[AF_IUCV]: Add lock when updating accept_q

The accept_queue of an af_iucv socket will be corrupted, if
adding and deleting of entries in this queue occurs at the
same time (connect request from one client, while accept call
is processed for another client).
Solution: add locking when updating accept_q

Signed-off-by: Ursula Braun <[e-mail]>
Acked-by: Frank Pavlic <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/net/iucv/af_iucv.h

···
 	char			dst_user_id[8];
 	char			dst_name[8];
 	struct list_head	accept_q;
+	spinlock_t		accept_q_lock;
 	struct sock		*parent;
 	struct iucv_path	*path;
 	struct sk_buff_head	send_skb_q;

net/iucv/af_iucv.c

···
 
 	sock_init_data(sock, sk);
 	INIT_LIST_HEAD(&iucv_sk(sk)->accept_q);
+	spin_lock_init(&iucv_sk(sk)->accept_q_lock);
 	skb_queue_head_init(&iucv_sk(sk)->send_skb_q);
 	skb_queue_head_init(&iucv_sk(sk)->backlog_skb_q);
 	iucv_sk(sk)->send_tag = 0;
···
 
 void iucv_accept_enqueue(struct sock *parent, struct sock *sk)
 {
+	unsigned long flags;
+	struct iucv_sock *par = iucv_sk(parent);
+
 	sock_hold(sk);
-	list_add_tail(&iucv_sk(sk)->accept_q, &iucv_sk(parent)->accept_q);
+	spin_lock_irqsave(&par->accept_q_lock, flags);
+	list_add_tail(&iucv_sk(sk)->accept_q, &par->accept_q);
+	spin_unlock_irqrestore(&par->accept_q_lock, flags);
 	iucv_sk(sk)->parent = parent;
 	parent->sk_ack_backlog++;
 }
 
 void iucv_accept_unlink(struct sock *sk)
 {
+	unsigned long flags;
+	struct iucv_sock *par = iucv_sk(iucv_sk(sk)->parent);
+
+	spin_lock_irqsave(&par->accept_q_lock, flags);
 	list_del_init(&iucv_sk(sk)->accept_q);
+	spin_unlock_irqrestore(&par->accept_q_lock, flags);
 	iucv_sk(sk)->parent->sk_ack_backlog--;
 	iucv_sk(sk)->parent = NULL;
 	sock_put(sk);
···
 		lock_sock(sk);
 
 		if (sk->sk_state == IUCV_CLOSED) {
-			release_sock(sk);
 			iucv_accept_unlink(sk);
+			release_sock(sk);
 			continue;
 		}
 
···
 	/* Find out if this path belongs to af_iucv. */
 	read_lock(&iucv_sk_list.lock);
 	iucv = NULL;
+	sk = NULL;
 	sk_for_each(sk, node, &iucv_sk_list.head)
 		if (sk->sk_state == IUCV_LISTEN &&
 		    !memcmp(&iucv_sk(sk)->src_name, src_name, 8)) {