--- sys/netgraph/ng_iface.c.orig	2017-02-15 13:05:35.564006000 +0700
+++ sys/netgraph/ng_iface.c	2017-06-17 04:41:46.200314000 +0700
@@ -112,9 +112,15 @@ struct ng_iface_private {
 	int	unit;			/* Interface unit number */
 	node_p	node;			/* Our netgraph node */
 	hook_p	hooks[NUM_FAMILIES];	/* Hook for each address family */
+	struct rwlock	lock;		/* Protect private data changes */
 };
 typedef struct ng_iface_private *priv_p;
 
+#define	PRIV_RLOCK(priv)	rw_rlock(&priv->lock)
+#define	PRIV_RUNLOCK(priv)	rw_runlock(&priv->lock)
+#define	PRIV_WLOCK(priv)	rw_wlock(&priv->lock)
+#define	PRIV_WUNLOCK(priv)	rw_wunlock(&priv->lock)
+
 /* Interface methods */
 static void	ng_iface_start(struct ifnet *ifp);
 static int	ng_iface_ioctl(struct ifnet *ifp, u_long cmd, caddr_t data);
@@ -448,7 +454,9 @@ ng_iface_send(struct ifnet *ifp, struct 
 
 	/* Send packet. If hook is not connected, mbuf will get freed. */
 	NG_OUTBOUND_THREAD_REF();
+	PRIV_RLOCK(priv);
 	NG_SEND_DATA_ONLY(error, *get_hook_from_iffam(priv, iffam), m);
+	PRIV_RUNLOCK(priv);
 	NG_OUTBOUND_THREAD_UNREF();
 
 	/* Update stats. */
@@ -516,6 +524,8 @@ ng_iface_constructor(node_p node)
 		return (ENOMEM);
 	}
 
+	rw_init(&priv->lock, "ng_iface private mutex");
+
 	/* Link them together */
 	ifp->if_softc = priv;
 	priv->ifp = ifp;
@@ -562,16 +572,19 @@ static int
 ng_iface_newhook(node_p node, hook_p hook, const char *name)
 {
 	const iffam_p iffam = get_iffam_from_name(name);
+	const priv_p priv = NG_NODE_PRIVATE(node);
 	hook_p *hookptr;
 
 	if (iffam == NULL)
 		return (EPFNOSUPPORT);
-	hookptr = get_hook_from_iffam(NG_NODE_PRIVATE(node), iffam);
+	PRIV_WLOCK(priv);
+	hookptr = get_hook_from_iffam(priv, iffam);
 	if (*hookptr != NULL)
 		return (EISCONN);
 	*hookptr = hook;
 	NG_HOOK_HI_STACK(hook);
 	NG_HOOK_SET_TO_INBOUND(hook);
+	PRIV_WUNLOCK(priv);
 	return (0);
 }
 
@@ -730,6 +743,7 @@ ng_iface_shutdown(node_p node)
 	CURVNET_RESTORE();
 	priv->ifp = NULL;
 	free_unr(V_ng_iface_unit, priv->unit);
+	rw_destroy(&priv->lock);
 	free(priv, M_NETGRAPH_IFACE);
 	NG_NODE_SET_PRIVATE(node, NULL);
 	NG_NODE_UNREF(node);
@@ -748,7 +762,9 @@ ng_iface_disconnect(hook_p hook)
 
 	if (iffam == NULL)
 		panic("%s", __func__);
+	PRIV_WLOCK(priv);
 	*get_hook_from_iffam(priv, iffam) = NULL;
+	PRIV_WUNLOCK(priv);
 	return (0);
 }