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