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
  19#include "ima.h"
  20
  21/* flags definitions */
  22#define IMA_FUNC        0x0001
  23#define IMA_MASK        0x0002
  24#define IMA_FSMAGIC     0x0004
  25#define IMA_UID         0x0008
  26
  27enum ima_action { UNKNOWN = -1, DONT_MEASURE = 0, MEASURE };
  28
  29#define MAX_LSM_RULES 6
  30enum lsm_rule_types { LSM_OBJ_USER, LSM_OBJ_ROLE, LSM_OBJ_TYPE,
  31        LSM_SUBJ_USER, LSM_SUBJ_ROLE, LSM_SUBJ_TYPE
  32};
  33
  34struct ima_measure_rule_entry {
  35        struct list_head list;
  36        enum ima_action action;
  37        unsigned int flags;
  38        enum ima_hooks func;
  39        int mask;
  40        unsigned long fsmagic;
  41        uid_t uid;
  42        struct {
  43                void *rule;     /* LSM file metadata specific */
  44                int type;       /* audit type */
  45        } lsm[MAX_LSM_RULES];
  46};
  47
  48/*
  49 * Without LSM specific knowledge, the default policy can only be
  50 * written in terms of .action, .func, .mask, .fsmagic, and .uid
  51 */
  52
  53/*
  54 * The minimum rule set to allow for full TCB coverage.  Measures all files
  55 * opened or mmap for exec and everything read by root.  Dangerous because
  56 * normal users can easily run the machine out of memory simply building
  57 * and running executables.
  58 */
  59static struct ima_measure_rule_entry default_rules[] = {
  60        {.action = DONT_MEASURE,.fsmagic = PROC_SUPER_MAGIC,.flags = IMA_FSMAGIC},
  61        {.action = DONT_MEASURE,.fsmagic = SYSFS_MAGIC,.flags = IMA_FSMAGIC},
  62        {.action = DONT_MEASURE,.fsmagic = DEBUGFS_MAGIC,.flags = IMA_FSMAGIC},
  63        {.action = DONT_MEASURE,.fsmagic = TMPFS_MAGIC,.flags = IMA_FSMAGIC},
  64        {.action = DONT_MEASURE,.fsmagic = SECURITYFS_MAGIC,.flags = IMA_FSMAGIC},
  65        {.action = DONT_MEASURE,.fsmagic = SELINUX_MAGIC,.flags = IMA_FSMAGIC},
  66        {.action = MEASURE,.func = FILE_MMAP,.mask = MAY_EXEC,
  67         .flags = IMA_FUNC | IMA_MASK},
  68        {.action = MEASURE,.func = BPRM_CHECK,.mask = MAY_EXEC,
  69         .flags = IMA_FUNC | IMA_MASK},
  70        {.action = MEASURE,.func = PATH_CHECK,.mask = MAY_READ,.uid = 0,
  71         .flags = IMA_FUNC | IMA_MASK | IMA_UID},
  72};
  73
  74static LIST_HEAD(measure_default_rules);
  75static LIST_HEAD(measure_policy_rules);
  76static struct list_head *ima_measure;
  77
  78static DEFINE_MUTEX(ima_measure_mutex);
  79
  80static bool ima_use_tcb __initdata;
  81static int __init default_policy_setup(char *str)
  82{
  83        ima_use_tcb = 1;
  84        return 1;
  85}
  86__setup("ima_tcb", default_policy_setup);
  87
  88/**
  89 * ima_match_rules - determine whether an inode matches the measure rule.
  90 * @rule: a pointer to a rule
  91 * @inode: a pointer to an inode
  92 * @func: LIM hook identifier
  93 * @mask: requested action (MAY_READ | MAY_WRITE | MAY_APPEND | MAY_EXEC)
  94 *
  95 * Returns true on rule match, false on failure.
  96 */
  97static bool ima_match_rules(struct ima_measure_rule_entry *rule,
  98                            struct inode *inode, enum ima_hooks func, int mask)
  99{
 100        struct task_struct *tsk = current;
 101        int i;
 102
 103        if ((rule->flags & IMA_FUNC) && rule->func != func)
 104                return false;
 105        if ((rule->flags & IMA_MASK) && rule->mask != mask)
 106                return false;
 107        if ((rule->flags & IMA_FSMAGIC)
 108            && rule->fsmagic != inode->i_sb->s_magic)
 109                return false;
 110        if ((rule->flags & IMA_UID) && rule->uid != tsk->cred->uid)
 111                return false;
 112        for (i = 0; i < MAX_LSM_RULES; i++) {
 113                int rc = 0;
 114                u32 osid, sid;
 115
 116                if (!rule->lsm[i].rule)
 117                        continue;
 118
 119                switch (i) {
 120                case LSM_OBJ_USER:
 121                case LSM_OBJ_ROLE:
 122                case LSM_OBJ_TYPE:
 123                        security_inode_getsecid(inode, &osid);
 124                        rc = security_filter_rule_match(osid,
 125                                                        rule->lsm[i].type,
 126                                                        Audit_equal,
 127                                                        rule->lsm[i].rule,
 128                                                        NULL);
 129                        break;
 130                case LSM_SUBJ_USER:
 131                case LSM_SUBJ_ROLE:
 132                case LSM_SUBJ_TYPE:
 133                        security_task_getsecid(tsk, &sid);
 134                        rc = security_filter_rule_match(sid,
 135                                                        rule->lsm[i].type,
 136                                                        Audit_equal,
 137                                                        rule->lsm[i].rule,
 138                                                        NULL);
 139                default:
 140                        break;
 141                }
 142                if (!rc)
 143                        return false;
 144        }
 145        return true;
 146}
 147
 148/**
 149 * ima_match_policy - decision based on LSM and other conditions
 150 * @inode: pointer to an inode for which the policy decision is being made
 151 * @func: IMA hook identifier
 152 * @mask: requested action (MAY_READ | MAY_WRITE | MAY_APPEND | MAY_EXEC)
 153 *
 154 * Measure decision based on func/mask/fsmagic and LSM(subj/obj/type)
 155 * conditions.
 156 *
 157 * (There is no need for locking when walking the policy list,
 158 * as elements in the list are never deleted, nor does the list
 159 * change.)
 160 */
 161int ima_match_policy(struct inode *inode, enum ima_hooks func, int mask)
 162{
 163        struct ima_measure_rule_entry *entry;
 164
 165        list_for_each_entry(entry, ima_measure, list) {
 166                bool rc;
 167
 168                rc = ima_match_rules(entry, inode, func, mask);
 169                if (rc)
 170                        return entry->action;
 171        }
 172        return 0;
 173}
 174
 175/**
 176 * ima_init_policy - initialize the default measure rules.
 177 *
 178 * ima_measure points to either the measure_default_rules or the
 179 * the new measure_policy_rules.
 180 */
 181void __init ima_init_policy(void)
 182{
 183        int i, entries;
 184
 185        /* if !ima_use_tcb set entries = 0 so we load NO default rules */
 186        if (ima_use_tcb)
 187                entries = ARRAY_SIZE(default_rules);
 188        else
 189                entries = 0;
 190
 191        for (i = 0; i < entries; i++)
 192                list_add_tail(&default_rules[i].list, &measure_default_rules);
 193        ima_measure = &measure_default_rules;
 194}
 195
 196/**
 197 * ima_update_policy - update default_rules with new measure rules
 198 *
 199 * Called on file .release to update the default rules with a complete new
 200 * policy.  Once updated, the policy is locked, no additional rules can be
 201 * added to the policy.
 202 */
 203void ima_update_policy(void)
 204{
 205        const char *op = "policy_update";
 206        const char *cause = "already exists";
 207        int result = 1;
 208        int audit_info = 0;
 209
 210        if (ima_measure == &measure_default_rules) {
 211                ima_measure = &measure_policy_rules;
 212                cause = "complete";
 213                result = 0;
 214        }
 215        integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL,
 216                            NULL, op, cause, result, audit_info);
 217}
 218
 219enum {
 220        Opt_err = -1,
 221        Opt_measure = 1, Opt_dont_measure,
 222        Opt_obj_user, Opt_obj_role, Opt_obj_type,
 223        Opt_subj_user, Opt_subj_role, Opt_subj_type,
 224        Opt_func, Opt_mask, Opt_fsmagic, Opt_uid
 225};
 226
 227static match_table_t policy_tokens = {
 228        {Opt_measure, "measure"},
 229        {Opt_dont_measure, "dont_measure"},
 230        {Opt_obj_user, "obj_user=%s"},
 231        {Opt_obj_role, "obj_role=%s"},
 232        {Opt_obj_type, "obj_type=%s"},
 233        {Opt_subj_user, "subj_user=%s"},
 234        {Opt_subj_role, "subj_role=%s"},
 235        {Opt_subj_type, "subj_type=%s"},
 236        {Opt_func, "func=%s"},
 237        {Opt_mask, "mask=%s"},
 238        {Opt_fsmagic, "fsmagic=%s"},
 239        {Opt_uid, "uid=%s"},
 240        {Opt_err, NULL}
 241};
 242
 243static int ima_lsm_rule_init(struct ima_measure_rule_entry *entry,
 244                             char *args, int lsm_rule, int audit_type)
 245{
 246        int result;
 247
 248        entry->lsm[lsm_rule].type = audit_type;
 249        result = security_filter_rule_init(entry->lsm[lsm_rule].type,
 250                                           Audit_equal, args,
 251                                           &entry->lsm[lsm_rule].rule);
 252        return result;
 253}
 254
 255static int ima_parse_rule(char *rule, struct ima_measure_rule_entry *entry)
 256{
 257        struct audit_buffer *ab;
 258        char *p;
 259        int result = 0;
 260
 261        ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_INTEGRITY_RULE);
 262
 263        entry->action = -1;
 264        while ((p = strsep(&rule, " \n")) != NULL) {
 265                substring_t args[MAX_OPT_ARGS];
 266                int token;
 267                unsigned long lnum;
 268
 269                if (result < 0)
 270                        break;
 271                if (!*p)
 272                        continue;
 273                token = match_token(p, policy_tokens, args);
 274                switch (token) {
 275                case Opt_measure:
 276                        audit_log_format(ab, "%s ", "measure");
 277                        entry->action = MEASURE;
 278                        break;
 279                case Opt_dont_measure:
 280                        audit_log_format(ab, "%s ", "dont_measure");
 281                        entry->action = DONT_MEASURE;
 282                        break;
 283                case Opt_func:
 284                        audit_log_format(ab, "func=%s ", args[0].from);
 285                        if (strcmp(args[0].from, "PATH_CHECK") == 0)
 286                                entry->func = PATH_CHECK;
 287                        else if (strcmp(args[0].from, "FILE_MMAP") == 0)
 288                                entry->func = FILE_MMAP;
 289                        else if (strcmp(args[0].from, "BPRM_CHECK") == 0)
 290                                entry->func = BPRM_CHECK;
 291                        else
 292                                result = -EINVAL;
 293                        if (!result)
 294                                entry->flags |= IMA_FUNC;
 295                        break;
 296                case Opt_mask:
 297                        audit_log_format(ab, "mask=%s ", args[0].from);
 298                        if ((strcmp(args[0].from, "MAY_EXEC")) == 0)
 299                                entry->mask = MAY_EXEC;
 300                        else if (strcmp(args[0].from, "MAY_WRITE") == 0)
 301                                entry->mask = MAY_WRITE;
 302                        else if (strcmp(args[0].from, "MAY_READ") == 0)
 303                                entry->mask = MAY_READ;
 304                        else if (strcmp(args[0].from, "MAY_APPEND") == 0)
 305                                entry->mask = MAY_APPEND;
 306                        else
 307                                result = -EINVAL;
 308                        if (!result)
 309                                entry->flags |= IMA_MASK;
 310                        break;
 311                case Opt_fsmagic:
 312                        audit_log_format(ab, "fsmagic=%s ", args[0].from);
 313                        result = strict_strtoul(args[0].from, 16,
 314                                                &entry->fsmagic);
 315                        if (!result)
 316                                entry->flags |= IMA_FSMAGIC;
 317                        break;
 318                case Opt_uid:
 319                        audit_log_format(ab, "uid=%s ", args[0].from);
 320                        result = strict_strtoul(args[0].from, 10, &lnum);
 321                        if (!result) {
 322                                entry->uid = (uid_t) lnum;
 323                                if (entry->uid != lnum)
 324                                        result = -EINVAL;
 325                                else
 326                                        entry->flags |= IMA_UID;
 327                        }
 328                        break;
 329                case Opt_obj_user:
 330                        audit_log_format(ab, "obj_user=%s ", args[0].from);
 331                        result = ima_lsm_rule_init(entry, args[0].from,
 332                                                   LSM_OBJ_USER,
 333                                                   AUDIT_OBJ_USER);
 334                        break;
 335                case Opt_obj_role:
 336                        audit_log_format(ab, "obj_role=%s ", args[0].from);
 337                        result = ima_lsm_rule_init(entry, args[0].from,
 338                                                   LSM_OBJ_ROLE,
 339                                                   AUDIT_OBJ_ROLE);
 340                        break;
 341                case Opt_obj_type:
 342                        audit_log_format(ab, "obj_type=%s ", args[0].from);
 343                        result = ima_lsm_rule_init(entry, args[0].from,
 344                                                   LSM_OBJ_TYPE,
 345                                                   AUDIT_OBJ_TYPE);
 346                        break;
 347                case Opt_subj_user:
 348                        audit_log_format(ab, "subj_user=%s ", args[0].from);
 349                        result = ima_lsm_rule_init(entry, args[0].from,
 350                                                   LSM_SUBJ_USER,
 351                                                   AUDIT_SUBJ_USER);
 352                        break;
 353                case Opt_subj_role:
 354                        audit_log_format(ab, "subj_role=%s ", args[0].from);
 355                        result = ima_lsm_rule_init(entry, args[0].from,
 356                                                   LSM_SUBJ_ROLE,
 357                                                   AUDIT_SUBJ_ROLE);
 358                        break;
 359                case Opt_subj_type:
 360                        audit_log_format(ab, "subj_type=%s ", args[0].from);
 361                        result = ima_lsm_rule_init(entry, args[0].from,
 362                                                   LSM_SUBJ_TYPE,
 363                                                   AUDIT_SUBJ_TYPE);
 364                        break;
 365                case Opt_err:
 366                        audit_log_format(ab, "UNKNOWN=%s ", p);
 367                        break;
 368                }
 369        }
 370        if (entry->action == UNKNOWN)
 371                result = -EINVAL;
 372
 373        audit_log_format(ab, "res=%d", !result ? 0 : 1);
 374        audit_log_end(ab);
 375        return result;
 376}
 377
 378/**
 379 * ima_parse_add_rule - add a rule to measure_policy_rules
 380 * @rule - ima measurement policy rule
 381 *
 382 * Uses a mutex to protect the policy list from multiple concurrent writers.
 383 * Returns 0 on success, an error code on failure.
 384 */
 385int ima_parse_add_rule(char *rule)
 386{
 387        const char *op = "update_policy";
 388        struct ima_measure_rule_entry *entry;
 389        int result = 0;
 390        int audit_info = 0;
 391
 392        /* Prevent installed policy from changing */
 393        if (ima_measure != &measure_default_rules) {
 394                integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL,
 395                                    NULL, op, "already exists",
 396                                    -EACCES, audit_info);
 397                return -EACCES;
 398        }
 399
 400        entry = kzalloc(sizeof(*entry), GFP_KERNEL);
 401        if (!entry) {
 402                integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL,
 403                                    NULL, op, "-ENOMEM", -ENOMEM, audit_info);
 404                return -ENOMEM;
 405        }
 406
 407        INIT_LIST_HEAD(&entry->list);
 408
 409        result = ima_parse_rule(rule, entry);
 410        if (!result) {
 411                mutex_lock(&ima_measure_mutex);
 412                list_add_tail(&entry->list, &measure_policy_rules);
 413                mutex_unlock(&ima_measure_mutex);
 414        } else {
 415                kfree(entry);
 416                integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL,
 417                                    NULL, op, "invalid policy", result,
 418                                    audit_info);
 419        }
 420        return result;
 421}
 422
 423/* ima_delete_rules called to cleanup invalid policy */
 424void ima_delete_rules(void)
 425{
 426        struct ima_measure_rule_entry *entry, *tmp;
 427
 428        mutex_lock(&ima_measure_mutex);
 429        list_for_each_entry_safe(entry, tmp, &measure_policy_rules, list) {
 430                list_del(&entry->list);
 431                kfree(entry);
 432        }
 433        mutex_unlock(&ima_measure_mutex);
 434}
 435