Pileus Git - ~andy/linux/blob - 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 = RAMFS_MAGIC,.flags = IMA_FSMAGIC},
  66         {.action = DONT_MEASURE,.fsmagic = SECURITYFS_MAGIC,.flags = IMA_FSMAGIC},
  67         {.action = DONT_MEASURE,.fsmagic = SELINUX_MAGIC,.flags = IMA_FSMAGIC},
  68         {.action = MEASURE,.func = FILE_MMAP,.mask = MAY_EXEC,
  69          .flags = IMA_FUNC | IMA_MASK},
  70         {.action = MEASURE,.func = BPRM_CHECK,.mask = MAY_EXEC,
  71          .flags = IMA_FUNC | IMA_MASK},
  72         {.action = MEASURE,.func = FILE_CHECK,.mask = MAY_READ,.uid = 0,
  73          .flags = IMA_FUNC | IMA_MASK | IMA_UID},
  74 };
  75
  76 static LIST_HEAD(measure_default_rules);
  77 static LIST_HEAD(measure_policy_rules);
  78 static struct list_head *ima_measure;
  79
  80 static DEFINE_MUTEX(ima_measure_mutex);
  81
  82 static bool ima_use_tcb __initdata;
  83 static int __init default_policy_setup(char *str)
  84 {
  85         ima_use_tcb = 1;
  86         return 1;
  87 }
  88 __setup("ima_tcb", default_policy_setup);
  89
  90 /**
  91  * ima_match_rules - determine whether an inode matches the measure rule.
  92  * @rule: a pointer to a rule
  93  * @inode: a pointer to an inode
  94  * @func: LIM hook identifier
  95  * @mask: requested action (MAY_READ | MAY_WRITE | MAY_APPEND | MAY_EXEC)
  96  *
  97  * Returns true on rule match, false on failure.
  98  */
  99 static bool ima_match_rules(struct ima_measure_rule_entry *rule,
 100                             struct inode *inode, enum ima_hooks func, int mask)
 101 {
 102         struct task_struct *tsk = current;
 103         const struct cred *cred = current_cred();
 104         int i;
 105
 106         if ((rule->flags & IMA_FUNC) && rule->func != func)
 107                 return false;
 108         if ((rule->flags & IMA_MASK) && rule->mask != mask)
 109                 return false;
 110         if ((rule->flags & IMA_FSMAGIC)
 111             && rule->fsmagic != inode->i_sb->s_magic)
 112                 return false;
 113         if ((rule->flags & IMA_UID) && rule->uid != cred->uid)
 114                 return false;
 115         for (i = 0; i < MAX_LSM_RULES; i++) {
 116                 int rc = 0;
 117                 u32 osid, sid;
 118
 119                 if (!rule->lsm[i].rule)
 120                         continue;
 121
 122                 switch (i) {
 123                 case LSM_OBJ_USER:
 124                 case LSM_OBJ_ROLE:
 125                 case LSM_OBJ_TYPE:
 126                         security_inode_getsecid(inode, &osid);
 127                         rc = security_filter_rule_match(osid,
 128                                                         rule->lsm[i].type,
 129                                                         Audit_equal,
 130                                                         rule->lsm[i].rule,
 131                                                         NULL);
 132                         break;
 133                 case LSM_SUBJ_USER:
 134                 case LSM_SUBJ_ROLE:
 135                 case LSM_SUBJ_TYPE:
 136                         security_task_getsecid(tsk, &sid);
 137                         rc = security_filter_rule_match(sid,
 138                                                         rule->lsm[i].type,
 139                                                         Audit_equal,
 140                                                         rule->lsm[i].rule,
 141                                                         NULL);
 142                 default:
 143                         break;
 144                 }
 145                 if (!rc)
 146                         return false;
 147         }
 148         return true;
 149 }
 150
 151 /**
 152  * ima_match_policy - decision based on LSM and other conditions
 153  * @inode: pointer to an inode for which the policy decision is being made
 154  * @func: IMA hook identifier
 155  * @mask: requested action (MAY_READ | MAY_WRITE | MAY_APPEND | MAY_EXEC)
 156  *
 157  * Measure decision based on func/mask/fsmagic and LSM(subj/obj/type)
 158  * conditions.
 159  *
 160  * (There is no need for locking when walking the policy list,
 161  * as elements in the list are never deleted, nor does the list
 162  * change.)
 163  */
 164 int ima_match_policy(struct inode *inode, enum ima_hooks func, int mask)
 165 {
 166         struct ima_measure_rule_entry *entry;
 167
 168         list_for_each_entry(entry, ima_measure, list) {
 169                 bool rc;
 170
 171                 rc = ima_match_rules(entry, inode, func, mask);
 172                 if (rc)
 173                         return entry->action;
 174         }
 175         return 0;
 176 }
 177
 178 /**
 179  * ima_init_policy - initialize the default measure rules.
 180  *
 181  * ima_measure points to either the measure_default_rules or the
 182  * the new measure_policy_rules.
 183  */
 184 void __init ima_init_policy(void)
 185 {
 186         int i, entries;
 187
 188         /* if !ima_use_tcb set entries = 0 so we load NO default rules */
 189         if (ima_use_tcb)
 190                 entries = ARRAY_SIZE(default_rules);
 191         else
 192                 entries = 0;
 193
 194         for (i = 0; i < entries; i++)
 195                 list_add_tail(&default_rules[i].list, &measure_default_rules);
 196         ima_measure = &measure_default_rules;
 197 }
 198
 199 /**
 200  * ima_update_policy - update default_rules with new measure rules
 201  *
 202  * Called on file .release to update the default rules with a complete new
 203  * policy.  Once updated, the policy is locked, no additional rules can be
 204  * added to the policy.
 205  */
 206 void ima_update_policy(void)
 207 {
 208         const char *op = "policy_update";
 209         const char *cause = "already exists";
 210         int result = 1;
 211         int audit_info = 0;
 212
 213         if (ima_measure == &measure_default_rules) {
 214                 ima_measure = &measure_policy_rules;
 215                 cause = "complete";
 216                 result = 0;
 217         }
 218         integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL,
 219                             NULL, op, cause, result, audit_info);
 220 }
 221
 222 enum {
 223         Opt_err = -1,
 224         Opt_measure = 1, Opt_dont_measure,
 225         Opt_obj_user, Opt_obj_role, Opt_obj_type,
 226         Opt_subj_user, Opt_subj_role, Opt_subj_type,
 227         Opt_func, Opt_mask, Opt_fsmagic, Opt_uid
 228 };
 229
 230 static match_table_t policy_tokens = {
 231         {Opt_measure, "measure"},
 232         {Opt_dont_measure, "dont_measure"},
 233         {Opt_obj_user, "obj_user=%s"},
 234         {Opt_obj_role, "obj_role=%s"},
 235         {Opt_obj_type, "obj_type=%s"},
 236         {Opt_subj_user, "subj_user=%s"},
 237         {Opt_subj_role, "subj_role=%s"},
 238         {Opt_subj_type, "subj_type=%s"},
 239         {Opt_func, "func=%s"},
 240         {Opt_mask, "mask=%s"},
 241         {Opt_fsmagic, "fsmagic=%s"},
 242         {Opt_uid, "uid=%s"},
 243         {Opt_err, NULL}
 244 };
 245
 246 static int ima_lsm_rule_init(struct ima_measure_rule_entry *entry,
 247                              char *args, int lsm_rule, int audit_type)
 248 {
 249         int result;
 250
 251         if (entry->lsm[lsm_rule].rule)
 252                 return -EINVAL;
 253
 254         entry->lsm[lsm_rule].type = audit_type;
 255         result = security_filter_rule_init(entry->lsm[lsm_rule].type,
 256                                            Audit_equal, args,
 257                                            &entry->lsm[lsm_rule].rule);
 258         if (!entry->lsm[lsm_rule].rule)
 259                 return -EINVAL;
 260         return result;
 261 }
 262
 263 static void ima_log_string(struct audit_buffer *ab, char *key, char *value)
 264 {
 265         audit_log_format(ab, "%s=", key);
 266         audit_log_untrustedstring(ab, value);
 267         audit_log_format(ab, " ");
 268 }
 269
 270 static int ima_parse_rule(char *rule, struct ima_measure_rule_entry *entry)
 271 {
 272         struct audit_buffer *ab;
 273         char *p;
 274         int result = 0;
 275
 276         ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_INTEGRITY_RULE);
 277
 278         entry->uid = -1;
 279         entry->action = UNKNOWN;
 280         while ((p = strsep(&rule, " \t")) != NULL) {
 281                 substring_t args[MAX_OPT_ARGS];
 282                 int token;
 283                 unsigned long lnum;
 284
 285                 if (result < 0)
 286                         break;
 287                 if ((*p == '\0') || (*p == ' ') || (*p == '\t'))
 288                         continue;
 289                 token = match_token(p, policy_tokens, args);
 290                 switch (token) {
 291                 case Opt_measure:
 292                         ima_log_string(ab, "action", "measure");
 293
 294                         if (entry->action != UNKNOWN)
 295                                 result = -EINVAL;
 296
 297                         entry->action = MEASURE;
 298                         break;
 299                 case Opt_dont_measure:
 300                         ima_log_string(ab, "action", "dont_measure");
 301
 302                         if (entry->action != UNKNOWN)
 303                                 result = -EINVAL;
 304
 305                         entry->action = DONT_MEASURE;
 306                         break;
 307                 case Opt_func:
 308                         ima_log_string(ab, "func", args[0].from);
 309
 310                         if (entry->func)
 311                                 result  = -EINVAL;
 312
 313                         if (strcmp(args[0].from, "FILE_CHECK") == 0)
 314                                 entry->func = FILE_CHECK;
 315                         /* PATH_CHECK is for backwards compat */
 316                         else if (strcmp(args[0].from, "PATH_CHECK") == 0)
 317                                 entry->func = FILE_CHECK;
 318                         else if (strcmp(args[0].from, "FILE_MMAP") == 0)
 319                                 entry->func = FILE_MMAP;
 320                         else if (strcmp(args[0].from, "BPRM_CHECK") == 0)
 321                                 entry->func = BPRM_CHECK;
 322                         else
 323                                 result = -EINVAL;
 324                         if (!result)
 325                                 entry->flags |= IMA_FUNC;
 326                         break;
 327                 case Opt_mask:
 328                         ima_log_string(ab, "mask", args[0].from);
 329
 330                         if (entry->mask)
 331                                 result = -EINVAL;
 332
 333                         if ((strcmp(args[0].from, "MAY_EXEC")) == 0)
 334                                 entry->mask = MAY_EXEC;
 335                         else if (strcmp(args[0].from, "MAY_WRITE") == 0)
 336                                 entry->mask = MAY_WRITE;
 337                         else if (strcmp(args[0].from, "MAY_READ") == 0)
 338                                 entry->mask = MAY_READ;
 339                         else if (strcmp(args[0].from, "MAY_APPEND") == 0)
 340                                 entry->mask = MAY_APPEND;
 341                         else
 342                                 result = -EINVAL;
 343                         if (!result)
 344                                 entry->flags |= IMA_MASK;
 345                         break;
 346                 case Opt_fsmagic:
 347                         ima_log_string(ab, "fsmagic", args[0].from);
 348
 349                         if (entry->fsmagic) {
 350                                 result = -EINVAL;
 351                                 break;
 352                         }
 353
 354                         result = strict_strtoul(args[0].from, 16,
 355                                                 &entry->fsmagic);
 356                         if (!result)
 357                                 entry->flags |= IMA_FSMAGIC;
 358                         break;
 359                 case Opt_uid:
 360                         ima_log_string(ab, "uid", args[0].from);
 361
 362                         if (entry->uid != -1) {
 363                                 result = -EINVAL;
 364                                 break;
 365                         }
 366
 367                         result = strict_strtoul(args[0].from, 10, &lnum);
 368                         if (!result) {
 369                                 entry->uid = (uid_t) lnum;
 370                                 if (entry->uid != lnum)
 371                                         result = -EINVAL;
 372                                 else
 373                                         entry->flags |= IMA_UID;
 374                         }
 375                         break;
 376                 case Opt_obj_user:
 377                         ima_log_string(ab, "obj_user", args[0].from);
 378                         result = ima_lsm_rule_init(entry, args[0].from,
 379                                                    LSM_OBJ_USER,
 380                                                    AUDIT_OBJ_USER);
 381                         break;
 382                 case Opt_obj_role:
 383                         ima_log_string(ab, "obj_role", args[0].from);
 384                         result = ima_lsm_rule_init(entry, args[0].from,
 385                                                    LSM_OBJ_ROLE,
 386                                                    AUDIT_OBJ_ROLE);
 387                         break;
 388                 case Opt_obj_type:
 389                         ima_log_string(ab, "obj_type", args[0].from);
 390                         result = ima_lsm_rule_init(entry, args[0].from,
 391                                                    LSM_OBJ_TYPE,
 392                                                    AUDIT_OBJ_TYPE);
 393                         break;
 394                 case Opt_subj_user:
 395                         ima_log_string(ab, "subj_user", args[0].from);
 396                         result = ima_lsm_rule_init(entry, args[0].from,
 397                                                    LSM_SUBJ_USER,
 398                                                    AUDIT_SUBJ_USER);
 399                         break;
 400                 case Opt_subj_role:
 401                         ima_log_string(ab, "subj_role", args[0].from);
 402                         result = ima_lsm_rule_init(entry, args[0].from,
 403                                                    LSM_SUBJ_ROLE,
 404                                                    AUDIT_SUBJ_ROLE);
 405                         break;
 406                 case Opt_subj_type:
 407                         ima_log_string(ab, "subj_type", args[0].from);
 408                         result = ima_lsm_rule_init(entry, args[0].from,
 409                                                    LSM_SUBJ_TYPE,
 410                                                    AUDIT_SUBJ_TYPE);
 411                         break;
 412                 case Opt_err:
 413                         ima_log_string(ab, "UNKNOWN", p);
 414                         result = -EINVAL;
 415                         break;
 416                 }
 417         }
 418         if (!result && (entry->action == UNKNOWN))
 419                 result = -EINVAL;
 420
 421         audit_log_format(ab, "res=%d", !result);
 422         audit_log_end(ab);
 423         return result;
 424 }
 425
 426 /**
 427  * ima_parse_add_rule - add a rule to measure_policy_rules
 428  * @rule - ima measurement policy rule
 429  *
 430  * Uses a mutex to protect the policy list from multiple concurrent writers.
 431  * Returns the length of the rule parsed, an error code on failure
 432  */
 433 ssize_t ima_parse_add_rule(char *rule)
 434 {
 435         const char *op = "update_policy";
 436         char *p;
 437         struct ima_measure_rule_entry *entry;
 438         ssize_t result, len;
 439         int audit_info = 0;
 440
 441         /* Prevent installed policy from changing */
 442         if (ima_measure != &measure_default_rules) {
 443                 integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL,
 444                                     NULL, op, "already exists",
 445                                     -EACCES, audit_info);
 446                 return -EACCES;
 447         }
 448
 449         entry = kzalloc(sizeof(*entry), GFP_KERNEL);
 450         if (!entry) {
 451                 integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL,
 452                                     NULL, op, "-ENOMEM", -ENOMEM, audit_info);
 453                 return -ENOMEM;
 454         }
 455
 456         INIT_LIST_HEAD(&entry->list);
 457
 458         p = strsep(&rule, "\n");
 459         len = strlen(p) + 1;
 460
 461         if (*p == '#') {
 462                 kfree(entry);
 463                 return len;
 464         }
 465
 466         result = ima_parse_rule(p, entry);
 467         if (result) {
 468                 kfree(entry);
 469                 integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL,
 470                                     NULL, op, "invalid policy", result,
 471                                     audit_info);
 472                 return result;
 473         }
 474
 475         mutex_lock(&ima_measure_mutex);
 476         list_add_tail(&entry->list, &measure_policy_rules);
 477         mutex_unlock(&ima_measure_mutex);
 478
 479         return len;
 480 }
 481
 482 /* ima_delete_rules called to cleanup invalid policy */
 483 void ima_delete_rules(void)
 484 {
 485         struct ima_measure_rule_entry *entry, *tmp;
 486
 487         mutex_lock(&ima_measure_mutex);
 488         list_for_each_entry_safe(entry, tmp, &measure_policy_rules, list) {
 489                 list_del(&entry->list);
 490                 kfree(entry);
 491         }
 492         mutex_unlock(&ima_measure_mutex);
 493 }