#include "alloc-util.h"
#include "fd-util.h"
#include "fileio.h"
-#include "formats-util.h"
+#include "format-util.h"
#include "macro.h"
#include "missing.h"
#include "parse-util.h"
bool uid_is_valid(uid_t uid) {
+ /* Also see POSIX IEEE Std 1003.1-2008, 2016 Edition, 3.436. */
+
/* Some libc APIs use UID_INVALID as special placeholder */
if (uid == (uid_t) UINT32_C(0xFFFFFFFF))
return false;
const char *i;
long sz;
- /* Checks if the specified name is a valid user/group name. */
+ /* Checks if the specified name is a valid user/group name. Also see POSIX IEEE Std 1003.1-2008, 2016 Edition,
+ * 3.437. We are a bit stricter here however. Specifically we deviate from POSIX rules:
+ *
+ * - We don't allow any dots (this would break chown syntax which permits dots as user/group name separator)
+ * - We require that names fit into the appropriate utmp field
+ * - We don't allow empty user names
+ *
+ * Note that other systems are even more restrictive, and don't permit underscores or uppercase characters.
+ */
if (isempty(u))
return false;