security/integrity/ima/ima_policy.c

   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 #define IMA_FOWNER      0x0010
  28
  29 #define UNKNOWN         0
  30 #define MEASURE         0x0001  /* same as IMA_MEASURE */
  31 #define DONT_MEASURE    0x0002
  32 #define APPRAISE        0x0004  /* same as IMA_APPRAISE */
  33 #define DONT_APPRAISE   0x0008
  34 #define AUDIT           0x0040
  35
  36 #define MAX_LSM_RULES 6
  37 enum lsm_rule_types { LSM_OBJ_USER, LSM_OBJ_ROLE, LSM_OBJ_TYPE,
  38         LSM_SUBJ_USER, LSM_SUBJ_ROLE, LSM_SUBJ_TYPE
  39 };
  40
  41 struct ima_rule_entry {
  42         struct list_head list;
  43         int action;
  44         unsigned int flags;
  45         enum ima_hooks func;
  46         int mask;
  47         unsigned long fsmagic;
  48         uid_t uid;
  49         uid_t fowner;
  50         struct {
  51                 void *rule;     /* LSM file metadata specific */
  52                 int type;       /* audit type */
  53         } lsm[MAX_LSM_RULES];
  54 };
  55
  56 /*
  57  * Without LSM specific knowledge, the default policy can only be
  58  * written in terms of .action, .func, .mask, .fsmagic, .uid, and .fowner
  59  */
  60
  61 /*
  62  * The minimum rule set to allow for full TCB coverage.  Measures all files
  63  * opened or mmap for exec and everything read by root.  Dangerous because
  64  * normal users can easily run the machine out of memory simply building
  65  * and running executables.
  66  */
  67 static struct ima_rule_entry default_rules[] = {
  68         {.action = DONT_MEASURE,.fsmagic = PROC_SUPER_MAGIC,.flags = IMA_FSMAGIC},
  69         {.action = DONT_MEASURE,.fsmagic = SYSFS_MAGIC,.flags = IMA_FSMAGIC},
  70         {.action = DONT_MEASURE,.fsmagic = DEBUGFS_MAGIC,.flags = IMA_FSMAGIC},
  71         {.action = DONT_MEASURE,.fsmagic = TMPFS_MAGIC,.flags = IMA_FSMAGIC},
  72         {.action = DONT_MEASURE,.fsmagic = RAMFS_MAGIC,.flags = IMA_FSMAGIC},
  73         {.action = DONT_MEASURE,.fsmagic = DEVPTS_SUPER_MAGIC,.flags = IMA_FSMAGIC},
  74         {.action = DONT_MEASURE,.fsmagic = BINFMTFS_MAGIC,.flags = IMA_FSMAGIC},
  75         {.action = DONT_MEASURE,.fsmagic = SECURITYFS_MAGIC,.flags = IMA_FSMAGIC},
  76         {.action = DONT_MEASURE,.fsmagic = SELINUX_MAGIC,.flags = IMA_FSMAGIC},
  77         {.action = MEASURE,.func = FILE_MMAP,.mask = MAY_EXEC,
  78          .flags = IMA_FUNC | IMA_MASK},
  79         {.action = MEASURE,.func = BPRM_CHECK,.mask = MAY_EXEC,
  80          .flags = IMA_FUNC | IMA_MASK},
  81         {.action = MEASURE,.func = FILE_CHECK,.mask = MAY_READ,.uid = 0,
  82          .flags = IMA_FUNC | IMA_MASK | IMA_UID},
  83 };
  84
  85 static struct ima_rule_entry default_appraise_rules[] = {
  86         {.action = DONT_APPRAISE,.fsmagic = PROC_SUPER_MAGIC,.flags = IMA_FSMAGIC},
  87         {.action = DONT_APPRAISE,.fsmagic = SYSFS_MAGIC,.flags = IMA_FSMAGIC},
  88         {.action = DONT_APPRAISE,.fsmagic = DEBUGFS_MAGIC,.flags = IMA_FSMAGIC},
  89         {.action = DONT_APPRAISE,.fsmagic = TMPFS_MAGIC,.flags = IMA_FSMAGIC},
  90         {.action = DONT_APPRAISE,.fsmagic = RAMFS_MAGIC,.flags = IMA_FSMAGIC},
  91         {.action = DONT_APPRAISE,.fsmagic = DEVPTS_SUPER_MAGIC,.flags = IMA_FSMAGIC},
  92         {.action = DONT_APPRAISE,.fsmagic = BINFMTFS_MAGIC,.flags = IMA_FSMAGIC},
  93         {.action = DONT_APPRAISE,.fsmagic = SECURITYFS_MAGIC,.flags = IMA_FSMAGIC},
  94         {.action = DONT_APPRAISE,.fsmagic = SELINUX_MAGIC,.flags = IMA_FSMAGIC},
  95         {.action = DONT_APPRAISE,.fsmagic = CGROUP_SUPER_MAGIC,.flags = IMA_FSMAGIC},
  96         {.action = APPRAISE,.fowner = 0,.flags = IMA_FOWNER},
  97 };
  98
  99 static LIST_HEAD(ima_default_rules);
 100 static LIST_HEAD(ima_policy_rules);
 101 static struct list_head *ima_rules;
 102
 103 static DEFINE_MUTEX(ima_rules_mutex);
 104
 105 static bool ima_use_tcb __initdata;
 106 static int __init default_measure_policy_setup(char *str)
 107 {
 108         ima_use_tcb = 1;
 109         return 1;
 110 }
 111 __setup("ima_tcb", default_measure_policy_setup);
 112
 113 static bool ima_use_appraise_tcb __initdata;
 114 static int __init default_appraise_policy_setup(char *str)
 115 {
 116         ima_use_appraise_tcb = 1;
 117         return 1;
 118 }
 119 __setup("ima_appraise_tcb", default_appraise_policy_setup);
 120
 121 /**
 122  * ima_match_rules - determine whether an inode matches the measure rule.
 123  * @rule: a pointer to a rule
 124  * @inode: a pointer to an inode
 125  * @func: LIM hook identifier
 126  * @mask: requested action (MAY_READ | MAY_WRITE | MAY_APPEND | MAY_EXEC)
 127  *
 128  * Returns true on rule match, false on failure.
 129  */
 130 static bool ima_match_rules(struct ima_rule_entry *rule,
 131                             struct inode *inode, enum ima_hooks func, int mask)
 132 {
 133         struct task_struct *tsk = current;
 134         const struct cred *cred = current_cred();
 135         int i;
 136
 137         if ((rule->flags & IMA_FUNC) && rule->func != func)
 138                 return false;
 139         if ((rule->flags & IMA_MASK) && rule->mask != mask)
 140                 return false;
 141         if ((rule->flags & IMA_FSMAGIC)
 142             && rule->fsmagic != inode->i_sb->s_magic)
 143                 return false;
 144         if ((rule->flags & IMA_UID) && rule->uid != cred->uid)
 145                 return false;
 146         if ((rule->flags & IMA_FOWNER) && rule->fowner != inode->i_uid)
 147                 return false;
 148         for (i = 0; i < MAX_LSM_RULES; i++) {
 149                 int rc = 0;
 150                 u32 osid, sid;
 151
 152                 if (!rule->lsm[i].rule)
 153                         continue;
 154
 155                 switch (i) {
 156                 case LSM_OBJ_USER:
 157                 case LSM_OBJ_ROLE:
 158                 case LSM_OBJ_TYPE:
 159                         security_inode_getsecid(inode, &osid);
 160                         rc = security_filter_rule_match(osid,
 161                                                         rule->lsm[i].type,
 162                                                         Audit_equal,
 163                                                         rule->lsm[i].rule,
 164                                                         NULL);
 165                         break;
 166                 case LSM_SUBJ_USER:
 167                 case LSM_SUBJ_ROLE:
 168                 case LSM_SUBJ_TYPE:
 169                         security_task_getsecid(tsk, &sid);
 170                         rc = security_filter_rule_match(sid,
 171                                                         rule->lsm[i].type,
 172                                                         Audit_equal,
 173                                                         rule->lsm[i].rule,
 174                                                         NULL);
 175                 default:
 176                         break;
 177                 }
 178                 if (!rc)
 179                         return false;
 180         }
 181         return true;
 182 }
 183
 184 /**
 185  * ima_match_policy - decision based on LSM and other conditions
 186  * @inode: pointer to an inode for which the policy decision is being made
 187  * @func: IMA hook identifier
 188  * @mask: requested action (MAY_READ | MAY_WRITE | MAY_APPEND | MAY_EXEC)
 189  *
 190  * Measure decision based on func/mask/fsmagic and LSM(subj/obj/type)
 191  * conditions.
 192  *
 193  * (There is no need for locking when walking the policy list,
 194  * as elements in the list are never deleted, nor does the list
 195  * change.)
 196  */
 197 int ima_match_policy(struct inode *inode, enum ima_hooks func, int mask,
 198                      int flags)
 199 {
 200         struct ima_rule_entry *entry;
 201         int action = 0, actmask = flags | (flags << 1);
 202
 203         list_for_each_entry(entry, ima_rules, list) {
 204
 205                 if (!(entry->action & actmask))
 206                         continue;
 207
 208                 if (!ima_match_rules(entry, inode, func, mask))
 209                         continue;
 210
 211                 action |= entry->action & IMA_DO_MASK;
 212                 if (entry->action & IMA_DO_MASK)
 213                         actmask &= ~(entry->action | entry->action << 1);
 214                 else
 215                         actmask &= ~(entry->action | entry->action >> 1);
 216
 217                 if (!actmask)
 218                         break;
 219         }
 220
 221         return action;
 222 }
 223
 224 /**
 225  * ima_init_policy - initialize the default measure rules.
 226  *
 227  * ima_rules points to either the ima_default_rules or the
 228  * the new ima_policy_rules.
 229  */
 230 void __init ima_init_policy(void)
 231 {
 232         int i, measure_entries, appraise_entries;
 233
 234         /* if !ima_use_tcb set entries = 0 so we load NO default rules */
 235         measure_entries = ima_use_tcb ? ARRAY_SIZE(default_rules) : 0;
 236         appraise_entries = ima_use_appraise_tcb ?
 237                          ARRAY_SIZE(default_appraise_rules) : 0;
 238
 239         for (i = 0; i < measure_entries + appraise_entries; i++) {
 240                 if (i < measure_entries)
 241                         list_add_tail(&default_rules[i].list,
 242                                       &ima_default_rules);
 243                 else {
 244                         int j = i - measure_entries;
 245
 246                         list_add_tail(&default_appraise_rules[j].list,
 247                                       &ima_default_rules);
 248                 }
 249         }
 250
 251         ima_rules = &ima_default_rules;
 252 }
 253
 254 /**
 255  * ima_update_policy - update default_rules with new measure rules
 256  *
 257  * Called on file .release to update the default rules with a complete new
 258  * policy.  Once updated, the policy is locked, no additional rules can be
 259  * added to the policy.
 260  */
 261 void ima_update_policy(void)
 262 {
 263         const char *op = "policy_update";
 264         const char *cause = "already exists";
 265         int result = 1;
 266         int audit_info = 0;
 267
 268         if (ima_rules == &ima_default_rules) {
 269                 ima_rules = &ima_policy_rules;
 270                 cause = "complete";
 271                 result = 0;
 272         }
 273         integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL,
 274                             NULL, op, cause, result, audit_info);
 275 }
 276
 277 enum {
 278         Opt_err = -1,
 279         Opt_measure = 1, Opt_dont_measure,
 280         Opt_appraise, Opt_dont_appraise,
 281         Opt_audit,
 282         Opt_obj_user, Opt_obj_role, Opt_obj_type,
 283         Opt_subj_user, Opt_subj_role, Opt_subj_type,
 284         Opt_func, Opt_mask, Opt_fsmagic, Opt_uid, Opt_fowner
 285 };
 286
 287 static match_table_t policy_tokens = {
 288         {Opt_measure, "measure"},
 289         {Opt_dont_measure, "dont_measure"},
 290         {Opt_appraise, "appraise"},
 291         {Opt_dont_appraise, "dont_appraise"},
 292         {Opt_audit, "audit"},
 293         {Opt_obj_user, "obj_user=%s"},
 294         {Opt_obj_role, "obj_role=%s"},
 295         {Opt_obj_type, "obj_type=%s"},
 296         {Opt_subj_user, "subj_user=%s"},
 297         {Opt_subj_role, "subj_role=%s"},
 298         {Opt_subj_type, "subj_type=%s"},
 299         {Opt_func, "func=%s"},
 300         {Opt_mask, "mask=%s"},
 301         {Opt_fsmagic, "fsmagic=%s"},
 302         {Opt_uid, "uid=%s"},
 303         {Opt_fowner, "fowner=%s"},
 304         {Opt_err, NULL}
 305 };
 306
 307 static int ima_lsm_rule_init(struct ima_rule_entry *entry,
 308                              char *args, int lsm_rule, int audit_type)
 309 {
 310         int result;
 311
 312         if (entry->lsm[lsm_rule].rule)
 313                 return -EINVAL;
 314
 315         entry->lsm[lsm_rule].type = audit_type;
 316         result = security_filter_rule_init(entry->lsm[lsm_rule].type,
 317                                            Audit_equal, args,
 318                                            &entry->lsm[lsm_rule].rule);
 319         if (!entry->lsm[lsm_rule].rule)
 320                 return -EINVAL;
 321         return result;
 322 }
 323
 324 static void ima_log_string(struct audit_buffer *ab, char *key, char *value)
 325 {
 326         audit_log_format(ab, "%s=", key);
 327         audit_log_untrustedstring(ab, value);
 328         audit_log_format(ab, " ");
 329 }
 330
 331 static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
 332 {
 333         struct audit_buffer *ab;
 334         char *p;
 335         int result = 0;
 336
 337         ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_INTEGRITY_RULE);
 338
 339         entry->uid = -1;
 340         entry->fowner = -1;
 341         entry->action = UNKNOWN;
 342         while ((p = strsep(&rule, " \t")) != NULL) {
 343                 substring_t args[MAX_OPT_ARGS];
 344                 int token;
 345                 unsigned long lnum;
 346
 347                 if (result < 0)
 348                         break;
 349                 if ((*p == '\0') || (*p == ' ') || (*p == '\t'))
 350                         continue;
 351                 token = match_token(p, policy_tokens, args);
 352                 switch (token) {
 353                 case Opt_measure:
 354                         ima_log_string(ab, "action", "measure");
 355
 356                         if (entry->action != UNKNOWN)
 357                                 result = -EINVAL;
 358
 359                         entry->action = MEASURE;
 360                         break;
 361                 case Opt_dont_measure:
 362                         ima_log_string(ab, "action", "dont_measure");
 363
 364                         if (entry->action != UNKNOWN)
 365                                 result = -EINVAL;
 366
 367                         entry->action = DONT_MEASURE;
 368                         break;
 369                 case Opt_appraise:
 370                         ima_log_string(ab, "action", "appraise");
 371
 372                         if (entry->action != UNKNOWN)
 373                                 result = -EINVAL;
 374
 375                         entry->action = APPRAISE;
 376                         break;
 377                 case Opt_dont_appraise:
 378                         ima_log_string(ab, "action", "dont_appraise");
 379
 380                         if (entry->action != UNKNOWN)
 381                                 result = -EINVAL;
 382
 383                         entry->action = DONT_APPRAISE;
 384                         break;
 385                 case Opt_audit:
 386                         ima_log_string(ab, "action", "audit");
 387
 388                         if (entry->action != UNKNOWN)
 389                                 result = -EINVAL;
 390
 391                         entry->action = AUDIT;
 392                         break;
 393                 case Opt_func:
 394                         ima_log_string(ab, "func", args[0].from);
 395
 396                         if (entry->func)
 397                                 result = -EINVAL;
 398
 399                         if (strcmp(args[0].from, "FILE_CHECK") == 0)
 400                                 entry->func = FILE_CHECK;
 401                         /* PATH_CHECK is for backwards compat */
 402                         else if (strcmp(args[0].from, "PATH_CHECK") == 0)
 403                                 entry->func = FILE_CHECK;
 404                         else if (strcmp(args[0].from, "FILE_MMAP") == 0)
 405                                 entry->func = FILE_MMAP;
 406                         else if (strcmp(args[0].from, "BPRM_CHECK") == 0)
 407                                 entry->func = BPRM_CHECK;
 408                         else
 409                                 result = -EINVAL;
 410                         if (!result)
 411                                 entry->flags |= IMA_FUNC;
 412                         break;
 413                 case Opt_mask:
 414                         ima_log_string(ab, "mask", args[0].from);
 415
 416                         if (entry->mask)
 417                                 result = -EINVAL;
 418
 419                         if ((strcmp(args[0].from, "MAY_EXEC")) == 0)
 420                                 entry->mask = MAY_EXEC;
 421                         else if (strcmp(args[0].from, "MAY_WRITE") == 0)
 422                                 entry->mask = MAY_WRITE;
 423                         else if (strcmp(args[0].from, "MAY_READ") == 0)
 424                                 entry->mask = MAY_READ;
 425                         else if (strcmp(args[0].from, "MAY_APPEND") == 0)
 426                                 entry->mask = MAY_APPEND;
 427                         else
 428                                 result = -EINVAL;
 429                         if (!result)
 430                                 entry->flags |= IMA_MASK;
 431                         break;
 432                 case Opt_fsmagic:
 433                         ima_log_string(ab, "fsmagic", args[0].from);
 434
 435                         if (entry->fsmagic) {
 436                                 result = -EINVAL;
 437                                 break;
 438                         }
 439
 440                         result = strict_strtoul(args[0].from, 16,
 441                                                 &entry->fsmagic);
 442                         if (!result)
 443                                 entry->flags |= IMA_FSMAGIC;
 444                         break;
 445                 case Opt_uid:
 446                         ima_log_string(ab, "uid", args[0].from);
 447
 448                         if (entry->uid != -1) {
 449                                 result = -EINVAL;
 450                                 break;
 451                         }
 452
 453                         result = strict_strtoul(args[0].from, 10, &lnum);
 454                         if (!result) {
 455                                 entry->uid = (uid_t) lnum;
 456                                 if (entry->uid != lnum)
 457                                         result = -EINVAL;
 458                                 else
 459                                         entry->flags |= IMA_UID;
 460                         }
 461                         break;
 462                 case Opt_fowner:
 463                         ima_log_string(ab, "fowner", args[0].from);
 464
 465                         if (entry->fowner != -1) {
 466                                 result = -EINVAL;
 467                                 break;
 468                         }
 469
 470                         result = strict_strtoul(args[0].from, 10, &lnum);
 471                         if (!result) {
 472                                 entry->fowner = (uid_t) lnum;
 473                                 if (entry->fowner != lnum)
 474                                         result = -EINVAL;
 475                                 else
 476                                         entry->flags |= IMA_FOWNER;
 477                         }
 478                         break;
 479                 case Opt_obj_user:
 480                         ima_log_string(ab, "obj_user", args[0].from);
 481                         result = ima_lsm_rule_init(entry, args[0].from,
 482                                                    LSM_OBJ_USER,
 483                                                    AUDIT_OBJ_USER);
 484                         break;
 485                 case Opt_obj_role:
 486                         ima_log_string(ab, "obj_role", args[0].from);
 487                         result = ima_lsm_rule_init(entry, args[0].from,
 488                                                    LSM_OBJ_ROLE,
 489                                                    AUDIT_OBJ_ROLE);
 490                         break;
 491                 case Opt_obj_type:
 492                         ima_log_string(ab, "obj_type", args[0].from);
 493                         result = ima_lsm_rule_init(entry, args[0].from,
 494                                                    LSM_OBJ_TYPE,
 495                                                    AUDIT_OBJ_TYPE);
 496                         break;
 497                 case Opt_subj_user:
 498                         ima_log_string(ab, "subj_user", args[0].from);
 499                         result = ima_lsm_rule_init(entry, args[0].from,
 500                                                    LSM_SUBJ_USER,
 501                                                    AUDIT_SUBJ_USER);
 502                         break;
 503                 case Opt_subj_role:
 504                         ima_log_string(ab, "subj_role", args[0].from);
 505                         result = ima_lsm_rule_init(entry, args[0].from,
 506                                                    LSM_SUBJ_ROLE,
 507                                                    AUDIT_SUBJ_ROLE);
 508                         break;
 509                 case Opt_subj_type:
 510                         ima_log_string(ab, "subj_type", args[0].from);
 511                         result = ima_lsm_rule_init(entry, args[0].from,
 512                                                    LSM_SUBJ_TYPE,
 513                                                    AUDIT_SUBJ_TYPE);
 514                         break;
 515                 case Opt_err:
 516                         ima_log_string(ab, "UNKNOWN", p);
 517                         result = -EINVAL;
 518                         break;
 519                 }
 520         }
 521         if (!result && (entry->action == UNKNOWN))
 522                 result = -EINVAL;
 523
 524         audit_log_format(ab, "res=%d", !result);
 525         audit_log_end(ab);
 526         return result;
 527 }
 528
 529 /**
 530  * ima_parse_add_rule - add a rule to ima_policy_rules
 531  * @rule - ima measurement policy rule
 532  *
 533  * Uses a mutex to protect the policy list from multiple concurrent writers.
 534  * Returns the length of the rule parsed, an error code on failure
 535  */
 536 ssize_t ima_parse_add_rule(char *rule)
 537 {
 538         const char *op = "update_policy";
 539         char *p;
 540         struct ima_rule_entry *entry;
 541         ssize_t result, len;
 542         int audit_info = 0;
 543
 544         /* Prevent installed policy from changing */
 545         if (ima_rules != &ima_default_rules) {
 546                 integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL,
 547                                     NULL, op, "already exists",
 548                                     -EACCES, audit_info);
 549                 return -EACCES;
 550         }
 551
 552         entry = kzalloc(sizeof(*entry), GFP_KERNEL);
 553         if (!entry) {
 554                 integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL,
 555                                     NULL, op, "-ENOMEM", -ENOMEM, audit_info);
 556                 return -ENOMEM;
 557         }
 558
 559         INIT_LIST_HEAD(&entry->list);
 560
 561         p = strsep(&rule, "\n");
 562         len = strlen(p) + 1;
 563
 564         if (*p == '#') {
 565                 kfree(entry);
 566                 return len;
 567         }
 568
 569         result = ima_parse_rule(p, entry);
 570         if (result) {
 571                 kfree(entry);
 572                 integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL,
 573                                     NULL, op, "invalid policy", result,
 574                                     audit_info);
 575                 return result;
 576         }
 577
 578         mutex_lock(&ima_rules_mutex);
 579         list_add_tail(&entry->list, &ima_policy_rules);
 580         mutex_unlock(&ima_rules_mutex);
 581
 582         return len;
 583 }
 584
 585 /* ima_delete_rules called to cleanup invalid policy */
 586 void ima_delete_rules(void)
 587 {
 588         struct ima_rule_entry *entry, *tmp;
 589
 590         mutex_lock(&ima_rules_mutex);
 591         list_for_each_entry_safe(entry, tmp, &ima_policy_rules, list) {
 592                 list_del(&entry->list);
 593                 kfree(entry);
 594         }
 595         mutex_unlock(&ima_rules_mutex);
 596 }