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 int smk_access_entry(char *subject_label, char *object_label,
  89                         struct list_head *rule_list)
  90 {
  91         int may = -ENOENT;
  92         struct smack_rule *srp;
  93
  94         list_for_each_entry_rcu(srp, rule_list, list) {
  95                 if (srp->smk_object == object_label &&
  96                     srp->smk_subject == subject_label) {
  97                         may = srp->smk_access;
  98                         break;
  99                 }
 100         }
 101
 102         return may;
 103 }
 104
 105 /**
 106  * smk_access - determine if a subject has a specific access to an object
 107  * @subject_label: a pointer to the subject's Smack label
 108  * @object_label: a pointer to the object's Smack label
 109  * @request: the access requested, in "MAY" format
 110  * @a : a pointer to the audit data
 111  *
 112  * This function looks up the subject/object pair in the
 113  * access rule list and returns 0 if the access is permitted,
 114  * non zero otherwise.
 115  *
 116  * Smack labels are shared on smack_list
 117  */
 118 int smk_access(char *subject_label, char *object_label, int request,
 119                struct smk_audit_info *a)
 120 {
 121         struct smack_known *skp;
 122         int may = MAY_NOT;
 123         int rc = 0;
 124
 125         /*
 126          * Hardcoded comparisons.
 127          *
 128          * A star subject can't access any object.
 129          */
 130         if (subject_label == smack_known_star.smk_known) {
 131                 rc = -EACCES;
 132                 goto out_audit;
 133         }
 134         /*
 135          * An internet object can be accessed by any subject.
 136          * Tasks cannot be assigned the internet label.
 137          * An internet subject can access any object.
 138          */
 139         if (object_label == smack_known_web.smk_known ||
 140             subject_label == smack_known_web.smk_known)
 141                 goto out_audit;
 142         /*
 143          * A star object can be accessed by any subject.
 144          */
 145         if (object_label == smack_known_star.smk_known)
 146                 goto out_audit;
 147         /*
 148          * An object can be accessed in any way by a subject
 149          * with the same label.
 150          */
 151         if (subject_label == object_label)
 152                 goto out_audit;
 153         /*
 154          * A hat subject can read any object.
 155          * A floor object can be read by any subject.
 156          */
 157         if ((request & MAY_ANYREAD) == request) {
 158                 if (object_label == smack_known_floor.smk_known)
 159                         goto out_audit;
 160                 if (subject_label == smack_known_hat.smk_known)
 161                         goto out_audit;
 162         }
 163         /*
 164          * Beyond here an explicit relationship is required.
 165          * If the requested access is contained in the available
 166          * access (e.g. read is included in readwrite) it's
 167          * good. A negative response from smk_access_entry()
 168          * indicates there is no entry for this pair.
 169          */
 170         skp = smk_find_entry(subject_label);
 171         rcu_read_lock();
 172         may = smk_access_entry(subject_label, object_label, &skp->smk_rules);
 173         rcu_read_unlock();
 174
 175         if (may > 0 && (request & may) == request)
 176                 goto out_audit;
 177
 178         rc = -EACCES;
 179 out_audit:
 180 #ifdef CONFIG_AUDIT
 181         if (a)
 182                 smack_log(subject_label, object_label, request, rc, a);
 183 #endif
 184         return rc;
 185 }
 186
 187 /**
 188  * smk_curacc - determine if current has a specific access to an object
 189  * @obj_label: a pointer to the object's Smack label
 190  * @mode: the access requested, in "MAY" format
 191  * @a : common audit data
 192  *
 193  * This function checks the current subject label/object label pair
 194  * in the access rule list and returns 0 if the access is permitted,
 195  * non zero otherwise. It allows that current may have the capability
 196  * to override the rules.
 197  */
 198 int smk_curacc(char *obj_label, u32 mode, struct smk_audit_info *a)
 199 {
 200         struct task_smack *tsp = current_security();
 201         char *sp = smk_of_task(tsp);
 202         int may;
 203         int rc;
 204
 205         /*
 206          * Check the global rule list
 207          */
 208         rc = smk_access(sp, obj_label, mode, NULL);
 209         if (rc == 0) {
 210                 /*
 211                  * If there is an entry in the task's rule list
 212                  * it can further restrict access.
 213                  */
 214                 may = smk_access_entry(sp, obj_label, &tsp->smk_rules);
 215                 if (may < 0)
 216                         goto out_audit;
 217                 if ((mode & may) == mode)
 218                         goto out_audit;
 219                 rc = -EACCES;
 220         }
 221
 222         /*
 223          * Allow for priviliged to override policy.
 224          */
 225         if (rc != 0 && smack_privileged(CAP_MAC_OVERRIDE))
 226                 rc = 0;
 227
 228 out_audit:
 229 #ifdef CONFIG_AUDIT
 230         if (a)
 231                 smack_log(sp, obj_label, mode, rc, a);
 232 #endif
 233         return rc;
 234 }
 235
 236 #ifdef CONFIG_AUDIT
 237 /**
 238  * smack_str_from_perm : helper to transalate an int to a
 239  * readable string
 240  * @string : the string to fill
 241  * @access : the int
 242  *
 243  */
 244 static inline void smack_str_from_perm(char *string, int access)
 245 {
 246         int i = 0;
 247         if (access & MAY_READ)
 248                 string[i++] = 'r';
 249         if (access & MAY_WRITE)
 250                 string[i++] = 'w';
 251         if (access & MAY_EXEC)
 252                 string[i++] = 'x';
 253         if (access & MAY_APPEND)
 254                 string[i++] = 'a';
 255         if (access & MAY_TRANSMUTE)
 256                 string[i++] = 't';
 257         string[i] = '\0';
 258 }
 259 /**
 260  * smack_log_callback - SMACK specific information
 261  * will be called by generic audit code
 262  * @ab : the audit_buffer
 263  * @a  : audit_data
 264  *
 265  */
 266 static void smack_log_callback(struct audit_buffer *ab, void *a)
 267 {
 268         struct common_audit_data *ad = a;
 269         struct smack_audit_data *sad = ad->smack_audit_data;
 270         audit_log_format(ab, "lsm=SMACK fn=%s action=%s",
 271                          ad->smack_audit_data->function,
 272                          sad->result ? "denied" : "granted");
 273         audit_log_format(ab, " subject=");
 274         audit_log_untrustedstring(ab, sad->subject);
 275         audit_log_format(ab, " object=");
 276         audit_log_untrustedstring(ab, sad->object);
 277         audit_log_format(ab, " requested=%s", sad->request);
 278 }
 279
 280 /**
 281  *  smack_log - Audit the granting or denial of permissions.
 282  *  @subject_label : smack label of the requester
 283  *  @object_label  : smack label of the object being accessed
 284  *  @request: requested permissions
 285  *  @result: result from smk_access
 286  *  @a:  auxiliary audit data
 287  *
 288  * Audit the granting or denial of permissions in accordance
 289  * with the policy.
 290  */
 291 void smack_log(char *subject_label, char *object_label, int request,
 292                int result, struct smk_audit_info *ad)
 293 {
 294         char request_buffer[SMK_NUM_ACCESS_TYPE + 1];
 295         struct smack_audit_data *sad;
 296         struct common_audit_data *a = &ad->a;
 297
 298         /* check if we have to log the current event */
 299         if (result != 0 && (log_policy & SMACK_AUDIT_DENIED) == 0)
 300                 return;
 301         if (result == 0 && (log_policy & SMACK_AUDIT_ACCEPT) == 0)
 302                 return;
 303
 304         sad = a->smack_audit_data;
 305
 306         if (sad->function == NULL)
 307                 sad->function = "unknown";
 308
 309         /* end preparing the audit data */
 310         smack_str_from_perm(request_buffer, request);
 311         sad->subject = subject_label;
 312         sad->object  = object_label;
 313         sad->request = request_buffer;
 314         sad->result  = result;
 315
 316         common_lsm_audit(a, smack_log_callback, NULL);
 317 }
 318 #else /* #ifdef CONFIG_AUDIT */
 319 void smack_log(char *subject_label, char *object_label, int request,
 320                int result, struct smk_audit_info *ad)
 321 {
 322 }
 323 #endif
 324
 325 DEFINE_MUTEX(smack_known_lock);
 326
 327 /**
 328  * smk_find_entry - find a label on the list, return the list entry
 329  * @string: a text string that might be a Smack label
 330  *
 331  * Returns a pointer to the entry in the label list that
 332  * matches the passed string.
 333  */
 334 struct smack_known *smk_find_entry(const char *string)
 335 {
 336         struct smack_known *skp;
 337
 338         list_for_each_entry_rcu(skp, &smack_known_list, list) {
 339                 if (strcmp(skp->smk_known, string) == 0)
 340                         return skp;
 341         }
 342
 343         return NULL;
 344 }
 345
 346 /**
 347  * smk_parse_smack - parse smack label from a text string
 348  * @string: a text string that might contain a Smack label
 349  * @len: the maximum size, or zero if it is NULL terminated.
 350  *
 351  * Returns a pointer to the clean label, or NULL
 352  */
 353 char *smk_parse_smack(const char *string, int len)
 354 {
 355         char *smack;
 356         int i;
 357
 358         if (len <= 0)
 359                 len = strlen(string) + 1;
 360
 361         /*
 362          * Reserve a leading '-' as an indicator that
 363          * this isn't a label, but an option to interfaces
 364          * including /smack/cipso and /smack/cipso2
 365          */
 366         if (string[0] == '-')
 367                 return NULL;
 368
 369         for (i = 0; i < len; i++)
 370                 if (string[i] > '~' || string[i] <= ' ' || string[i] == '/' ||
 371                     string[i] == '"' || string[i] == '\\' || string[i] == '\'')
 372                         break;
 373
 374         if (i == 0 || i >= SMK_LONGLABEL)
 375                 return NULL;
 376
 377         smack = kzalloc(i + 1, GFP_KERNEL);
 378         if (smack != NULL) {
 379                 strncpy(smack, string, i + 1);
 380                 smack[i] = '\0';
 381         }
 382         return smack;
 383 }
 384
 385 /**
 386  * smk_netlbl_mls - convert a catset to netlabel mls categories
 387  * @catset: the Smack categories
 388  * @sap: where to put the netlabel categories
 389  *
 390  * Allocates and fills attr.mls
 391  * Returns 0 on success, error code on failure.
 392  */
 393 int smk_netlbl_mls(int level, char *catset, struct netlbl_lsm_secattr *sap,
 394                         int len)
 395 {
 396         unsigned char *cp;
 397         unsigned char m;
 398         int cat;
 399         int rc;
 400         int byte;
 401
 402         sap->flags |= NETLBL_SECATTR_MLS_CAT;
 403         sap->attr.mls.lvl = level;
 404         sap->attr.mls.cat = netlbl_secattr_catmap_alloc(GFP_ATOMIC);
 405         sap->attr.mls.cat->startbit = 0;
 406
 407         for (cat = 1, cp = catset, byte = 0; byte < len; cp++, byte++)
 408                 for (m = 0x80; m != 0; m >>= 1, cat++) {
 409                         if ((m & *cp) == 0)
 410                                 continue;
 411                         rc = netlbl_secattr_catmap_setbit(sap->attr.mls.cat,
 412                                                           cat, GFP_ATOMIC);
 413                         if (rc < 0) {
 414                                 netlbl_secattr_catmap_free(sap->attr.mls.cat);
 415                                 return rc;
 416                         }
 417                 }
 418
 419         return 0;
 420 }
 421
 422 /**
 423  * smk_import_entry - import a label, return the list entry
 424  * @string: a text string that might be a Smack label
 425  * @len: the maximum size, or zero if it is NULL terminated.
 426  *
 427  * Returns a pointer to the entry in the label list that
 428  * matches the passed string, adding it if necessary.
 429  */
 430 struct smack_known *smk_import_entry(const char *string, int len)
 431 {
 432         struct smack_known *skp;
 433         char *smack;
 434         int slen;
 435         int rc;
 436
 437         smack = smk_parse_smack(string, len);
 438         if (smack == NULL)
 439                 return NULL;
 440
 441         mutex_lock(&smack_known_lock);
 442
 443         skp = smk_find_entry(smack);
 444         if (skp != NULL)
 445                 goto freeout;
 446
 447         skp = kzalloc(sizeof(*skp), GFP_KERNEL);
 448         if (skp == NULL)
 449                 goto freeout;
 450
 451         skp->smk_known = smack;
 452         skp->smk_secid = smack_next_secid++;
 453         skp->smk_netlabel.domain = skp->smk_known;
 454         skp->smk_netlabel.flags =
 455                 NETLBL_SECATTR_DOMAIN | NETLBL_SECATTR_MLS_LVL;
 456         /*
 457          * If direct labeling works use it.
 458          * Otherwise use mapped labeling.
 459          */
 460         slen = strlen(smack);
 461         if (slen < SMK_CIPSOLEN)
 462                 rc = smk_netlbl_mls(smack_cipso_direct, skp->smk_known,
 463                                &skp->smk_netlabel, slen);
 464         else
 465                 rc = smk_netlbl_mls(smack_cipso_mapped, (char *)&skp->smk_secid,
 466                                &skp->smk_netlabel, sizeof(skp->smk_secid));
 467
 468         if (rc >= 0) {
 469                 INIT_LIST_HEAD(&skp->smk_rules);
 470                 mutex_init(&skp->smk_rules_lock);
 471                 /*
 472                  * Make sure that the entry is actually
 473                  * filled before putting it on the list.
 474                  */
 475                 list_add_rcu(&skp->list, &smack_known_list);
 476                 goto unlockout;
 477         }
 478         /*
 479          * smk_netlbl_mls failed.
 480          */
 481         kfree(skp);
 482         skp = NULL;
 483 freeout:
 484         kfree(smack);
 485 unlockout:
 486         mutex_unlock(&smack_known_lock);
 487
 488         return skp;
 489 }
 490
 491 /**
 492  * smk_import - import a smack label
 493  * @string: a text string that might be a Smack label
 494  * @len: the maximum size, or zero if it is NULL terminated.
 495  *
 496  * Returns a pointer to the label in the label list that
 497  * matches the passed string, adding it if necessary.
 498  */
 499 char *smk_import(const char *string, int len)
 500 {
 501         struct smack_known *skp;
 502
 503         /* labels cannot begin with a '-' */
 504         if (string[0] == '-')
 505                 return NULL;
 506         skp = smk_import_entry(string, len);
 507         if (skp == NULL)
 508                 return NULL;
 509         return skp->smk_known;
 510 }
 511
 512 /**
 513  * smack_from_secid - find the Smack label associated with a secid
 514  * @secid: an integer that might be associated with a Smack label
 515  *
 516  * Returns a pointer to the appropriate Smack label if there is one,
 517  * otherwise a pointer to the invalid Smack label.
 518  */
 519 char *smack_from_secid(const u32 secid)
 520 {
 521         struct smack_known *skp;
 522
 523         rcu_read_lock();
 524         list_for_each_entry_rcu(skp, &smack_known_list, list) {
 525                 if (skp->smk_secid == secid) {
 526                         rcu_read_unlock();
 527                         return skp->smk_known;
 528                 }
 529         }
 530
 531         /*
 532          * If we got this far someone asked for the translation
 533          * of a secid that is not on the list.
 534          */
 535         rcu_read_unlock();
 536         return smack_known_invalid.smk_known;
 537 }
 538
 539 /**
 540  * smack_to_secid - find the secid associated with a Smack label
 541  * @smack: the Smack label
 542  *
 543  * Returns the appropriate secid if there is one,
 544  * otherwise 0
 545  */
 546 u32 smack_to_secid(const char *smack)
 547 {
 548         struct smack_known *skp = smk_find_entry(smack);
 549
 550         if (skp == NULL)
 551                 return 0;
 552         return skp->smk_secid;
 553 }