-
-/**
- * @brief Determine whether or not the given path is a directory.
- *
- * @param path
- * The path to test.
- *
- * @return true if @c path is a directory, false otherwise.
- */
-bool is_path_directory(const char* path) {
- if (path == NULL) {
- return false;
- }
-
- struct stat s;
- int result = lstat(path, &s);
- if (result == 0) {
- return S_ISDIR(s.st_mode);
- }
- else {
- return false;
- }
-}
-
-
-
-/**
- * @brief Update (or create) an entry in an @b minimal ACL.
- *
- * This function will not work if @c aclp contains extended
- * entries. This is fine for our purposes, since we call @c wipe_acls
- * on each path before applying the default to it.
- *
- * The assumption that there are no extended entries makes things much
- * simpler. For example, we only have to update the @c ACL_USER_OBJ,
- * @c ACL_GROUP_OBJ, and @c ACL_OTHER entries -- all others can simply
- * be created anew. This means we don't have to fool around comparing
- * named-user/group entries.
- *
- * @param aclp
- * A pointer to the acl_t structure whose entry we want to modify.
- *
- * @param entry
- * The new entry. If @c entry contains a user/group/other entry, we
- * update the existing one. Otherwise we create a new entry.
- *
- * @return If there is an unexpected library error, @c ACL_ERROR is
- * returned. Otherwise, @c ACL_SUCCESS.
- *
- */
-int acl_set_entry(acl_t* aclp,
- acl_entry_t entry) {
-
- acl_tag_t entry_tag;
- int gt_result = acl_get_tag_type(entry, &entry_tag);
- if (gt_result == ACL_ERROR) {
- perror("acl_set_entry (acl_get_tag_type)");
- return ACL_ERROR;
- }
-
- acl_permset_t entry_permset;
- int ps_result = acl_get_permset(entry, &entry_permset);
- if (ps_result == ACL_ERROR) {
- perror("acl_set_entry (acl_get_permset)");
- return ACL_ERROR;
- }
-
- acl_entry_t existing_entry;
- /* Loop through the given ACL looking for matching entries. */
- int result = acl_get_entry(*aclp, ACL_FIRST_ENTRY, &existing_entry);
-
- while (result == ACL_SUCCESS) {
- acl_tag_t existing_tag = ACL_UNDEFINED_TAG;
- int tag_result = acl_get_tag_type(existing_entry, &existing_tag);
-
- if (tag_result == ACL_ERROR) {
- perror("set_acl_tag_permset (acl_get_tag_type)");
- return ACL_ERROR;
- }
-
- if (existing_tag == entry_tag) {
- if (entry_tag == ACL_USER_OBJ ||
- entry_tag == ACL_GROUP_OBJ ||
- entry_tag == ACL_OTHER) {
- /* Only update for these three since all other tags will have
- been wiped. These three are guaranteed to exist, so if we
- match one of them, we're allowed to return ACL_SUCCESS
- below and bypass the rest of the function. */
- acl_permset_t existing_permset;
- int gep_result = acl_get_permset(existing_entry, &existing_permset);
- if (gep_result == ACL_ERROR) {
- perror("acl_set_entry (acl_get_permset)");
- return ACL_ERROR;
- }
-
- int s_result = acl_set_permset(existing_entry, entry_permset);
- if (s_result == ACL_ERROR) {
- perror("acl_set_entry (acl_set_permset)");
- return ACL_ERROR;
- }
-
- return ACL_SUCCESS;
- }
-
- }
-
- result = acl_get_entry(*aclp, ACL_NEXT_ENTRY, &existing_entry);
- }
-
- /* This catches both the initial acl_get_entry and the ones at the
- end of the loop. */
- if (result == ACL_ERROR) {
- perror("acl_set_entry (acl_get_entry)");
- return ACL_ERROR;
- }
-
- /* If we've made it this far, we need to add a new entry to the
- ACL. */
- acl_entry_t new_entry;
-
- /* The acl_create_entry() function can allocate new memory and/or
- * change the location of the ACL structure entirely. When that
- * happens, the value pointed to by aclp is updated, which means
- * that a new acl_t gets "passed out" to our caller, eventually to
- * be fed to acl_free(). In other words, we should still be freeing
- * the right thing, even if the value pointed to by aclp changes.
- */
- int c_result = acl_create_entry(aclp, &new_entry);
- if (c_result == ACL_ERROR) {
- perror("acl_set_entry (acl_create_entry)");
- return ACL_ERROR;
- }
-
- int st_result = acl_set_tag_type(new_entry, entry_tag);
- if (st_result == ACL_ERROR) {
- perror("acl_set_entry (acl_set_tag_type)");
- return ACL_ERROR;
- }
-
- int s_result = acl_set_permset(new_entry, entry_permset);
- if (s_result == ACL_ERROR) {
- perror("acl_set_entry (acl_set_permset)");
- return ACL_ERROR;
- }
-
- if (entry_tag == ACL_USER || entry_tag == ACL_GROUP) {
- /* We need to set the qualifier too. */
- void* entry_qual = acl_get_qualifier(entry);
- if (entry_qual == (void*)NULL) {
- perror("acl_set_entry (acl_get_qualifier)");
- return ACL_ERROR;
- }
-
- int sq_result = acl_set_qualifier(new_entry, entry_qual);
- if (sq_result == ACL_ERROR) {
- perror("acl_set_entry (acl_set_qualifier)");
- return ACL_ERROR;
- }
- }
-
- return ACL_SUCCESS;
-}
-
-
-
-/**
- * @brief Determine the number of entries in the given ACL.
- *
- * @param acl
- * The ACL to inspect.
- *
- * @return Either the non-negative number of entries in @c acl, or
- * @c ACL_ERROR on error.
- */
-int acl_entry_count(acl_t acl) {
-
- acl_entry_t entry;
- int entry_count = 0;
- int result = acl_get_entry(acl, ACL_FIRST_ENTRY, &entry);
-
- while (result == ACL_SUCCESS) {
- entry_count++;
- result = acl_get_entry(acl, ACL_NEXT_ENTRY, &entry);
- }
-
- if (result == ACL_ERROR) {
- perror("acl_entry_count (acl_get_entry)");
- return ACL_ERROR;
- }
-
- return entry_count;
-}
-
-
-
-/**
- * @brief Determine whether or not the given ACL is minimal.
- *
- * An ACL is minimal if it has fewer than four entries.
- *
- * @param acl
- * The ACL whose minimality is in question.
- *
- * @return
- * - @c ACL_SUCCESS - @c acl is minimal
- * - @c ACL_FAILURE - @c acl is not minimal
- * - @c ACL_ERROR - Unexpected library error
- */
-int acl_is_minimal(acl_t acl) {
-
- int ec = acl_entry_count(acl);
-
- if (ec == ACL_ERROR) {
- perror("acl_is_minimal (acl_entry_count)");
- return ACL_ERROR;
- }
-
- if (ec < 4) {
- return ACL_SUCCESS;
- }
- else {
- return ACL_FAILURE;
- }
-}
-
-
-
-/**
- * @brief Determine whether the given ACL's mask denies execute.
- *
- * @param acl
- * The ACL whose mask we want to check.
- *
- * @return
- * - @c ACL_SUCCESS - The @c acl has a mask which denies execute.
- * - @c ACL_FAILURE - The @c acl has a mask which does not deny execute.
- * - @c ACL_ERROR - Unexpected library error.
- */
-int acl_execute_masked(acl_t acl) {
-
- acl_entry_t entry;
- int ge_result = acl_get_entry(acl, ACL_FIRST_ENTRY, &entry);
-
- while (ge_result == ACL_SUCCESS) {
- acl_tag_t tag = ACL_UNDEFINED_TAG;
- int tag_result = acl_get_tag_type(entry, &tag);
-
- if (tag_result == ACL_ERROR) {
- perror("acl_execute_masked (acl_get_tag_type)");
- return ACL_ERROR;
- }
-
- if (tag == ACL_MASK) {
- /* This is the mask entry, get its permissions, and see if
- execute is specified. */
- acl_permset_t permset;
-
- int ps_result = acl_get_permset(entry, &permset);
- if (ps_result == ACL_ERROR) {
- perror("acl_execute_masked (acl_get_permset)");
- return ACL_ERROR;
- }
-
- int gp_result = acl_get_perm(permset, ACL_EXECUTE);
- if (gp_result == ACL_ERROR) {
- perror("acl_execute_masked (acl_get_perm)");
- return ACL_ERROR;
- }
-
- if (gp_result == ACL_FAILURE) {
- /* No execute bit set in the mask; execute not allowed. */
- return ACL_SUCCESS;
- }
- }
-
- ge_result = acl_get_entry(acl, ACL_NEXT_ENTRY, &entry);
- }
-
- return ACL_FAILURE;
-}
-
-
-
-/**
- * @brief Determine whether @c path is executable (by anyone) or a
- * directory.
- *
- * This is used as part of the heuristic to determine whether or not
- * we should mask the execute bit when inheriting an ACL. If @c path
- * is a directory, the answer is a clear-cut yes. This behavior is
- * modeled after the capital 'X' perms of setfacl.
- *
- * If @c path is a file, we check the @a effective permissions,
- * contrary to what setfacl does.
- *
- * @param path
- * The path to check.
- *
- * @return
- * - @c ACL_SUCCESS - @c path is a directory, or someone has effective
- execute permissions.
- * - @c ACL_FAILURE - @c path is a regular file and nobody can execute
- it.
- * - @c ACL_ERROR - Unexpected library error.
- */
-int any_can_execute_or_dir(const char* path) {
-
- if (is_path_directory(path)) {
- /* That was easy... */
- return ACL_SUCCESS;
- }
-
- acl_t acl = acl_get_file(path, ACL_TYPE_ACCESS);
-
- if (acl == (acl_t)NULL) {
- perror("any_can_execute_or_dir (acl_get_file)");
- return ACL_ERROR;
- }
-
- /* Our return value. */
- int result = ACL_FAILURE;
-
- if (acl_is_minimal(acl)) {
- mode_t mode = get_mode(path);
- if (mode & (S_IXUSR | S_IXOTH | S_IXGRP)) {
- result = ACL_SUCCESS;
- goto cleanup;
- }
- else {
- result = ACL_FAILURE;
- goto cleanup;
- }
- }
-
- acl_entry_t entry;
- int ge_result = acl_get_entry(acl, ACL_FIRST_ENTRY, &entry);
-
- while (ge_result == ACL_SUCCESS) {
- /* The first thing we do is check to see if this is a mask
- entry. If it is, we skip it entirely. */
- acl_tag_t tag = ACL_UNDEFINED_TAG;
- int tag_result = acl_get_tag_type(entry, &tag);
-
- if (tag_result == ACL_ERROR) {
- perror("any_can_execute_or_dir (acl_get_tag_type)");
- result = ACL_ERROR;
- goto cleanup;
- }
-
- if (tag == ACL_MASK) {
- ge_result = acl_get_entry(acl, ACL_NEXT_ENTRY, &entry);
- continue;
- }
-
- /* Ok, so it's not a mask entry. Check the execute perms. */
- acl_permset_t permset;
-
- int ps_result = acl_get_permset(entry, &permset);
- if (ps_result == ACL_ERROR) {
- perror("any_can_execute_or_dir (acl_get_permset)");
- result = ACL_ERROR;
- goto cleanup;
- }
-
- int gp_result = acl_get_perm(permset, ACL_EXECUTE);
- if (gp_result == ACL_ERROR) {
- perror("any_can_execute_or_dir (acl_get_perm)");
- result = ACL_ERROR;
- goto cleanup;
- }
-
- if (gp_result == ACL_SUCCESS) {
- /* Only return ACL_SUCCESS if this execute bit is not masked. */
- if (acl_execute_masked(acl) != ACL_SUCCESS) {
- result = ACL_SUCCESS;
- goto cleanup;
- }
- }
-
- ge_result = acl_get_entry(acl, ACL_NEXT_ENTRY, &entry);
- }
-
- if (ge_result == ACL_ERROR) {
- perror("any_can_execute_or_dir (acl_get_entry)");
- result = ACL_ERROR;
- goto cleanup;
- }
-
- cleanup:
- acl_free(acl);
- return result;
-}
-
-
-
-/**
- * @brief Set @c acl as the default ACL on @c path if it's a directory.
- *
- * This overwrites any existing default ACL on @c path. If no default
- * ACL exists, then one is created. If @c path is not a directory, we
- * return ACL_FAILURE but no error is raised.
- *
- * @param path
- * The target directory whose ACL we wish to replace or create.
- *
- * @param acl
- * The ACL to set as default on @c path.
- *
- * @return
- * - @c ACL_SUCCESS - The default ACL was assigned successfully.
- * - @c ACL_FAILURE - If @c path is not a directory.
- * - @c ACL_ERROR - Unexpected library error.
- */
-int assign_default_acl(const char* path, acl_t acl) {
-
- if (path == NULL) {
- errno = ENOENT;
- return ACL_ERROR;
- }
-
- if (!is_path_directory(path)) {
- return ACL_FAILURE;
- }
-
- /* Our return value; success unless something bad happens. */
- int result = ACL_SUCCESS;
- acl_t path_acl = acl_dup(acl);
-
- if (path_acl == (acl_t)NULL) {
- perror("inherit_default_acl (acl_dup)");
- return ACL_ERROR; /* Nothing to clean up in this case. */
- }
-
- int sf_result = acl_set_file(path, ACL_TYPE_DEFAULT, path_acl);
- if (sf_result == -1) {
- perror("inherit_default_acl (acl_set_file)");
- result = ACL_ERROR;
- }
-
- acl_free(path_acl);
- return result;
-}
-
-
-
-/**
- * @brief Remove @c ACL_USER, @c ACL_GROUP, and @c ACL_MASK entries
- * from the given path.
- *
- * @param path
- * The path whose ACLs we want to wipe.
- *
- * @return
- * - @c ACL_SUCCESS - The ACLs were wiped successfully, or none
- * existed in the first place.
- * - @c ACL_ERROR - Unexpected library error.
- */
-int wipe_acls(const char* path) {
-
- if (path == NULL) {
- errno = ENOENT;
- return ACL_ERROR;
- }
-
- acl_t acl = acl_get_file(path, ACL_TYPE_ACCESS);
- if (acl == (acl_t)NULL) {
- perror("wipe_acls (acl_get_file)");
- return ACL_ERROR;
- }
-
- /* Our return value. */
- int result = ACL_SUCCESS;
-
- acl_entry_t entry;
- int ge_result = acl_get_entry(acl, ACL_FIRST_ENTRY, &entry);
-
- while (ge_result == ACL_SUCCESS) {
- int d_result = acl_delete_entry(acl, entry);
- if (d_result == ACL_ERROR) {
- perror("wipe_acls (acl_delete_entry)");
- result = ACL_ERROR;
- goto cleanup;
- }
-
- ge_result = acl_get_entry(acl, ACL_NEXT_ENTRY, &entry);
- }
-
- /* Catches the first acl_get_entry as well as the ones at the end of
- the loop. */
- if (ge_result == ACL_ERROR) {
- perror("wipe_acls (acl_get_entry)");
- result = ACL_ERROR;
- goto cleanup;
- }
-
- int sf_result = acl_set_file(path, ACL_TYPE_ACCESS, acl);
- if (sf_result == ACL_ERROR) {
- perror("wipe_acls (acl_set_file)");
- result = ACL_ERROR;
- goto cleanup;
- }
-
- cleanup:
- acl_free(acl);
- return result;
-}
-
-
-
-/**
- * @brief Apply parent default ACL to a path.
- *
- * This overwrites any existing ACLs on @c path.
- *
- * @param path
- * The path whose ACL we would like to reset to its default.
- *
- * @param no_exec_mask
- * The value (either true or false) of the --no-exec-mask flag.
- *
- * @return
- * - @c ACL_SUCCESS - The parent default ACL was inherited successfully.
- * - @c ACL_FAILURE - The target path is not a regular file/directory,
- * or the parent of @c path is not a directory.
- * - @c ACL_ERROR - Unexpected library error.
- */
-int apply_default_acl(const char* path, bool no_exec_mask) {
-
- if (path == NULL) {
- errno = ENOENT;
- return ACL_ERROR;
- }
-
- /* Refuse to operate on hard links, which can be abused by an
- * attacker to trick us into changing the ACL on a file we didn't
- * intend to; namely the "target" of the hard link. To truly prevent
- * that sort of mischief, we should be using file descriptors for
- * the target and its parent directory. Then modulo a tiny race
- * condition, we would be sure that "path" and "parent" don't change
- * their nature between the time that we test them and when we
- * utilize them. For contrast, the same attacker is free to replace
- * "path" with a hard link after is_hardlink_safe() has returned
- * "true" below.
- *
- * Unfortunately, our API is lacking in this area. For example,
- * acl_set_fd() is only capable of setting the ACL_TYPE_ACCESS list,
- * and not the ACL_TYPE_DEFAULT. Apparently the only way to operate
- * on default ACLs is through the path name, which is inherently
- * unreliable since the acl_*_file() calls themselves might follow
- * links (both hard and symbolic).
- *
- * Some improvement could still be made by using descriptors where
- * possible -- this would shrink the exploit window -- but for now
- * we use a naive implementation that only keeps honest men honest.
- */
- if (!is_hardlink_safe(path)) {
- return ACL_FAILURE;
- }
-
- if (!is_regular_file(path) && !is_path_directory(path)) {
- return ACL_FAILURE;
- }
-
- /* dirname mangles its argument */
- char path_copy[PATH_MAX];
- strncpy(path_copy, path, PATH_MAX-1);
- path_copy[PATH_MAX-1] = 0;
-
- char* parent = dirname(path_copy);
- if (!is_path_directory(parent)) {
- /* Make sure dirname() did what we think it did. */
- return ACL_FAILURE;
- }
-
- /* Default to not masking the exec bit; i.e. applying the default
- ACL literally. If --no-exec-mask was not specified, then we try
- to "guess" whether or not to mask the exec bit. */
- bool allow_exec = true;
-
- if (!no_exec_mask) {
- int ace_result = any_can_execute_or_dir(path);
-
- if (ace_result == ACL_ERROR) {
- perror("apply_default_acl (any_can_execute_or_dir)");
- return ACL_ERROR;
- }
-
- allow_exec = (bool)ace_result;
- }
-
- acl_t defacl = acl_get_file(parent, ACL_TYPE_DEFAULT);
-
- if (defacl == (acl_t)NULL) {
- perror("apply_default_acl (acl_get_file)");
- return ACL_ERROR;
- }
-
- /* Our return value. */
- int result = ACL_SUCCESS;
-
- int wipe_result = wipe_acls(path);
- if (wipe_result == ACL_ERROR) {
- perror("apply_default_acl (wipe_acls)");
- result = ACL_ERROR;
- goto cleanup;
- }
-
- /* Do this after wipe_acls(), otherwise we'll overwrite the wiped
- ACL with this one. */
- acl_t acl = acl_get_file(path, ACL_TYPE_ACCESS);
- if (acl == (acl_t)NULL) {
- perror("apply_default_acl (acl_get_file)");
- result = ACL_ERROR;
- goto cleanup;
- }
-
- /* If it's a directory, inherit the parent's default. */
- int inherit_result = assign_default_acl(path, defacl);
- if (inherit_result == ACL_ERROR) {
- perror("apply_default_acl (inherit_acls)");
- result = ACL_ERROR;
- goto cleanup;
- }
-
- acl_entry_t entry;
- int ge_result = acl_get_entry(defacl, ACL_FIRST_ENTRY, &entry);
-
- while (ge_result == ACL_SUCCESS) {
- acl_tag_t tag = ACL_UNDEFINED_TAG;
- int tag_result = acl_get_tag_type(entry, &tag);
-
- if (tag_result == ACL_ERROR) {
- perror("apply_default_acl (acl_get_tag_type)");
- result = ACL_ERROR;
- goto cleanup;
- }
-
-
- /* We've got an entry/tag from the default ACL. Get its permset. */
- acl_permset_t permset;
- int ps_result = acl_get_permset(entry, &permset);
- if (ps_result == ACL_ERROR) {
- perror("apply_default_acl (acl_get_permset)");
- result = ACL_ERROR;
- goto cleanup;
- }
-
- /* If this is a default mask, fix it up. */
- if (tag == ACL_MASK ||
- tag == ACL_USER_OBJ ||
- tag == ACL_GROUP_OBJ ||
- tag == ACL_OTHER) {
-
- if (!allow_exec) {
- /* The mask doesn't affect acl_user_obj, acl_group_obj (in
- minimal ACLs) or acl_other entries, so if execute should be
- masked, we have to do it manually. */
- int d_result = acl_delete_perm(permset, ACL_EXECUTE);
- if (d_result == ACL_ERROR) {
- perror("apply_default_acl (acl_delete_perm)");
- result = ACL_ERROR;
- goto cleanup;
- }
-
- int sp_result = acl_set_permset(entry, permset);
- if (sp_result == ACL_ERROR) {
- perror("apply_default_acl (acl_set_permset)");
- result = ACL_ERROR;
- goto cleanup;
- }
- }
- }
-
- /* Finally, add the permset to the access ACL. It's actually
- * important that we pass in the address of "acl" here, and not
- * "acl" itself. Why? The call to acl_create_entry() within
- * acl_set_entry() can allocate new memory for the entry.
- * Sometimes that can be done in-place, in which case everything
- * is cool and the new memory gets released when we call
- * acl_free(acl).
- *
- * But occasionally, the whole ACL structure will have to be moved
- * in order to allocate the extra space. When that happens,
- * acl_create_entry() modifies the pointer it was passed (in this
- * case, &acl) to point to the new location. We want to call
- * acl_free() on the new location, and since acl_free() gets
- * called right here, we need acl_create_entry() to update the
- * value of "acl". To do that, it needs the address of "acl".
- */
- int set_result = acl_set_entry(&acl, entry);
- if (set_result == ACL_ERROR) {
- perror("apply_default_acl (acl_set_entry)");
- result = ACL_ERROR;
- goto cleanup;
- }
-
- ge_result = acl_get_entry(defacl, ACL_NEXT_ENTRY, &entry);
- }
-
- /* Catches the first acl_get_entry as well as the ones at the end of
- the loop. */
- if (ge_result == ACL_ERROR) {
- perror("apply_default_acl (acl_get_entry)");
- result = ACL_ERROR;
- goto cleanup;
- }
-
- int sf_result = acl_set_file(path, ACL_TYPE_ACCESS, acl);
- if (sf_result == ACL_ERROR) {
- perror("apply_default_acl (acl_set_file)");
- result = ACL_ERROR;
- goto cleanup;
- }
-
- cleanup:
- acl_free(defacl);
- return result;
-}
-
-
-