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
  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         if (!entry->lsm[lsm_rule].rule)
 257                 return -EINVAL;
 258         return result;
 259 }
 260
 261 static void ima_log_string(struct audit_buffer *ab, char *key, char *value)
 262 {
 263         audit_log_format(ab, "%s=", key);
 264         audit_log_untrustedstring(ab, value);
 265         audit_log_format(ab, " ");
 266 }
 267
 268 static int ima_parse_rule(char *rule, struct ima_measure_rule_entry *entry)
 269 {
 270         struct audit_buffer *ab;
 271         char *p;
 272         int result = 0;
 273
 274         ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_INTEGRITY_RULE);
 275
 276         entry->uid = -1;
 277         entry->action = UNKNOWN;
 278         while ((p = strsep(&rule, " \t")) != NULL) {
 279                 substring_t args[MAX_OPT_ARGS];
 280                 int token;
 281                 unsigned long lnum;
 282
 283                 if (result < 0)
 284                         break;
 285                 if ((*p == '\0') || (*p == ' ') || (*p == '\t'))
 286                         continue;
 287                 token = match_token(p, policy_tokens, args);
 288                 switch (token) {
 289                 case Opt_measure:
 290                         ima_log_string(ab, "action", "measure");
 291
 292                         if (entry->action != UNKNOWN)
 293                                 result = -EINVAL;
 294
 295                         entry->action = MEASURE;
 296                         break;
 297                 case Opt_dont_measure:
 298                         ima_log_string(ab, "action", "dont_measure");
 299
 300                         if (entry->action != UNKNOWN)
 301                                 result = -EINVAL;
 302
 303                         entry->action = DONT_MEASURE;
 304                         break;
 305                 case Opt_func:
 306                         ima_log_string(ab, "func", args[0].from);
 307
 308                         if (entry->func)
 309                                 result  = -EINVAL;
 310
 311                         if (strcmp(args[0].from, "FILE_CHECK") == 0)
 312                                 entry->func = FILE_CHECK;
 313                         /* PATH_CHECK is for backwards compat */
 314                         else if (strcmp(args[0].from, "PATH_CHECK") == 0)
 315                                 entry->func = FILE_CHECK;
 316                         else if (strcmp(args[0].from, "FILE_MMAP") == 0)
 317                                 entry->func = FILE_MMAP;
 318                         else if (strcmp(args[0].from, "BPRM_CHECK") == 0)
 319                                 entry->func = BPRM_CHECK;
 320                         else
 321                                 result = -EINVAL;
 322                         if (!result)
 323                                 entry->flags |= IMA_FUNC;
 324                         break;
 325                 case Opt_mask:
 326                         ima_log_string(ab, "mask", args[0].from);
 327
 328                         if (entry->mask)
 329                                 result = -EINVAL;
 330
 331                         if ((strcmp(args[0].from, "MAY_EXEC")) == 0)
 332                                 entry->mask = MAY_EXEC;
 333                         else if (strcmp(args[0].from, "MAY_WRITE") == 0)
 334                                 entry->mask = MAY_WRITE;
 335                         else if (strcmp(args[0].from, "MAY_READ") == 0)
 336                                 entry->mask = MAY_READ;
 337                         else if (strcmp(args[0].from, "MAY_APPEND") == 0)
 338                                 entry->mask = MAY_APPEND;
 339                         else
 340                                 result = -EINVAL;
 341                         if (!result)
 342                                 entry->flags |= IMA_MASK;
 343                         break;
 344                 case Opt_fsmagic:
 345                         ima_log_string(ab, "fsmagic", args[0].from);
 346
 347                         if (entry->fsmagic) {
 348                                 result = -EINVAL;
 349                                 break;
 350                         }
 351
 352                         result = strict_strtoul(args[0].from, 16,
 353                                                 &entry->fsmagic);
 354                         if (!result)
 355                                 entry->flags |= IMA_FSMAGIC;
 356                         break;
 357                 case Opt_uid:
 358                         ima_log_string(ab, "uid", args[0].from);
 359
 360                         if (entry->uid != -1) {
 361                                 result = -EINVAL;
 362                                 break;
 363                         }
 364
 365                         result = strict_strtoul(args[0].from, 10, &lnum);
 366                         if (!result) {
 367                                 entry->uid = (uid_t) lnum;
 368                                 if (entry->uid != lnum)
 369                                         result = -EINVAL;
 370                                 else
 371                                         entry->flags |= IMA_UID;
 372                         }
 373                         break;
 374                 case Opt_obj_user:
 375                         ima_log_string(ab, "obj_user", args[0].from);
 376                         result = ima_lsm_rule_init(entry, args[0].from,
 377                                                    LSM_OBJ_USER,
 378                                                    AUDIT_OBJ_USER);
 379                         break;
 380                 case Opt_obj_role:
 381                         ima_log_string(ab, "obj_role", args[0].from);
 382                         result = ima_lsm_rule_init(entry, args[0].from,
 383                                                    LSM_OBJ_ROLE,
 384                                                    AUDIT_OBJ_ROLE);
 385                         break;
 386                 case Opt_obj_type:
 387                         ima_log_string(ab, "obj_type", args[0].from);
 388                         result = ima_lsm_rule_init(entry, args[0].from,
 389                                                    LSM_OBJ_TYPE,
 390                                                    AUDIT_OBJ_TYPE);
 391                         break;
 392                 case Opt_subj_user:
 393                         ima_log_string(ab, "subj_user", args[0].from);
 394                         result = ima_lsm_rule_init(entry, args[0].from,
 395                                                    LSM_SUBJ_USER,
 396                                                    AUDIT_SUBJ_USER);
 397                         break;
 398                 case Opt_subj_role:
 399                         ima_log_string(ab, "subj_role", args[0].from);
 400                         result = ima_lsm_rule_init(entry, args[0].from,
 401                                                    LSM_SUBJ_ROLE,
 402                                                    AUDIT_SUBJ_ROLE);
 403                         break;
 404                 case Opt_subj_type:
 405                         ima_log_string(ab, "subj_type", args[0].from);
 406                         result = ima_lsm_rule_init(entry, args[0].from,
 407                                                    LSM_SUBJ_TYPE,
 408                                                    AUDIT_SUBJ_TYPE);
 409                         break;
 410                 case Opt_err:
 411                         ima_log_string(ab, "UNKNOWN", p);
 412                         result = -EINVAL;
 413                         break;
 414                 }
 415         }
 416         if (!result && (entry->action == UNKNOWN))
 417                 result = -EINVAL;
 418
 419         audit_log_format(ab, "res=%d", !!result);
 420         audit_log_end(ab);
 421         return result;
 422 }
 423
 424 /**
 425  * ima_parse_add_rule - add a rule to measure_policy_rules
 426  * @rule - ima measurement policy rule
 427  *
 428  * Uses a mutex to protect the policy list from multiple concurrent writers.
 429  * Returns the length of the rule parsed, an error code on failure
 430  */
 431 ssize_t ima_parse_add_rule(char *rule)
 432 {
 433         const char *op = "update_policy";
 434         char *p;
 435         struct ima_measure_rule_entry *entry;
 436         ssize_t result, len;
 437         int audit_info = 0;
 438
 439         /* Prevent installed policy from changing */
 440         if (ima_measure != &measure_default_rules) {
 441                 integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL,
 442                                     NULL, op, "already exists",
 443                                     -EACCES, audit_info);
 444                 return -EACCES;
 445         }
 446
 447         entry = kzalloc(sizeof(*entry), GFP_KERNEL);
 448         if (!entry) {
 449                 integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL,
 450                                     NULL, op, "-ENOMEM", -ENOMEM, audit_info);
 451                 return -ENOMEM;
 452         }
 453
 454         INIT_LIST_HEAD(&entry->list);
 455
 456         p = strsep(&rule, "\n");
 457         len = strlen(p) + 1;
 458
 459         if (*p == '#') {
 460                 kfree(entry);
 461                 return len;
 462         }
 463
 464         result = ima_parse_rule(p, entry);
 465         if (result) {
 466                 kfree(entry);
 467                 integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL,
 468                                     NULL, op, "invalid policy", result,
 469                                     audit_info);
 470                 return result;
 471         }
 472
 473         mutex_lock(&ima_measure_mutex);
 474         list_add_tail(&entry->list, &measure_policy_rules);
 475         mutex_unlock(&ima_measure_mutex);
 476
 477         return len;
 478 }
 479
 480 /* ima_delete_rules called to cleanup invalid policy */
 481 void ima_delete_rules(void)
 482 {
 483         struct ima_measure_rule_entry *entry, *tmp;
 484
 485         mutex_lock(&ima_measure_mutex);
 486         list_for_each_entry_safe(entry, tmp, &measure_policy_rules, list) {
 487                 list_del(&entry->list);
 488                 kfree(entry);
 489         }
 490         mutex_unlock(&ima_measure_mutex);
 491 }