sctp: fix an array overflow when all ext chunks are set

Marcelo noticed an array overflow caused by commit c28445c3
("sctp: add reconf_enable in asoc ep and netns"), in which sctp
would add SCTP_CID_RECONF into extensions when reconf_enable is
set in sctp_make_init and sctp_make_init_ack.

Then now when all ext chunks are set, 4 ext chunk ids can be put
into extensions array while extensions array size is 3. It would
cause a kernel panic because of this overflow.

This patch is to fix it by defining extensions array size is 4 in
both sctp_make_init and sctp_make_init_ack.

Fixes: c28445c3 ("sctp: add reconf_enable in asoc ep and netns")
Signed-off-by: NXin Long <lucien.xin@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/sctp/sm_make_chunk.c

@@ -228,7 +228,7 @@ struct sctp_chunk *sctp_make_init(const struct sctp_association *asoc,
 	sctp_adaptation_ind_param_t aiparam;
 	sctp_supported_ext_param_t ext_param;
 	int num_ext = 0;
-	__u8 extensions[3];
+	__u8 extensions[4];
 	struct sctp_paramhdr *auth_chunks = NULL,
 			*auth_hmacs = NULL;
 
@@ -396,7 +396,7 @@ struct sctp_chunk *sctp_make_init_ack(const struct sctp_association *asoc,
 	sctp_adaptation_ind_param_t aiparam;
 	sctp_supported_ext_param_t ext_param;
 	int num_ext = 0;
-	__u8 extensions[3];
+	__u8 extensions[4];
 	struct sctp_paramhdr *auth_chunks = NULL,
 			*auth_hmacs = NULL,
 			*auth_random = NULL;