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         const struct cred *cred = current_cred();
 103         int i;
 104
 105         if ((rule->flags & IMA_FUNC) && rule->func != func)
 106                 return false;
 107         if ((rule->flags & IMA_MASK) && rule->mask != mask)
 108                 return false;
 109         if ((rule->flags & IMA_FSMAGIC)
 110             && rule->fsmagic != inode->i_sb->s_magic)
 111                 return false;
 112         if ((rule->flags & IMA_UID) && rule->uid != cred->uid)
 113                 return false;
 114         for (i = 0; i < MAX_LSM_RULES; i++) {
 115                 int rc = 0;
 116                 u32 osid, sid;
 117
 118                 if (!rule->lsm[i].rule)
 119                         continue;
 120
 121                 switch (i) {
 122                 case LSM_OBJ_USER:
 123                 case LSM_OBJ_ROLE:
 124                 case LSM_OBJ_TYPE:
 125                         security_inode_getsecid(inode, &osid);
 126                         rc = security_filter_rule_match(osid,
 127                                                         rule->lsm[i].type,
 128                                                         Audit_equal,
 129                                                         rule->lsm[i].rule,
 130                                                         NULL);
 131                         break;
 132                 case LSM_SUBJ_USER:
 133                 case LSM_SUBJ_ROLE:
 134                 case LSM_SUBJ_TYPE:
 135                         security_task_getsecid(tsk, &sid);
 136                         rc = security_filter_rule_match(sid,
 137                                                         rule->lsm[i].type,
 138                                                         Audit_equal,
 139                                                         rule->lsm[i].rule,
 140                                                         NULL);
 141                 default:
 142                         break;
 143                 }
 144                 if (!rc)
 145                         return false;
 146         }
 147         return true;
 148 }
 149
 150 /**
 151  * ima_match_policy - decision based on LSM and other conditions
 152  * @inode: pointer to an inode for which the policy decision is being made
 153  * @func: IMA hook identifier
 154  * @mask: requested action (MAY_READ | MAY_WRITE | MAY_APPEND | MAY_EXEC)
 155  *
 156  * Measure decision based on func/mask/fsmagic and LSM(subj/obj/type)
 157  * conditions.
 158  *
 159  * (There is no need for locking when walking the policy list,
 160  * as elements in the list are never deleted, nor does the list
 161  * change.)
 162  */
 163 int ima_match_policy(struct inode *inode, enum ima_hooks func, int mask)
 164 {
 165         struct ima_measure_rule_entry *entry;
 166
 167         list_for_each_entry(entry, ima_measure, list) {
 168                 bool rc;
 169
 170                 rc = ima_match_rules(entry, inode, func, mask);
 171                 if (rc)
 172                         return entry->action;
 173         }
 174         return 0;
 175 }
 176
 177 /**
 178  * ima_init_policy - initialize the default measure rules.
 179  *
 180  * ima_measure points to either the measure_default_rules or the
 181  * the new measure_policy_rules.
 182  */
 183 void __init ima_init_policy(void)
 184 {
 185         int i, entries;
 186
 187         /* if !ima_use_tcb set entries = 0 so we load NO default rules */
 188         if (ima_use_tcb)
 189                 entries = ARRAY_SIZE(default_rules);
 190         else
 191                 entries = 0;
 192
 193         for (i = 0; i < entries; i++)
 194                 list_add_tail(&default_rules[i].list, &measure_default_rules);
 195         ima_measure = &measure_default_rules;
 196 }
 197
 198 /**
 199  * ima_update_policy - update default_rules with new measure rules
 200  *
 201  * Called on file .release to update the default rules with a complete new
 202  * policy.  Once updated, the policy is locked, no additional rules can be
 203  * added to the policy.
 204  */
 205 void ima_update_policy(void)
 206 {
 207         const char *op = "policy_update";
 208         const char *cause = "already exists";
 209         int result = 1;
 210         int audit_info = 0;
 211
 212         if (ima_measure == &measure_default_rules) {
 213                 ima_measure = &measure_policy_rules;
 214                 cause = "complete";
 215                 result = 0;
 216         }
 217         integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL,
 218                             NULL, op, cause, result, audit_info);
 219 }
 220
 221 enum {
 222         Opt_err = -1,
 223         Opt_measure = 1, Opt_dont_measure,
 224         Opt_obj_user, Opt_obj_role, Opt_obj_type,
 225         Opt_subj_user, Opt_subj_role, Opt_subj_type,
 226         Opt_func, Opt_mask, Opt_fsmagic, Opt_uid
 227 };
 228
 229 static match_table_t policy_tokens = {
 230         {Opt_measure, "measure"},
 231         {Opt_dont_measure, "dont_measure"},
 232         {Opt_obj_user, "obj_user=%s"},
 233         {Opt_obj_role, "obj_role=%s"},
 234         {Opt_obj_type, "obj_type=%s"},
 235         {Opt_subj_user, "subj_user=%s"},
 236         {Opt_subj_role, "subj_role=%s"},
 237         {Opt_subj_type, "subj_type=%s"},
 238         {Opt_func, "func=%s"},
 239         {Opt_mask, "mask=%s"},
 240         {Opt_fsmagic, "fsmagic=%s"},
 241         {Opt_uid, "uid=%s"},
 242         {Opt_err, NULL}
 243 };
 244
 245 static int ima_lsm_rule_init(struct ima_measure_rule_entry *entry,
 246                              char *args, int lsm_rule, int audit_type)
 247 {
 248         int result;
 249
 250         if (entry->lsm[lsm_rule].rule)
 251                 return -EINVAL;
 252
 253         entry->lsm[lsm_rule].type = audit_type;
 254         result = security_filter_rule_init(entry->lsm[lsm_rule].type,
 255                                            Audit_equal, args,
 256                                            &entry->lsm[lsm_rule].rule);
 257         if (!entry->lsm[lsm_rule].rule)
 258                 return -EINVAL;
 259         return result;
 260 }
 261
 262 static void ima_log_string(struct audit_buffer *ab, char *key, char *value)
 263 {
 264         audit_log_format(ab, "%s=", key);
 265         audit_log_untrustedstring(ab, value);
 266         audit_log_format(ab, " ");
 267 }
 268
 269 static int ima_parse_rule(char *rule, struct ima_measure_rule_entry *entry)
 270 {
 271         struct audit_buffer *ab;
 272         char *p;
 273         int result = 0;
 274
 275         ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_INTEGRITY_RULE);
 276
 277         entry->uid = -1;
 278         entry->action = UNKNOWN;
 279         while ((p = strsep(&rule, " \t")) != NULL) {
 280                 substring_t args[MAX_OPT_ARGS];
 281                 int token;
 282                 unsigned long lnum;
 283
 284                 if (result < 0)
 285                         break;
 286                 if ((*p == '\0') || (*p == ' ') || (*p == '\t'))
 287                         continue;
 288                 token = match_token(p, policy_tokens, args);
 289                 switch (token) {
 290                 case Opt_measure:
 291                         ima_log_string(ab, "action", "measure");
 292
 293                         if (entry->action != UNKNOWN)
 294                                 result = -EINVAL;
 295
 296                         entry->action = MEASURE;
 297                         break;
 298                 case Opt_dont_measure:
 299                         ima_log_string(ab, "action", "dont_measure");
 300
 301                         if (entry->action != UNKNOWN)
 302                                 result = -EINVAL;
 303
 304                         entry->action = DONT_MEASURE;
 305                         break;
 306                 case Opt_func:
 307                         ima_log_string(ab, "func", args[0].from);
 308
 309                         if (entry->func)
 310                                 result  = -EINVAL;
 311
 312                         if (strcmp(args[0].from, "FILE_CHECK") == 0)
 313                                 entry->func = FILE_CHECK;
 314                         /* PATH_CHECK is for backwards compat */
 315                         else if (strcmp(args[0].from, "PATH_CHECK") == 0)
 316                                 entry->func = FILE_CHECK;
 317                         else if (strcmp(args[0].from, "FILE_MMAP") == 0)
 318                                 entry->func = FILE_MMAP;
 319                         else if (strcmp(args[0].from, "BPRM_CHECK") == 0)
 320                                 entry->func = BPRM_CHECK;
 321                         else
 322                                 result = -EINVAL;
 323                         if (!result)
 324                                 entry->flags |= IMA_FUNC;
 325                         break;
 326                 case Opt_mask:
 327                         ima_log_string(ab, "mask", args[0].from);
 328
 329                         if (entry->mask)
 330                                 result = -EINVAL;
 331
 332                         if ((strcmp(args[0].from, "MAY_EXEC")) == 0)
 333                                 entry->mask = MAY_EXEC;
 334                         else if (strcmp(args[0].from, "MAY_WRITE") == 0)
 335                                 entry->mask = MAY_WRITE;
 336                         else if (strcmp(args[0].from, "MAY_READ") == 0)
 337                                 entry->mask = MAY_READ;
 338                         else if (strcmp(args[0].from, "MAY_APPEND") == 0)
 339                                 entry->mask = MAY_APPEND;
 340                         else
 341                                 result = -EINVAL;
 342                         if (!result)
 343                                 entry->flags |= IMA_MASK;
 344                         break;
 345                 case Opt_fsmagic:
 346                         ima_log_string(ab, "fsmagic", args[0].from);
 347
 348                         if (entry->fsmagic) {
 349                                 result = -EINVAL;
 350                                 break;
 351                         }
 352
 353                         result = strict_strtoul(args[0].from, 16,
 354                                                 &entry->fsmagic);
 355                         if (!result)
 356                                 entry->flags |= IMA_FSMAGIC;
 357                         break;
 358                 case Opt_uid:
 359                         ima_log_string(ab, "uid", args[0].from);
 360
 361                         if (entry->uid != -1) {
 362                                 result = -EINVAL;
 363                                 break;
 364                         }
 365
 366                         result = strict_strtoul(args[0].from, 10, &lnum);
 367                         if (!result) {
 368                                 entry->uid = (uid_t) lnum;
 369                                 if (entry->uid != lnum)
 370                                         result = -EINVAL;
 371                                 else
 372                                         entry->flags |= IMA_UID;
 373                         }
 374                         break;
 375                 case Opt_obj_user:
 376                         ima_log_string(ab, "obj_user", args[0].from);
 377                         result = ima_lsm_rule_init(entry, args[0].from,
 378                                                    LSM_OBJ_USER,
 379                                                    AUDIT_OBJ_USER);
 380                         break;
 381                 case Opt_obj_role:
 382                         ima_log_string(ab, "obj_role", args[0].from);
 383                         result = ima_lsm_rule_init(entry, args[0].from,
 384                                                    LSM_OBJ_ROLE,
 385                                                    AUDIT_OBJ_ROLE);
 386                         break;
 387                 case Opt_obj_type:
 388                         ima_log_string(ab, "obj_type", args[0].from);
 389                         result = ima_lsm_rule_init(entry, args[0].from,
 390                                                    LSM_OBJ_TYPE,
 391                                                    AUDIT_OBJ_TYPE);
 392                         break;
 393                 case Opt_subj_user:
 394                         ima_log_string(ab, "subj_user", args[0].from);
 395                         result = ima_lsm_rule_init(entry, args[0].from,
 396                                                    LSM_SUBJ_USER,
 397                                                    AUDIT_SUBJ_USER);
 398                         break;
 399                 case Opt_subj_role:
 400                         ima_log_string(ab, "subj_role", args[0].from);
 401                         result = ima_lsm_rule_init(entry, args[0].from,
 402                                                    LSM_SUBJ_ROLE,
 403                                                    AUDIT_SUBJ_ROLE);
 404                         break;
 405                 case Opt_subj_type:
 406                         ima_log_string(ab, "subj_type", args[0].from);
 407                         result = ima_lsm_rule_init(entry, args[0].from,
 408                                                    LSM_SUBJ_TYPE,
 409                                                    AUDIT_SUBJ_TYPE);
 410                         break;
 411                 case Opt_err:
 412                         ima_log_string(ab, "UNKNOWN", p);
 413                         result = -EINVAL;
 414                         break;
 415                 }
 416         }
 417         if (!result && (entry->action == UNKNOWN))
 418                 result = -EINVAL;
 419
 420         audit_log_format(ab, "res=%d", !!result);
 421         audit_log_end(ab);
 422         return result;
 423 }
 424
 425 /**
 426  * ima_parse_add_rule - add a rule to measure_policy_rules
 427  * @rule - ima measurement policy rule
 428  *
 429  * Uses a mutex to protect the policy list from multiple concurrent writers.
 430  * Returns the length of the rule parsed, an error code on failure
 431  */
 432 ssize_t ima_parse_add_rule(char *rule)
 433 {
 434         const char *op = "update_policy";
 435         char *p;
 436         struct ima_measure_rule_entry *entry;
 437         ssize_t result, len;
 438         int audit_info = 0;
 439
 440         /* Prevent installed policy from changing */
 441         if (ima_measure != &measure_default_rules) {
 442                 integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL,
 443                                     NULL, op, "already exists",
 444                                     -EACCES, audit_info);
 445                 return -EACCES;
 446         }
 447
 448         entry = kzalloc(sizeof(*entry), GFP_KERNEL);
 449         if (!entry) {
 450                 integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL,
 451                                     NULL, op, "-ENOMEM", -ENOMEM, audit_info);
 452                 return -ENOMEM;
 453         }
 454
 455         INIT_LIST_HEAD(&entry->list);
 456
 457         p = strsep(&rule, "\n");
 458         len = strlen(p) + 1;
 459
 460         if (*p == '#') {
 461                 kfree(entry);
 462                 return len;
 463         }
 464
 465         result = ima_parse_rule(p, entry);
 466         if (result) {
 467                 kfree(entry);
 468                 integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL,
 469                                     NULL, op, "invalid policy", result,
 470                                     audit_info);
 471                 return result;
 472         }
 473
 474         mutex_lock(&ima_measure_mutex);
 475         list_add_tail(&entry->list, &measure_policy_rules);
 476         mutex_unlock(&ima_measure_mutex);
 477
 478         return len;
 479 }
 480
 481 /* ima_delete_rules called to cleanup invalid policy */
 482 void ima_delete_rules(void)
 483 {
 484         struct ima_measure_rule_entry *entry, *tmp;
 485
 486         mutex_lock(&ima_measure_mutex);
 487         list_for_each_entry_safe(entry, tmp, &measure_policy_rules, list) {
 488                 list_del(&entry->list);
 489                 kfree(entry);
 490         }
 491         mutex_unlock(&ima_measure_mutex);
 492 }