src/apply-default-acl.c

   1 /**
   2  * @file apply-default-acl.c
   3  *
   4  * @brief The entire implementation.
   5  *
   6  */
   7
   8 /* On Linux, ftw.h needs this special voodoo to work. */
   9 #define _XOPEN_SOURCE 500
  10 #define _GNU_SOURCE
  11
  12 #include <errno.h>
  13 #include <fcntl.h>  /* AT_FOO constants */
  14 #include <ftw.h>    /* nftw() et al. */
  15 #include <getopt.h>
  16 #include <libgen.h> /* dirname()     */
  17 #include <limits.h> /* PATH_MAX      */
  18 #include <stdbool.h>
  19 #include <stdio.h>
  20 #include <stdlib.h>
  21 #include <string.h>
  22 #include <sys/stat.h>
  23 #include <unistd.h>
  24
  25 /* ACLs */
  26 #include <acl/libacl.h> /* acl_get_perm, not portable */
  27 #include <sys/types.h>
  28 #include <sys/acl.h>
  29
  30 /* Most of the libacl functions return 1 for success, 0 for failure,
  31    and -1 on error */
  32 #define ACL_ERROR -1
  33 #define ACL_FAILURE 0
  34 #define ACL_SUCCESS 1
  35
  36
  37
  38 /**
  39  * @brief Get the mode bits from the given path.
  40  *
  41  * @param path
  42  *   The path (file or directory) whose mode we want.
  43  *
  44  * @return A mode_t (st_mode) structure containing the mode bits.
  45  *   See sys/stat.h for details.
  46  */
  47 mode_t get_mode(const char* path) {
  48   if (path == NULL) {
  49     errno = ENOENT;
  50     return -1;
  51   }
  52
  53   struct stat s;
  54   int result = lstat(path, &s);
  55
  56   if (result == 0) {
  57     return s.st_mode;
  58   }
  59   else {
  60     /* errno will be set already by lstat() */
  61     return result;
  62   }
  63 }
  64
  65
  66
  67 /**
  68  * @brief Determine if the given path might refer to an (unsafe) hard link.
  69  *
  70  * @param path
  71  *   The path to test.
  72  *
  73  * @return true if we are certain that @c path does not refer to a hard
  74  *   link, and false otherwise. In case of error, false is returned,
  75  *   because we are not sure that @c path is not a hard link.
  76  */
  77 bool is_hardlink_safe(const char* path) {
  78   if (path == NULL) {
  79     return false;
  80   }
  81   struct stat s;
  82   int result = lstat(path, &s);
  83   if (result == 0) {
  84     return (s.st_nlink == 1 || S_ISDIR(s.st_mode));
  85   }
  86   else {
  87     return false;
  88   }
  89 }
  90
  91
  92 /**
  93  * @brief Determine whether or not the given path is a regular file.
  94  *
  95  * @param path
  96  *   The path to test.
  97  *
  98  * @return true if @c path is a regular file, false otherwise.
  99  */
 100 bool is_regular_file(const char* path) {
 101   if (path == NULL) {
 102     return false;
 103   }
 104
 105   struct stat s;
 106   int result = lstat(path, &s);
 107   if (result == 0) {
 108     return S_ISREG(s.st_mode);
 109   }
 110   else {
 111     return false;
 112   }
 113 }
 114
 115
 116
 117 /**
 118  * @brief Determine whether or not the given path is accessible.
 119  *
 120  * @param path
 121  *   The path to test.
 122  *
 123  * @return true if @c path is accessible to the current effective
 124  *   user/group, false otherwise.
 125  */
 126 bool path_accessible(const char* path) {
 127   if (path == NULL) {
 128     return false;
 129   }
 130
 131   /*  Test for access using the effective user and group rather than
 132       the real one. */
 133   int flags = AT_EACCESS;
 134
 135   /* Don't follow symlinks when checking for a path's existence,
 136      since we won't follow them to set its ACLs either. */
 137   flags |= AT_SYMLINK_NOFOLLOW;
 138
 139   /* If the path is relative, interpret it relative to the current
 140      working directory (just like the access() system call). */
 141   int result = faccessat(AT_FDCWD, path, F_OK, flags);
 142
 143   if (result == 0) {
 144     return true;
 145   }
 146   else {
 147     return false;
 148   }
 149 }
 150
 151
 152
 153 /**
 154  * @brief Determine whether or not the given path is a directory.
 155  *
 156  * @param path
 157  *   The path to test.
 158  *
 159  * @return true if @c path is a directory, false otherwise.
 160  */
 161 bool is_directory(const char* path) {
 162   if (path == NULL) {
 163     return false;
 164   }
 165
 166   struct stat s;
 167   int result = lstat(path, &s);
 168   if (result == 0) {
 169     return S_ISDIR(s.st_mode);
 170   }
 171   else {
 172     return false;
 173   }
 174 }
 175
 176
 177
 178 /**
 179  * @brief Update (or create) an entry in an @b minimal ACL.
 180  *
 181  * This function will not work if @c aclp contains extended
 182  * entries. This is fine for our purposes, since we call @c wipe_acls
 183  * on each path before applying the default to it.
 184  *
 185  * The assumption that there are no extended entries makes things much
 186  * simpler. For example, we only have to update the @c ACL_USER_OBJ,
 187  * @c ACL_GROUP_OBJ, and @c ACL_OTHER entries -- all others can simply
 188  * be created anew. This means we don't have to fool around comparing
 189  * named-user/group entries.
 190  *
 191  * @param aclp
 192  *   A pointer to the acl_t structure whose entry we want to modify.
 193  *
 194  * @param entry
 195  *   The new entry. If @c entry contains a user/group/other entry, we
 196  *   update the existing one. Otherwise we create a new entry.
 197  *
 198  * @return If there is an unexpected library error, @c ACL_ERROR is
 199  *   returned. Otherwise, @c ACL_SUCCESS.
 200  *
 201  */
 202 int acl_set_entry(acl_t* aclp,
 203                   acl_entry_t entry) {
 204
 205   acl_tag_t entry_tag;
 206   int gt_result = acl_get_tag_type(entry, &entry_tag);
 207   if (gt_result == ACL_ERROR) {
 208     perror("acl_set_entry (acl_get_tag_type)");
 209     return ACL_ERROR;
 210   }
 211
 212   acl_permset_t entry_permset;
 213   int ps_result = acl_get_permset(entry, &entry_permset);
 214   if (ps_result == ACL_ERROR) {
 215     perror("acl_set_entry (acl_get_permset)");
 216     return ACL_ERROR;
 217   }
 218
 219   acl_entry_t existing_entry;
 220   /* Loop through the given ACL looking for matching entries. */
 221   int result = acl_get_entry(*aclp, ACL_FIRST_ENTRY, &existing_entry);
 222
 223   while (result == ACL_SUCCESS) {
 224     acl_tag_t existing_tag = ACL_UNDEFINED_TAG;
 225     int tag_result = acl_get_tag_type(existing_entry, &existing_tag);
 226
 227     if (tag_result == ACL_ERROR) {
 228        perror("set_acl_tag_permset (acl_get_tag_type)");
 229        return ACL_ERROR;
 230     }
 231
 232     if (existing_tag == entry_tag) {
 233       if (entry_tag == ACL_USER_OBJ ||
 234           entry_tag == ACL_GROUP_OBJ ||
 235           entry_tag == ACL_OTHER) {
 236         /* Only update for these three since all other tags will have
 237            been wiped. These three are guaranteed to exist, so if we
 238            match one of them, we're allowed to return ACL_SUCCESS
 239            below and bypass the rest of the function. */
 240         acl_permset_t existing_permset;
 241         int gep_result = acl_get_permset(existing_entry, &existing_permset);
 242         if (gep_result == ACL_ERROR) {
 243           perror("acl_set_entry (acl_get_permset)");
 244           return ACL_ERROR;
 245         }
 246
 247         int s_result = acl_set_permset(existing_entry, entry_permset);
 248         if (s_result == ACL_ERROR) {
 249           perror("acl_set_entry (acl_set_permset)");
 250           return ACL_ERROR;
 251         }
 252
 253         return ACL_SUCCESS;
 254       }
 255
 256     }
 257
 258     result = acl_get_entry(*aclp, ACL_NEXT_ENTRY, &existing_entry);
 259   }
 260
 261   /* This catches both the initial acl_get_entry and the ones at the
 262      end of the loop. */
 263   if (result == ACL_ERROR) {
 264     perror("acl_set_entry (acl_get_entry)");
 265     return ACL_ERROR;
 266   }
 267
 268   /* If we've made it this far, we need to add a new entry to the
 269      ACL. */
 270   acl_entry_t new_entry;
 271
 272   /* We allocate memory here that we should release! */
 273   int c_result = acl_create_entry(aclp, &new_entry);
 274   if (c_result == ACL_ERROR) {
 275     perror("acl_set_entry (acl_create_entry)");
 276     return ACL_ERROR;
 277   }
 278
 279   int st_result = acl_set_tag_type(new_entry, entry_tag);
 280   if (st_result == ACL_ERROR) {
 281     perror("acl_set_entry (acl_set_tag_type)");
 282     return ACL_ERROR;
 283   }
 284
 285   int s_result = acl_set_permset(new_entry, entry_permset);
 286   if (s_result == ACL_ERROR) {
 287     perror("acl_set_entry (acl_set_permset)");
 288     return ACL_ERROR;
 289   }
 290
 291   if (entry_tag == ACL_USER || entry_tag == ACL_GROUP) {
 292     /* We need to set the qualifier too. */
 293     void* entry_qual = acl_get_qualifier(entry);
 294     if (entry_qual == (void*)NULL) {
 295       perror("acl_set_entry (acl_get_qualifier)");
 296       return ACL_ERROR;
 297     }
 298
 299     int sq_result = acl_set_qualifier(new_entry, entry_qual);
 300     if (sq_result == ACL_ERROR) {
 301       perror("acl_set_entry (acl_set_qualifier)");
 302       return ACL_ERROR;
 303     }
 304   }
 305
 306   return ACL_SUCCESS;
 307 }
 308
 309
 310
 311 /**
 312  * @brief Determine the number of entries in the given ACL.
 313  *
 314  * @param acl
 315  *   A pointer to an @c acl_t structure.
 316  *
 317  * @return Either the non-negative number of entries in @c acl, or
 318  *   @c ACL_ERROR on error.
 319  */
 320 int acl_entry_count(acl_t* acl) {
 321
 322   acl_entry_t entry;
 323   int entry_count = 0;
 324   int result = acl_get_entry(*acl, ACL_FIRST_ENTRY, &entry);
 325
 326   while (result == ACL_SUCCESS) {
 327     entry_count++;
 328     result = acl_get_entry(*acl, ACL_NEXT_ENTRY, &entry);
 329   }
 330
 331   if (result == ACL_ERROR) {
 332     perror("acl_entry_count (acl_get_entry)");
 333     return ACL_ERROR;
 334   }
 335
 336   return entry_count;
 337 }
 338
 339
 340
 341 /**
 342  * @brief Determine whether or not the given ACL is minimal.
 343  *
 344  * An ACL is minimal if it has fewer than four entries.
 345  *
 346  * @param acl
 347  *   A pointer to an acl_t structure.
 348  *
 349  * @return
 350  *   - @c ACL_SUCCESS - @c acl is minimal
 351  *   - @c ACL_FAILURE - @c acl is not minimal
 352  *   - @c ACL_ERROR - Unexpected library error
 353  */
 354 int acl_is_minimal(acl_t* acl) {
 355
 356   int ec = acl_entry_count(acl);
 357
 358   if (ec == ACL_ERROR) {
 359     perror("acl_is_minimal (acl_entry_count)");
 360     return ACL_ERROR;
 361   }
 362
 363   if (ec < 4) {
 364     return ACL_SUCCESS;
 365   }
 366   else {
 367     return ACL_FAILURE;
 368   }
 369 }
 370
 371
 372
 373 /**
 374  * @brief Determine whether the given path has an ACL whose mask
 375  *   denies execute.
 376  *
 377  * @param path
 378  *   The path to check.
 379  *
 380  * @return
 381  *   - @c ACL_SUCCESS - @c path has a mask which denies execute.
 382  *   - @c ACL_FAILURE - The ACL for @c path does not deny execute,
 383  *     or @c path has no extended ACL at all.
 384  *   - @c ACL_ERROR - Unexpected library error.
 385  */
 386 int acl_execute_masked(const char* path) {
 387
 388   acl_t acl = acl_get_file(path, ACL_TYPE_ACCESS);
 389
 390   if (acl == (acl_t)NULL) {
 391     perror("acl_execute_masked (acl_get_file)");
 392     return ACL_ERROR;
 393   }
 394
 395   /* Our return value. */
 396   int result = ACL_FAILURE;
 397
 398   acl_entry_t entry;
 399   int ge_result = acl_get_entry(acl, ACL_FIRST_ENTRY, &entry);
 400
 401   while (ge_result == ACL_SUCCESS) {
 402     acl_tag_t tag = ACL_UNDEFINED_TAG;
 403     int tag_result = acl_get_tag_type(entry, &tag);
 404
 405     if (tag_result == ACL_ERROR) {
 406        perror("acl_execute_masked (acl_get_tag_type)");
 407        result = ACL_ERROR;
 408        goto cleanup;
 409     }
 410
 411     if (tag == ACL_MASK) {
 412       /* This is the mask entry, get its permissions, and see if
 413          execute is specified. */
 414       acl_permset_t permset;
 415
 416       int ps_result = acl_get_permset(entry, &permset);
 417       if (ps_result == ACL_ERROR) {
 418         perror("acl_execute_masked (acl_get_permset)");
 419         result = ACL_ERROR;
 420         goto cleanup;
 421       }
 422
 423       int gp_result = acl_get_perm(permset, ACL_EXECUTE);
 424       if (gp_result == ACL_ERROR) {
 425         perror("acl_execute_masked (acl_get_perm)");
 426         result = ACL_ERROR;
 427         goto cleanup;
 428       }
 429
 430       if (gp_result == ACL_FAILURE) {
 431         /* No execute bit set in the mask; execute not allowed. */
 432         return ACL_SUCCESS;
 433       }
 434     }
 435
 436     ge_result = acl_get_entry(acl, ACL_NEXT_ENTRY, &entry);
 437   }
 438
 439  cleanup:
 440   acl_free(acl);
 441   return result;
 442 }
 443
 444
 445
 446 /**
 447  * @brief Determine whether @c path is executable (by anyone) or a
 448  *   directory.
 449  *
 450  * This is used as part of the heuristic to determine whether or not
 451  * we should mask the execute bit when inheriting an ACL. If @c path
 452  * is a directory, the answer is a clear-cut yes. This behavior is
 453  * modeled after the capital 'X' perms of setfacl.
 454  *
 455  * If @c path is a file, we check the @a effective permissions,
 456  * contrary to what setfacl does.
 457  *
 458  * @param path
 459  *   The path to check.
 460  *
 461  * @return
 462  *   - @c ACL_SUCCESS - @c path is a directory, or someone has effective
 463        execute permissions.
 464  *   - @c ACL_FAILURE - @c path is a regular file and nobody can execute
 465        it.
 466  *   - @c ACL_ERROR - Unexpected library error.
 467  */
 468 int any_can_execute_or_dir(const char* path) {
 469
 470   if (is_directory(path)) {
 471     /* That was easy... */
 472     return ACL_SUCCESS;
 473   }
 474
 475   acl_t acl = acl_get_file(path, ACL_TYPE_ACCESS);
 476
 477   if (acl == (acl_t)NULL) {
 478     perror("any_can_execute_or_dir (acl_get_file)");
 479     return ACL_ERROR;
 480   }
 481
 482   /* Our return value. */
 483   int result = ACL_FAILURE;
 484
 485   if (acl_is_minimal(&acl)) {
 486     mode_t mode = get_mode(path);
 487     if (mode & (S_IXUSR | S_IXOTH | S_IXGRP)) {
 488       result = ACL_SUCCESS;
 489       goto cleanup;
 490     }
 491     else {
 492       result = ACL_FAILURE;
 493       goto cleanup;
 494     }
 495   }
 496
 497   acl_entry_t entry;
 498   int ge_result = acl_get_entry(acl, ACL_FIRST_ENTRY, &entry);
 499
 500   while (ge_result == ACL_SUCCESS) {
 501     /* The first thing we do is check to see if this is a mask
 502        entry. If it is, we skip it entirely. */
 503     acl_tag_t tag = ACL_UNDEFINED_TAG;
 504     int tag_result = acl_get_tag_type(entry, &tag);
 505
 506     if (tag_result == ACL_ERROR) {
 507       perror("any_can_execute_or_dir (acl_get_tag_type)");
 508       result = ACL_ERROR;
 509       goto cleanup;
 510     }
 511
 512     if (tag == ACL_MASK) {
 513       ge_result = acl_get_entry(acl, ACL_NEXT_ENTRY, &entry);
 514       continue;
 515     }
 516
 517     /* Ok, so it's not a mask entry. Check the execute perms. */
 518     acl_permset_t permset;
 519
 520     int ps_result = acl_get_permset(entry, &permset);
 521     if (ps_result == ACL_ERROR) {
 522       perror("any_can_execute_or_dir (acl_get_permset)");
 523       result = ACL_ERROR;
 524       goto cleanup;
 525     }
 526
 527     int gp_result = acl_get_perm(permset, ACL_EXECUTE);
 528     if (gp_result == ACL_ERROR) {
 529       perror("any_can_execute_or_dir (acl_get_perm)");
 530       result = ACL_ERROR;
 531       goto cleanup;
 532     }
 533
 534     if (gp_result == ACL_SUCCESS) {
 535       /* Only return ACL_SUCCESS if this execute bit is not masked. */
 536       if (acl_execute_masked(path) != ACL_SUCCESS) {
 537         result = ACL_SUCCESS;
 538         goto cleanup;
 539       }
 540     }
 541
 542     ge_result = acl_get_entry(acl, ACL_NEXT_ENTRY, &entry);
 543   }
 544
 545   if (ge_result == ACL_ERROR) {
 546     perror("any_can_execute_or_dir (acl_get_entry)");
 547     result = ACL_ERROR;
 548     goto cleanup;
 549   }
 550
 551  cleanup:
 552   acl_free(acl);
 553   return result;
 554 }
 555
 556
 557
 558 /**
 559  * @brief Set @c acl as the default ACL on @c path if it's a directory.
 560  *
 561  * This overwrites any existing default ACL on @c path. If no default
 562  * ACL exists, then one is created. If @c path is not a directory, we
 563  * return ACL_FAILURE but no error is raised.
 564  *
 565  * @param path
 566  *   The target directory whose ACL we wish to replace or create.
 567  *
 568   * @param acl
 569  *   The ACL to set as default on @c path.
 570  *
 571  * @return
 572  *   - @c ACL_SUCCESS - The default ACL was assigned successfully.
 573  *   - @c ACL_FAILURE - If @c path is not a directory.
 574  *   - @c ACL_ERROR - Unexpected library error.
 575  */
 576 int assign_default_acl(const char* path, acl_t acl) {
 577
 578   if (path == NULL) {
 579     errno = ENOENT;
 580     return ACL_ERROR;
 581   }
 582
 583   if (!is_directory(path)) {
 584     return ACL_FAILURE;
 585   }
 586
 587     /* Our return value; success unless something bad happens. */
 588   int result = ACL_SUCCESS;
 589   acl_t path_acl = acl_dup(acl);
 590
 591   if (path_acl == (acl_t)NULL) {
 592     perror("inherit_default_acl (acl_dup)");
 593     return ACL_ERROR; /* Nothing to clean up in this case. */
 594   }
 595
 596   int sf_result = acl_set_file(path, ACL_TYPE_DEFAULT, path_acl);
 597   if (sf_result == -1) {
 598     perror("inherit_default_acl (acl_set_file)");
 599     result = ACL_ERROR;
 600   }
 601
 602   acl_free(path_acl);
 603   return result;
 604 }
 605
 606
 607
 608 /**
 609  * @brief Remove @c ACL_USER, @c ACL_GROUP, and @c ACL_MASK entries
 610  *   from the given path.
 611  *
 612  * @param path
 613  *   The path whose ACLs we want to wipe.
 614  *
 615  * @return
 616  *   - @c ACL_SUCCESS - The ACLs were wiped successfully, or none
 617  *     existed in the first place.
 618  *   - @c ACL_ERROR - Unexpected library error.
 619  */
 620 int wipe_acls(const char* path) {
 621
 622   if (path == NULL) {
 623     errno = ENOENT;
 624     return ACL_ERROR;
 625   }
 626
 627   acl_t acl = acl_get_file(path, ACL_TYPE_ACCESS);
 628   if (acl == (acl_t)NULL) {
 629     perror("wipe_acls (acl_get_file)");
 630     return ACL_ERROR;
 631   }
 632
 633   /* Our return value. */
 634   int result = ACL_SUCCESS;
 635
 636   acl_entry_t entry;
 637   int ge_result = acl_get_entry(acl, ACL_FIRST_ENTRY, &entry);
 638
 639   while (ge_result == ACL_SUCCESS) {
 640     int d_result = acl_delete_entry(acl, entry);
 641     if (d_result == ACL_ERROR) {
 642       perror("wipe_acls (acl_delete_entry)");
 643       result = ACL_ERROR;
 644       goto cleanup;
 645     }
 646
 647     ge_result = acl_get_entry(acl, ACL_NEXT_ENTRY, &entry);
 648   }
 649
 650   /* Catches the first acl_get_entry as well as the ones at the end of
 651      the loop. */
 652   if (ge_result == ACL_ERROR) {
 653     perror("wipe_acls (acl_get_entry)");
 654     result = ACL_ERROR;
 655     goto cleanup;
 656   }
 657
 658   int sf_result = acl_set_file(path, ACL_TYPE_ACCESS, acl);
 659   if (sf_result == ACL_ERROR) {
 660     perror("wipe_acls (acl_set_file)");
 661     result = ACL_ERROR;
 662     goto cleanup;
 663   }
 664
 665  cleanup:
 666   acl_free(acl);
 667   return result;
 668 }
 669
 670
 671
 672 /**
 673  * @brief Apply parent default ACL to a path.
 674  *
 675  * This overwrites any existing ACLs on @c path.
 676  *
 677  * @param path
 678  *   The path whose ACL we would like to reset to its default.
 679  *
 680  * @param no_exec_mask
 681  *   The value (either true or false) of the --no-exec-mask flag.
 682  *
 683  * @return
 684  *   - @c ACL_SUCCESS - The parent default ACL was inherited successfully.
 685  *   - @c ACL_FAILURE - The target path is not a regular file/directory,
 686  *     or the parent of @c path is not a directory.
 687  *   - @c ACL_ERROR - Unexpected library error.
 688  */
 689 int apply_default_acl(const char* path, bool no_exec_mask) {
 690
 691   if (path == NULL) {
 692     errno = ENOENT;
 693     return ACL_ERROR;
 694   }
 695
 696   /* Refuse to operate on hard links, which can be abused by an
 697    * attacker to trick us into changing the ACL on a file we didn't
 698    * intend to; namely the "target" of the hard link. To truly prevent
 699    * that sort of mischief, we should be using file descriptors for
 700    * the target and its parent directory. Then modulo a tiny race
 701    * condition, we would be sure that "path" and "parent" don't change
 702    * their nature between the time that we test them and when we
 703    * utilize them. For contrast, the same attacker is free to replace
 704    * "path" with a hard link after is_hardlink_safe() has returned
 705    * "true" below.
 706    *
 707    * Unfortunately, our API is lacking in this area. For example,
 708    * acl_set_fd() is only capable of setting the ACL_TYPE_ACCESS list,
 709    * and not the ACL_TYPE_DEFAULT. Apparently the only way to operate
 710    * on default ACLs is through the path name, which is inherently
 711    * unreliable since the acl_*_file() calls themselves might follow
 712    * links (both hard and symbolic).
 713    *
 714    * Some improvement could still be made by using descriptors where
 715    * possible -- this would shrink the exploit window -- but for now
 716    * we use a naive implementation that only keeps honest men honest.
 717   */
 718   if (!is_hardlink_safe(path)) {
 719     return ACL_FAILURE;
 720   }
 721
 722   if (!is_regular_file(path) && !is_directory(path)) {
 723     return ACL_FAILURE;
 724   }
 725
 726   /* dirname mangles its argument */
 727   char path_copy[PATH_MAX];
 728   strncpy(path_copy, path, PATH_MAX-1);
 729   path_copy[PATH_MAX-1] = 0;
 730
 731   char* parent = dirname(path_copy);
 732   if (!is_directory(parent)) {
 733     /* Make sure dirname() did what we think it did. */
 734     return ACL_FAILURE;
 735   }
 736
 737   /* Default to not masking the exec bit; i.e. applying the default
 738      ACL literally. If --no-exec-mask was not specified, then we try
 739      to "guess" whether or not to mask the exec bit. */
 740   bool allow_exec = true;
 741
 742   if (!no_exec_mask) {
 743     int ace_result = any_can_execute_or_dir(path);
 744
 745     if (ace_result == ACL_ERROR) {
 746       perror("apply_default_acl (any_can_execute_or_dir)");
 747       return ACL_ERROR;
 748     }
 749
 750     allow_exec = (bool)ace_result;
 751   }
 752
 753   acl_t defacl = acl_get_file(parent, ACL_TYPE_DEFAULT);
 754
 755   if (defacl == (acl_t)NULL) {
 756     perror("apply_default_acl (acl_get_file)");
 757     return ACL_ERROR;
 758   }
 759
 760   /* Our return value. */
 761   int result = ACL_SUCCESS;
 762
 763   int wipe_result = wipe_acls(path);
 764   if (wipe_result == ACL_ERROR) {
 765     perror("apply_default_acl (wipe_acls)");
 766     result = ACL_ERROR;
 767     goto cleanup;
 768   }
 769
 770   /* Do this after wipe_acls(), otherwise we'll overwrite the wiped
 771      ACL with this one. */
 772   acl_t acl = acl_get_file(path, ACL_TYPE_ACCESS);
 773   if (acl == (acl_t)NULL) {
 774     perror("apply_default_acl (acl_get_file)");
 775     return ACL_ERROR;
 776   }
 777
 778   /* If it's a directory, inherit the parent's default. */
 779   int inherit_result = assign_default_acl(path, defacl);
 780   if (inherit_result == ACL_ERROR) {
 781     perror("apply_default_acl (inherit_acls)");
 782     result = ACL_ERROR;
 783     goto cleanup;
 784   }
 785
 786   acl_entry_t entry;
 787   int ge_result = acl_get_entry(defacl, ACL_FIRST_ENTRY, &entry);
 788
 789   while (ge_result == ACL_SUCCESS) {
 790     acl_tag_t tag = ACL_UNDEFINED_TAG;
 791     int tag_result = acl_get_tag_type(entry, &tag);
 792
 793     if (tag_result == ACL_ERROR) {
 794        perror("apply_default_acl (acl_get_tag_type)");
 795        result = ACL_ERROR;
 796        goto cleanup;
 797     }
 798
 799
 800     /* We've got an entry/tag from the default ACL. Get its permset. */
 801     acl_permset_t permset;
 802     int ps_result = acl_get_permset(entry, &permset);
 803     if (ps_result == ACL_ERROR) {
 804       perror("apply_default_acl (acl_get_permset)");
 805       result = ACL_ERROR;
 806       goto cleanup;
 807     }
 808
 809     /* If this is a default mask, fix it up. */
 810     if (tag == ACL_MASK ||
 811         tag == ACL_USER_OBJ ||
 812         tag == ACL_GROUP_OBJ ||
 813         tag == ACL_OTHER) {
 814
 815       if (!allow_exec) {
 816         /* The mask doesn't affect acl_user_obj, acl_group_obj (in
 817            minimal ACLs) or acl_other entries, so if execute should be
 818            masked, we have to do it manually. */
 819         int d_result = acl_delete_perm(permset, ACL_EXECUTE);
 820         if (d_result == ACL_ERROR) {
 821           perror("apply_default_acl (acl_delete_perm)");
 822           result = ACL_ERROR;
 823           goto cleanup;
 824         }
 825
 826         int sp_result = acl_set_permset(entry, permset);
 827         if (sp_result == ACL_ERROR) {
 828           perror("apply_default_acl (acl_set_permset)");
 829           result = ACL_ERROR;
 830           goto cleanup;
 831         }
 832       }
 833     }
 834
 835     /* Finally, add the permset to the access ACL. */
 836     int set_result = acl_set_entry(&acl, entry);
 837     if (set_result == ACL_ERROR) {
 838       perror("apply_default_acl (acl_set_entry)");
 839       result = ACL_ERROR;
 840       goto cleanup;
 841     }
 842
 843     ge_result = acl_get_entry(defacl, ACL_NEXT_ENTRY, &entry);
 844   }
 845
 846   /* Catches the first acl_get_entry as well as the ones at the end of
 847      the loop. */
 848   if (ge_result == ACL_ERROR) {
 849     perror("apply_default_acl (acl_get_entry)");
 850     result = ACL_ERROR;
 851     goto cleanup;
 852   }
 853
 854   int sf_result = acl_set_file(path, ACL_TYPE_ACCESS, acl);
 855   if (sf_result == ACL_ERROR) {
 856     perror("apply_default_acl (acl_set_file)");
 857     result = ACL_ERROR;
 858     goto cleanup;
 859   }
 860
 861  cleanup:
 862   acl_free(defacl);
 863   return result;
 864 }
 865
 866
 867
 868 /**
 869  * @brief Display program usage information.
 870  *
 871  * @param program_name
 872  *   The program name to use in the output.
 873  *
 874  */
 875 void usage(const char* program_name) {
 876   printf("Apply any applicable default ACLs to the given files or "
 877          "directories.\n\n");
 878   printf("Usage: %s [flags] <target1> [<target2> [ <target3>...]]\n\n",
 879          program_name);
 880   printf("Flags:\n");
 881   printf(" -h, --help         Print this help message\n");
 882   printf(" -r, --recursive    Act on any given directories recursively\n");
 883   printf(" -x, --no-exec-mask Apply execute permissions unconditionally\n");
 884
 885   return;
 886 }
 887
 888
 889 /**
 890  * @brief Wrapper around @c apply_default_acl() for use with @c nftw().
 891  *
 892  * For parameter information, see the @c nftw man page.
 893  *
 894  * @return If the ACL was applied to @c target successfully, we return
 895  *   @c FTW_CONTINUE to signal to @ nftw() that we should proceed onto
 896  *   the next file or directory. Otherwise, we return @c FTW_STOP to
 897  *   signal failure.
 898  *
 899  */
 900 int apply_default_acl_nftw(const char *target,
 901                            const struct stat *s,
 902                            int info,
 903                            struct FTW *ftw) {
 904
 905   bool app_result = apply_default_acl(target, false);
 906   if (app_result) {
 907     return FTW_CONTINUE;
 908   }
 909   else {
 910     return FTW_STOP;
 911   }
 912 }
 913
 914
 915
 916 /**
 917  * @brief Wrapper around @c apply_default_acl() for use with @c nftw().
 918  *
 919  * This is identical to @c apply_default_acl_nftw(), except it passes
 920  * @c true to @c apply_default_acl() as its no_exec_mask argument.
 921  *
 922  */
 923 int apply_default_acl_nftw_x(const char *target,
 924                              const struct stat *s,
 925                              int info,
 926                              struct FTW *ftw) {
 927
 928   bool app_result = apply_default_acl(target, true);
 929   if (app_result) {
 930     return FTW_CONTINUE;
 931   }
 932   else {
 933     return FTW_STOP;
 934   }
 935 }
 936
 937
 938
 939 /**
 940  * @brief Recursive version of @c apply_default_acl().
 941  *
 942  * If @c target is a directory, we use @c nftw() to call @c
 943  * apply_default_acl() recursively on all of its children. Otherwise,
 944  * we just delegate to @c apply_default_acl().
 945  *
 946  * We ignore symlinks for consistency with chmod -r.
 947  *
 948  * @param target
 949  *   The root (path) of the recursive application.
 950  *
 951  * @param no_exec_mask
 952  *   The value (either true or false) of the --no-exec-mask flag.
 953  *
 954  * @return
 955  *   If @c target is not a directory, we return the result of
 956  *   calling @c apply_default_acl() on @c target. Otherwise, we convert
 957  *   the return value of @c nftw(). If @c nftw() succeeds (returns 0),
 958  *   then we return @c true. Otherwise, we return @c false.
 959  *   \n\n
 960  *   If there is an error, it will be reported via @c perror, but
 961  *   we still return @c false.
 962  */
 963 bool apply_default_acl_recursive(const char *target, bool no_exec_mask) {
 964
 965   if (!is_directory(target)) {
 966     return apply_default_acl(target, no_exec_mask);
 967   }
 968
 969   int max_levels = 256;
 970   int flags = FTW_PHYS; /* Don't follow links. */
 971
 972   /* There are two separate functions that could be passed to
 973      nftw(). One passes no_exec_mask = true to apply_default_acl(),
 974      and the other passes no_exec_mask = false. Since the function we
 975      pass to nftw() cannot have parameters, we have to create separate
 976      options and make the decision here. */
 977   int (*fn)(const char *, const struct stat *, int, struct FTW *) = NULL;
 978   fn = no_exec_mask ? apply_default_acl_nftw_x : apply_default_acl_nftw;
 979
 980   int nftw_result = nftw(target, fn, max_levels, flags);
 981
 982   if (nftw_result == 0) {
 983     /* Success */
 984     return true;
 985   }
 986
 987   /* nftw will return -1 on error, or if the supplied function
 988    * (apply_default_acl_nftw) returns a non-zero result, nftw will
 989    * return that.
 990    */
 991   if (nftw_result == -1) {
 992     perror("apply_default_acl_recursive (nftw)");
 993   }
 994
 995   return false;
 996 }
 997
 998
 999
1000 /**
1001  * @brief Call apply_default_acl (possibly recursively) on each
1002  * command-line argument.
1003  *
1004  * @return Either @c EXIT_FAILURE or @c EXIT_SUCCESS. If everything
1005  *   goes as expected, we return @c EXIT_SUCCESS. Otherwise, we return
1006  *   @c EXIT_FAILURE.
1007  */
1008 int main(int argc, char* argv[]) {
1009
1010   if (argc < 2) {
1011     usage(argv[0]);
1012     return EXIT_FAILURE;
1013   }
1014
1015   bool recursive = false;
1016   bool no_exec_mask = false;
1017
1018   struct option long_options[] = {
1019     /* These options set a flag. */
1020     {"help",      no_argument, NULL, 'h'},
1021     {"recursive", no_argument, NULL, 'r'},
1022     {"no-exec-mask", no_argument, NULL, 'x'},
1023     {NULL,        0,           NULL, 0}
1024   };
1025
1026   int opt = 0;
1027
1028   while ((opt = getopt_long(argc, argv, "hrx", long_options, NULL)) != -1) {
1029     switch (opt) {
1030     case 'h':
1031       usage(argv[0]);
1032       return EXIT_SUCCESS;
1033     case 'r':
1034       recursive = true;
1035       break;
1036     case 'x':
1037       no_exec_mask = true;
1038       break;
1039     default:
1040       usage(argv[0]);
1041       return EXIT_FAILURE;
1042     }
1043   }
1044
1045   int result = EXIT_SUCCESS;
1046
1047   int arg_index = 1;
1048   for (arg_index = optind; arg_index < argc; arg_index++) {
1049     const char* target = argv[arg_index];
1050     bool reapp_result = false;
1051
1052     /* Make sure we can access the given path before we go out of our
1053      * way to please it. Doing this check outside of
1054      * apply_default_acl() lets us spit out a better error message for
1055      * typos, too.
1056      */
1057     if (!path_accessible(target)) {
1058       fprintf(stderr, "%s: %s: No such file or directory\n", argv[0], target);
1059       result = EXIT_FAILURE;
1060       continue;
1061     }
1062
1063     if (recursive) {
1064       reapp_result = apply_default_acl_recursive(target, no_exec_mask);
1065     }
1066     else {
1067       /* It's either a normal file, or we're not operating recursively. */
1068       reapp_result = apply_default_acl(target, no_exec_mask);
1069     }
1070
1071     if (!reapp_result) {
1072       result = EXIT_FAILURE;
1073     }
1074   }
1075
1076   return result;
1077 }