LXR linux/security/integrity/ima/ima

   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
  28enum ima_action { UNKNOWN = -1, DONT_MEASURE = 0, MEASURE };
  29
  30#define MAX_LSM_RULES 6
  31enum lsm_rule_types { LSM_OBJ_USER, LSM_OBJ_ROLE, LSM_OBJ_TYPE,
  32        LSM_SUBJ_USER, LSM_SUBJ_ROLE, LSM_SUBJ_TYPE
  33};
  34
  35struct 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 */
  60static 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
  75static LIST_HEAD(measure_default_rules);
  76static LIST_HEAD(measure_policy_rules);
  77static struct list_head *ima_measure;
  78
  79static DEFINE_MUTEX(ima_measure_mutex);
  80
  81static bool ima_use_tcb __initdata;
  82static 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 */
  98static 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 */
 162int 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 */
 182void __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 */
 204void 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
 220enum {
 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
 228static 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
 244static 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
 261static 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
 268static 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 */
 431ssize_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 */
 481void 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}
 492