netfilter: add back stackpointer size checks

The rationale for removing the check is only correct for rulesets
generated by ip(6)tables.

In iptables, a jump can only occur to a user-defined chain, i.e.
because we size the stack based on number of user-defined chains we
cannot exceed stack size.

However, the underlying binary format has no such restriction,
and the validation step only ensures that the jump target is a
valid rule start point.

IOW, its possible to build a rule blob that has no user-defined
chains but does contain a jump.

If this happens, no jump stack gets allocated and crash occurs
because no jumpstack was allocated.

Fixes: 7814b6ec6d0d6 ("netfilter: xtables: don't save/restore jumpstack offset")
Reported-by: syzbot+e783f671527912cd9403@syzkaller.appspotmail.com
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
compat_do_ipt_set_ctl(struct sock *sk,	int cmd, void __user *user,
		      unsigned int len)
{
	int ret;

	if (!ns_capable(sock_net(sk)->user_ns, CAP_NET_ADMIN))
		return -EPERM;

	switch (cmd) {
	case IPT_SO_SET_REPLACE:
		ret = compat_do_replace(sock_net(sk), user, len);
		break;

	case IPT_SO_SET_ADD_COUNTERS:
		ret = do_add_counters(sock_net(sk), user, len, 1);
		break;

	default:
		ret = -EINVAL;
	}

	return ret;
}

compat_do_ipt_set_ctl(struct sock *sk,	int cmd, void __user *user,
		      unsigned int len)
{
	int ret;

	if (!ns_capable(sock_net(sk)->user_ns, CAP_NET_ADMIN))
		return -EPERM;

	switch (cmd) {
	case IPT_SO_SET_REPLACE:
		ret = compat_do_replace(sock_net(sk), user, len);
		break;

	case IPT_SO_SET_ADD_COUNTERS:
		ret = do_add_counters(sock_net(sk), user, len, 1);
		break;

	default:
		ret = -EINVAL;
	}

	return ret;
}
