#include <fcntl.h> /* AT_FOO constants */
#include <ftw.h> /* nftw() et al. */
#include <getopt.h>
-#include <libgen.h> /* dirname() */
-#include <limits.h> /* PATH_MAX */
+#include <libgen.h> /* basename(), dirname() */
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
/**
- * @brief Get the mode bits from the given path.
+ * @brief Get the mode bits from the given file descriptor.
*
- * @param path
- * The path (file or directory) whose mode we want.
+ * @param fd
+ * The file descriptor (which may reference a directory) whose
+ * mode we want.
*
* @return A mode_t (st_mode) structure containing the mode bits.
* See sys/stat.h for details.
*/
-mode_t get_mode(const char* path) {
- if (path == NULL) {
+mode_t get_mode(int fd) {
+ if (fd <= 0) {
errno = ENOENT;
- return -1;
+ return ACL_ERROR;
}
struct stat s;
- int result = lstat(path, &s);
+ int result = fstat(fd, &s);
if (result == 0) {
return s.st_mode;
/**
- * @brief Determine if the given path might refer to an (unsafe) hard link.
+ * @brief Determine if the given file descriptor might refer to an
+ * (unsafe) hard link.
*
- * @param path
- * The path to test.
+ * @param fd
+ * The file descriptor whose link count we want to investigate.
*
- * @return true if we are certain that @c path does not refer to a hard
+ * @return true if we are certain that @c fd does not describe a hard
* link, and false otherwise. In case of error, false is returned,
- * because we are not sure that @c path is not a hard link.
+ * because we are not sure that @c fd is not a hard link.
*/
-bool is_hardlink_safe(const char* path) {
- if (path == NULL) {
+bool is_hardlink_safe(int fd) {
+ if (fd <= 0) {
return false;
}
struct stat s;
- int result = lstat(path, &s);
+ int result = fstat(fd, &s);
if (result == 0) {
return (s.st_nlink == 1 || S_ISDIR(s.st_mode));
}
/**
- * @brief Determine whether or not the given path is a regular file.
+ * @brief Determine whether or not the given file descriptor is for
+ * a regular file.
*
- * @param path
- * The path to test.
+ * @param fd
+ * The file descriptor to test for regular-fileness.
*
- * @return true if @c path is a regular file, false otherwise.
+ * @return true if @c fd describes a regular file, and false otherwise.
*/
-bool is_regular_file(const char* path) {
- if (path == NULL) {
+bool is_regular_file(int fd) {
+ if (fd <= 0) {
return false;
}
struct stat s;
- int result = lstat(path, &s);
+ int result = fstat(fd, &s);
if (result == 0) {
return S_ISREG(s.st_mode);
}
}
+/**
+ * @brief Determine whether or not the given file descriptor is for
+ * a directory.
+ *
+ * @param fd
+ * The file descriptor whose directoryness is in question.
+ *
+ * @return true if @c fd describes a directory, and false otherwise.
+ */
+bool is_directory(int fd) {
+ if (fd <= 0) {
+ return false;
+ }
+
+ struct stat s;
+ int result = fstat(fd, &s);
+ if (result == 0) {
+ return S_ISDIR(s.st_mode);
+ }
+ else {
+ return false;
+ }
+}
+
+
/**
* @brief Update (or create) an entry in an @b minimal ACL.
/**
- * @brief Determine whether @c path is executable (by anyone) or a
+ * @brief Determine whether @c fd 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.
+ * we should mask the execute bit when inheriting an ACL. If @c fd
+ * describes 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,
+ * If @c fd describes a file, we check the @a effective permissions,
* contrary to what setfacl does.
*
- * @param path
- * The path to check.
+ * @param fd
+ * The file descriptor to check.
*
* @return
- * - @c ACL_SUCCESS - @c path is a directory, or someone has effective
+ * - @c ACL_SUCCESS - @c fd describes a directory, or someone has effective
execute permissions.
- * - @c ACL_FAILURE - @c path is a regular file and nobody can execute
+ * - @c ACL_FAILURE - @c fd describes a regular file and nobody can execute
it.
* - @c ACL_ERROR - Unexpected library error.
*/
-int any_can_execute_or_dir(const char* path) {
+int any_can_execute_or_dir(int fd) {
- if (is_path_directory(path)) {
+ if (is_directory(fd)) {
/* That was easy... */
return ACL_SUCCESS;
}
- acl_t acl = acl_get_file(path, ACL_TYPE_ACCESS);
+ acl_t acl = acl_get_fd(fd);
if (acl == (acl_t)NULL) {
perror("any_can_execute_or_dir (acl_get_file)");
int result = ACL_FAILURE;
if (acl_is_minimal(acl)) {
- mode_t mode = get_mode(path);
+ mode_t mode = get_mode(fd);
if (mode & (S_IXUSR | S_IXOTH | S_IXGRP)) {
result = ACL_SUCCESS;
goto cleanup;
acl_t path_acl = acl_dup(acl);
if (path_acl == (acl_t)NULL) {
- perror("inherit_default_acl (acl_dup)");
+ perror("assign_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)");
+ if (sf_result == ACL_ERROR) {
+ perror("assign_default_acl (acl_set_file)");
result = ACL_ERROR;
}
/**
* @brief Remove @c ACL_USER, @c ACL_GROUP, and @c ACL_MASK entries
- * from the given path.
+ * from the given file descriptor.
*
- * @param path
- * The path whose ACLs we want to wipe.
+ * @param fd
+ * The file descriptor 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) {
+int wipe_acls(int fd) {
- if (path == NULL) {
+ if (fd <= 0) {
errno = ENOENT;
return ACL_ERROR;
}
- acl_t acl = acl_get_file(path, ACL_TYPE_ACCESS);
+ acl_t acl = acl_get_fd(fd);
if (acl == (acl_t)NULL) {
- perror("wipe_acls (acl_get_file)");
+ perror("wipe_acls (acl_get_fd)");
return ACL_ERROR;
}
goto cleanup;
}
- int sf_result = acl_set_file(path, ACL_TYPE_ACCESS, acl);
+ int sf_result = acl_set_fd(fd, acl);
if (sf_result == ACL_ERROR) {
- perror("wipe_acls (acl_set_file)");
+ perror("wipe_acls (acl_set_fd)");
result = ACL_ERROR;
goto cleanup;
}
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;
+ /* Define these next three variables here because we may have to
+ * jump to the cleanup routine which expects them to exist.
+ */
+
+ /* Our return value. */
+ int result = ACL_SUCCESS;
+
+ /* The default ACL on path's parent directory */
+ acl_t defacl = (acl_t)NULL;
+
+ /* The file descriptor corresponding to "path" */
+ int fd = 0;
+
+ /* Split "path" into base/dirname parts to be used with openat().
+ * We duplicate the strings involved because dirname/basename mangle
+ * their arguments.
+ */
+ char* path_copy = strdup(path);
+ if (path_copy == NULL) {
+ perror("apply_default_acl (strdup)");
+ return ACL_ERROR;
}
+ char* parent = dirname(path_copy);
- if (!is_regular_file(path) && !is_path_directory(path)) {
- return ACL_FAILURE;
+ fd = open(path, O_NOFOLLOW);
+ if (fd == -1) {
+ if (errno == ELOOP) {
+ result = ACL_FAILURE; /* hit a symlink */
+ goto cleanup;
+ }
+ else {
+ perror("apply_default_acl (open fd)");
+ result = ACL_ERROR;
+ goto cleanup;
+ }
}
- /* 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;
+ /* 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. There is TOCTOU
+ * race condition here, but the window is as small as possible
+ * between when we open the file descriptor (look above) and when we
+ * fstat it.
+ */
+ if (!is_hardlink_safe(fd)) {
+ result = ACL_FAILURE;
+ goto cleanup;
+ }
+
+ if (!is_regular_file(fd) && !is_directory(fd)) {
+ result = ACL_FAILURE;
+ goto cleanup;
}
/* Default to not masking the exec bit; i.e. applying the default
bool allow_exec = true;
if (!no_exec_mask) {
- int ace_result = any_can_execute_or_dir(path);
+ int ace_result = any_can_execute_or_dir(fd);
if (ace_result == ACL_ERROR) {
perror("apply_default_acl (any_can_execute_or_dir)");
- return ACL_ERROR;
+ result = ACL_ERROR;
+ goto cleanup;
}
allow_exec = (bool)ace_result;
}
- acl_t defacl = acl_get_file(parent, ACL_TYPE_DEFAULT);
+ defacl = acl_get_file(parent, ACL_TYPE_DEFAULT);
if (defacl == (acl_t)NULL) {
perror("apply_default_acl (acl_get_file)");
- return ACL_ERROR;
+ result = ACL_ERROR;
+ goto cleanup;
}
- /* Our return value. */
- int result = ACL_SUCCESS;
-
- int wipe_result = wipe_acls(path);
+ int wipe_result = wipe_acls(fd);
if (wipe_result == ACL_ERROR) {
perror("apply_default_acl (wipe_acls)");
result = ACL_ERROR;
/* 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);
+ acl_t acl = acl_get_fd(fd);
if (acl == (acl_t)NULL) {
- perror("apply_default_acl (acl_get_file)");
+ perror("apply_default_acl (acl_get_fd)");
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)");
+ perror("apply_default_acl (assign_default_acl)");
result = ACL_ERROR;
goto cleanup;
}
goto cleanup;
}
- int sf_result = acl_set_file(path, ACL_TYPE_ACCESS, acl);
+ int sf_result = acl_set_fd(fd, acl);
if (sf_result == ACL_ERROR) {
- perror("apply_default_acl (acl_set_file)");
+ perror("apply_default_acl (acl_set_fd)");
result = ACL_ERROR;
goto cleanup;
}
cleanup:
- acl_free(defacl);
+ free(path_copy);
+ if (defacl != (acl_t)NULL) {
+ acl_free(defacl);
+ }
+ if (fd >= 0 && close(fd) == -1) {
+ perror("apply_default_acl (close)");
+ result = ACL_ERROR;
+ }
return result;
}
projects / apply-default-acl.git / commitdiff