#define _GNU_SOURCE
#include <errno.h>
+#include <fcntl.h> /* AT_FOO constants */
#include <ftw.h> /* nftw() et al. */
#include <getopt.h>
#include <libgen.h> /* dirname() */
}
struct stat s;
- int result = stat(path, &s);
+ int result = lstat(path, &s);
if (result == 0) {
return s.st_mode;
}
else {
- /* errno will be set already by stat() */
+ /* errno will be set already by lstat() */
return result;
}
}
+/**
+ * @brief Determine if the given path might refer to an (unsafe) hard link.
+ *
+ * @param path
+ * The path to test.
+ *
+ * @return true if we are certain that @c path does not refer to 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.
+ */
+bool is_hardlink_safe(const char* path) {
+ if (path == NULL) {
+ return false;
+ }
+ struct stat s;
+ int result = lstat(path, &s);
+ if (result == 0) {
+ return (s.st_nlink == 1 || S_ISDIR(s.st_mode));
+ }
+ else {
+ return false;
+ }
+}
+
+
/**
* @brief Determine whether or not the given path is a regular file.
*
}
struct stat s;
- int result = stat(path, &s);
+ int result = lstat(path, &s);
if (result == 0) {
return S_ISREG(s.st_mode);
}
+/**
+ * @brief Determine whether or not the given path is accessible.
+ *
+ * @param path
+ * The path to test.
+ *
+ * @return true if @c path is accessible to the current effective
+ * user/group, false otherwise.
+ */
+bool path_accessible(const char* path) {
+ if (path == NULL) {
+ return false;
+ }
+
+ /* Test for access using the effective user and group rather than
+ the real one. */
+ int flags = AT_EACCESS;
+
+ /* Don't follow symlinks when checking for a path's existence,
+ since we won't follow them to set its ACLs either. */
+ flags |= AT_SYMLINK_NOFOLLOW;
+
+ /* If the path is relative, interpret it relative to the current
+ working directory (just like the access() system call). */
+ int result = faccessat(AT_FDCWD, path, F_OK, flags);
+
+ if (result == 0) {
+ return true;
+ }
+ else {
+ return false;
+ }
+}
+
+
+
/**
* @brief Determine whether or not the given path is a directory.
*
}
struct stat s;
- int result = stat(path, &s);
+ int result = lstat(path, &s);
if (result == 0) {
return S_ISDIR(s.st_mode);
}
}
+
/**
* @brief Determine whether @c path is executable (by anyone) or a
* directory.
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 (gp_result == ACL_SUCCESS) {
- /* Only return one if this execute bit is not masked. */
+ /* Only return ACL_SUCCESS if this execute bit is not masked. */
if (acl_execute_masked(path) != ACL_SUCCESS) {
result = ACL_SUCCESS;
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;
+ }
+
if (!is_regular_file(path) && !is_directory(path)) {
return ACL_FAILURE;
}
* The program name to use in the output.
*
*/
-void usage(char* program_name) {
+void usage(const char* program_name) {
printf("Apply any applicable default ACLs to the given files or "
"directories.\n\n");
printf("Usage: %s [flags] <target1> [<target2> [ <target3>...]]\n\n",
const char* target = argv[arg_index];
bool reapp_result = false;
+ /* Make sure we can access the given path before we go out of our
+ * way to please it. Doing this check outside of
+ * apply_default_acl() lets us spit out a better error message for
+ * typos, too.
+ */
+ if (!path_accessible(target)) {
+ fprintf(stderr, "%s: %s: No such file or directory\n", argv[0], target);
+ result = EXIT_FAILURE;
+ continue;
+ }
+
if (recursive) {
reapp_result = apply_default_acl_recursive(target, no_exec_mask);
}
else {
- /* It's either normal file, or we're not operating recursively. */
+ /* It's either a normal file, or we're not operating recursively. */
reapp_result = apply_default_acl(target, no_exec_mask);
}
projects / apply-default-acl.git / blobdiff