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: 7814b6ec ("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>
Git-repo: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Git-commit: 57ebd808a97d7c5b1e1afb937c2db22beba3c1f8
[srkupp@codeaurora.org: Resolved minor conflict]
Signed-off-by: Srinivasa Rao Kuppala <srkupp@codeaurora.org>
Change-Id: I417d9164f95aae0d4ca2164a26d5d2fb7ec1ab10