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/fs.h>
  15 #include <linux/sched.h>
  16 #include "smack.h"
  17
  18 struct smack_known smack_known_huh = {
  19         .smk_known      = "?",
  20         .smk_secid      = 2,
  21         .smk_cipso      = NULL,
  22 };
  23
  24 struct smack_known smack_known_hat = {
  25         .smk_known      = "^",
  26         .smk_secid      = 3,
  27         .smk_cipso      = NULL,
  28 };
  29
  30 struct smack_known smack_known_star = {
  31         .smk_known      = "*",
  32         .smk_secid      = 4,
  33         .smk_cipso      = NULL,
  34 };
  35
  36 struct smack_known smack_known_floor = {
  37         .smk_known      = "_",
  38         .smk_secid      = 5,
  39         .smk_cipso      = NULL,
  40 };
  41
  42 struct smack_known smack_known_invalid = {
  43         .smk_known      = "",
  44         .smk_secid      = 6,
  45         .smk_cipso      = NULL,
  46 };
  47
  48 struct smack_known smack_known_web = {
  49         .smk_known      = "@",
  50         .smk_secid      = 7,
  51         .smk_cipso      = NULL,
  52 };
  53
  54 LIST_HEAD(smack_known_list);
  55
  56 /*
  57  * The initial value needs to be bigger than any of the
  58  * known values above.
  59  */
  60 static u32 smack_next_secid = 10;
  61
  62 /*
  63  * what events do we log
  64  * can be overwritten at run-time by /smack/logging
  65  */
  66 int log_policy = SMACK_AUDIT_DENIED;
  67
  68 /**
  69  * smk_access - determine if a subject has a specific access to an object
  70  * @subject_label: a pointer to the subject's Smack label
  71  * @object_label: a pointer to the object's Smack label
  72  * @request: the access requested, in "MAY" format
  73  * @a : a pointer to the audit data
  74  *
  75  * This function looks up the subject/object pair in the
  76  * access rule list and returns 0 if the access is permitted,
  77  * non zero otherwise.
  78  *
  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(char *subject_label, char *object_label, int request,
  89                struct smk_audit_info *a)
  90 {
  91         u32 may = MAY_NOT;
  92         struct smack_rule *srp;
  93         int rc = 0;
  94
  95         /*
  96          * Hardcoded comparisons.
  97          *
  98          * A star subject can't access any object.
  99          */
 100         if (subject_label == smack_known_star.smk_known ||
 101             strcmp(subject_label, smack_known_star.smk_known) == 0) {
 102                 rc = -EACCES;
 103                 goto out_audit;
 104         }
 105         /*
 106          * An internet object can be accessed by any subject.
 107          * Tasks cannot be assigned the internet label.
 108          * An internet subject can access any object.
 109          */
 110         if (object_label == smack_known_web.smk_known ||
 111             subject_label == smack_known_web.smk_known ||
 112             strcmp(object_label, smack_known_web.smk_known) == 0 ||
 113             strcmp(subject_label, smack_known_web.smk_known) == 0)
 114                 goto out_audit;
 115         /*
 116          * A star object can be accessed by any subject.
 117          */
 118         if (object_label == smack_known_star.smk_known ||
 119             strcmp(object_label, smack_known_star.smk_known) == 0)
 120                 goto out_audit;
 121         /*
 122          * An object can be accessed in any way by a subject
 123          * with the same label.
 124          */
 125         if (subject_label == object_label ||
 126             strcmp(subject_label, object_label) == 0)
 127                 goto out_audit;
 128         /*
 129          * A hat subject can read any object.
 130          * A floor object can be read by any subject.
 131          */
 132         if ((request & MAY_ANYREAD) == request) {
 133                 if (object_label == smack_known_floor.smk_known ||
 134                     strcmp(object_label, smack_known_floor.smk_known) == 0)
 135                         goto out_audit;
 136                 if (subject_label == smack_known_hat.smk_known ||
 137                     strcmp(subject_label, smack_known_hat.smk_known) == 0)
 138                         goto out_audit;
 139         }
 140         /*
 141          * Beyond here an explicit relationship is required.
 142          * If the requested access is contained in the available
 143          * access (e.g. read is included in readwrite) it's
 144          * good.
 145          */
 146         rcu_read_lock();
 147         list_for_each_entry_rcu(srp, &smack_rule_list, list) {
 148                 if (srp->smk_subject == subject_label ||
 149                     strcmp(srp->smk_subject, subject_label) == 0) {
 150                         if (srp->smk_object == object_label ||
 151                             strcmp(srp->smk_object, object_label) == 0) {
 152                                 may = srp->smk_access;
 153                                 break;
 154                         }
 155                 }
 156         }
 157         rcu_read_unlock();
 158         /*
 159          * This is a bit map operation.
 160          */
 161         if ((request & may) == request)
 162                 goto out_audit;
 163
 164         rc = -EACCES;
 165 out_audit:
 166 #ifdef CONFIG_AUDIT
 167         if (a)
 168                 smack_log(subject_label, object_label, request, rc, a);
 169 #endif
 170         return rc;
 171 }
 172
 173 /**
 174  * smk_curacc - determine if current has a specific access to an object
 175  * @obj_label: a pointer to the object's Smack label
 176  * @mode: the access requested, in "MAY" format
 177  * @a : common audit data
 178  *
 179  * This function checks the current subject label/object label pair
 180  * in the access rule list and returns 0 if the access is permitted,
 181  * non zero otherwise. It allows that current may have the capability
 182  * to override the rules.
 183  */
 184 int smk_curacc(char *obj_label, u32 mode, struct smk_audit_info *a)
 185 {
 186         int rc;
 187         char *sp = current_security();
 188
 189         rc = smk_access(sp, obj_label, mode, NULL);
 190         if (rc == 0)
 191                 goto out_audit;
 192
 193         /*
 194          * Return if a specific label has been designated as the
 195          * only one that gets privilege and current does not
 196          * have that label.
 197          */
 198         if (smack_onlycap != NULL && smack_onlycap != current->cred->security)
 199                 goto out_audit;
 200
 201         if (capable(CAP_MAC_OVERRIDE))
 202                 return 0;
 203
 204 out_audit:
 205 #ifdef CONFIG_AUDIT
 206         if (a)
 207                 smack_log(sp, obj_label, mode, rc, a);
 208 #endif
 209         return rc;
 210 }
 211
 212 #ifdef CONFIG_AUDIT
 213 /**
 214  * smack_str_from_perm : helper to transalate an int to a
 215  * readable string
 216  * @string : the string to fill
 217  * @access : the int
 218  *
 219  */
 220 static inline void smack_str_from_perm(char *string, int access)
 221 {
 222         int i = 0;
 223         if (access & MAY_READ)
 224                 string[i++] = 'r';
 225         if (access & MAY_WRITE)
 226                 string[i++] = 'w';
 227         if (access & MAY_EXEC)
 228                 string[i++] = 'x';
 229         if (access & MAY_APPEND)
 230                 string[i++] = 'a';
 231         string[i] = '\0';
 232 }
 233 /**
 234  * smack_log_callback - SMACK specific information
 235  * will be called by generic audit code
 236  * @ab : the audit_buffer
 237  * @a  : audit_data
 238  *
 239  */
 240 static void smack_log_callback(struct audit_buffer *ab, void *a)
 241 {
 242         struct common_audit_data *ad = a;
 243         struct smack_audit_data *sad = &ad->smack_audit_data;
 244         audit_log_format(ab, "lsm=SMACK fn=%s action=%s",
 245                          ad->smack_audit_data.function,
 246                          sad->result ? "denied" : "granted");
 247         audit_log_format(ab, " subject=");
 248         audit_log_untrustedstring(ab, sad->subject);
 249         audit_log_format(ab, " object=");
 250         audit_log_untrustedstring(ab, sad->object);
 251         audit_log_format(ab, " requested=%s", sad->request);
 252 }
 253
 254 /**
 255  *  smack_log - Audit the granting or denial of permissions.
 256  *  @subject_label : smack label of the requester
 257  *  @object_label  : smack label of the object being accessed
 258  *  @request: requested permissions
 259  *  @result: result from smk_access
 260  *  @a:  auxiliary audit data
 261  *
 262  * Audit the granting or denial of permissions in accordance
 263  * with the policy.
 264  */
 265 void smack_log(char *subject_label, char *object_label, int request,
 266                int result, struct smk_audit_info *ad)
 267 {
 268         char request_buffer[SMK_NUM_ACCESS_TYPE + 1];
 269         struct smack_audit_data *sad;
 270         struct common_audit_data *a = &ad->a;
 271
 272         /* check if we have to log the current event */
 273         if (result != 0 && (log_policy & SMACK_AUDIT_DENIED) == 0)
 274                 return;
 275         if (result == 0 && (log_policy & SMACK_AUDIT_ACCEPT) == 0)
 276                 return;
 277
 278         if (a->smack_audit_data.function == NULL)
 279                 a->smack_audit_data.function = "unknown";
 280
 281         /* end preparing the audit data */
 282         sad = &a->smack_audit_data;
 283         smack_str_from_perm(request_buffer, request);
 284         sad->subject = subject_label;
 285         sad->object  = object_label;
 286         sad->request = request_buffer;
 287         sad->result  = result;
 288         a->lsm_pre_audit = smack_log_callback;
 289
 290         common_lsm_audit(a);
 291 }
 292 #else /* #ifdef CONFIG_AUDIT */
 293 void smack_log(char *subject_label, char *object_label, int request,
 294                int result, struct smk_audit_info *ad)
 295 {
 296 }
 297 #endif
 298
 299 static DEFINE_MUTEX(smack_known_lock);
 300
 301 /**
 302  * smk_import_entry - import a label, return the list entry
 303  * @string: a text string that might be a Smack label
 304  * @len: the maximum size, or zero if it is NULL terminated.
 305  *
 306  * Returns a pointer to the entry in the label list that
 307  * matches the passed string, adding it if necessary.
 308  */
 309 struct smack_known *smk_import_entry(const char *string, int len)
 310 {
 311         struct smack_known *skp;
 312         char smack[SMK_LABELLEN];
 313         int found;
 314         int i;
 315
 316         if (len <= 0 || len > SMK_MAXLEN)
 317                 len = SMK_MAXLEN;
 318
 319         for (i = 0, found = 0; i < SMK_LABELLEN; i++) {
 320                 if (found)
 321                         smack[i] = '\0';
 322                 else if (i >= len || string[i] > '~' || string[i] <= ' ' ||
 323                          string[i] == '/' || string[i] == '"' ||
 324                          string[i] == '\\' || string[i] == '\'') {
 325                         smack[i] = '\0';
 326                         found = 1;
 327                 } else
 328                         smack[i] = string[i];
 329         }
 330
 331         if (smack[0] == '\0')
 332                 return NULL;
 333
 334         mutex_lock(&smack_known_lock);
 335
 336         found = 0;
 337         list_for_each_entry_rcu(skp, &smack_known_list, list) {
 338                 if (strncmp(skp->smk_known, smack, SMK_MAXLEN) == 0) {
 339                         found = 1;
 340                         break;
 341                 }
 342         }
 343
 344         if (found == 0) {
 345                 skp = kzalloc(sizeof(struct smack_known), GFP_KERNEL);
 346                 if (skp != NULL) {
 347                         strncpy(skp->smk_known, smack, SMK_MAXLEN);
 348                         skp->smk_secid = smack_next_secid++;
 349                         skp->smk_cipso = NULL;
 350                         spin_lock_init(&skp->smk_cipsolock);
 351                         /*
 352                          * Make sure that the entry is actually
 353                          * filled before putting it on the list.
 354                          */
 355                         list_add_rcu(&skp->list, &smack_known_list);
 356                 }
 357         }
 358
 359         mutex_unlock(&smack_known_lock);
 360
 361         return skp;
 362 }
 363
 364 /**
 365  * smk_import - import a smack label
 366  * @string: a text string that might be a Smack label
 367  * @len: the maximum size, or zero if it is NULL terminated.
 368  *
 369  * Returns a pointer to the label in the label list that
 370  * matches the passed string, adding it if necessary.
 371  */
 372 char *smk_import(const char *string, int len)
 373 {
 374         struct smack_known *skp;
 375
 376         /* labels cannot begin with a '-' */
 377         if (string[0] == '-')
 378                 return NULL;
 379         skp = smk_import_entry(string, len);
 380         if (skp == NULL)
 381                 return NULL;
 382         return skp->smk_known;
 383 }
 384
 385 /**
 386  * smack_from_secid - find the Smack label associated with a secid
 387  * @secid: an integer that might be associated with a Smack label
 388  *
 389  * Returns a pointer to the appropraite Smack label if there is one,
 390  * otherwise a pointer to the invalid Smack label.
 391  */
 392 char *smack_from_secid(const u32 secid)
 393 {
 394         struct smack_known *skp;
 395
 396         rcu_read_lock();
 397         list_for_each_entry_rcu(skp, &smack_known_list, list) {
 398                 if (skp->smk_secid == secid) {
 399                         rcu_read_unlock();
 400                         return skp->smk_known;
 401                 }
 402         }
 403
 404         /*
 405          * If we got this far someone asked for the translation
 406          * of a secid that is not on the list.
 407          */
 408         rcu_read_unlock();
 409         return smack_known_invalid.smk_known;
 410 }
 411
 412 /**
 413  * smack_to_secid - find the secid associated with a Smack label
 414  * @smack: the Smack label
 415  *
 416  * Returns the appropriate secid if there is one,
 417  * otherwise 0
 418  */
 419 u32 smack_to_secid(const char *smack)
 420 {
 421         struct smack_known *skp;
 422
 423         rcu_read_lock();
 424         list_for_each_entry_rcu(skp, &smack_known_list, list) {
 425                 if (strncmp(skp->smk_known, smack, SMK_MAXLEN) == 0) {
 426                         rcu_read_unlock();
 427                         return skp->smk_secid;
 428                 }
 429         }
 430         rcu_read_unlock();
 431         return 0;
 432 }
 433
 434 /**
 435  * smack_from_cipso - find the Smack label associated with a CIPSO option
 436  * @level: Bell & LaPadula level from the network
 437  * @cp: Bell & LaPadula categories from the network
 438  * @result: where to put the Smack value
 439  *
 440  * This is a simple lookup in the label table.
 441  *
 442  * This is an odd duck as far as smack handling goes in that
 443  * it sends back a copy of the smack label rather than a pointer
 444  * to the master list. This is done because it is possible for
 445  * a foreign host to send a smack label that is new to this
 446  * machine and hence not on the list. That would not be an
 447  * issue except that adding an entry to the master list can't
 448  * be done at that point.
 449  */
 450 void smack_from_cipso(u32 level, char *cp, char *result)
 451 {
 452         struct smack_known *kp;
 453         char *final = NULL;
 454
 455         rcu_read_lock();
 456         list_for_each_entry(kp, &smack_known_list, list) {
 457                 if (kp->smk_cipso == NULL)
 458                         continue;
 459
 460                 spin_lock_bh(&kp->smk_cipsolock);
 461
 462                 if (kp->smk_cipso->smk_level == level &&
 463                     memcmp(kp->smk_cipso->smk_catset, cp, SMK_LABELLEN) == 0)
 464                         final = kp->smk_known;
 465
 466                 spin_unlock_bh(&kp->smk_cipsolock);
 467         }
 468         rcu_read_unlock();
 469         if (final == NULL)
 470                 final = smack_known_huh.smk_known;
 471         strncpy(result, final, SMK_MAXLEN);
 472         return;
 473 }
 474
 475 /**
 476  * smack_to_cipso - find the CIPSO option to go with a Smack label
 477  * @smack: a pointer to the smack label in question
 478  * @cp: where to put the result
 479  *
 480  * Returns zero if a value is available, non-zero otherwise.
 481  */
 482 int smack_to_cipso(const char *smack, struct smack_cipso *cp)
 483 {
 484         struct smack_known *kp;
 485         int found = 0;
 486
 487         rcu_read_lock();
 488         list_for_each_entry_rcu(kp, &smack_known_list, list) {
 489                 if (kp->smk_known == smack ||
 490                     strcmp(kp->smk_known, smack) == 0) {
 491                         found = 1;
 492                         break;
 493                 }
 494         }
 495         rcu_read_unlock();
 496
 497         if (found == 0 || kp->smk_cipso == NULL)
 498                 return -ENOENT;
 499
 500         memcpy(cp, kp->smk_cipso, sizeof(struct smack_cipso));
 501         return 0;
 502 }