UPSTREAM: netfilter: xt_sctp: validate the flag_info count

commit e99476497687ef9e850748fe6d232264f30bc8f9 upstream.

sctp_mt_check doesn't validate the flag_count field. An attacker can
take advantage of that to trigger a OOB read and leak memory
information.

Add the field validation in the checkentry function.

Bug: 304913898
Fixes: 2e4e6a17 ("[NETFILTER] x_tables: Abstraction layer for {ip,ip6,arp}_tables")
Cc: stable@vger.kernel.org
Reported-by: Lucas Leong <wmliang@infosec.exchange>
Signed-off-by: Wander Lairson Costa <wander@redhat.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit 4921f9349b66da7c5a2b6418fe45e9ae0ae72924)
Signed-off-by: Lee Jones <joneslee@google.com>
Change-Id: Ife4e69f6218fdaca2a8647b5ed00d875a5ed0d34