sctp: validate chunk size in __rcv_asconf_lookup

commit b6ffe7671b24689c09faa5675dd58f93758a97ae upstream.

In one of the fallbacks that SCTP has for identifying an association for an
incoming packet, it looks for AddIp chunk (from ASCONF) and take a peek.
Thing is, at this stage nothing was validating that the chunk actually had
enough content for that, allowing the peek to happen over uninitialized
memory.

Similar check already exists in actual asconf handling in
sctp_verify_asconf().

Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Change-Id: Ibfe53fc724143423353ed6b2984d2508ee4fc457
Issue: FP3SEC-257
(cherry picked from commit 6b536186)
(cherry picked from commit fa937471883c64692ba6d36f68e37aef4f46783f)