Code: static void sctp_sock_migrate(struct sock *oldsk, struct sock *newsk,
			      struct sctp_association *assoc,
			      sctp_socket_type_t type)
{
	struct sctp_sock *oldsp = sctp_sk(oldsk);
	struct sctp_sock *newsp = sctp_sk(newsk);
	struct sctp_bind_bucket *pp; /* hash list port iterator */
	struct sctp_endpoint *newep = newsp->ep;
 	struct sk_buff *skb, *tmp;
 	struct sctp_ulpevent *event;
 	struct sctp_bind_hashbucket *head;
	struct list_head tmplist;
 
 	/* Migrate socket buffer sizes and all the socket level options to the
 	 * new socket.
 	 */
 	newsk->sk_sndbuf = oldsk->sk_sndbuf;
 	newsk->sk_rcvbuf = oldsk->sk_rcvbuf;
 	/* Brute force copy old sctp opt. */
	if (oldsp->do_auto_asconf) {
		memcpy(&tmplist, &newsp->auto_asconf_list, sizeof(tmplist));
		inet_sk_copy_descendant(newsk, oldsk);
		memcpy(&newsp->auto_asconf_list, &tmplist, sizeof(tmplist));
	} else
		inet_sk_copy_descendant(newsk, oldsk);
 
 	/* Restore the ep value that was overwritten with the above structure
 	 * copy.
	 */
	newsp->ep = newep;
	newsp->hmac = NULL;

	/* Hook this new socket in to the bind_hash list. */
	head = &sctp_port_hashtable[sctp_phashfn(sock_net(oldsk),
						 inet_sk(oldsk)->inet_num)];
	local_bh_disable();
	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)->inet_num = inet_sk(oldsk)->inet_num;
	spin_unlock(&head->lock);
	local_bh_enable();

	/* Copy the bind_addr list from the original endpoint to the new
	 * endpoint so that we can handle restarts properly
	 */
	sctp_bind_addr_dup(&newsp->ep->base.bind_addr,
				&oldsp->ep->base.bind_addr, GFP_KERNEL);

	/* Move any messages in the old socket's receive queue that are for the
	 * peeled off association to the new socket's receive queue.
	 */
	sctp_skb_for_each(skb, &oldsk->sk_receive_queue, tmp) {
		event = sctp_skb2event(skb);
		if (event->asoc == assoc) {
			__skb_unlink(skb, &oldsk->sk_receive_queue);
			__skb_queue_tail(&newsk->sk_receive_queue, skb);
			sctp_skb_set_owner_r_frag(skb, newsk);
		}
	}

	/* Clean up any messages pending delivery due to partial
	 * delivery.   Three cases:
	 * 1) No partial deliver;  no work.
	 * 2) Peeling off partial delivery; keep pd_lobby in new pd_lobby.
	 * 3) Peeling off non-partial delivery; move pd_lobby to receive_queue.
	 */
	skb_queue_head_init(&newsp->pd_lobby);
	atomic_set(&sctp_sk(newsk)->pd_mode, assoc->ulpq.pd_mode);

	if (atomic_read(&sctp_sk(oldsk)->pd_mode)) {
		struct sk_buff_head *queue;

		/* Decide which queue to move pd_lobby skbs to. */
		if (assoc->ulpq.pd_mode) {
			queue = &newsp->pd_lobby;
		} else
			queue = &newsk->sk_receive_queue;

		/* Walk through the pd_lobby, looking for skbs that
		 * need moved to the new socket.
		 */
		sctp_skb_for_each(skb, &oldsp->pd_lobby, tmp) {
			event = sctp_skb2event(skb);
			if (event->asoc == assoc) {
				__skb_unlink(skb, &oldsp->pd_lobby);
				__skb_queue_tail(queue, skb);
				sctp_skb_set_owner_r_frag(skb, newsk);
			}
		}

		/* Clear up any skbs waiting for the partial
		 * delivery to finish.
		 */
		if (assoc->ulpq.pd_mode)
			sctp_clear_pd(oldsk, NULL);

	}

	sctp_skb_for_each(skb, &assoc->ulpq.reasm, tmp)
		sctp_skb_set_owner_r_frag(skb, newsk);

	sctp_skb_for_each(skb, &assoc->ulpq.lobby, tmp)
		sctp_skb_set_owner_r_frag(skb, newsk);

	/* Set the type of socket to indicate that it is peeled off from the
	 * original UDP-style socket or created with the accept() call on a
	 * TCP-style socket..
	 */
	newsp->type = type;

	/* Mark the new socket "in-use" by the user so that any packets
	 * that may arrive on the association after we've moved it are
	 * queued to the backlog.  This prevents a potential race between
	 * backlog processing on the old socket and new-packet processing
	 * on the new socket.
	 *
	 * The caller has just allocated newsk so we can guarantee that other
	 * paths won't try to lock it and then oldsk.
	 */
	lock_sock_nested(newsk, SINGLE_DEPTH_NESTING);
	sctp_assoc_migrate(assoc, newsk);

	/* If the association on the newsk is already closed before accept()
	 * is called, set RCV_SHUTDOWN flag.
	 */
	if (sctp_state(assoc, CLOSED) && sctp_style(newsk, TCP))
		newsk->sk_shutdown |= RCV_SHUTDOWN;

	newsk->sk_state = SCTP_SS_ESTABLISHED;
	release_sock(newsk);
}

Vulnerability Type: DoS 
CWE ID: CWE-362
Summary: Race condition in net/sctp/socket.c in the Linux kernel before 4.1.2 allows local users to cause a denial of service (list corruption and panic) via a rapid series of system calls related to sockets, as demonstrated by setsockopt calls.
Commit Message: sctp: fix ASCONF list handling

->auto_asconf_splist is per namespace and mangled by functions like
sctp_setsockopt_auto_asconf() which doesn't guarantee any serialization.

Also, the call to inet_sk_copy_descendant() was backuping
->auto_asconf_list through the copy but was not honoring
->do_auto_asconf, which could lead to list corruption if it was
different between both sockets.

This commit thus fixes the list handling by using ->addr_wq_lock
spinlock to protect the list. A special handling is done upon socket
creation and destruction for that. Error handlig on sctp_init_sock()
will never return an error after having initialized asconf, so
sctp_destroy_sock() can be called without addrq_wq_lock. The lock now
will be take on sctp_close_sock(), before locking the socket, so we
don't do it in inverse order compared to sctp_addr_wq_timeout_handler().

Instead of taking the lock on sctp_sock_migrate() for copying and
restoring the list values, it's preferred to avoid rewritting it by
implementing sctp_copy_descendant().

Issue was found with a test application that kept flipping sysctl
default_auto_asconf on and off, but one could trigger it by issuing
simultaneous setsockopt() calls on multiple sockets or by
creating/destroying sockets fast enough. This is only triggerable
locally.

Fixes: 9f7d653b67ae ("sctp: Add Auto-ASCONF support (core).")
Reported-by: Ji Jianwen <jiji@redhat.com>
Suggested-by: Neil Horman <nhorman@tuxdriver.com>
Suggested-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>