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