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 = DEVPTS_SUPER_MAGIC,.flags = IMA_FSMAGIC},
  67         {.action = DONT_MEASURE,.fsmagic = BINFMTFS_MAGIC,.flags = IMA_FSMAGIC},
  68         {.action = DONT_MEASURE,.fsmagic = SECURITYFS_MAGIC,.flags = IMA_FSMAGIC},
  69         {.action = DONT_MEASURE,.fsmagic = SELINUX_MAGIC,.flags = IMA_FSMAGIC},
  70         {.action = MEASURE,.func = FILE_MMAP,.mask = MAY_EXEC,
  71          .flags = IMA_FUNC | IMA_MASK},
  72         {.action = MEASURE,.func = BPRM_CHECK,.mask = MAY_EXEC,
  73          .flags = IMA_FUNC | IMA_MASK},
  74         {.action = MEASURE,.func = FILE_CHECK,.mask = MAY_READ,.uid = 0,
  75          .flags = IMA_FUNC | IMA_MASK | IMA_UID},
  76 };
  77
  78 static LIST_HEAD(measure_default_rules);
  79 static LIST_HEAD(measure_policy_rules);
  80 static struct list_head *ima_measure;
  81
  82 static DEFINE_MUTEX(ima_measure_mutex);
  83
  84 static bool ima_use_tcb __initdata;
  85 static int __init default_policy_setup(char *str)
  86 {
  87         ima_use_tcb = 1;
  88         return 1;
  89 }
  90 __setup("ima_tcb", default_policy_setup);
  91
  92 /**
  93  * ima_match_rules - determine whether an inode matches the measure rule.
  94  * @rule: a pointer to a rule
  95  * @inode: a pointer to an inode
  96  * @func: LIM hook identifier
  97  * @mask: requested action (MAY_READ | MAY_WRITE | MAY_APPEND | MAY_EXEC)
  98  *
  99  * Returns true on rule match, false on failure.
 100  */
 101 static bool ima_match_rules(struct ima_measure_rule_entry *rule,
 102                             struct inode *inode, enum ima_hooks func, int mask)
 103 {
 104         struct task_struct *tsk = current;
 105         const struct cred *cred = current_cred();
 106         int i;
 107
 108         if ((rule->flags & IMA_FUNC) && rule->func != func)
 109                 return false;
 110         if ((rule->flags & IMA_MASK) && rule->mask != mask)
 111                 return false;
 112         if ((rule->flags & IMA_FSMAGIC)
 113             && rule->fsmagic != inode->i_sb->s_magic)
 114                 return false;
 115         if ((rule->flags & IMA_UID) && rule->uid != cred->uid)
 116                 return false;
 117         for (i = 0; i < MAX_LSM_RULES; i++) {
 118                 int rc = 0;
 119                 u32 osid, sid;
 120
 121                 if (!rule->lsm[i].rule)
 122                         continue;
 123
 124                 switch (i) {
 125                 case LSM_OBJ_USER:
 126                 case LSM_OBJ_ROLE:
 127                 case LSM_OBJ_TYPE:
 128                         security_inode_getsecid(inode, &osid);
 129                         rc = security_filter_rule_match(osid,
 130                                                         rule->lsm[i].type,
 131                                                         Audit_equal,
 132                                                         rule->lsm[i].rule,
 133                                                         NULL);
 134                         break;
 135                 case LSM_SUBJ_USER:
 136                 case LSM_SUBJ_ROLE:
 137                 case LSM_SUBJ_TYPE:
 138                         security_task_getsecid(tsk, &sid);
 139                         rc = security_filter_rule_match(sid,
 140                                                         rule->lsm[i].type,
 141                                                         Audit_equal,
 142                                                         rule->lsm[i].rule,
 143                                                         NULL);
 144                 default:
 145                         break;
 146                 }
 147                 if (!rc)
 148                         return false;
 149         }
 150         return true;
 151 }
 152
 153 /**
 154  * ima_match_policy - decision based on LSM and other conditions
 155  * @inode: pointer to an inode for which the policy decision is being made
 156  * @func: IMA hook identifier
 157  * @mask: requested action (MAY_READ | MAY_WRITE | MAY_APPEND | MAY_EXEC)
 158  *
 159  * Measure decision based on func/mask/fsmagic and LSM(subj/obj/type)
 160  * conditions.
 161  *
 162  * (There is no need for locking when walking the policy list,
 163  * as elements in the list are never deleted, nor does the list
 164  * change.)
 165  */
 166 int ima_match_policy(struct inode *inode, enum ima_hooks func, int mask)
 167 {
 168         struct ima_measure_rule_entry *entry;
 169
 170         list_for_each_entry(entry, ima_measure, list) {
 171                 bool rc;
 172
 173                 rc = ima_match_rules(entry, inode, func, mask);
 174                 if (rc)
 175                         return entry->action;
 176         }
 177         return 0;
 178 }
 179
 180 /**
 181  * ima_init_policy - initialize the default measure rules.
 182  *
 183  * ima_measure points to either the measure_default_rules or the
 184  * the new measure_policy_rules.
 185  */
 186 void __init ima_init_policy(void)
 187 {
 188         int i, entries;
 189
 190         /* if !ima_use_tcb set entries = 0 so we load NO default rules */
 191         if (ima_use_tcb)
 192                 entries = ARRAY_SIZE(default_rules);
 193         else
 194                 entries = 0;
 195
 196         for (i = 0; i < entries; i++)
 197                 list_add_tail(&default_rules[i].list, &measure_default_rules);
 198         ima_measure = &measure_default_rules;
 199 }
 200
 201 /**
 202  * ima_update_policy - update default_rules with new measure rules
 203  *
 204  * Called on file .release to update the default rules with a complete new
 205  * policy.  Once updated, the policy is locked, no additional rules can be
 206  * added to the policy.
 207  */
 208 void ima_update_policy(void)
 209 {
 210         const char *op = "policy_update";
 211         const char *cause = "already exists";
 212         int result = 1;
 213         int audit_info = 0;
 214
 215         if (ima_measure == &measure_default_rules) {
 216                 ima_measure = &measure_policy_rules;
 217                 cause = "complete";
 218                 result = 0;
 219         }
 220         integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL,
 221                             NULL, op, cause, result, audit_info);
 222 }
 223
 224 enum {
 225         Opt_err = -1,
 226         Opt_measure = 1, Opt_dont_measure,
 227         Opt_obj_user, Opt_obj_role, Opt_obj_type,
 228         Opt_subj_user, Opt_subj_role, Opt_subj_type,
 229         Opt_func, Opt_mask, Opt_fsmagic, Opt_uid
 230 };
 231
 232 static match_table_t policy_tokens = {
 233         {Opt_measure, "measure"},
 234         {Opt_dont_measure, "dont_measure"},
 235         {Opt_obj_user, "obj_user=%s"},
 236         {Opt_obj_role, "obj_role=%s"},
 237         {Opt_obj_type, "obj_type=%s"},
 238         {Opt_subj_user, "subj_user=%s"},
 239         {Opt_subj_role, "subj_role=%s"},
 240         {Opt_subj_type, "subj_type=%s"},
 241         {Opt_func, "func=%s"},
 242         {Opt_mask, "mask=%s"},
 243         {Opt_fsmagic, "fsmagic=%s"},
 244         {Opt_uid, "uid=%s"},
 245         {Opt_err, NULL}
 246 };
 247
 248 static int ima_lsm_rule_init(struct ima_measure_rule_entry *entry,
 249                              char *args, int lsm_rule, int audit_type)
 250 {
 251         int result;
 252
 253         if (entry->lsm[lsm_rule].rule)
 254                 return -EINVAL;
 255
 256         entry->lsm[lsm_rule].type = audit_type;
 257         result = security_filter_rule_init(entry->lsm[lsm_rule].type,
 258                                            Audit_equal, args,
 259                                            &entry->lsm[lsm_rule].rule);
 260         if (!entry->lsm[lsm_rule].rule)
 261                 return -EINVAL;
 262         return result;
 263 }
 264
 265 static void ima_log_string(struct audit_buffer *ab, char *key, char *value)
 266 {
 267         audit_log_format(ab, "%s=", key);
 268         audit_log_untrustedstring(ab, value);
 269         audit_log_format(ab, " ");
 270 }
 271
 272 static int ima_parse_rule(char *rule, struct ima_measure_rule_entry *entry)
 273 {
 274         struct audit_buffer *ab;
 275         char *p;
 276         int result = 0;
 277
 278         ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_INTEGRITY_RULE);
 279
 280         entry->uid = -1;
 281         entry->action = UNKNOWN;
 282         while ((p = strsep(&rule, " \t")) != NULL) {
 283                 substring_t args[MAX_OPT_ARGS];
 284                 int token;
 285                 unsigned long lnum;
 286
 287                 if (result < 0)
 288                         break;
 289                 if ((*p == '\0') || (*p == ' ') || (*p == '\t'))
 290                         continue;
 291                 token = match_token(p, policy_tokens, args);
 292                 switch (token) {
 293                 case Opt_measure:
 294                         ima_log_string(ab, "action", "measure");
 295
 296                         if (entry->action != UNKNOWN)
 297                                 result = -EINVAL;
 298
 299                         entry->action = MEASURE;
 300                         break;
 301                 case Opt_dont_measure:
 302                         ima_log_string(ab, "action", "dont_measure");
 303
 304                         if (entry->action != UNKNOWN)
 305                                 result = -EINVAL;
 306
 307                         entry->action = DONT_MEASURE;
 308                         break;
 309                 case Opt_func:
 310                         ima_log_string(ab, "func", args[0].from);
 311
 312                         if (entry->func)
 313                                 result  = -EINVAL;
 314
 315                         if (strcmp(args[0].from, "FILE_CHECK") == 0)
 316                                 entry->func = FILE_CHECK;
 317                         /* PATH_CHECK is for backwards compat */
 318                         else if (strcmp(args[0].from, "PATH_CHECK") == 0)
 319                                 entry->func = FILE_CHECK;
 320                         else if (strcmp(args[0].from, "FILE_MMAP") == 0)
 321                                 entry->func = FILE_MMAP;
 322                         else if (strcmp(args[0].from, "BPRM_CHECK") == 0)
 323                                 entry->func = BPRM_CHECK;
 324                         else
 325                                 result = -EINVAL;
 326                         if (!result)
 327                                 entry->flags |= IMA_FUNC;
 328                         break;
 329                 case Opt_mask:
 330                         ima_log_string(ab, "mask", args[0].from);
 331
 332                         if (entry->mask)
 333                                 result = -EINVAL;
 334
 335                         if ((strcmp(args[0].from, "MAY_EXEC")) == 0)
 336                                 entry->mask = MAY_EXEC;
 337                         else if (strcmp(args[0].from, "MAY_WRITE") == 0)
 338                                 entry->mask = MAY_WRITE;
 339                         else if (strcmp(args[0].from, "MAY_READ") == 0)
 340                                 entry->mask = MAY_READ;
 341                         else if (strcmp(args[0].from, "MAY_APPEND") == 0)
 342                                 entry->mask = MAY_APPEND;
 343                         else
 344                                 result = -EINVAL;
 345                         if (!result)
 346                                 entry->flags |= IMA_MASK;
 347                         break;
 348                 case Opt_fsmagic:
 349                         ima_log_string(ab, "fsmagic", args[0].from);
 350
 351                         if (entry->fsmagic) {
 352                                 result = -EINVAL;
 353                                 break;
 354                         }
 355
 356                         result = strict_strtoul(args[0].from, 16,
 357                                                 &entry->fsmagic);
 358                         if (!result)
 359                                 entry->flags |= IMA_FSMAGIC;
 360                         break;
 361                 case Opt_uid:
 362                         ima_log_string(ab, "uid", args[0].from);
 363
 364                         if (entry->uid != -1) {
 365                                 result = -EINVAL;
 366                                 break;
 367                         }
 368
 369                         result = strict_strtoul(args[0].from, 10, &lnum);
 370                         if (!result) {
 371                                 entry->uid = (uid_t) lnum;
 372                                 if (entry->uid != lnum)
 373                                         result = -EINVAL;
 374                                 else
 375                                         entry->flags |= IMA_UID;
 376                         }
 377                         break;
 378                 case Opt_obj_user:
 379                         ima_log_string(ab, "obj_user", args[0].from);
 380                         result = ima_lsm_rule_init(entry, args[0].from,
 381                                                    LSM_OBJ_USER,
 382                                                    AUDIT_OBJ_USER);
 383                         break;
 384                 case Opt_obj_role:
 385                         ima_log_string(ab, "obj_role", args[0].from);
 386                         result = ima_lsm_rule_init(entry, args[0].from,
 387                                                    LSM_OBJ_ROLE,
 388                                                    AUDIT_OBJ_ROLE);
 389                         break;
 390                 case Opt_obj_type:
 391                         ima_log_string(ab, "obj_type", args[0].from);
 392                         result = ima_lsm_rule_init(entry, args[0].from,
 393                                                    LSM_OBJ_TYPE,
 394                                                    AUDIT_OBJ_TYPE);
 395                         break;
 396                 case Opt_subj_user:
 397                         ima_log_string(ab, "subj_user", args[0].from);
 398                         result = ima_lsm_rule_init(entry, args[0].from,
 399                                                    LSM_SUBJ_USER,
 400                                                    AUDIT_SUBJ_USER);
 401                         break;
 402                 case Opt_subj_role:
 403                         ima_log_string(ab, "subj_role", args[0].from);
 404                         result = ima_lsm_rule_init(entry, args[0].from,
 405                                                    LSM_SUBJ_ROLE,
 406                                                    AUDIT_SUBJ_ROLE);
 407                         break;
 408                 case Opt_subj_type:
 409                         ima_log_string(ab, "subj_type", args[0].from);
 410                         result = ima_lsm_rule_init(entry, args[0].from,
 411                                                    LSM_SUBJ_TYPE,
 412                                                    AUDIT_SUBJ_TYPE);
 413                         break;
 414                 case Opt_err:
 415                         ima_log_string(ab, "UNKNOWN", p);
 416                         result = -EINVAL;
 417                         break;
 418                 }
 419         }
 420         if (!result && (entry->action == UNKNOWN))
 421                 result = -EINVAL;
 422
 423         audit_log_format(ab, "res=%d", !result);
 424         audit_log_end(ab);
 425         return result;
 426 }
 427
 428 /**
 429  * ima_parse_add_rule - add a rule to measure_policy_rules
 430  * @rule - ima measurement policy rule
 431  *
 432  * Uses a mutex to protect the policy list from multiple concurrent writers.
 433  * Returns the length of the rule parsed, an error code on failure
 434  */
 435 ssize_t ima_parse_add_rule(char *rule)
 436 {
 437         const char *op = "update_policy";
 438         char *p;
 439         struct ima_measure_rule_entry *entry;
 440         ssize_t result, len;
 441         int audit_info = 0;
 442
 443         /* Prevent installed policy from changing */
 444         if (ima_measure != &measure_default_rules) {
 445                 integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL,
 446                                     NULL, op, "already exists",
 447                                     -EACCES, audit_info);
 448                 return -EACCES;
 449         }
 450
 451         entry = kzalloc(sizeof(*entry), GFP_KERNEL);
 452         if (!entry) {
 453                 integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL,
 454                                     NULL, op, "-ENOMEM", -ENOMEM, audit_info);
 455                 return -ENOMEM;
 456         }
 457
 458         INIT_LIST_HEAD(&entry->list);
 459
 460         p = strsep(&rule, "\n");
 461         len = strlen(p) + 1;
 462
 463         if (*p == '#') {
 464                 kfree(entry);
 465                 return len;
 466         }
 467
 468         result = ima_parse_rule(p, entry);
 469         if (result) {
 470                 kfree(entry);
 471                 integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL,
 472                                     NULL, op, "invalid policy", result,
 473                                     audit_info);
 474                 return result;
 475         }
 476
 477         mutex_lock(&ima_measure_mutex);
 478         list_add_tail(&entry->list, &measure_policy_rules);
 479         mutex_unlock(&ima_measure_mutex);
 480
 481         return len;
 482 }
 483
 484 /* ima_delete_rules called to cleanup invalid policy */
 485 void ima_delete_rules(void)
 486 {
 487         struct ima_measure_rule_entry *entry, *tmp;
 488
 489         mutex_lock(&ima_measure_mutex);
 490         list_for_each_entry_safe(entry, tmp, &measure_policy_rules, list) {
 491                 list_del(&entry->list);
 492                 kfree(entry);
 493         }
 494         mutex_unlock(&ima_measure_mutex);
 495 }