security/apparmor/file.c

   1 /*
   2  * AppArmor security module
   3  *
   4  * This file contains AppArmor mediation of files
   5  *
   6  * Copyright (C) 1998-2008 Novell/SUSE
   7  * Copyright 2009-2010 Canonical Ltd.
   8  *
   9  * This program is free software; you can redistribute it and/or
  10  * modify it under the terms of the GNU General Public License as
  11  * published by the Free Software Foundation, version 2 of the
  12  * License.
  13  */
  14
  15 #include <linux/tty.h>
  16 #include <linux/fdtable.h>
  17 #include <linux/file.h>
  18
  19 #include "include/apparmor.h"
  20 #include "include/audit.h"
  21 #include "include/context.h"
  22 #include "include/file.h"
  23 #include "include/match.h"
  24 #include "include/path.h"
  25 #include "include/policy.h"
  26 #include "include/label.h"
  27
  28 static u32 map_mask_to_chr_mask(u32 mask)
  29 {
  30         u32 m = mask & PERMS_CHRS_MASK;
  31
  32         if (mask & AA_MAY_GETATTR)
  33                 m |= MAY_READ;
  34         if (mask & (AA_MAY_SETATTR | AA_MAY_CHMOD | AA_MAY_CHOWN))
  35                 m |= MAY_WRITE;
  36
  37         return m;
  38 }
  39
  40 /**
  41  * audit_file_mask - convert mask to permission string
  42  * @buffer: buffer to write string to (NOT NULL)
  43  * @mask: permission mask to convert
  44  */
  45 static void audit_file_mask(struct audit_buffer *ab, u32 mask)
  46 {
  47         char str[10];
  48
  49         aa_perm_mask_to_str(str, aa_file_perm_chrs, map_mask_to_chr_mask(mask));
  50         audit_log_string(ab, str);
  51 }
  52
  53 /**
  54  * file_audit_cb - call back for file specific audit fields
  55  * @ab: audit_buffer  (NOT NULL)
  56  * @va: audit struct to audit values of  (NOT NULL)
  57  */
  58 static void file_audit_cb(struct audit_buffer *ab, void *va)
  59 {
  60         struct common_audit_data *sa = va;
  61         kuid_t fsuid = current_fsuid();
  62
  63         if (aad(sa)->request & AA_AUDIT_FILE_MASK) {
  64                 audit_log_format(ab, " requested_mask=");
  65                 audit_file_mask(ab, aad(sa)->request);
  66         }
  67         if (aad(sa)->denied & AA_AUDIT_FILE_MASK) {
  68                 audit_log_format(ab, " denied_mask=");
  69                 audit_file_mask(ab, aad(sa)->denied);
  70         }
  71         if (aad(sa)->request & AA_AUDIT_FILE_MASK) {
  72                 audit_log_format(ab, " fsuid=%d",
  73                                  from_kuid(&init_user_ns, fsuid));
  74                 audit_log_format(ab, " ouid=%d",
  75                                  from_kuid(&init_user_ns, aad(sa)->fs.ouid));
  76         }
  77
  78         if (aad(sa)->peer) {
  79                 audit_log_format(ab, " target=");
  80                 aa_label_xaudit(ab, labels_ns(aad(sa)->label), aad(sa)->peer,
  81                                 FLAG_VIEW_SUBNS, GFP_ATOMIC);
  82         } else if (aad(sa)->fs.target) {
  83                 audit_log_format(ab, " target=");
  84                 audit_log_untrustedstring(ab, aad(sa)->fs.target);
  85         }
  86 }
  87
  88 /**
  89  * aa_audit_file - handle the auditing of file operations
  90  * @profile: the profile being enforced  (NOT NULL)
  91  * @perms: the permissions computed for the request (NOT NULL)
  92  * @op: operation being mediated
  93  * @request: permissions requested
  94  * @name: name of object being mediated (MAYBE NULL)
  95  * @target: name of target (MAYBE NULL)
  96  * @tlabel: target label (MAY BE NULL)
  97  * @ouid: object uid
  98  * @info: extra information message (MAYBE NULL)
  99  * @error: 0 if operation allowed else failure error code
 100  *
 101  * Returns: %0 or error on failure
 102  */
 103 int aa_audit_file(struct aa_profile *profile, struct aa_perms *perms,
 104                   const char *op, u32 request, const char *name,
 105                   const char *target, struct aa_label *tlabel,
 106                   kuid_t ouid, const char *info, int error)
 107 {
 108         int type = AUDIT_APPARMOR_AUTO;
 109         DEFINE_AUDIT_DATA(sa, LSM_AUDIT_DATA_TASK, op);
 110
 111         sa.u.tsk = NULL;
 112         aad(&sa)->request = request;
 113         aad(&sa)->name = name;
 114         aad(&sa)->fs.target = target;
 115         aad(&sa)->peer = tlabel;
 116         aad(&sa)->fs.ouid = ouid;
 117         aad(&sa)->info = info;
 118         aad(&sa)->error = error;
 119         sa.u.tsk = NULL;
 120
 121         if (likely(!aad(&sa)->error)) {
 122                 u32 mask = perms->audit;
 123
 124                 if (unlikely(AUDIT_MODE(profile) == AUDIT_ALL))
 125                         mask = 0xffff;
 126
 127                 /* mask off perms that are not being force audited */
 128                 aad(&sa)->request &= mask;
 129
 130                 if (likely(!aad(&sa)->request))
 131                         return 0;
 132                 type = AUDIT_APPARMOR_AUDIT;
 133         } else {
 134                 /* only report permissions that were denied */
 135                 aad(&sa)->request = aad(&sa)->request & ~perms->allow;
 136                 AA_BUG(!aad(&sa)->request);
 137
 138                 if (aad(&sa)->request & perms->kill)
 139                         type = AUDIT_APPARMOR_KILL;
 140
 141                 /* quiet known rejects, assumes quiet and kill do not overlap */
 142                 if ((aad(&sa)->request & perms->quiet) &&
 143                     AUDIT_MODE(profile) != AUDIT_NOQUIET &&
 144                     AUDIT_MODE(profile) != AUDIT_ALL)
 145                         aad(&sa)->request &= ~perms->quiet;
 146
 147                 if (!aad(&sa)->request)
 148                         return aad(&sa)->error;
 149         }
 150
 151         aad(&sa)->denied = aad(&sa)->request & ~perms->allow;
 152         return aa_audit(type, profile, &sa, file_audit_cb);
 153 }
 154
 155 /**
 156  * map_old_perms - map old file perms layout to the new layout
 157  * @old: permission set in old mapping
 158  *
 159  * Returns: new permission mapping
 160  */
 161 static u32 map_old_perms(u32 old)
 162 {
 163         u32 new = old & 0xf;
 164         if (old & MAY_READ)
 165                 new |= AA_MAY_GETATTR | AA_MAY_OPEN;
 166         if (old & MAY_WRITE)
 167                 new |= AA_MAY_SETATTR | AA_MAY_CREATE | AA_MAY_DELETE |
 168                        AA_MAY_CHMOD | AA_MAY_CHOWN | AA_MAY_OPEN;
 169         if (old & 0x10)
 170                 new |= AA_MAY_LINK;
 171         /* the old mapping lock and link_subset flags where overlaid
 172          * and use was determined by part of a pair that they were in
 173          */
 174         if (old & 0x20)
 175                 new |= AA_MAY_LOCK | AA_LINK_SUBSET;
 176         if (old & 0x40) /* AA_EXEC_MMAP */
 177                 new |= AA_EXEC_MMAP;
 178
 179         return new;
 180 }
 181
 182 /**
 183  * aa_compute_fperms - convert dfa compressed perms to internal perms
 184  * @dfa: dfa to compute perms for   (NOT NULL)
 185  * @state: state in dfa
 186  * @cond:  conditions to consider  (NOT NULL)
 187  *
 188  * TODO: convert from dfa + state to permission entry, do computation conversion
 189  *       at load time.
 190  *
 191  * Returns: computed permission set
 192  */
 193 struct aa_perms aa_compute_fperms(struct aa_dfa *dfa, unsigned int state,
 194                                   struct path_cond *cond)
 195 {
 196         struct aa_perms perms;
 197
 198         /* FIXME: change over to new dfa format
 199          * currently file perms are encoded in the dfa, new format
 200          * splits the permissions from the dfa.  This mapping can be
 201          * done at profile load
 202          */
 203         perms.deny = 0;
 204         perms.kill = perms.stop = 0;
 205         perms.complain = perms.cond = 0;
 206         perms.hide = 0;
 207         perms.prompt = 0;
 208
 209         if (uid_eq(current_fsuid(), cond->uid)) {
 210                 perms.allow = map_old_perms(dfa_user_allow(dfa, state));
 211                 perms.audit = map_old_perms(dfa_user_audit(dfa, state));
 212                 perms.quiet = map_old_perms(dfa_user_quiet(dfa, state));
 213                 perms.xindex = dfa_user_xindex(dfa, state);
 214         } else {
 215                 perms.allow = map_old_perms(dfa_other_allow(dfa, state));
 216                 perms.audit = map_old_perms(dfa_other_audit(dfa, state));
 217                 perms.quiet = map_old_perms(dfa_other_quiet(dfa, state));
 218                 perms.xindex = dfa_other_xindex(dfa, state);
 219         }
 220         perms.allow |= AA_MAY_GETATTR;
 221
 222         /* change_profile wasn't determined by ownership in old mapping */
 223         if (ACCEPT_TABLE(dfa)[state] & 0x80000000)
 224                 perms.allow |= AA_MAY_CHANGE_PROFILE;
 225         if (ACCEPT_TABLE(dfa)[state] & 0x40000000)
 226                 perms.allow |= AA_MAY_ONEXEC;
 227
 228         return perms;
 229 }
 230
 231 /**
 232  * aa_str_perms - find permission that match @name
 233  * @dfa: to match against  (MAYBE NULL)
 234  * @state: state to start matching in
 235  * @name: string to match against dfa  (NOT NULL)
 236  * @cond: conditions to consider for permission set computation  (NOT NULL)
 237  * @perms: Returns - the permissions found when matching @name
 238  *
 239  * Returns: the final state in @dfa when beginning @start and walking @name
 240  */
 241 unsigned int aa_str_perms(struct aa_dfa *dfa, unsigned int start,
 242                           const char *name, struct path_cond *cond,
 243                           struct aa_perms *perms)
 244 {
 245         unsigned int state;
 246         state = aa_dfa_match(dfa, start, name);
 247         *perms = aa_compute_fperms(dfa, state, cond);
 248
 249         return state;
 250 }
 251
 252 /**
 253  * is_deleted - test if a file has been completely unlinked
 254  * @dentry: dentry of file to test for deletion  (NOT NULL)
 255  *
 256  * Returns: %1 if deleted else %0
 257  */
 258 static inline bool is_deleted(struct dentry *dentry)
 259 {
 260         if (d_unlinked(dentry) && d_backing_inode(dentry)->i_nlink == 0)
 261                 return 1;
 262         return 0;
 263 }
 264
 265 /**
 266  * aa_path_perm - do permissions check & audit for @path
 267  * @op: operation being checked
 268  * @profile: profile being enforced  (NOT NULL)
 269  * @path: path to check permissions of  (NOT NULL)
 270  * @flags: any additional path flags beyond what the profile specifies
 271  * @request: requested permissions
 272  * @cond: conditional info for this request  (NOT NULL)
 273  *
 274  * Returns: %0 else error if access denied or other error
 275  */
 276 int aa_path_perm(const char *op, struct aa_profile *profile,
 277                  const struct path *path, int flags, u32 request,
 278                  struct path_cond *cond)
 279 {
 280         char *buffer = NULL;
 281         struct aa_perms perms = {};
 282         const char *name, *info = NULL;
 283         int error;
 284
 285         flags |= profile->path_flags | (S_ISDIR(cond->mode) ? PATH_IS_DIR : 0);
 286         get_buffers(buffer);
 287         error = aa_path_name(path, flags, buffer, &name, &info,
 288                              profile->disconnected);
 289         if (error) {
 290                 if (error == -ENOENT && is_deleted(path->dentry)) {
 291                         /* Access to open files that are deleted are
 292                          * give a pass (implicit delegation)
 293                          */
 294                         error = 0;
 295                         info = NULL;
 296                         perms.allow = request;
 297                 }
 298         } else {
 299                 aa_str_perms(profile->file.dfa, profile->file.start, name, cond,
 300                              &perms);
 301                 if (request & ~perms.allow)
 302                         error = -EACCES;
 303         }
 304         error = aa_audit_file(profile, &perms, op, request, name, NULL, NULL,
 305                               cond->uid, info, error);
 306         put_buffers(buffer);
 307
 308         return error;
 309 }
 310
 311 /**
 312  * xindex_is_subset - helper for aa_path_link
 313  * @link: link permission set
 314  * @target: target permission set
 315  *
 316  * test target x permissions are equal OR a subset of link x permissions
 317  * this is done as part of the subset test, where a hardlink must have
 318  * a subset of permissions that the target has.
 319  *
 320  * Returns: %1 if subset else %0
 321  */
 322 static inline bool xindex_is_subset(u32 link, u32 target)
 323 {
 324         if (((link & ~AA_X_UNSAFE) != (target & ~AA_X_UNSAFE)) ||
 325             ((link & AA_X_UNSAFE) && !(target & AA_X_UNSAFE)))
 326                 return 0;
 327
 328         return 1;
 329 }
 330
 331 /**
 332  * aa_path_link - Handle hard link permission check
 333  * @profile: the profile being enforced  (NOT NULL)
 334  * @old_dentry: the target dentry  (NOT NULL)
 335  * @new_dir: directory the new link will be created in  (NOT NULL)
 336  * @new_dentry: the link being created  (NOT NULL)
 337  *
 338  * Handle the permission test for a link & target pair.  Permission
 339  * is encoded as a pair where the link permission is determined
 340  * first, and if allowed, the target is tested.  The target test
 341  * is done from the point of the link match (not start of DFA)
 342  * making the target permission dependent on the link permission match.
 343  *
 344  * The subset test if required forces that permissions granted
 345  * on link are a subset of the permission granted to target.
 346  *
 347  * Returns: %0 if allowed else error
 348  */
 349 int aa_path_link(struct aa_profile *profile, struct dentry *old_dentry,
 350                  const struct path *new_dir, struct dentry *new_dentry)
 351 {
 352         struct path link = { .mnt = new_dir->mnt, .dentry = new_dentry };
 353         struct path target = { .mnt = new_dir->mnt, .dentry = old_dentry };
 354         struct path_cond cond = {
 355                 d_backing_inode(old_dentry)->i_uid,
 356                 d_backing_inode(old_dentry)->i_mode
 357         };
 358         char *buffer = NULL, *buffer2 = NULL;
 359         const char *lname, *tname = NULL, *info = NULL;
 360         struct aa_perms lperms, perms;
 361         u32 request = AA_MAY_LINK;
 362         unsigned int state;
 363         int error;
 364
 365         get_buffers(buffer, buffer2);
 366         lperms = nullperms;
 367
 368         /* buffer freed below, lname is pointer in buffer */
 369         error = aa_path_name(&link, profile->path_flags, buffer, &lname,
 370                              &info, profile->disconnected);
 371         if (error)
 372                 goto audit;
 373
 374         /* buffer2 freed below, tname is pointer in buffer2 */
 375         error = aa_path_name(&target, profile->path_flags, buffer2, &tname,
 376                              &info, profile->disconnected);
 377         if (error)
 378                 goto audit;
 379
 380         error = -EACCES;
 381         /* aa_str_perms - handles the case of the dfa being NULL */
 382         state = aa_str_perms(profile->file.dfa, profile->file.start, lname,
 383                              &cond, &lperms);
 384
 385         if (!(lperms.allow & AA_MAY_LINK))
 386                 goto audit;
 387
 388         /* test to see if target can be paired with link */
 389         state = aa_dfa_null_transition(profile->file.dfa, state);
 390         aa_str_perms(profile->file.dfa, state, tname, &cond, &perms);
 391
 392         /* force audit/quiet masks for link are stored in the second entry
 393          * in the link pair.
 394          */
 395         lperms.audit = perms.audit;
 396         lperms.quiet = perms.quiet;
 397         lperms.kill = perms.kill;
 398
 399         if (!(perms.allow & AA_MAY_LINK)) {
 400                 info = "target restricted";
 401                 goto audit;
 402         }
 403
 404         /* done if link subset test is not required */
 405         if (!(perms.allow & AA_LINK_SUBSET))
 406                 goto done_tests;
 407
 408         /* Do link perm subset test requiring allowed permission on link are a
 409          * subset of the allowed permissions on target.
 410          */
 411         aa_str_perms(profile->file.dfa, profile->file.start, tname, &cond,
 412                      &perms);
 413
 414         /* AA_MAY_LINK is not considered in the subset test */
 415         request = lperms.allow & ~AA_MAY_LINK;
 416         lperms.allow &= perms.allow | AA_MAY_LINK;
 417
 418         request |= AA_AUDIT_FILE_MASK & (lperms.allow & ~perms.allow);
 419         if (request & ~lperms.allow) {
 420                 goto audit;
 421         } else if ((lperms.allow & MAY_EXEC) &&
 422                    !xindex_is_subset(lperms.xindex, perms.xindex)) {
 423                 lperms.allow &= ~MAY_EXEC;
 424                 request |= MAY_EXEC;
 425                 info = "link not subset of target";
 426                 goto audit;
 427         }
 428
 429 done_tests:
 430         error = 0;
 431
 432 audit:
 433         error = aa_audit_file(profile, &lperms, OP_LINK, request,
 434                               lname, tname, NULL, cond.uid, info, error);
 435         put_buffers(buffer, buffer2);
 436
 437         return error;
 438 }
 439
 440 /**
 441  * aa_file_perm - do permission revalidation check & audit for @file
 442  * @op: operation being checked
 443  * @label: label being enforced   (NOT NULL)
 444  * @file: file to revalidate access permissions on  (NOT NULL)
 445  * @request: requested permissions
 446  *
 447  * Returns: %0 if access allowed else error
 448  */
 449 int aa_file_perm(const char *op, struct aa_label *label, struct file *file,
 450                  u32 request)
 451 {
 452         struct path_cond cond = {
 453                 .uid = file_inode(file)->i_uid,
 454                 .mode = file_inode(file)->i_mode
 455         };
 456         struct aa_file_ctx *fctx;
 457         struct aa_label *flabel;
 458         u32 denied;
 459         int error = 0;
 460
 461         AA_BUG(!label);
 462         AA_BUG(!file);
 463
 464         fctx = file_ctx(file);
 465
 466         rcu_read_lock();
 467         flabel  = rcu_dereference(fctx->label);
 468         AA_BUG(!flabel);
 469
 470         /* revalidate access, if task is unconfined, or the cached cred
 471          * doesn't match or if the request is for more permissions than
 472          * was granted.
 473          *
 474          * Note: the test for !unconfined(flabel) is to handle file
 475          *       delegation from unconfined tasks
 476          */
 477         denied = request & ~fctx->allow;
 478         if (unconfined(label) || unconfined(flabel) ||
 479             (!denied && aa_label_is_subset(flabel, label)))
 480                 goto done;
 481
 482         /* TODO: label cross check */
 483
 484         if (file->f_path.mnt && path_mediated_fs(file->f_path.dentry))
 485                 error = aa_path_perm(op, labels_profile(label), &file->f_path,
 486                                      PATH_DELEGATE_DELETED, request, &cond);
 487
 488 done:
 489         rcu_read_unlock();
 490
 491         return error;
 492 }
 493
 494 static void revalidate_tty(struct aa_label *label)
 495 {
 496         struct tty_struct *tty;
 497         int drop_tty = 0;
 498
 499         tty = get_current_tty();
 500         if (!tty)
 501                 return;
 502
 503         spin_lock(&tty->files_lock);
 504         if (!list_empty(&tty->tty_files)) {
 505                 struct tty_file_private *file_priv;
 506                 struct file *file;
 507                 /* TODO: Revalidate access to controlling tty. */
 508                 file_priv = list_first_entry(&tty->tty_files,
 509                                              struct tty_file_private, list);
 510                 file = file_priv->file;
 511
 512                 if (aa_file_perm(OP_INHERIT, label, file, MAY_READ | MAY_WRITE))
 513                         drop_tty = 1;
 514         }
 515         spin_unlock(&tty->files_lock);
 516         tty_kref_put(tty);
 517
 518         if (drop_tty)
 519                 no_tty();
 520 }
 521
 522 static int match_file(const void *p, struct file *file, unsigned int fd)
 523 {
 524         struct aa_label *label = (struct aa_label *)p;
 525
 526         if (aa_file_perm(OP_INHERIT, label, file, aa_map_file_to_perms(file)))
 527                 return fd + 1;
 528         return 0;
 529 }
 530
 531
 532 /* based on selinux's flush_unauthorized_files */
 533 void aa_inherit_files(const struct cred *cred, struct files_struct *files)
 534 {
 535         struct aa_label *label = aa_get_newest_cred_label(cred);
 536         struct file *devnull = NULL;
 537         unsigned int n;
 538
 539         revalidate_tty(label);
 540
 541         /* Revalidate access to inherited open files. */
 542         n = iterate_fd(files, 0, match_file, label);
 543         if (!n) /* none found? */
 544                 goto out;
 545
 546         devnull = dentry_open(&aa_null, O_RDWR, cred);
 547         if (IS_ERR(devnull))
 548                 devnull = NULL;
 549         /* replace all the matching ones with this */
 550         do {
 551                 replace_fd(n - 1, devnull, 0);
 552         } while ((n = iterate_fd(files, n, match_file, label)) != 0);
 553         if (devnull)
 554                 fput(devnull);
 555 out:
 556         aa_put_label(label);
 557 }