SCTP: Discard OOTB packetes with bundled INIT early.

RFC 4460 and future RFC 4960 (2960-bis) specify that packets
with bundled INIT chunks need to be dropped.  We currenlty do
that only after processing any leading chunks.  For OOTB chunks,
since we already walk the entire packet, we should discard packets
with bundled INITs.

There are other chunks chunks that MUST NOT be bundled, but the spec
is silent on theire treatment.  Thus, we'll leave their teatment
alone for the moment.
Signed-off-by: Vlad Yasevich <vladislav.yasevich@hp.com>
Acked-by: Wei Yongjun <yjwei@cn.fujitsu.com>

net/sctp/input.c

@@ -622,6 +622,14 @@ static int sctp_rcv_ootb(struct sk_buff *skb)
 		if (SCTP_CID_SHUTDOWN_COMPLETE == ch->type)
 			goto discard;
 
+		/* RFC 4460, 2.11.2
+		 * This will discard packets with INIT chunk bundled as
+		 * subsequent chunks in the packet.  When INIT is first,
+		 * the normal INIT processing will discard the chunk.
+		 */
+		if (SCTP_CID_INIT == ch->type && (void *)ch != skb->data)
+			goto discard;
+
 		/* RFC 8.4, 7) If the packet contains a "Stale cookie" ERROR
 		 * or a COOKIE ACK the SCTP Packet should be silently
 		 * discarded.