sctp: sctp_addr_id2transport should verify the addr before looking up assoc

sctp_addr_id2transport is a function for sockopt to look up assoc by
address. As the address is from userspace, it can be a v4-mapped v6
address. But in sctp protocol stack, it always handles a v4-mapped
v6 address as a v4 address. So it's necessary to convert it to a v4
address before looking up assoc by address.

This patch is to fix it by calling sctp_verify_addr in which it can do
this conversion before calling sctp_endpoint_lookup_assoc, just like
what sctp_sendmsg and __sctp_connect do for the address from users.
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sctp/socket.c

@@ -235,8 +235,12 @@ static struct sctp_transport *sctp_addr_id2transport(struct sock *sk,
 					      sctp_assoc_t id)
 {
 	struct sctp_association *addr_asoc = NULL, *id_asoc = NULL;
-	struct sctp_transport *transport;
+	struct sctp_af *af = sctp_get_af_specific(addr->ss_family);
 	union sctp_addr *laddr = (union sctp_addr *)addr;
+	struct sctp_transport *transport;
+
+	if (sctp_verify_addr(sk, laddr, af->sockaddr_len))
+		return NULL;
 
 	addr_asoc = sctp_endpoint_lookup_assoc(sctp_sk(sk)->ep,
 					       laddr,