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  *
  74  * This function looks up the subject/object pair in the
  75  * access rule list and returns pointer to the matching rule if found,
  76  * NULL otherwise.
  77  *
  78  * NOTE:
  79  * Even though Smack labels are usually shared on smack_list
  80  * labels that come in off the network can't be imported
  81  * and added to the list for locking reasons.
  82  *
  83  * Therefore, it is necessary to check the contents of the labels,
  84  * not just the pointer values. Of course, in most cases the labels
  85  * will be on the list, so checking the pointers may be a worthwhile
  86  * optimization.
  87  */
  88 int smk_access_entry(char *subject_label, char *object_label)
  89 {
  90         u32 may = MAY_NOT;
  91         struct smack_rule *srp;
  92
  93         rcu_read_lock();
  94         list_for_each_entry_rcu(srp, &smack_rule_list, list) {
  95                 if (srp->smk_subject == subject_label ||
  96                     strcmp(srp->smk_subject, subject_label) == 0) {
  97                         if (srp->smk_object == object_label ||
  98                             strcmp(srp->smk_object, object_label) == 0) {
  99                                 may = srp->smk_access;
 100                                 break;
 101                         }
 102                 }
 103         }
 104         rcu_read_unlock();
 105
 106         return may;
 107 }
 108
 109 /**
 110  * smk_access - determine if a subject has a specific access to an object
 111  * @subject_label: a pointer to the subject's Smack label
 112  * @object_label: a pointer to the object's Smack label
 113  * @request: the access requested, in "MAY" format
 114  * @a : a pointer to the audit data
 115  *
 116  * This function looks up the subject/object pair in the
 117  * access rule list and returns 0 if the access is permitted,
 118  * non zero otherwise.
 119  *
 120  * Even though Smack labels are usually shared on smack_list
 121  * labels that come in off the network can't be imported
 122  * and added to the list for locking reasons.
 123  *
 124  * Therefore, it is necessary to check the contents of the labels,
 125  * not just the pointer values. Of course, in most cases the labels
 126  * will be on the list, so checking the pointers may be a worthwhile
 127  * optimization.
 128  */
 129 int smk_access(char *subject_label, char *object_label, int request,
 130                struct smk_audit_info *a)
 131 {
 132         u32 may = MAY_NOT;
 133         int rc = 0;
 134
 135         /*
 136          * Hardcoded comparisons.
 137          *
 138          * A star subject can't access any object.
 139          */
 140         if (subject_label == smack_known_star.smk_known ||
 141             strcmp(subject_label, smack_known_star.smk_known) == 0) {
 142                 rc = -EACCES;
 143                 goto out_audit;
 144         }
 145         /*
 146          * An internet object can be accessed by any subject.
 147          * Tasks cannot be assigned the internet label.
 148          * An internet subject can access any object.
 149          */
 150         if (object_label == smack_known_web.smk_known ||
 151             subject_label == smack_known_web.smk_known ||
 152             strcmp(object_label, smack_known_web.smk_known) == 0 ||
 153             strcmp(subject_label, smack_known_web.smk_known) == 0)
 154                 goto out_audit;
 155         /*
 156          * A star object can be accessed by any subject.
 157          */
 158         if (object_label == smack_known_star.smk_known ||
 159             strcmp(object_label, smack_known_star.smk_known) == 0)
 160                 goto out_audit;
 161         /*
 162          * An object can be accessed in any way by a subject
 163          * with the same label.
 164          */
 165         if (subject_label == object_label ||
 166             strcmp(subject_label, object_label) == 0)
 167                 goto out_audit;
 168         /*
 169          * A hat subject can read any object.
 170          * A floor object can be read by any subject.
 171          */
 172         if ((request & MAY_ANYREAD) == request) {
 173                 if (object_label == smack_known_floor.smk_known ||
 174                     strcmp(object_label, smack_known_floor.smk_known) == 0)
 175                         goto out_audit;
 176                 if (subject_label == smack_known_hat.smk_known ||
 177                     strcmp(subject_label, smack_known_hat.smk_known) == 0)
 178                         goto out_audit;
 179         }
 180         /*
 181          * Beyond here an explicit relationship is required.
 182          * If the requested access is contained in the available
 183          * access (e.g. read is included in readwrite) it's
 184          * good.
 185          */
 186         may = smk_access_entry(subject_label, object_label);
 187         /*
 188          * This is a bit map operation.
 189          */
 190         if ((request & may) == request)
 191                 goto out_audit;
 192
 193         rc = -EACCES;
 194 out_audit:
 195 #ifdef CONFIG_AUDIT
 196         if (a)
 197                 smack_log(subject_label, object_label, request, rc, a);
 198 #endif
 199         return rc;
 200 }
 201
 202 /**
 203  * smk_curacc - determine if current has a specific access to an object
 204  * @obj_label: a pointer to the object's Smack label
 205  * @mode: the access requested, in "MAY" format
 206  * @a : common audit data
 207  *
 208  * This function checks the current subject label/object label pair
 209  * in the access rule list and returns 0 if the access is permitted,
 210  * non zero otherwise. It allows that current may have the capability
 211  * to override the rules.
 212  */
 213 int smk_curacc(char *obj_label, u32 mode, struct smk_audit_info *a)
 214 {
 215         int rc;
 216         char *sp = smk_of_current();
 217
 218         rc = smk_access(sp, obj_label, mode, NULL);
 219         if (rc == 0)
 220                 goto out_audit;
 221
 222         /*
 223          * Return if a specific label has been designated as the
 224          * only one that gets privilege and current does not
 225          * have that label.
 226          */
 227         if (smack_onlycap != NULL && smack_onlycap != sp)
 228                 goto out_audit;
 229
 230         if (capable(CAP_MAC_OVERRIDE))
 231                 return 0;
 232
 233 out_audit:
 234 #ifdef CONFIG_AUDIT
 235         if (a)
 236                 smack_log(sp, obj_label, mode, rc, a);
 237 #endif
 238         return rc;
 239 }
 240
 241 #ifdef CONFIG_AUDIT
 242 /**
 243  * smack_str_from_perm : helper to transalate an int to a
 244  * readable string
 245  * @string : the string to fill
 246  * @access : the int
 247  *
 248  */
 249 static inline void smack_str_from_perm(char *string, int access)
 250 {
 251         int i = 0;
 252         if (access & MAY_READ)
 253                 string[i++] = 'r';
 254         if (access & MAY_WRITE)
 255                 string[i++] = 'w';
 256         if (access & MAY_EXEC)
 257                 string[i++] = 'x';
 258         if (access & MAY_APPEND)
 259                 string[i++] = 'a';
 260         string[i] = '\0';
 261 }
 262 /**
 263  * smack_log_callback - SMACK specific information
 264  * will be called by generic audit code
 265  * @ab : the audit_buffer
 266  * @a  : audit_data
 267  *
 268  */
 269 static void smack_log_callback(struct audit_buffer *ab, void *a)
 270 {
 271         struct common_audit_data *ad = a;
 272         struct smack_audit_data *sad = &ad->smack_audit_data;
 273         audit_log_format(ab, "lsm=SMACK fn=%s action=%s",
 274                          ad->smack_audit_data.function,
 275                          sad->result ? "denied" : "granted");
 276         audit_log_format(ab, " subject=");
 277         audit_log_untrustedstring(ab, sad->subject);
 278         audit_log_format(ab, " object=");
 279         audit_log_untrustedstring(ab, sad->object);
 280         audit_log_format(ab, " requested=%s", sad->request);
 281 }
 282
 283 /**
 284  *  smack_log - Audit the granting or denial of permissions.
 285  *  @subject_label : smack label of the requester
 286  *  @object_label  : smack label of the object being accessed
 287  *  @request: requested permissions
 288  *  @result: result from smk_access
 289  *  @a:  auxiliary audit data
 290  *
 291  * Audit the granting or denial of permissions in accordance
 292  * with the policy.
 293  */
 294 void smack_log(char *subject_label, char *object_label, int request,
 295                int result, struct smk_audit_info *ad)
 296 {
 297         char request_buffer[SMK_NUM_ACCESS_TYPE + 1];
 298         struct smack_audit_data *sad;
 299         struct common_audit_data *a = &ad->a;
 300
 301         /* check if we have to log the current event */
 302         if (result != 0 && (log_policy & SMACK_AUDIT_DENIED) == 0)
 303                 return;
 304         if (result == 0 && (log_policy & SMACK_AUDIT_ACCEPT) == 0)
 305                 return;
 306
 307         if (a->smack_audit_data.function == NULL)
 308                 a->smack_audit_data.function = "unknown";
 309
 310         /* end preparing the audit data */
 311         sad = &a->smack_audit_data;
 312         smack_str_from_perm(request_buffer, request);
 313         sad->subject = subject_label;
 314         sad->object  = object_label;
 315         sad->request = request_buffer;
 316         sad->result  = result;
 317         a->lsm_pre_audit = smack_log_callback;
 318
 319         common_lsm_audit(a);
 320 }
 321 #else /* #ifdef CONFIG_AUDIT */
 322 void smack_log(char *subject_label, char *object_label, int request,
 323                int result, struct smk_audit_info *ad)
 324 {
 325 }
 326 #endif
 327
 328 static DEFINE_MUTEX(smack_known_lock);
 329
 330 /**
 331  * smk_import_entry - import a label, return the list entry
 332  * @string: a text string that might be a Smack label
 333  * @len: the maximum size, or zero if it is NULL terminated.
 334  *
 335  * Returns a pointer to the entry in the label list that
 336  * matches the passed string, adding it if necessary.
 337  */
 338 struct smack_known *smk_import_entry(const char *string, int len)
 339 {
 340         struct smack_known *skp;
 341         char smack[SMK_LABELLEN];
 342         int found;
 343         int i;
 344
 345         if (len <= 0 || len > SMK_MAXLEN)
 346                 len = SMK_MAXLEN;
 347
 348         for (i = 0, found = 0; i < SMK_LABELLEN; i++) {
 349                 if (found)
 350                         smack[i] = '\0';
 351                 else if (i >= len || string[i] > '~' || string[i] <= ' ' ||
 352                          string[i] == '/' || string[i] == '"' ||
 353                          string[i] == '\\' || string[i] == '\'') {
 354                         smack[i] = '\0';
 355                         found = 1;
 356                 } else
 357                         smack[i] = string[i];
 358         }
 359
 360         if (smack[0] == '\0')
 361                 return NULL;
 362
 363         mutex_lock(&smack_known_lock);
 364
 365         found = 0;
 366         list_for_each_entry_rcu(skp, &smack_known_list, list) {
 367                 if (strncmp(skp->smk_known, smack, SMK_MAXLEN) == 0) {
 368                         found = 1;
 369                         break;
 370                 }
 371         }
 372
 373         if (found == 0) {
 374                 skp = kzalloc(sizeof(struct smack_known), GFP_KERNEL);
 375                 if (skp != NULL) {
 376                         strncpy(skp->smk_known, smack, SMK_MAXLEN);
 377                         skp->smk_secid = smack_next_secid++;
 378                         skp->smk_cipso = NULL;
 379                         spin_lock_init(&skp->smk_cipsolock);
 380                         /*
 381                          * Make sure that the entry is actually
 382                          * filled before putting it on the list.
 383                          */
 384                         list_add_rcu(&skp->list, &smack_known_list);
 385                 }
 386         }
 387
 388         mutex_unlock(&smack_known_lock);
 389
 390         return skp;
 391 }
 392
 393 /**
 394  * smk_import - import a smack label
 395  * @string: a text string that might be a Smack label
 396  * @len: the maximum size, or zero if it is NULL terminated.
 397  *
 398  * Returns a pointer to the label in the label list that
 399  * matches the passed string, adding it if necessary.
 400  */
 401 char *smk_import(const char *string, int len)
 402 {
 403         struct smack_known *skp;
 404
 405         /* labels cannot begin with a '-' */
 406         if (string[0] == '-')
 407                 return NULL;
 408         skp = smk_import_entry(string, len);
 409         if (skp == NULL)
 410                 return NULL;
 411         return skp->smk_known;
 412 }
 413
 414 /**
 415  * smack_from_secid - find the Smack label associated with a secid
 416  * @secid: an integer that might be associated with a Smack label
 417  *
 418  * Returns a pointer to the appropraite Smack label if there is one,
 419  * otherwise a pointer to the invalid Smack label.
 420  */
 421 char *smack_from_secid(const u32 secid)
 422 {
 423         struct smack_known *skp;
 424
 425         rcu_read_lock();
 426         list_for_each_entry_rcu(skp, &smack_known_list, list) {
 427                 if (skp->smk_secid == secid) {
 428                         rcu_read_unlock();
 429                         return skp->smk_known;
 430                 }
 431         }
 432
 433         /*
 434          * If we got this far someone asked for the translation
 435          * of a secid that is not on the list.
 436          */
 437         rcu_read_unlock();
 438         return smack_known_invalid.smk_known;
 439 }
 440
 441 /**
 442  * smack_to_secid - find the secid associated with a Smack label
 443  * @smack: the Smack label
 444  *
 445  * Returns the appropriate secid if there is one,
 446  * otherwise 0
 447  */
 448 u32 smack_to_secid(const char *smack)
 449 {
 450         struct smack_known *skp;
 451
 452         rcu_read_lock();
 453         list_for_each_entry_rcu(skp, &smack_known_list, list) {
 454                 if (strncmp(skp->smk_known, smack, SMK_MAXLEN) == 0) {
 455                         rcu_read_unlock();
 456                         return skp->smk_secid;
 457                 }
 458         }
 459         rcu_read_unlock();
 460         return 0;
 461 }
 462
 463 /**
 464  * smack_from_cipso - find the Smack label associated with a CIPSO option
 465  * @level: Bell & LaPadula level from the network
 466  * @cp: Bell & LaPadula categories from the network
 467  * @result: where to put the Smack value
 468  *
 469  * This is a simple lookup in the label table.
 470  *
 471  * This is an odd duck as far as smack handling goes in that
 472  * it sends back a copy of the smack label rather than a pointer
 473  * to the master list. This is done because it is possible for
 474  * a foreign host to send a smack label that is new to this
 475  * machine and hence not on the list. That would not be an
 476  * issue except that adding an entry to the master list can't
 477  * be done at that point.
 478  */
 479 void smack_from_cipso(u32 level, char *cp, char *result)
 480 {
 481         struct smack_known *kp;
 482         char *final = NULL;
 483
 484         rcu_read_lock();
 485         list_for_each_entry(kp, &smack_known_list, list) {
 486                 if (kp->smk_cipso == NULL)
 487                         continue;
 488
 489                 spin_lock_bh(&kp->smk_cipsolock);
 490
 491                 if (kp->smk_cipso->smk_level == level &&
 492                     memcmp(kp->smk_cipso->smk_catset, cp, SMK_LABELLEN) == 0)
 493                         final = kp->smk_known;
 494
 495                 spin_unlock_bh(&kp->smk_cipsolock);
 496         }
 497         rcu_read_unlock();
 498         if (final == NULL)
 499                 final = smack_known_huh.smk_known;
 500         strncpy(result, final, SMK_MAXLEN);
 501         return;
 502 }
 503
 504 /**
 505  * smack_to_cipso - find the CIPSO option to go with a Smack label
 506  * @smack: a pointer to the smack label in question
 507  * @cp: where to put the result
 508  *
 509  * Returns zero if a value is available, non-zero otherwise.
 510  */
 511 int smack_to_cipso(const char *smack, struct smack_cipso *cp)
 512 {
 513         struct smack_known *kp;
 514         int found = 0;
 515
 516         rcu_read_lock();
 517         list_for_each_entry_rcu(kp, &smack_known_list, list) {
 518                 if (kp->smk_known == smack ||
 519                     strcmp(kp->smk_known, smack) == 0) {
 520                         found = 1;
 521                         break;
 522                 }
 523         }
 524         rcu_read_unlock();
 525
 526         if (found == 0 || kp->smk_cipso == NULL)
 527                 return -ENOENT;
 528
 529         memcpy(cp, kp->smk_cipso, sizeof(struct smack_cipso));
 530         return 0;
 531 }