2 * @file apply-default-acl.c
4 * @brief The entire implementation.
8 /* On Linux, ftw.h needs this special voodoo to work. */
9 #define _XOPEN_SOURCE 500
13 #include <fcntl.h> /* AT_FOO constants */
14 #include <ftw.h> /* nftw() et al. */
16 #include <libgen.h> /* basename(), dirname() */
25 #include <acl/libacl.h> /* acl_get_perm, not portable */
26 #include <sys/types.h>
29 /* Most of the libacl functions return 1 for success, 0 for failure,
39 * @brief Determine whether or not the given path is accessible.
44 * @return true if @c path is accessible to the current effective
45 * user/group, false otherwise.
47 bool path_accessible(const char* path
) {
52 /* Test for access using the effective user and group rather than
54 int flags
= AT_EACCESS
;
56 /* Don't follow symlinks when checking for a path's existence,
57 since we won't follow them to set its ACLs either. */
58 flags
|= AT_SYMLINK_NOFOLLOW
;
60 /* If the path is relative, interpret it relative to the current
61 working directory (just like the access() system call). */
62 if (faccessat(AT_FDCWD
, path
, F_OK
, flags
) == 0) {
73 * @brief Determine whether or not the given path is a directory.
78 * @return true if @c path is a directory, false otherwise.
80 bool is_path_directory(const char* path
) {
86 if (lstat(path
, &s
) == 0) {
87 return S_ISDIR(s
.st_mode
);
98 * @brief Update (or create) an entry in an @b minimal ACL.
100 * This function will not work if @c aclp contains extended
101 * entries. This is fine for our purposes, since we call @c wipe_acls
102 * on each path before applying the default to it.
104 * The assumption that there are no extended entries makes things much
105 * simpler. For example, we only have to update the @c ACL_USER_OBJ,
106 * @c ACL_GROUP_OBJ, and @c ACL_OTHER entries -- all others can simply
107 * be created anew. This means we don't have to fool around comparing
108 * named-user/group entries.
111 * A pointer to the acl_t structure whose entry we want to modify.
114 * The new entry. If @c entry contains a user/group/other entry, we
115 * update the existing one. Otherwise we create a new entry.
117 * @return If there is an unexpected library error, @c ACL_ERROR is
118 * returned. Otherwise, @c ACL_SUCCESS.
121 int acl_set_entry(acl_t
* aclp
, acl_entry_t entry
) {
124 if (acl_get_tag_type(entry
, &entry_tag
) == ACL_ERROR
) {
125 perror("acl_set_entry (acl_get_tag_type)");
129 acl_permset_t entry_permset
;
130 if (acl_get_permset(entry
, &entry_permset
) == ACL_ERROR
) {
131 perror("acl_set_entry (acl_get_permset)");
135 acl_entry_t existing_entry
;
136 /* Loop through the given ACL looking for matching entries. */
137 int result
= acl_get_entry(*aclp
, ACL_FIRST_ENTRY
, &existing_entry
);
139 while (result
== ACL_SUCCESS
) {
140 acl_tag_t existing_tag
= ACL_UNDEFINED_TAG
;
142 if (acl_get_tag_type(existing_entry
, &existing_tag
) == ACL_ERROR
) {
143 perror("set_acl_tag_permset (acl_get_tag_type)");
147 if (existing_tag
== entry_tag
) {
148 if (entry_tag
== ACL_USER_OBJ
||
149 entry_tag
== ACL_GROUP_OBJ
||
150 entry_tag
== ACL_OTHER
) {
151 /* Only update for these three since all other tags will have
152 been wiped. These three are guaranteed to exist, so if we
153 match one of them, we're allowed to return ACL_SUCCESS
154 below and bypass the rest of the function. */
155 acl_permset_t existing_permset
;
156 if (acl_get_permset(existing_entry
, &existing_permset
) == ACL_ERROR
) {
157 perror("acl_set_entry (acl_get_permset)");
161 if (acl_set_permset(existing_entry
, entry_permset
) == ACL_ERROR
) {
162 perror("acl_set_entry (acl_set_permset)");
171 result
= acl_get_entry(*aclp
, ACL_NEXT_ENTRY
, &existing_entry
);
174 /* This catches both the initial acl_get_entry and the ones at the
176 if (result
== ACL_ERROR
) {
177 perror("acl_set_entry (acl_get_entry)");
181 /* If we've made it this far, we need to add a new entry to the
183 acl_entry_t new_entry
;
185 /* The acl_create_entry() function can allocate new memory and/or
186 * change the location of the ACL structure entirely. When that
187 * happens, the value pointed to by aclp is updated, which means
188 * that a new acl_t gets "passed out" to our caller, eventually to
189 * be fed to acl_free(). In other words, we should still be freeing
190 * the right thing, even if the value pointed to by aclp changes.
192 if (acl_create_entry(aclp
, &new_entry
) == ACL_ERROR
) {
193 perror("acl_set_entry (acl_create_entry)");
197 if (acl_set_tag_type(new_entry
, entry_tag
) == ACL_ERROR
) {
198 perror("acl_set_entry (acl_set_tag_type)");
202 if (acl_set_permset(new_entry
, entry_permset
) == ACL_ERROR
) {
203 perror("acl_set_entry (acl_set_permset)");
207 if (entry_tag
== ACL_USER
|| entry_tag
== ACL_GROUP
) {
208 /* We need to set the qualifier too. */
209 void* entry_qual
= acl_get_qualifier(entry
);
210 if (entry_qual
== (void*)NULL
) {
211 perror("acl_set_entry (acl_get_qualifier)");
215 if (acl_set_qualifier(new_entry
, entry_qual
) == ACL_ERROR
) {
216 perror("acl_set_entry (acl_set_qualifier)");
227 * @brief Determine the number of entries in the given ACL.
230 * The ACL to inspect.
232 * @return Either the non-negative number of entries in @c acl, or
233 * @c ACL_ERROR on error.
235 int acl_entry_count(acl_t acl
) {
239 int result
= acl_get_entry(acl
, ACL_FIRST_ENTRY
, &entry
);
241 while (result
== ACL_SUCCESS
) {
243 result
= acl_get_entry(acl
, ACL_NEXT_ENTRY
, &entry
);
246 if (result
== ACL_ERROR
) {
247 perror("acl_entry_count (acl_get_entry)");
257 * @brief Determine whether or not the given ACL is minimal.
259 * An ACL is minimal if it has fewer than four entries.
262 * The ACL whose minimality is in question.
265 * - @c ACL_SUCCESS - @c acl is minimal
266 * - @c ACL_FAILURE - @c acl is not minimal
267 * - @c ACL_ERROR - Unexpected library error
269 int acl_is_minimal(acl_t acl
) {
271 int ec
= acl_entry_count(acl
);
273 if (ec
== ACL_ERROR
) {
274 perror("acl_is_minimal (acl_entry_count)");
289 * @brief Determine whether the given ACL's mask denies execute.
292 * The ACL whose mask we want to check.
295 * - @c ACL_SUCCESS - The @c acl has a mask which denies execute.
296 * - @c ACL_FAILURE - The @c acl has a mask which does not deny execute.
297 * - @c ACL_ERROR - Unexpected library error.
299 int acl_execute_masked(acl_t acl
) {
302 int ge_result
= acl_get_entry(acl
, ACL_FIRST_ENTRY
, &entry
);
304 while (ge_result
== ACL_SUCCESS
) {
305 acl_tag_t tag
= ACL_UNDEFINED_TAG
;
307 if (acl_get_tag_type(entry
, &tag
) == ACL_ERROR
) {
308 perror("acl_execute_masked (acl_get_tag_type)");
312 if (tag
== ACL_MASK
) {
313 /* This is the mask entry, get its permissions, and see if
314 execute is specified. */
315 acl_permset_t permset
;
317 if (acl_get_permset(entry
, &permset
) == ACL_ERROR
) {
318 perror("acl_execute_masked (acl_get_permset)");
322 int gp_result
= acl_get_perm(permset
, ACL_EXECUTE
);
323 if (gp_result
== ACL_ERROR
) {
324 perror("acl_execute_masked (acl_get_perm)");
328 if (gp_result
== ACL_FAILURE
) {
329 /* No execute bit set in the mask; execute not allowed. */
334 ge_result
= acl_get_entry(acl
, ACL_NEXT_ENTRY
, &entry
);
343 * @brief Determine whether @c fd is executable by anyone.
346 * This is used as part of the heuristic to determine whether or not
347 * we should mask the execute bit when inheriting an ACL. If @c fd
348 * describes a file, we check the @a effective permissions, contrary
349 * to what setfacl does.
352 * The file descriptor to check.
355 * - @c ACL_SUCCESS - Someone has effective execute permissions on @c fd.
356 * - @c ACL_FAILURE - Nobody can execute @c fd.
357 * - @c ACL_ERROR - Unexpected library error.
359 int any_can_execute(int fd
) {
360 acl_t acl
= acl_get_fd(fd
);
362 if (acl
== (acl_t
)NULL
) {
363 perror("any_can_execute (acl_get_file)");
367 /* Our return value. */
368 int result
= ACL_FAILURE
;
370 if (acl_is_minimal(acl
)) {
372 if (fstat(fd
, &s
) == -1) {
373 perror("any_can_execute (fstat)");
377 if (s
.st_mode
& (S_IXUSR
| S_IXOTH
| S_IXGRP
)) {
378 result
= ACL_SUCCESS
;
382 result
= ACL_FAILURE
;
388 int ge_result
= acl_get_entry(acl
, ACL_FIRST_ENTRY
, &entry
);
390 while (ge_result
== ACL_SUCCESS
) {
391 /* The first thing we do is check to see if this is a mask
392 entry. If it is, we skip it entirely. */
393 acl_tag_t tag
= ACL_UNDEFINED_TAG
;
395 if (acl_get_tag_type(entry
, &tag
) == ACL_ERROR
) {
396 perror("any_can_execute_or (acl_get_tag_type)");
401 if (tag
== ACL_MASK
) {
402 ge_result
= acl_get_entry(acl
, ACL_NEXT_ENTRY
, &entry
);
406 /* Ok, so it's not a mask entry. Check the execute perms. */
407 acl_permset_t permset
;
409 if (acl_get_permset(entry
, &permset
) == ACL_ERROR
) {
410 perror("any_can_execute_or (acl_get_permset)");
415 int gp_result
= acl_get_perm(permset
, ACL_EXECUTE
);
416 if (gp_result
== ACL_ERROR
) {
417 perror("any_can_execute (acl_get_perm)");
422 if (gp_result
== ACL_SUCCESS
) {
423 /* Only return ACL_SUCCESS if this execute bit is not masked. */
424 if (acl_execute_masked(acl
) != ACL_SUCCESS
) {
425 result
= ACL_SUCCESS
;
430 ge_result
= acl_get_entry(acl
, ACL_NEXT_ENTRY
, &entry
);
433 if (ge_result
== ACL_ERROR
) {
434 perror("any_can_execute (acl_get_entry)");
447 * @brief Set @c acl as the default ACL on @c path if it's a directory.
449 * This overwrites any existing default ACL on @c path. If no default
450 * ACL exists, then one is created. If @c path is not a directory, we
451 * return ACL_FAILURE but no error is raised.
454 * The target directory whose ACL we wish to replace or create.
457 * The ACL to set as default on @c path.
460 * - @c ACL_SUCCESS - The default ACL was assigned successfully.
461 * - @c ACL_FAILURE - If @c path is not a directory.
462 * - @c ACL_ERROR - Unexpected library error.
464 int assign_default_acl(const char* path
, acl_t acl
) {
471 if (!is_path_directory(path
)) {
475 /* Our return value; success unless something bad happens. */
476 int result
= ACL_SUCCESS
;
477 acl_t path_acl
= acl_dup(acl
);
479 if (path_acl
== (acl_t
)NULL
) {
480 perror("assign_default_acl (acl_dup)");
481 return ACL_ERROR
; /* Nothing to clean up in this case. */
484 if (acl_set_file(path
, ACL_TYPE_DEFAULT
, path_acl
) == ACL_ERROR
) {
485 perror("assign_default_acl (acl_set_file)");
496 * @brief Remove all @c ACL_TYPE_ACCESS entries from the given file
497 * descriptor, leaving the UNIX permission bits.
500 * The file descriptor whose ACLs we want to wipe.
503 * - @c ACL_SUCCESS - The ACLs were wiped successfully, or none
504 * existed in the first place.
505 * - @c ACL_ERROR - Unexpected library error.
507 int wipe_acls(int fd
) {
508 /* Initialize an empty ACL, and then overwrite the one on "fd" with it. */
509 acl_t empty_acl
= acl_init(0);
511 if (empty_acl
== (acl_t
)NULL
) {
512 perror("wipe_acls (acl_init)");
516 if (acl_set_fd(fd
, empty_acl
) == ACL_ERROR
) {
517 perror("wipe_acls (acl_set_fd)");
529 * @brief Apply parent default ACL to a path.
531 * This overwrites any existing ACLs on @c path.
534 * The path whose ACL we would like to reset to its default.
536 * @param no_exec_mask
537 * The value (either true or false) of the --no-exec-mask flag.
540 * - @c ACL_SUCCESS - The parent default ACL was inherited successfully.
541 * - @c ACL_FAILURE - The target path is not a regular file/directory,
542 * or the parent of @c path is not a directory.
543 * - @c ACL_ERROR - Unexpected library error.
545 int apply_default_acl(const char* path
, bool no_exec_mask
) {
549 perror("apply_default_acl (args)");
553 /* Define these next three variables here because we may have to
554 * jump to the cleanup routine which expects them to exist.
557 /* Our return value. */
558 int result
= ACL_SUCCESS
;
560 /* The default ACL on path's parent directory */
561 acl_t defacl
= (acl_t
)NULL
;
563 /* The file descriptor corresponding to "path" */
566 /* Split "path" into base/dirname parts to be used with openat().
567 * We duplicate the strings involved because dirname/basename mangle
570 char* path_copy
= strdup(path
);
571 if (path_copy
== NULL
) {
572 perror("apply_default_acl (strdup)");
575 char* parent
= dirname(path_copy
);
577 fd
= open(path
, O_NOFOLLOW
);
579 if (errno
== ELOOP
) {
580 result
= ACL_FAILURE
; /* hit a symlink */
584 perror("apply_default_acl (open fd)");
591 /* Refuse to operate on hard links, which can be abused by an
592 * attacker to trick us into changing the ACL on a file we didn't
593 * intend to; namely the "target" of the hard link. There is TOCTOU
594 * race condition here, but the window is as small as possible
595 * between when we open the file descriptor (look above) and when we
599 if (fstat(fd
, &s
) == -1) {
600 perror("apply_default_acl (fstat)");
603 if (!S_ISDIR(s
.st_mode
)) {
604 /* If it's not a directory, make sure it's a regular,
605 non-hard-linked file. */
606 if (!S_ISREG(s
.st_mode
) || s
.st_nlink
!= 1) {
607 result
= ACL_FAILURE
;
613 /* Default to not masking the exec bit; i.e. applying the default
614 ACL literally. If --no-exec-mask was not specified, then we try
615 to "guess" whether or not to mask the exec bit. This behavior
616 is modeled after the capital 'X' perms of setfacl. */
617 bool allow_exec
= true;
620 /* Never mask the execute bit on directories. */
621 int ace_result
= any_can_execute(fd
) || S_ISDIR(s
.st_mode
);
623 if (ace_result
== ACL_ERROR
) {
624 perror("apply_default_acl (any_can_execute)");
629 allow_exec
= (bool)ace_result
;
632 defacl
= acl_get_file(parent
, ACL_TYPE_DEFAULT
);
634 if (defacl
== (acl_t
)NULL
) {
635 perror("apply_default_acl (acl_get_file)");
640 if (wipe_acls(fd
) == ACL_ERROR
) {
641 perror("apply_default_acl (wipe_acls)");
646 /* Do this after wipe_acls(), otherwise we'll overwrite the wiped
647 ACL with this one. */
648 acl_t acl
= acl_get_fd(fd
);
649 if (acl
== (acl_t
)NULL
) {
650 perror("apply_default_acl (acl_get_fd)");
655 /* If it's a directory, inherit the parent's default. */
656 if (assign_default_acl(path
, defacl
) == ACL_ERROR
) {
657 perror("apply_default_acl (assign_default_acl)");
663 int ge_result
= acl_get_entry(defacl
, ACL_FIRST_ENTRY
, &entry
);
665 while (ge_result
== ACL_SUCCESS
) {
666 acl_tag_t tag
= ACL_UNDEFINED_TAG
;
668 if (acl_get_tag_type(entry
, &tag
) == ACL_ERROR
) {
669 perror("apply_default_acl (acl_get_tag_type)");
675 /* We've got an entry/tag from the default ACL. Get its permset. */
676 acl_permset_t permset
;
677 if (acl_get_permset(entry
, &permset
) == ACL_ERROR
) {
678 perror("apply_default_acl (acl_get_permset)");
683 /* If this is a default mask, fix it up. */
684 if (tag
== ACL_MASK
||
685 tag
== ACL_USER_OBJ
||
686 tag
== ACL_GROUP_OBJ
||
690 /* The mask doesn't affect acl_user_obj, acl_group_obj (in
691 minimal ACLs) or acl_other entries, so if execute should be
692 masked, we have to do it manually. */
693 if (acl_delete_perm(permset
, ACL_EXECUTE
) == ACL_ERROR
) {
694 perror("apply_default_acl (acl_delete_perm)");
699 if (acl_set_permset(entry
, permset
) == ACL_ERROR
) {
700 perror("apply_default_acl (acl_set_permset)");
707 /* Finally, add the permset to the access ACL. It's actually
708 * important that we pass in the address of "acl" here, and not
709 * "acl" itself. Why? The call to acl_create_entry() within
710 * acl_set_entry() can allocate new memory for the entry.
711 * Sometimes that can be done in-place, in which case everything
712 * is cool and the new memory gets released when we call
715 * But occasionally, the whole ACL structure will have to be moved
716 * in order to allocate the extra space. When that happens,
717 * acl_create_entry() modifies the pointer it was passed (in this
718 * case, &acl) to point to the new location. We want to call
719 * acl_free() on the new location, and since acl_free() gets
720 * called right here, we need acl_create_entry() to update the
721 * value of "acl". To do that, it needs the address of "acl".
723 if (acl_set_entry(&acl
, entry
) == ACL_ERROR
) {
724 perror("apply_default_acl (acl_set_entry)");
729 ge_result
= acl_get_entry(defacl
, ACL_NEXT_ENTRY
, &entry
);
732 /* Catches the first acl_get_entry as well as the ones at the end of
734 if (ge_result
== ACL_ERROR
) {
735 perror("apply_default_acl (acl_get_entry)");
740 if (acl_set_fd(fd
, acl
) == ACL_ERROR
) {
741 perror("apply_default_acl (acl_set_fd)");
748 if (defacl
!= (acl_t
)NULL
) {
751 if (fd
>= 0 && close(fd
) == -1) {
752 perror("apply_default_acl (close)");
761 * @brief Display program usage information.
763 * @param program_name
764 * The program name to use in the output.
767 void usage(const char* program_name
) {
768 printf("Apply any applicable default ACLs to the given files or "
770 printf("Usage: %s [flags] <target1> [<target2> [ <target3>...]]\n\n",
773 printf(" -h, --help Print this help message\n");
774 printf(" -r, --recursive Act on any given directories recursively\n");
775 printf(" -x, --no-exec-mask Apply execute permissions unconditionally\n");
782 * @brief Wrapper around @c apply_default_acl() for use with @c nftw().
784 * For parameter information, see the @c nftw man page.
786 * @return If the ACL was applied to @c target successfully, we return
787 * @c FTW_CONTINUE to signal to @ nftw() that we should proceed onto
788 * the next file or directory. Otherwise, we return @c FTW_STOP to
792 int apply_default_acl_nftw(const char *target
,
793 const struct stat
*s
,
797 if (apply_default_acl(target
, false)) {
808 * @brief Wrapper around @c apply_default_acl() for use with @c nftw().
810 * This is identical to @c apply_default_acl_nftw(), except it passes
811 * @c true to @c apply_default_acl() as its no_exec_mask argument.
814 int apply_default_acl_nftw_x(const char *target
,
815 const struct stat
*s
,
819 if (apply_default_acl(target
, true)) {
830 * @brief Recursive version of @c apply_default_acl().
832 * If @c target is a directory, we use @c nftw() to call @c
833 * apply_default_acl() recursively on all of its children. Otherwise,
834 * we just delegate to @c apply_default_acl().
836 * We ignore symlinks for consistency with chmod -r.
839 * The root (path) of the recursive application.
841 * @param no_exec_mask
842 * The value (either true or false) of the --no-exec-mask flag.
845 * If @c target is not a directory, we return the result of
846 * calling @c apply_default_acl() on @c target. Otherwise, we convert
847 * the return value of @c nftw(). If @c nftw() succeeds (returns 0),
848 * then we return @c true. Otherwise, we return @c false.
850 * If there is an error, it will be reported via @c perror, but
851 * we still return @c false.
853 bool apply_default_acl_recursive(const char *target
, bool no_exec_mask
) {
855 if (!is_path_directory(target
)) {
856 return apply_default_acl(target
, no_exec_mask
);
859 int max_levels
= 256;
860 int flags
= FTW_PHYS
; /* Don't follow links. */
862 /* There are two separate functions that could be passed to
863 nftw(). One passes no_exec_mask = true to apply_default_acl(),
864 and the other passes no_exec_mask = false. Since the function we
865 pass to nftw() cannot have parameters, we have to create separate
866 options and make the decision here. */
867 int (*fn
)(const char *, const struct stat
*, int, struct FTW
*) = NULL
;
868 fn
= no_exec_mask
? apply_default_acl_nftw_x
: apply_default_acl_nftw
;
870 int nftw_result
= nftw(target
, fn
, max_levels
, flags
);
872 if (nftw_result
== 0) {
877 /* nftw will return -1 on error, or if the supplied function
878 * (apply_default_acl_nftw) returns a non-zero result, nftw will
881 if (nftw_result
== -1) {
882 perror("apply_default_acl_recursive (nftw)");
891 * @brief Call apply_default_acl (possibly recursively) on each
892 * command-line argument.
894 * @return Either @c EXIT_FAILURE or @c EXIT_SUCCESS. If everything
895 * goes as expected, we return @c EXIT_SUCCESS. Otherwise, we return
898 int main(int argc
, char* argv
[]) {
905 bool recursive
= false;
906 bool no_exec_mask
= false;
908 struct option long_options
[] = {
909 /* These options set a flag. */
910 {"help", no_argument
, NULL
, 'h'},
911 {"recursive", no_argument
, NULL
, 'r'},
912 {"no-exec-mask", no_argument
, NULL
, 'x'},
918 while ((opt
= getopt_long(argc
, argv
, "hrx", long_options
, NULL
)) != -1) {
935 int result
= EXIT_SUCCESS
;
938 for (arg_index
= optind
; arg_index
< argc
; arg_index
++) {
939 const char* target
= argv
[arg_index
];
940 bool reapp_result
= false;
942 /* Make sure we can access the given path before we go out of our
943 * way to please it. Doing this check outside of
944 * apply_default_acl() lets us spit out a better error message for
947 if (!path_accessible(target
)) {
948 fprintf(stderr
, "%s: %s: No such file or directory\n", argv
[0], target
);
949 result
= EXIT_FAILURE
;
954 reapp_result
= apply_default_acl_recursive(target
, no_exec_mask
);
957 /* It's either a normal file, or we're not operating recursively. */
958 reapp_result
= apply_default_acl(target
, no_exec_mask
);
962 result
= EXIT_FAILURE
;