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         .smk_cipso      = NULL,
  23 };
  24
  25 struct smack_known smack_known_hat = {
  26         .smk_known      = "^",
  27         .smk_secid      = 3,
  28         .smk_cipso      = NULL,
  29 };
  30
  31 struct smack_known smack_known_star = {
  32         .smk_known      = "*",
  33         .smk_secid      = 4,
  34         .smk_cipso      = NULL,
  35 };
  36
  37 struct smack_known smack_known_floor = {
  38         .smk_known      = "_",
  39         .smk_secid      = 5,
  40         .smk_cipso      = NULL,
  41 };
  42
  43 struct smack_known smack_known_invalid = {
  44         .smk_known      = "",
  45         .smk_secid      = 6,
  46         .smk_cipso      = NULL,
  47 };
  48
  49 struct smack_known smack_known_web = {
  50         .smk_known      = "@",
  51         .smk_secid      = 7,
  52         .smk_cipso      = NULL,
  53 };
  54
  55 LIST_HEAD(smack_known_list);
  56
  57 /*
  58  * The initial value needs to be bigger than any of the
  59  * known values above.
  60  */
  61 static u32 smack_next_secid = 10;
  62
  63 /*
  64  * what events do we log
  65  * can be overwritten at run-time by /smack/logging
  66  */
  67 int log_policy = SMACK_AUDIT_DENIED;
  68
  69 /**
  70  * smk_access_entry - look up matching access rule
  71  * @subject_label: a pointer to the subject's Smack label
  72  * @object_label: a pointer to the object's Smack label
  73  * @rule_list: the list of rules to search
  74  *
  75  * This function looks up the subject/object pair in the
  76  * access rule list and returns the access mode. If no
  77  * entry is found returns -ENOENT.
  78  *
  79  * NOTE:
  80  *
  81  * Earlier versions of this function allowed for labels that
  82  * were not on the label list. This was done to allow for
  83  * labels to come over the network that had never been seen
  84  * before on this host. Unless the receiving socket has the
  85  * star label this will always result in a failure check. The
  86  * star labeled socket case is now handled in the networking
  87  * hooks so there is no case where the label is not on the
  88  * label list. Checking to see if the address of two labels
  89  * is the same is now a reliable test.
  90  *
  91  * Do the object check first because that is more
  92  * likely to differ.
  93  */
  94 int smk_access_entry(char *subject_label, char *object_label,
  95                         struct list_head *rule_list)
  96 {
  97         int may = -ENOENT;
  98         struct smack_rule *srp;
  99
 100         list_for_each_entry_rcu(srp, rule_list, list) {
 101                 if (srp->smk_object == object_label &&
 102                     srp->smk_subject == subject_label) {
 103                         may = srp->smk_access;
 104                         break;
 105                 }
 106         }
 107
 108         return may;
 109 }
 110
 111 /**
 112  * smk_access - determine if a subject has a specific access to an object
 113  * @subject_label: a pointer to the subject's Smack label
 114  * @object_label: a pointer to the object's Smack label
 115  * @request: the access requested, in "MAY" format
 116  * @a : a pointer to the audit data
 117  *
 118  * This function looks up the subject/object pair in the
 119  * access rule list and returns 0 if the access is permitted,
 120  * non zero otherwise.
 121  *
 122  * Smack labels are shared on smack_list
 123  */
 124 int smk_access(char *subject_label, char *object_label, int request,
 125                struct smk_audit_info *a)
 126 {
 127         struct smack_known *skp;
 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_label == smack_known_star.smk_known) {
 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_label == smack_known_web.smk_known ||
 146             subject_label == smack_known_web.smk_known)
 147                 goto out_audit;
 148         /*
 149          * A star object can be accessed by any subject.
 150          */
 151         if (object_label == smack_known_star.smk_known)
 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_label == object_label)
 158                 goto out_audit;
 159         /*
 160          * A hat subject can read any object.
 161          * A floor object can be read by any subject.
 162          */
 163         if ((request & MAY_ANYREAD) == request) {
 164                 if (object_label == smack_known_floor.smk_known)
 165                         goto out_audit;
 166                 if (subject_label == smack_known_hat.smk_known)
 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         skp = smk_find_entry(subject_label);
 177         rcu_read_lock();
 178         may = smk_access_entry(subject_label, object_label, &skp->smk_rules);
 179         rcu_read_unlock();
 180
 181         if (may > 0 && (request & may) == request)
 182                 goto out_audit;
 183
 184         rc = -EACCES;
 185 out_audit:
 186 #ifdef CONFIG_AUDIT
 187         if (a)
 188                 smack_log(subject_label, object_label, request, rc, a);
 189 #endif
 190         return rc;
 191 }
 192
 193 /**
 194  * smk_curacc - determine if current has a specific access to an object
 195  * @obj_label: a pointer to the object's Smack label
 196  * @mode: the access requested, in "MAY" format
 197  * @a : common audit data
 198  *
 199  * This function checks the current subject label/object label pair
 200  * in the access rule list and returns 0 if the access is permitted,
 201  * non zero otherwise. It allows that current may have the capability
 202  * to override the rules.
 203  */
 204 int smk_curacc(char *obj_label, u32 mode, struct smk_audit_info *a)
 205 {
 206         struct task_smack *tsp = current_security();
 207         char *sp = smk_of_task(tsp);
 208         int may;
 209         int rc;
 210
 211         /*
 212          * Check the global rule list
 213          */
 214         rc = smk_access(sp, obj_label, mode, NULL);
 215         if (rc == 0) {
 216                 /*
 217                  * If there is an entry in the task's rule list
 218                  * it can further restrict access.
 219                  */
 220                 may = smk_access_entry(sp, obj_label, &tsp->smk_rules);
 221                 if (may < 0)
 222                         goto out_audit;
 223                 if ((mode & may) == mode)
 224                         goto out_audit;
 225                 rc = -EACCES;
 226         }
 227
 228         /*
 229          * Return if a specific label has been designated as the
 230          * only one that gets privilege and current does not
 231          * have that label.
 232          */
 233         if (smack_onlycap != NULL && smack_onlycap != sp)
 234                 goto out_audit;
 235
 236         if (capable(CAP_MAC_OVERRIDE))
 237                 rc = 0;
 238
 239 out_audit:
 240 #ifdef CONFIG_AUDIT
 241         if (a)
 242                 smack_log(sp, obj_label, mode, rc, a);
 243 #endif
 244         return rc;
 245 }
 246
 247 #ifdef CONFIG_AUDIT
 248 /**
 249  * smack_str_from_perm : helper to transalate an int to a
 250  * readable string
 251  * @string : the string to fill
 252  * @access : the int
 253  *
 254  */
 255 static inline void smack_str_from_perm(char *string, int access)
 256 {
 257         int i = 0;
 258         if (access & MAY_READ)
 259                 string[i++] = 'r';
 260         if (access & MAY_WRITE)
 261                 string[i++] = 'w';
 262         if (access & MAY_EXEC)
 263                 string[i++] = 'x';
 264         if (access & MAY_APPEND)
 265                 string[i++] = 'a';
 266         string[i] = '\0';
 267 }
 268 /**
 269  * smack_log_callback - SMACK specific information
 270  * will be called by generic audit code
 271  * @ab : the audit_buffer
 272  * @a  : audit_data
 273  *
 274  */
 275 static void smack_log_callback(struct audit_buffer *ab, void *a)
 276 {
 277         struct common_audit_data *ad = a;
 278         struct smack_audit_data *sad = ad->smack_audit_data;
 279         audit_log_format(ab, "lsm=SMACK fn=%s action=%s",
 280                          ad->smack_audit_data->function,
 281                          sad->result ? "denied" : "granted");
 282         audit_log_format(ab, " subject=");
 283         audit_log_untrustedstring(ab, sad->subject);
 284         audit_log_format(ab, " object=");
 285         audit_log_untrustedstring(ab, sad->object);
 286         audit_log_format(ab, " requested=%s", sad->request);
 287 }
 288
 289 /**
 290  *  smack_log - Audit the granting or denial of permissions.
 291  *  @subject_label : smack label of the requester
 292  *  @object_label  : smack label of the object being accessed
 293  *  @request: requested permissions
 294  *  @result: result from smk_access
 295  *  @a:  auxiliary audit data
 296  *
 297  * Audit the granting or denial of permissions in accordance
 298  * with the policy.
 299  */
 300 void smack_log(char *subject_label, char *object_label, int request,
 301                int result, struct smk_audit_info *ad)
 302 {
 303         char request_buffer[SMK_NUM_ACCESS_TYPE + 1];
 304         struct smack_audit_data *sad;
 305         struct common_audit_data *a = &ad->a;
 306
 307         /* check if we have to log the current event */
 308         if (result != 0 && (log_policy & SMACK_AUDIT_DENIED) == 0)
 309                 return;
 310         if (result == 0 && (log_policy & SMACK_AUDIT_ACCEPT) == 0)
 311                 return;
 312
 313         sad = a->smack_audit_data;
 314
 315         if (sad->function == NULL)
 316                 sad->function = "unknown";
 317
 318         /* end preparing the audit data */
 319         smack_str_from_perm(request_buffer, request);
 320         sad->subject = subject_label;
 321         sad->object  = object_label;
 322         sad->request = request_buffer;
 323         sad->result  = result;
 324
 325         common_lsm_audit(a, smack_log_callback, NULL);
 326 }
 327 #else /* #ifdef CONFIG_AUDIT */
 328 void smack_log(char *subject_label, char *object_label, int request,
 329                int result, struct smk_audit_info *ad)
 330 {
 331 }
 332 #endif
 333
 334 static DEFINE_MUTEX(smack_known_lock);
 335
 336 /**
 337  * smk_find_entry - find a label on the list, return the list entry
 338  * @string: a text string that might be a Smack label
 339  *
 340  * Returns a pointer to the entry in the label list that
 341  * matches the passed string.
 342  */
 343 struct smack_known *smk_find_entry(const char *string)
 344 {
 345         struct smack_known *skp;
 346
 347         list_for_each_entry_rcu(skp, &smack_known_list, list) {
 348                 if (strncmp(skp->smk_known, string, SMK_MAXLEN) == 0)
 349                         return skp;
 350         }
 351
 352         return NULL;
 353 }
 354
 355 /**
 356  * smk_parse_smack - parse smack label from a text string
 357  * @string: a text string that might contain a Smack label
 358  * @len: the maximum size, or zero if it is NULL terminated.
 359  * @smack: parsed smack label, or NULL if parse error
 360  */
 361 void smk_parse_smack(const char *string, int len, char *smack)
 362 {
 363         int found;
 364         int i;
 365
 366         if (len <= 0 || len > SMK_MAXLEN)
 367                 len = SMK_MAXLEN;
 368
 369         for (i = 0, found = 0; i < SMK_LABELLEN; i++) {
 370                 if (found)
 371                         smack[i] = '\0';
 372                 else if (i >= len || string[i] > '~' || string[i] <= ' ' ||
 373                          string[i] == '/' || string[i] == '"' ||
 374                          string[i] == '\\' || string[i] == '\'') {
 375                         smack[i] = '\0';
 376                         found = 1;
 377                 } else
 378                         smack[i] = string[i];
 379         }
 380 }
 381
 382 /**
 383  * smk_import_entry - import a label, return the list entry
 384  * @string: a text string that might be a Smack label
 385  * @len: the maximum size, or zero if it is NULL terminated.
 386  *
 387  * Returns a pointer to the entry in the label list that
 388  * matches the passed string, adding it if necessary.
 389  */
 390 struct smack_known *smk_import_entry(const char *string, int len)
 391 {
 392         struct smack_known *skp;
 393         char smack[SMK_LABELLEN];
 394
 395         smk_parse_smack(string, len, smack);
 396         if (smack[0] == '\0')
 397                 return NULL;
 398
 399         mutex_lock(&smack_known_lock);
 400
 401         skp = smk_find_entry(smack);
 402
 403         if (skp == NULL) {
 404                 skp = kzalloc(sizeof(struct smack_known), GFP_KERNEL);
 405                 if (skp != NULL) {
 406                         strncpy(skp->smk_known, smack, SMK_MAXLEN);
 407                         skp->smk_secid = smack_next_secid++;
 408                         skp->smk_cipso = NULL;
 409                         INIT_LIST_HEAD(&skp->smk_rules);
 410                         spin_lock_init(&skp->smk_cipsolock);
 411                         mutex_init(&skp->smk_rules_lock);
 412                         /*
 413                          * Make sure that the entry is actually
 414                          * filled before putting it on the list.
 415                          */
 416                         list_add_rcu(&skp->list, &smack_known_list);
 417                 }
 418         }
 419
 420         mutex_unlock(&smack_known_lock);
 421
 422         return skp;
 423 }
 424
 425 /**
 426  * smk_import - import a smack label
 427  * @string: a text string that might be a Smack label
 428  * @len: the maximum size, or zero if it is NULL terminated.
 429  *
 430  * Returns a pointer to the label in the label list that
 431  * matches the passed string, adding it if necessary.
 432  */
 433 char *smk_import(const char *string, int len)
 434 {
 435         struct smack_known *skp;
 436
 437         /* labels cannot begin with a '-' */
 438         if (string[0] == '-')
 439                 return NULL;
 440         skp = smk_import_entry(string, len);
 441         if (skp == NULL)
 442                 return NULL;
 443         return skp->smk_known;
 444 }
 445
 446 /**
 447  * smack_from_secid - find the Smack label associated with a secid
 448  * @secid: an integer that might be associated with a Smack label
 449  *
 450  * Returns a pointer to the appropriate Smack label if there is one,
 451  * otherwise a pointer to the invalid Smack label.
 452  */
 453 char *smack_from_secid(const u32 secid)
 454 {
 455         struct smack_known *skp;
 456
 457         rcu_read_lock();
 458         list_for_each_entry_rcu(skp, &smack_known_list, list) {
 459                 if (skp->smk_secid == secid) {
 460                         rcu_read_unlock();
 461                         return skp->smk_known;
 462                 }
 463         }
 464
 465         /*
 466          * If we got this far someone asked for the translation
 467          * of a secid that is not on the list.
 468          */
 469         rcu_read_unlock();
 470         return smack_known_invalid.smk_known;
 471 }
 472
 473 /**
 474  * smack_to_secid - find the secid associated with a Smack label
 475  * @smack: the Smack label
 476  *
 477  * Returns the appropriate secid if there is one,
 478  * otherwise 0
 479  */
 480 u32 smack_to_secid(const char *smack)
 481 {
 482         struct smack_known *skp;
 483
 484         rcu_read_lock();
 485         list_for_each_entry_rcu(skp, &smack_known_list, list) {
 486                 if (strncmp(skp->smk_known, smack, SMK_MAXLEN) == 0) {
 487                         rcu_read_unlock();
 488                         return skp->smk_secid;
 489                 }
 490         }
 491         rcu_read_unlock();
 492         return 0;
 493 }
 494
 495 /**
 496  * smack_from_cipso - find the Smack label associated with a CIPSO option
 497  * @level: Bell & LaPadula level from the network
 498  * @cp: Bell & LaPadula categories from the network
 499  *
 500  * This is a simple lookup in the label table.
 501  *
 502  * Return the matching label from the label list or NULL.
 503  */
 504 char *smack_from_cipso(u32 level, char *cp)
 505 {
 506         struct smack_known *kp;
 507         char *final = NULL;
 508
 509         rcu_read_lock();
 510         list_for_each_entry(kp, &smack_known_list, list) {
 511                 if (kp->smk_cipso == NULL)
 512                         continue;
 513
 514                 spin_lock_bh(&kp->smk_cipsolock);
 515
 516                 if (kp->smk_cipso->smk_level == level &&
 517                     memcmp(kp->smk_cipso->smk_catset, cp, SMK_LABELLEN) == 0)
 518                         final = kp->smk_known;
 519
 520                 spin_unlock_bh(&kp->smk_cipsolock);
 521
 522                 if (final != NULL)
 523                         break;
 524         }
 525         rcu_read_unlock();
 526
 527         return final;
 528 }
 529
 530 /**
 531  * smack_to_cipso - find the CIPSO option to go with a Smack label
 532  * @smack: a pointer to the smack label in question
 533  * @cp: where to put the result
 534  *
 535  * Returns zero if a value is available, non-zero otherwise.
 536  */
 537 int smack_to_cipso(const char *smack, struct smack_cipso *cp)
 538 {
 539         struct smack_known *kp;
 540         int found = 0;
 541
 542         rcu_read_lock();
 543         list_for_each_entry_rcu(kp, &smack_known_list, list) {
 544                 if (kp->smk_known == smack ||
 545                     strcmp(kp->smk_known, smack) == 0) {
 546                         found = 1;
 547                         break;
 548                 }
 549         }
 550         rcu_read_unlock();
 551
 552         if (found == 0 || kp->smk_cipso == NULL)
 553                 return -ENOENT;
 554
 555         memcpy(cp, kp->smk_cipso, sizeof(struct smack_cipso));
 556         return 0;
 557 }