].rule); 253 return result; 254 } 255 256 static int ima_parse_rule(char *rule, struct ima_measure_rule_entry *entry) 257 { 258 struct audit_buffer *ab; 259 char *p; 260 int result = 0; 261 262 ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_INTEGRITY_RULE); 263 264 entry->action = -1; 265 while ((p = strsep(&rule, " \n")) != NULL) { 266 substring_t args[MAX_OPT_ARGS]; 267 int token; 268 unsigned long lnum; 269 270 if (result < 0) 271 break; 272 if (!*p) 273 continue; 274 token = match_token(p, policy_tokens, args); 275 switch (token) { 276 case Opt_measure: 277 audit_log_format(ab, "%s ", "measure"); 278 entry->action = MEASURE; 279 break; 280 case Opt_dont_measure: 281 audit_log_format(ab, "%s ", "dont_measure"); 282 entry->action = DONT_MEASURE; 283 break; 284 case Opt_func: 285 audit_log_format(ab, "func=%s ", args[0].from); 286 if (strcmp(args[0].from, "FILE_CHECK") == 0) 287 entry->func = FILE_CHECK; 288 /* PATH_CHECK is for backwards compat */ 289 else if (strcmp(args[0].from, "PATH_CHECK") == 0) 290 entry->func = FILE_CHECK; 291 else if (strcmp(args[0].from, "FILE_MMAP") == 0) 292 entry->func = FILE_MMAP; 293 else if (strcmp(args[0].from, "BPRM_CHECK") == 0) 294 entry->func = BPRM_CHECK; 295 else 296 result = -EINVAL; 297 if (!result) 298 entry->flags |= IMA_FUNC; 299 break; 300 case Opt_mask: 301 audit_log_format(ab, "mask=%s ", args[0].from); 302 if ((strcmp(args[0].from, "MAY_EXEC")) == 0) 303 entry->mask = MAY_EXEC; 304 else if (strcmp(args[0].from, "MAY_WRITE") == 0) 305 entry->mask = MAY_WRITE; 306 else if (strcmp(args[0].from, "MAY_READ") == 0) 307 entry->mask = MAY_READ; 308 else if (strcmp(args[0].from, "MAY_APPEND") == 0) 309 entry->mask = MAY_APPEND; 310 else 311 result = -EINVAL; 312 if (!result) 313 entry->flags |= IMA_MASK; 314 break; 315 case Opt_fsmagic: 316 audit_log_format(ab, "fsmagic=%s ", args[0].from); 317 result = strict_strtoul(args[0].from, 16, 318 &entry->fsmagic); 319 if (!result) 320 entry->flags |= IMA_FSMAGIC; 321 break; 322 case Opt_uid: 323 audit_log_format(ab, "uid=%s ", args[0].from); 324 result = strict_strtoul(args[0].from, 10, &lnum); 325 if (!result) { 326 entry->uid = (uid_t) lnum; 327 if (entry->uid != lnum) 328 result = -EINVAL; 329 else 330 entry->flags |= IMA_UID; 331 } 332 break; 333 case Opt_obj_user: 334 audit_log_format(ab, "obj_user=%s ", args[0].from); 335 result = ima_lsm_rule_init(entry, args[0].from, 336 LSM_OBJ_USER, 337 AUDIT_OBJ_USER); 338 break; 339 case Opt_obj_role: 340 audit_log_format(ab, "obj_role=%s ", args[0].from); 341 result = ima_lsm_rule_init(entry, args[0].from, 342 LSM_OBJ_ROLE, 343 AUDIT_OBJ_ROLE); 344 break; 345 case Opt_obj_type: 346 audit_log_format(ab, "obj_type=%s ", args[0].from); 347 result = ima_lsm_rule_init(entry, args[0].from, 348 LSM_OBJ_TYPE, 349 AUDIT_OBJ_TYPE); 350 break; 351 case Opt_subj_user: 352 audit_log_format(ab, "subj_user=%s ", args[0].from); 353 result = ima_lsm_rule_init(entry, args[0].from, 354 LSM_SUBJ_USER, 355 AUDIT_SUBJ_USER); 356 break; 357 case Opt_subj_role: 358 audit_log_format(ab, "subj_role=%s ", args[0].from); 359 result = ima_lsm_rule_init(entry, args[0].from, 360 LSM_SUBJ_ROLE, 361 AUDIT_SUBJ_ROLE); 362 break; 363 case Opt_subj_type: 364 audit_log_format(ab, "subj_type=%s ", args[0].from); 365 result = ima_lsm_rule_init(entry, args[0].from, 366 LSM_SUBJ_TYPE, 367 AUDIT_SUBJ_TYPE); 368 break; 369 case Opt_err: 370 audit_log_format(ab, "UNKNOWN=%s ", p); 371 break; 372 } 373 } 374 if (entry->action == UNKNOWN) 375 result = -EINVAL; 376 377 audit_log_format(ab, "res=%d", !result ? 0 : 1); 378 audit_log_end(ab); 379 return result; 380 } 381 382 /** 383 * ima_parse_add_rule - add a rule to measure_policy_rules 384 * @rule - ima measurement policy rule 385 * 386 * Uses a mutex to protect the policy list from multiple concurrent writers. 387 * Returns 0 on success, an error code on failure. 388 */ 389 int ima_parse_add_rule(char *rule) 390 { 391 const char *op = "update_policy"; 392 struct ima_measure_rule_entry *entry; 393 int result = 0; 394 int audit_info = 0; 395 396 /* Prevent installed policy from changing */ 397 if (ima_measure != &measure_default_rules) { 398 integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL, 399 NULL, op, "already exists", 400 -EACCES, audit_info); 401 return -EACCES; 402 } 403 404 entry = kzalloc(sizeof(*entry), GFP_KERNEL); 405 if (!entry) { 406 integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL, 407 NULL, op, "-ENOMEM", -ENOMEM, audit_info); 408 return -ENOMEM; 409 } 410 411 INIT_LIST_HEAD(&entry->list); 412 413 result = ima_parse_rule(rule, entry); 414 if (!result) { 415 mutex_lock(&ima_measure_mutex); 416 list_add_tail(&entry->list, &measure_policy_rules); 417 mutex_unlock(&ima_measure_mutex); 418 } else { 419 kfree(entry); 420 integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL, 421 NULL, op, "invalid policy", result, 422 audit_info); 423 } 424 return result; 425 } 426 427 /* ima_delete_rules called to cleanup invalid policy */ 428 void ima_delete_rules(void) 429 { 430 struct ima_measure_rule_entry *entry, *tmp; 431 432 mutex_lock(&ima_measure_mutex); 433 list_for_each_entry_safe(entry, tmp, &measure_policy_rules, list) { 434 list_del(&entry->list); 435 kfree(entry); 436 } 437 mutex_unlock(&ima_measure_mutex); 438 } 439