Solar Designer found a race condition in do_add_counters(). The beginning of
paddc is supposed to be the same as tmp which was sanity-checked above, but it
might not be the same in reality. In case the integer overflow and/or the race
condition are triggered, paddc->num_counters might not match the allocation size
for paddc. If the check below (t->private->number != paddc->num_counters)
nevertheless passes (perhaps this requires the race condition to be triggered),
IPT_ENTRY_ITERATE() would read kernel memory beyond the allocation size,
potentially leaking sensitive data (e.g., passwords from host system or from
another VPS) via counter increments.