[SCTP]: Add bind hash locking to the migrate code

SCTP accept code tries to add a newliy created socket
to a bind bucket without holding a lock. On a really
busy system, that can causes slab corruptions.
Add a lock around this code.

Signed-off-by: Vlad Yasevich <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/sctp/socket.c

···
 	struct sctp_endpoint *newep = newsp->ep;
 	struct sk_buff *skb, *tmp;
 	struct sctp_ulpevent *event;
+	struct sctp_bind_hashbucket *head;
 	int flags = 0;
 
 	/* Migrate socket buffer sizes and all the socket level options to the
···
 	newsp->hmac = NULL;
 
 	/* Hook this new socket in to the bind_hash list. */
+	head = &sctp_port_hashtable[sctp_phashfn(inet_sk(oldsk)->num)];
+	sctp_local_bh_disable();
+	sctp_spin_lock(&head->lock);
 	pp = sctp_sk(oldsk)->bind_hash;
 	sk_add_bind_node(newsk, &pp->owner);
 	sctp_sk(newsk)->bind_hash = pp;
 	inet_sk(newsk)->num = inet_sk(oldsk)->num;
+	sctp_spin_unlock(&head->lock);
+	sctp_local_bh_enable();
 
 	/* Copy the bind_addr list from the original endpoint to the new
 	 * endpoint so that we can handle restarts properly