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          * A star subject can't access any object.
 135          */
 136         if (subject == &smack_known_star) {
 137                 rc = -EACCES;
 138                 goto out_audit;
 139         }
 140         /*
 141          * An internet object can be accessed by any subject.
 142          * Tasks cannot be assigned the internet label.
 143          * An internet subject can access any object.
 144          */
 145         if (object == &smack_known_web || subject == &smack_known_web)
 146                 goto out_audit;
 147         /*
 148          * A star object can be accessed by any subject.
 149          */
 150         if (object == &smack_known_star)
 151                 goto out_audit;
 152         /*
 153          * An object can be accessed in any way by a subject
 154          * with the same label.
 155          */
 156         if (subject->smk_known == object->smk_known)
 157                 goto out_audit;
 158         /*
 159          * A hat subject can read or lock any object.
 160          * A floor object can be read or locked by any subject.
 161          */
 162         if ((request & MAY_ANYREAD) == request ||
 163             (request & MAY_LOCK) == request) {
 164                 if (object == &smack_known_floor)
 165                         goto out_audit;
 166                 if (subject == &smack_known_hat)
 167                         goto out_audit;
 168         }
 169         /*
 170          * Beyond here an explicit relationship is required.
 171          * If the requested access is contained in the available
 172          * access (e.g. read is included in readwrite) it's
 173          * good. A negative response from smk_access_entry()
 174          * indicates there is no entry for this pair.
 175          */
 176         rcu_read_lock();
 177         may = smk_access_entry(subject->smk_known, object->smk_known,
 178                                &subject->smk_rules);
 179         rcu_read_unlock();
 180
 181         if (may <= 0 || (request & may) != request) {
 182                 rc = -EACCES;
 183                 goto out_audit;
 184         }
 185 #ifdef CONFIG_SECURITY_SMACK_BRINGUP
 186         /*
 187          * Return a positive value if using bringup mode.
 188          * This allows the hooks to identify checks that
 189          * succeed because of "b" rules.
 190          */
 191         if (may & MAY_BRINGUP)
 192                 rc = MAY_BRINGUP;
 193 #endif
 194
 195 out_audit:
 196 #ifdef CONFIG_AUDIT
 197         if (a)
 198                 smack_log(subject->smk_known, object->smk_known,
 199                           request, rc, a);
 200 #endif
 201
 202         return rc;
 203 }
 204
 205 /**
 206  * smk_tskacc - determine if a task has a specific access to an object
 207  * @tsp: a pointer to the subject's task
 208  * @obj_known: a pointer to the object's label entry
 209  * @mode: the access requested, in "MAY" format
 210  * @a : common audit data
 211  *
 212  * This function checks the subject task's label/object label pair
 213  * in the access rule list and returns 0 if the access is permitted,
 214  * non zero otherwise. It allows that the task may have the capability
 215  * to override the rules.
 216  */
 217 int smk_tskacc(struct task_smack *tsp, struct smack_known *obj_known,
 218                u32 mode, struct smk_audit_info *a)
 219 {
 220         struct smack_known *sbj_known = smk_of_task(tsp);
 221         int may;
 222         int rc;
 223
 224         /*
 225          * Check the global rule list
 226          */
 227         rc = smk_access(sbj_known, obj_known, mode, NULL);
 228         if (rc >= 0) {
 229                 /*
 230                  * If there is an entry in the task's rule list
 231                  * it can further restrict access.
 232                  */
 233                 may = smk_access_entry(sbj_known->smk_known,
 234                                        obj_known->smk_known,
 235                                        &tsp->smk_rules);
 236                 if (may < 0)
 237                         goto out_audit;
 238                 if ((mode & may) == mode)
 239                         goto out_audit;
 240                 rc = -EACCES;
 241         }
 242
 243         /*
 244          * Allow for priviliged to override policy.
 245          */
 246         if (rc != 0 && smack_privileged(CAP_MAC_OVERRIDE))
 247                 rc = 0;
 248
 249 out_audit:
 250 #ifdef CONFIG_AUDIT
 251         if (a)
 252                 smack_log(sbj_known->smk_known, obj_known->smk_known,
 253                           mode, rc, a);
 254 #endif
 255         return rc;
 256 }
 257
 258 /**
 259  * smk_curacc - determine if current has a specific access to an object
 260  * @obj_known: a pointer to the object's Smack label entry
 261  * @mode: the access requested, in "MAY" format
 262  * @a : common audit data
 263  *
 264  * This function checks the current subject label/object label pair
 265  * in the access rule list and returns 0 if the access is permitted,
 266  * non zero otherwise. It allows that current may have the capability
 267  * to override the rules.
 268  */
 269 int smk_curacc(struct smack_known *obj_known,
 270                u32 mode, struct smk_audit_info *a)
 271 {
 272         struct task_smack *tsp = current_security();
 273
 274         return smk_tskacc(tsp, obj_known, mode, a);
 275 }
 276
 277 #ifdef CONFIG_AUDIT
 278 /**
 279  * smack_str_from_perm : helper to transalate an int to a
 280  * readable string
 281  * @string : the string to fill
 282  * @access : the int
 283  *
 284  */
 285 static inline void smack_str_from_perm(char *string, int access)
 286 {
 287         int i = 0;
 288
 289         if (access & MAY_READ)
 290                 string[i++] = 'r';
 291         if (access & MAY_WRITE)
 292                 string[i++] = 'w';
 293         if (access & MAY_EXEC)
 294                 string[i++] = 'x';
 295         if (access & MAY_APPEND)
 296                 string[i++] = 'a';
 297         if (access & MAY_TRANSMUTE)
 298                 string[i++] = 't';
 299         if (access & MAY_LOCK)
 300                 string[i++] = 'l';
 301         string[i] = '\0';
 302 }
 303 /**
 304  * smack_log_callback - SMACK specific information
 305  * will be called by generic audit code
 306  * @ab : the audit_buffer
 307  * @a  : audit_data
 308  *
 309  */
 310 static void smack_log_callback(struct audit_buffer *ab, void *a)
 311 {
 312         struct common_audit_data *ad = a;
 313         struct smack_audit_data *sad = ad->smack_audit_data;
 314         audit_log_format(ab, "lsm=SMACK fn=%s action=%s",
 315                          ad->smack_audit_data->function,
 316                          sad->result ? "denied" : "granted");
 317         audit_log_format(ab, " subject=");
 318         audit_log_untrustedstring(ab, sad->subject);
 319         audit_log_format(ab, " object=");
 320         audit_log_untrustedstring(ab, sad->object);
 321         if (sad->request[0] == '\0')
 322                 audit_log_format(ab, " labels_differ");
 323         else
 324                 audit_log_format(ab, " requested=%s", sad->request);
 325 }
 326
 327 /**
 328  *  smack_log - Audit the granting or denial of permissions.
 329  *  @subject_label : smack label of the requester
 330  *  @object_label  : smack label of the object being accessed
 331  *  @request: requested permissions
 332  *  @result: result from smk_access
 333  *  @a:  auxiliary audit data
 334  *
 335  * Audit the granting or denial of permissions in accordance
 336  * with the policy.
 337  */
 338 void smack_log(char *subject_label, char *object_label, int request,
 339                int result, struct smk_audit_info *ad)
 340 {
 341         char request_buffer[SMK_NUM_ACCESS_TYPE + 1];
 342         struct smack_audit_data *sad;
 343         struct common_audit_data *a = &ad->a;
 344
 345 #ifdef CONFIG_SECURITY_SMACK_BRINGUP
 346         /*
 347          * The result may be positive in bringup mode.
 348          */
 349         if (result > 0)
 350                 result = 0;
 351 #endif
 352         /* check if we have to log the current event */
 353         if (result != 0 && (log_policy & SMACK_AUDIT_DENIED) == 0)
 354                 return;
 355         if (result == 0 && (log_policy & SMACK_AUDIT_ACCEPT) == 0)
 356                 return;
 357
 358         sad = a->smack_audit_data;
 359
 360         if (sad->function == NULL)
 361                 sad->function = "unknown";
 362
 363         /* end preparing the audit data */
 364         smack_str_from_perm(request_buffer, request);
 365         sad->subject = subject_label;
 366         sad->object  = object_label;
 367         sad->request = request_buffer;
 368         sad->result  = result;
 369
 370         common_lsm_audit(a, smack_log_callback, NULL);
 371 }
 372 #else /* #ifdef CONFIG_AUDIT */
 373 void smack_log(char *subject_label, char *object_label, int request,
 374                int result, struct smk_audit_info *ad)
 375 {
 376 }
 377 #endif
 378
 379 DEFINE_MUTEX(smack_known_lock);
 380
 381 struct hlist_head smack_known_hash[SMACK_HASH_SLOTS];
 382
 383 /**
 384  * smk_insert_entry - insert a smack label into a hash map,
 385  *
 386  * this function must be called under smack_known_lock
 387  */
 388 void smk_insert_entry(struct smack_known *skp)
 389 {
 390         unsigned int hash;
 391         struct hlist_head *head;
 392
 393         hash = full_name_hash(skp->smk_known, strlen(skp->smk_known));
 394         head = &smack_known_hash[hash & (SMACK_HASH_SLOTS - 1)];
 395
 396         hlist_add_head_rcu(&skp->smk_hashed, head);
 397         list_add_rcu(&skp->list, &smack_known_list);
 398 }
 399
 400 /**
 401  * smk_find_entry - find a label on the list, return the list entry
 402  * @string: a text string that might be a Smack label
 403  *
 404  * Returns a pointer to the entry in the label list that
 405  * matches the passed string.
 406  */
 407 struct smack_known *smk_find_entry(const char *string)
 408 {
 409         unsigned int hash;
 410         struct hlist_head *head;
 411         struct smack_known *skp;
 412
 413         hash = full_name_hash(string, strlen(string));
 414         head = &smack_known_hash[hash & (SMACK_HASH_SLOTS - 1)];
 415
 416         hlist_for_each_entry_rcu(skp, head, smk_hashed)
 417                 if (strcmp(skp->smk_known, string) == 0)
 418                         return skp;
 419
 420         return NULL;
 421 }
 422
 423 /**
 424  * smk_parse_smack - parse smack label from a text string
 425  * @string: a text string that might contain a Smack label
 426  * @len: the maximum size, or zero if it is NULL terminated.
 427  *
 428  * Returns a pointer to the clean label, or NULL
 429  */
 430 char *smk_parse_smack(const char *string, int len)
 431 {
 432         char *smack;
 433         int i;
 434
 435         if (len <= 0)
 436                 len = strlen(string) + 1;
 437
 438         /*
 439          * Reserve a leading '-' as an indicator that
 440          * this isn't a label, but an option to interfaces
 441          * including /smack/cipso and /smack/cipso2
 442          */
 443         if (string[0] == '-')
 444                 return NULL;
 445
 446         for (i = 0; i < len; i++)
 447                 if (string[i] > '~' || string[i] <= ' ' || string[i] == '/' ||
 448                     string[i] == '"' || string[i] == '\\' || string[i] == '\'')
 449                         break;
 450
 451         if (i == 0 || i >= SMK_LONGLABEL)
 452                 return NULL;
 453
 454         smack = kzalloc(i + 1, GFP_KERNEL);
 455         if (smack != NULL)
 456                 strncpy(smack, string, i);
 457
 458         return smack;
 459 }
 460
 461 /**
 462  * smk_netlbl_mls - convert a catset to netlabel mls categories
 463  * @catset: the Smack categories
 464  * @sap: where to put the netlabel categories
 465  *
 466  * Allocates and fills attr.mls
 467  * Returns 0 on success, error code on failure.
 468  */
 469 int smk_netlbl_mls(int level, char *catset, struct netlbl_lsm_secattr *sap,
 470                         int len)
 471 {
 472         unsigned char *cp;
 473         unsigned char m;
 474         int cat;
 475         int rc;
 476         int byte;
 477
 478         sap->flags |= NETLBL_SECATTR_MLS_CAT;
 479         sap->attr.mls.lvl = level;
 480         sap->attr.mls.cat = NULL;
 481
 482         for (cat = 1, cp = catset, byte = 0; byte < len; cp++, byte++)
 483                 for (m = 0x80; m != 0; m >>= 1, cat++) {
 484                         if ((m & *cp) == 0)
 485                                 continue;
 486                         rc = netlbl_catmap_setbit(&sap->attr.mls.cat,
 487                                                   cat, GFP_ATOMIC);
 488                         if (rc < 0) {
 489                                 netlbl_catmap_free(sap->attr.mls.cat);
 490                                 return rc;
 491                         }
 492                 }
 493
 494         return 0;
 495 }
 496
 497 /**
 498  * smk_import_entry - import a label, return the list entry
 499  * @string: a text string that might be a Smack label
 500  * @len: the maximum size, or zero if it is NULL terminated.
 501  *
 502  * Returns a pointer to the entry in the label list that
 503  * matches the passed string, adding it if necessary.
 504  */
 505 struct smack_known *smk_import_entry(const char *string, int len)
 506 {
 507         struct smack_known *skp;
 508         char *smack;
 509         int slen;
 510         int rc;
 511
 512         smack = smk_parse_smack(string, len);
 513         if (smack == NULL)
 514                 return NULL;
 515
 516         mutex_lock(&smack_known_lock);
 517
 518         skp = smk_find_entry(smack);
 519         if (skp != NULL)
 520                 goto freeout;
 521
 522         skp = kzalloc(sizeof(*skp), GFP_KERNEL);
 523         if (skp == NULL)
 524                 goto freeout;
 525
 526         skp->smk_known = smack;
 527         skp->smk_secid = smack_next_secid++;
 528         skp->smk_netlabel.domain = skp->smk_known;
 529         skp->smk_netlabel.flags =
 530                 NETLBL_SECATTR_DOMAIN | NETLBL_SECATTR_MLS_LVL;
 531         /*
 532          * If direct labeling works use it.
 533          * Otherwise use mapped labeling.
 534          */
 535         slen = strlen(smack);
 536         if (slen < SMK_CIPSOLEN)
 537                 rc = smk_netlbl_mls(smack_cipso_direct, skp->smk_known,
 538                                &skp->smk_netlabel, slen);
 539         else
 540                 rc = smk_netlbl_mls(smack_cipso_mapped, (char *)&skp->smk_secid,
 541                                &skp->smk_netlabel, sizeof(skp->smk_secid));
 542
 543         if (rc >= 0) {
 544                 INIT_LIST_HEAD(&skp->smk_rules);
 545                 mutex_init(&skp->smk_rules_lock);
 546                 /*
 547                  * Make sure that the entry is actually
 548                  * filled before putting it on the list.
 549                  */
 550                 smk_insert_entry(skp);
 551                 goto unlockout;
 552         }
 553         /*
 554          * smk_netlbl_mls failed.
 555          */
 556         kfree(skp);
 557         skp = NULL;
 558 freeout:
 559         kfree(smack);
 560 unlockout:
 561         mutex_unlock(&smack_known_lock);
 562
 563         return skp;
 564 }
 565
 566 /**
 567  * smack_from_secid - find the Smack label associated with a secid
 568  * @secid: an integer that might be associated with a Smack label
 569  *
 570  * Returns a pointer to the appropriate Smack label entry if there is one,
 571  * otherwise a pointer to the invalid Smack label.
 572  */
 573 struct smack_known *smack_from_secid(const u32 secid)
 574 {
 575         struct smack_known *skp;
 576
 577         rcu_read_lock();
 578         list_for_each_entry_rcu(skp, &smack_known_list, list) {
 579                 if (skp->smk_secid == secid) {
 580                         rcu_read_unlock();
 581                         return skp;
 582                 }
 583         }
 584
 585         /*
 586          * If we got this far someone asked for the translation
 587          * of a secid that is not on the list.
 588          */
 589         rcu_read_unlock();
 590         return &smack_known_invalid;
 591 }