security/smack/smack_access.c

   1 /*
   2  * Copyright (C) 2007 Casey Schaufler <casey@schaufler-ca.com>
   3  *
   4  *      This program is free software; you can redistribute it and/or modify
   5  *      it under the terms of the GNU General Public License as published by
   6  *      the Free Software Foundation, version 2.
   7  *
   8  * Author:
   9  *      Casey Schaufler <casey@schaufler-ca.com>
  10  *
  11  */
  12
  13 #include <linux/types.h>
  14 #include <linux/slab.h>
  15 #include <linux/fs.h>
  16 #include <linux/sched.h>
  17 #include "smack.h"
  18
  19 struct smack_known smack_known_huh = {
  20         .smk_known      = "?",
  21         .smk_secid      = 2,
  22 };
  23
  24 struct smack_known smack_known_hat = {
  25         .smk_known      = "^",
  26         .smk_secid      = 3,
  27 };
  28
  29 struct smack_known smack_known_star = {
  30         .smk_known      = "*",
  31         .smk_secid      = 4,
  32 };
  33
  34 struct smack_known smack_known_floor = {
  35         .smk_known      = "_",
  36         .smk_secid      = 5,
  37 };
  38
  39 struct smack_known smack_known_invalid = {
  40         .smk_known      = "",
  41         .smk_secid      = 6,
  42 };
  43
  44 struct smack_known smack_known_web = {
  45         .smk_known      = "@",
  46         .smk_secid      = 7,
  47 };
  48
  49 LIST_HEAD(smack_known_list);
  50
  51 /*
  52  * The initial value needs to be bigger than any of the
  53  * known values above.
  54  */
  55 static u32 smack_next_secid = 10;
  56
  57 /*
  58  * what events do we log
  59  * can be overwritten at run-time by /smack/logging
  60  */
  61 int log_policy = SMACK_AUDIT_DENIED;
  62
  63 /**
  64  * smk_access_entry - look up matching access rule
  65  * @subject_label: a pointer to the subject's Smack label
  66  * @object_label: a pointer to the object's Smack label
  67  * @rule_list: the list of rules to search
  68  *
  69  * This function looks up the subject/object pair in the
  70  * access rule list and returns the access mode. If no
  71  * entry is found returns -ENOENT.
  72  *
  73  * NOTE:
  74  *
  75  * Earlier versions of this function allowed for labels that
  76  * were not on the label list. This was done to allow for
  77  * labels to come over the network that had never been seen
  78  * before on this host. Unless the receiving socket has the
  79  * star label this will always result in a failure check. The
  80  * star labeled socket case is now handled in the networking
  81  * hooks so there is no case where the label is not on the
  82  * label list. Checking to see if the address of two labels
  83  * is the same is now a reliable test.
  84  *
  85  * Do the object check first because that is more
  86  * likely to differ.
  87  *
  88  * Allowing write access implies allowing locking.
  89  */
  90 int smk_access_entry(char *subject_label, char *object_label,
  91                         struct list_head *rule_list)
  92 {
  93         int may = -ENOENT;
  94         struct smack_rule *srp;
  95
  96         list_for_each_entry_rcu(srp, rule_list, list) {
  97                 if (srp->smk_object->smk_known == object_label &&
  98                     srp->smk_subject->smk_known == subject_label) {
  99                         may = srp->smk_access;
 100                         break;
 101                 }
 102         }
 103
 104         /*
 105          * MAY_WRITE implies MAY_LOCK.
 106          */
 107         if ((may & MAY_WRITE) == MAY_WRITE)
 108                 may |= MAY_LOCK;
 109         return may;
 110 }
 111
 112 /**
 113  * smk_access - determine if a subject has a specific access to an object
 114  * @subject: a pointer to the subject's Smack label entry
 115  * @object: a pointer to the object's Smack label entry
 116  * @request: the access requested, in "MAY" format
 117  * @a : a pointer to the audit data
 118  *
 119  * This function looks up the subject/object pair in the
 120  * access rule list and returns 0 if the access is permitted,
 121  * non zero otherwise.
 122  *
 123  * Smack labels are shared on smack_list
 124  */
 125 int smk_access(struct smack_known *subject, struct smack_known *object,
 126                int request, struct smk_audit_info *a)
 127 {
 128         int may = MAY_NOT;
 129         int rc = 0;
 130
 131         /*
 132          * Hardcoded comparisons.
 133          */
 134         /*
 135          * A star subject can't access any object.
 136          */
 137         if (subject == &smack_known_star) {
 138                 rc = -EACCES;
 139                 goto out_audit;
 140         }
 141         /*
 142          * An internet object can be accessed by any subject.
 143          * Tasks cannot be assigned the internet label.
 144          * An internet subject can access any object.
 145          */
 146         if (object == &smack_known_web || subject == &smack_known_web)
 147                 goto out_audit;
 148         /*
 149          * A star object can be accessed by any subject.
 150          */
 151         if (object == &smack_known_star)
 152                 goto out_audit;
 153         /*
 154          * An object can be accessed in any way by a subject
 155          * with the same label.
 156          */
 157         if (subject->smk_known == object->smk_known)
 158                 goto out_audit;
 159         /*
 160          * A hat subject can read or lock any object.
 161          * A floor object can be read or locked by any subject.
 162          */
 163         if ((request & MAY_ANYREAD) == request ||
 164             (request & MAY_LOCK) == request) {
 165                 if (object == &smack_known_floor)
 166                         goto out_audit;
 167                 if (subject == &smack_known_hat)
 168                         goto out_audit;
 169         }
 170         /*
 171          * Beyond here an explicit relationship is required.
 172          * If the requested access is contained in the available
 173          * access (e.g. read is included in readwrite) it's
 174          * good. A negative response from smk_access_entry()
 175          * indicates there is no entry for this pair.
 176          */
 177         rcu_read_lock();
 178         may = smk_access_entry(subject->smk_known, object->smk_known,
 179                                &subject->smk_rules);
 180         rcu_read_unlock();
 181
 182         if (may <= 0 || (request & may) != request) {
 183                 rc = -EACCES;
 184                 goto out_audit;
 185         }
 186 #ifdef CONFIG_SECURITY_SMACK_BRINGUP
 187         /*
 188          * Return a positive value if using bringup mode.
 189          * This allows the hooks to identify checks that
 190          * succeed because of "b" rules.
 191          */
 192         if (may & MAY_BRINGUP)
 193                 rc = SMACK_BRINGUP_ALLOW;
 194 #endif
 195
 196 out_audit:
 197
 198 #ifdef CONFIG_SECURITY_SMACK_BRINGUP
 199         if (rc < 0) {
 200                 if (object == smack_unconfined)
 201                         rc = SMACK_UNCONFINED_OBJECT;
 202                 if (subject == smack_unconfined)
 203                         rc = SMACK_UNCONFINED_SUBJECT;
 204         }
 205 #endif
 206
 207 #ifdef CONFIG_AUDIT
 208         if (a)
 209                 smack_log(subject->smk_known, object->smk_known,
 210                           request, rc, a);
 211 #endif
 212
 213         return rc;
 214 }
 215
 216 /**
 217  * smk_tskacc - determine if a task has a specific access to an object
 218  * @tsp: a pointer to the subject's task
 219  * @obj_known: a pointer to the object's label entry
 220  * @mode: the access requested, in "MAY" format
 221  * @a : common audit data
 222  *
 223  * This function checks the subject task's label/object label pair
 224  * in the access rule list and returns 0 if the access is permitted,
 225  * non zero otherwise. It allows that the task may have the capability
 226  * to override the rules.
 227  */
 228 int smk_tskacc(struct task_smack *tsp, struct smack_known *obj_known,
 229                u32 mode, struct smk_audit_info *a)
 230 {
 231         struct smack_known *sbj_known = smk_of_task(tsp);
 232         int may;
 233         int rc;
 234
 235         /*
 236          * Check the global rule list
 237          */
 238         rc = smk_access(sbj_known, obj_known, mode, NULL);
 239         if (rc >= 0) {
 240                 /*
 241                  * If there is an entry in the task's rule list
 242                  * it can further restrict access.
 243                  */
 244                 may = smk_access_entry(sbj_known->smk_known,
 245                                        obj_known->smk_known,
 246                                        &tsp->smk_rules);
 247                 if (may < 0)
 248                         goto out_audit;
 249                 if ((mode & may) == mode)
 250                         goto out_audit;
 251                 rc = -EACCES;
 252         }
 253
 254         /*
 255          * Allow for priviliged to override policy.
 256          */
 257         if (rc != 0 && smack_privileged(CAP_MAC_OVERRIDE))
 258                 rc = 0;
 259
 260 out_audit:
 261 #ifdef CONFIG_AUDIT
 262         if (a)
 263                 smack_log(sbj_known->smk_known, obj_known->smk_known,
 264                           mode, rc, a);
 265 #endif
 266         return rc;
 267 }
 268
 269 /**
 270  * smk_curacc - determine if current has a specific access to an object
 271  * @obj_known: a pointer to the object's Smack label entry
 272  * @mode: the access requested, in "MAY" format
 273  * @a : common audit data
 274  *
 275  * This function checks the current subject label/object label pair
 276  * in the access rule list and returns 0 if the access is permitted,
 277  * non zero otherwise. It allows that current may have the capability
 278  * to override the rules.
 279  */
 280 int smk_curacc(struct smack_known *obj_known,
 281                u32 mode, struct smk_audit_info *a)
 282 {
 283         struct task_smack *tsp = current_security();
 284
 285         return smk_tskacc(tsp, obj_known, mode, a);
 286 }
 287
 288 #ifdef CONFIG_AUDIT
 289 /**
 290  * smack_str_from_perm : helper to transalate an int to a
 291  * readable string
 292  * @string : the string to fill
 293  * @access : the int
 294  *
 295  */
 296 static inline void smack_str_from_perm(char *string, int access)
 297 {
 298         int i = 0;
 299
 300         if (access & MAY_READ)
 301                 string[i++] = 'r';
 302         if (access & MAY_WRITE)
 303                 string[i++] = 'w';
 304         if (access & MAY_EXEC)
 305                 string[i++] = 'x';
 306         if (access & MAY_APPEND)
 307                 string[i++] = 'a';
 308         if (access & MAY_TRANSMUTE)
 309                 string[i++] = 't';
 310         if (access & MAY_LOCK)
 311                 string[i++] = 'l';
 312         string[i] = '\0';
 313 }
 314 /**
 315  * smack_log_callback - SMACK specific information
 316  * will be called by generic audit code
 317  * @ab : the audit_buffer
 318  * @a  : audit_data
 319  *
 320  */
 321 static void smack_log_callback(struct audit_buffer *ab, void *a)
 322 {
 323         struct common_audit_data *ad = a;
 324         struct smack_audit_data *sad = ad->smack_audit_data;
 325         audit_log_format(ab, "lsm=SMACK fn=%s action=%s",
 326                          ad->smack_audit_data->function,
 327                          sad->result ? "denied" : "granted");
 328         audit_log_format(ab, " subject=");
 329         audit_log_untrustedstring(ab, sad->subject);
 330         audit_log_format(ab, " object=");
 331         audit_log_untrustedstring(ab, sad->object);
 332         if (sad->request[0] == '\0')
 333                 audit_log_format(ab, " labels_differ");
 334         else
 335                 audit_log_format(ab, " requested=%s", sad->request);
 336 }
 337
 338 /**
 339  *  smack_log - Audit the granting or denial of permissions.
 340  *  @subject_label : smack label of the requester
 341  *  @object_label  : smack label of the object being accessed
 342  *  @request: requested permissions
 343  *  @result: result from smk_access
 344  *  @a:  auxiliary audit data
 345  *
 346  * Audit the granting or denial of permissions in accordance
 347  * with the policy.
 348  */
 349 void smack_log(char *subject_label, char *object_label, int request,
 350                int result, struct smk_audit_info *ad)
 351 {
 352 #ifdef CONFIG_SECURITY_SMACK_BRINGUP
 353         char request_buffer[SMK_NUM_ACCESS_TYPE + 5];
 354 #else
 355         char request_buffer[SMK_NUM_ACCESS_TYPE + 1];
 356 #endif
 357         struct smack_audit_data *sad;
 358         struct common_audit_data *a = &ad->a;
 359
 360         /* check if we have to log the current event */
 361         if (result < 0 && (log_policy & SMACK_AUDIT_DENIED) == 0)
 362                 return;
 363         if (result == 0 && (log_policy & SMACK_AUDIT_ACCEPT) == 0)
 364                 return;
 365
 366         sad = a->smack_audit_data;
 367
 368         if (sad->function == NULL)
 369                 sad->function = "unknown";
 370
 371         /* end preparing the audit data */
 372         smack_str_from_perm(request_buffer, request);
 373         sad->subject = subject_label;
 374         sad->object  = object_label;
 375 #ifdef CONFIG_SECURITY_SMACK_BRINGUP
 376         /*
 377          * The result may be positive in bringup mode.
 378          * A positive result is an allow, but not for normal reasons.
 379          * Mark it as successful, but don't filter it out even if
 380          * the logging policy says to do so.
 381          */
 382         if (result == SMACK_UNCONFINED_SUBJECT)
 383                 strcat(request_buffer, "(US)");
 384         else if (result == SMACK_UNCONFINED_OBJECT)
 385                 strcat(request_buffer, "(UO)");
 386
 387         if (result > 0)
 388                 result = 0;
 389 #endif
 390         sad->request = request_buffer;
 391         sad->result  = result;
 392
 393         common_lsm_audit(a, smack_log_callback, NULL);
 394 }
 395 #else /* #ifdef CONFIG_AUDIT */
 396 void smack_log(char *subject_label, char *object_label, int request,
 397                int result, struct smk_audit_info *ad)
 398 {
 399 }
 400 #endif
 401
 402 DEFINE_MUTEX(smack_known_lock);
 403
 404 struct hlist_head smack_known_hash[SMACK_HASH_SLOTS];
 405
 406 /**
 407  * smk_insert_entry - insert a smack label into a hash map,
 408  *
 409  * this function must be called under smack_known_lock
 410  */
 411 void smk_insert_entry(struct smack_known *skp)
 412 {
 413         unsigned int hash;
 414         struct hlist_head *head;
 415
 416         hash = full_name_hash(NULL, skp->smk_known, strlen(skp->smk_known));
 417         head = &smack_known_hash[hash & (SMACK_HASH_SLOTS - 1)];
 418
 419         hlist_add_head_rcu(&skp->smk_hashed, head);
 420         list_add_rcu(&skp->list, &smack_known_list);
 421 }
 422
 423 /**
 424  * smk_find_entry - find a label on the list, return the list entry
 425  * @string: a text string that might be a Smack label
 426  *
 427  * Returns a pointer to the entry in the label list that
 428  * matches the passed string or NULL if not found.
 429  */
 430 struct smack_known *smk_find_entry(const char *string)
 431 {
 432         unsigned int hash;
 433         struct hlist_head *head;
 434         struct smack_known *skp;
 435
 436         hash = full_name_hash(NULL, string, strlen(string));
 437         head = &smack_known_hash[hash & (SMACK_HASH_SLOTS - 1)];
 438
 439         hlist_for_each_entry_rcu(skp, head, smk_hashed)
 440                 if (strcmp(skp->smk_known, string) == 0)
 441                         return skp;
 442
 443         return NULL;
 444 }
 445
 446 /**
 447  * smk_parse_smack - parse smack label from a text string
 448  * @string: a text string that might contain a Smack label
 449  * @len: the maximum size, or zero if it is NULL terminated.
 450  *
 451  * Returns a pointer to the clean label or an error code.
 452  */
 453 char *smk_parse_smack(const char *string, int len)
 454 {
 455         char *smack;
 456         int i;
 457
 458         if (len <= 0)
 459                 len = strlen(string) + 1;
 460
 461         /*
 462          * Reserve a leading '-' as an indicator that
 463          * this isn't a label, but an option to interfaces
 464          * including /smack/cipso and /smack/cipso2
 465          */
 466         if (string[0] == '-')
 467                 return ERR_PTR(-EINVAL);
 468
 469         for (i = 0; i < len; i++)
 470                 if (string[i] > '~' || string[i] <= ' ' || string[i] == '/' ||
 471                     string[i] == '"' || string[i] == '\\' || string[i] == '\'')
 472                         break;
 473
 474         if (i == 0 || i >= SMK_LONGLABEL)
 475                 return ERR_PTR(-EINVAL);
 476
 477         smack = kzalloc(i + 1, GFP_KERNEL);
 478         if (smack == NULL)
 479                 return ERR_PTR(-ENOMEM);
 480
 481         strncpy(smack, string, i);
 482
 483         return smack;
 484 }
 485
 486 /**
 487  * smk_netlbl_mls - convert a catset to netlabel mls categories
 488  * @catset: the Smack categories
 489  * @sap: where to put the netlabel categories
 490  *
 491  * Allocates and fills attr.mls
 492  * Returns 0 on success, error code on failure.
 493  */
 494 int smk_netlbl_mls(int level, char *catset, struct netlbl_lsm_secattr *sap,
 495                         int len)
 496 {
 497         unsigned char *cp;
 498         unsigned char m;
 499         int cat;
 500         int rc;
 501         int byte;
 502
 503         sap->flags |= NETLBL_SECATTR_MLS_CAT;
 504         sap->attr.mls.lvl = level;
 505         sap->attr.mls.cat = NULL;
 506
 507         for (cat = 1, cp = catset, byte = 0; byte < len; cp++, byte++)
 508                 for (m = 0x80; m != 0; m >>= 1, cat++) {
 509                         if ((m & *cp) == 0)
 510                                 continue;
 511                         rc = netlbl_catmap_setbit(&sap->attr.mls.cat,
 512                                                   cat, GFP_ATOMIC);
 513                         if (rc < 0) {
 514                                 netlbl_catmap_free(sap->attr.mls.cat);
 515                                 return rc;
 516                         }
 517                 }
 518
 519         return 0;
 520 }
 521
 522 /**
 523  * smk_import_entry - import a label, return the list entry
 524  * @string: a text string that might be a Smack label
 525  * @len: the maximum size, or zero if it is NULL terminated.
 526  *
 527  * Returns a pointer to the entry in the label list that
 528  * matches the passed string, adding it if necessary,
 529  * or an error code.
 530  */
 531 struct smack_known *smk_import_entry(const char *string, int len)
 532 {
 533         struct smack_known *skp;
 534         char *smack;
 535         int slen;
 536         int rc;
 537
 538         smack = smk_parse_smack(string, len);
 539         if (IS_ERR(smack))
 540                 return ERR_CAST(smack);
 541
 542         mutex_lock(&smack_known_lock);
 543
 544         skp = smk_find_entry(smack);
 545         if (skp != NULL)
 546                 goto freeout;
 547
 548         skp = kzalloc(sizeof(*skp), GFP_KERNEL);
 549         if (skp == NULL) {
 550                 skp = ERR_PTR(-ENOMEM);
 551                 goto freeout;
 552         }
 553
 554         skp->smk_known = smack;
 555         skp->smk_secid = smack_next_secid++;
 556         skp->smk_netlabel.domain = skp->smk_known;
 557         skp->smk_netlabel.flags =
 558                 NETLBL_SECATTR_DOMAIN | NETLBL_SECATTR_MLS_LVL;
 559         /*
 560          * If direct labeling works use it.
 561          * Otherwise use mapped labeling.
 562          */
 563         slen = strlen(smack);
 564         if (slen < SMK_CIPSOLEN)
 565                 rc = smk_netlbl_mls(smack_cipso_direct, skp->smk_known,
 566                                &skp->smk_netlabel, slen);
 567         else
 568                 rc = smk_netlbl_mls(smack_cipso_mapped, (char *)&skp->smk_secid,
 569                                &skp->smk_netlabel, sizeof(skp->smk_secid));
 570
 571         if (rc >= 0) {
 572                 INIT_LIST_HEAD(&skp->smk_rules);
 573                 mutex_init(&skp->smk_rules_lock);
 574                 /*
 575                  * Make sure that the entry is actually
 576                  * filled before putting it on the list.
 577                  */
 578                 smk_insert_entry(skp);
 579                 goto unlockout;
 580         }
 581         /*
 582          * smk_netlbl_mls failed.
 583          */
 584         kfree(skp);
 585         skp = ERR_PTR(rc);
 586 freeout:
 587         kfree(smack);
 588 unlockout:
 589         mutex_unlock(&smack_known_lock);
 590
 591         return skp;
 592 }
 593
 594 /**
 595  * smack_from_secid - find the Smack label associated with a secid
 596  * @secid: an integer that might be associated with a Smack label
 597  *
 598  * Returns a pointer to the appropriate Smack label entry if there is one,
 599  * otherwise a pointer to the invalid Smack label.
 600  */
 601 struct smack_known *smack_from_secid(const u32 secid)
 602 {
 603         struct smack_known *skp;
 604
 605         rcu_read_lock();
 606         list_for_each_entry_rcu(skp, &smack_known_list, list) {
 607                 if (skp->smk_secid == secid) {
 608                         rcu_read_unlock();
 609                         return skp;
 610                 }
 611         }
 612
 613         /*
 614          * If we got this far someone asked for the translation
 615          * of a secid that is not on the list.
 616          */
 617         rcu_read_unlock();
 618         return &smack_known_invalid;
 619 }
 620
 621 /*
 622  * Unless a process is running with one of these labels
 623  * even having CAP_MAC_OVERRIDE isn't enough to grant
 624  * privilege to violate MAC policy. If no labels are
 625  * designated (the empty list case) capabilities apply to
 626  * everyone.
 627  */
 628 LIST_HEAD(smack_onlycap_list);
 629 DEFINE_MUTEX(smack_onlycap_lock);
 630
 631 /*
 632  * Is the task privileged and allowed to be privileged
 633  * by the onlycap rule.
 634  *
 635  * Returns 1 if the task is allowed to be privileged, 0 if it's not.
 636  */
 637 int smack_privileged(int cap)
 638 {
 639         struct smack_known *skp = smk_of_current();
 640         struct smack_known_list_elem *sklep;
 641
 642         /*
 643          * All kernel tasks are privileged
 644          */
 645         if (unlikely(current->flags & PF_KTHREAD))
 646                 return 1;
 647
 648         if (!capable(cap))
 649                 return 0;
 650
 651         rcu_read_lock();
 652         if (list_empty(&smack_onlycap_list)) {
 653                 rcu_read_unlock();
 654                 return 1;
 655         }
 656
 657         list_for_each_entry_rcu(sklep, &smack_onlycap_list, list) {
 658                 if (sklep->smk_label == skp) {
 659                         rcu_read_unlock();
 660                         return 1;
 661                 }
 662         }
 663         rcu_read_unlock();
 664
 665         return 0;
 666 }