Index: net/if.c
===================================================================
RCS file: /cvs/src/sys/net/if.c,v
retrieving revision 1.363
diff -u -p -r1.363 if.c
--- net/if.c	1 Sep 2015 04:56:55 -0000	1.363
+++ net/if.c	9 Sep 2015 15:37:13 -0000
@@ -80,6 +80,7 @@
 #include <sys/domain.h>
 #include <sys/sysctl.h>
 #include <sys/task.h>
+#include <sys/atomic.h>
 
 #include <dev/rndvar.h>
 
@@ -260,7 +261,8 @@ if_attachsetup(struct ifnet *ifp)
 
 	if_addgroup(ifp, IFG_ALL);
 
-	ifindex2ifnet[if_index] = ifp;
+	ifp->if_refcnt = 0;
+	ifindex2ifnet[if_index] = if_ref(ifp);
 
 	if (ifp->if_snd.ifq_maxlen == 0)
 		IFQ_SET_MAXLEN(&ifp->if_snd, IFQ_MAXLEN);
@@ -664,6 +666,7 @@ if_detach(struct ifnet *ifp)
 	rt_ifannouncemsg(ifp, IFAN_DEPARTURE);
 
 	ifindex2ifnet[ifp->if_index] = NULL;
+	if_put(ifp);
 	splx(s);
 }
 
@@ -1231,7 +1234,24 @@ if_get(unsigned int index)
 	if (index < if_indexlim)
 		ifp = ifindex2ifnet[index];
 
+	return (if_ref(ifp));
+}
+
+struct ifnet *
+if_ref(struct ifnet *ifp)
+{
+	atomic_inc_int(&ifp->if_refcnt);
+
 	return (ifp);
+}
+
+void
+if_put(struct ifnet *ifp)
+{
+	if (ifp == NULL)
+		return;
+
+	atomic_dec_int(&ifp->if_refcnt);
 }
 
 /*
Index: net/if.h
===================================================================
RCS file: /cvs/src/sys/net/if.h,v
retrieving revision 1.165
diff -u -p -r1.165 if.h
--- net/if.h	30 Aug 2015 10:39:16 -0000	1.165
+++ net/if.h	9 Sep 2015 15:37:13 -0000
@@ -462,6 +462,8 @@ int	if_delgroup(struct ifnet *, const ch
 void	if_group_routechange(struct sockaddr *, struct sockaddr *);
 struct	ifnet *ifunit(const char *);
 struct	ifnet *if_get(unsigned int);
+struct	ifnet *if_ref(struct ifnet *);
+void	if_put(struct ifnet *);
 void	ifnewlladdr(struct ifnet *);
 void	if_congestion(void);
 int	if_congested(void);
Index: net/if_var.h
===================================================================
RCS file: /cvs/src/sys/net/if_var.h,v
retrieving revision 1.34
diff -u -p -r1.34 if_var.h
--- net/if_var.h	2 Jul 2015 09:40:02 -0000	1.34
+++ net/if_var.h	9 Sep 2015 15:37:14 -0000
@@ -127,6 +127,7 @@ TAILQ_HEAD(ifnet_head, ifnet);		/* the a
 
 struct ifnet {				/* and the entries */
 	void	*if_softc;		/* lower-level data for this if */
+	unsigned int if_refcnt;
 	TAILQ_ENTRY(ifnet) if_list;	/* all struct ifnets are chained */
 	TAILQ_ENTRY(ifnet) if_txlist;	/* list of ifnets ready to tx */
 	TAILQ_HEAD(, ifaddr) if_addrlist; /* linked list of addresses per if */