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
  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
  27 enum ima_action { UNKNOWN = -1, DONT_MEASURE = 0, MEASURE };
  28
  29 #define MAX_LSM_RULES 6
  30 enum lsm_rule_types { LSM_OBJ_USER, LSM_OBJ_ROLE, LSM_OBJ_TYPE,
  31         LSM_SUBJ_USER, LSM_SUBJ_ROLE, LSM_SUBJ_TYPE
  32 };
  33
  34 struct 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  */
  59 static 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
  74 static LIST_HEAD(measure_default_rules);
  75 static LIST_HEAD(measure_policy_rules);
  76 static struct list_head *ima_measure;
  77
  78 static DEFINE_MUTEX(ima_measure_mutex);
  79
  80 static bool ima_use_tcb __initdata;
  81 static 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  */
  97 static 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  */
 161 int 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  */
 181 void __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  */
 203 void 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
 219 enum {
 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
 227 static 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
 243 static 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
 255 static 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  */
 385 int 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 */
 424 void 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 }