Verify that the username length is smaller than MAXLOGNAME when

asked to verify a passwd file (pwd_mkdb -C).

Entries with oversized usernames are still permitted when building
the passwd database.

When entries are >= MAXLOGNAME in length, they are correctly stored
in passwd, pwd.db and spwd.db but are only correctly retrieved by
getpwent*() and getpwuid*().  getpwnam*() truncates to MAXLOGNAME - 1
when reading from a file (breaking at least sh, tcsh and bash)
and utilities such as su(1) check, complain and fail if the
passed name is >= MAXLOGNAME in length.

MFC after:	3 weeks

usr.sbin/pwd_mkdb/pwd_mkdb.c

@@ -204,7 +204,11 @@ main(int argc, char *argv[])
 
 	/* check only if password database is valid */
 	if (Cflag) {
-		for (cnt = 1; scan(fp, &pwd); ++cnt);
+		while (scan(fp, &pwd))
+			if (!is_comment && strlen(pwd.pw_name) >= MAXLOGNAME) {
+				warnx("%s: username too long", pwd.pw_name);
+				exit(1);
+			}
 		exit(0);
 	}