2 files changed, 21 insertions, 0 deletions

diff --git a/sys/netgraph/ng_iface.c b/sys/netgraph/ng_iface.c
index fec243215d35..f40cbe498eeb 100644
--- a/sys/netgraph/ng_iface.c
+++ b/sys/netgraph/ng_iface.c
@@ -353,6 +353,7 @@ static int
 ng_iface_output(struct ifnet *ifp, struct mbuf *m,
 		struct sockaddr *dst, struct rtentry *rt0)
 {
+	struct m_tag *mtag;
 	uint32_t af;
 	int error;
 
@@ -363,6 +364,23 @@ ng_iface_output(struct ifnet *ifp, struct mbuf *m,
 		return (ENETDOWN);
 	}
 
+	/* Protect from deadly infinite recursion. */
+	while ((mtag = m_tag_locate(m, MTAG_NGIF, MTAG_NGIF_CALLED, NULL))) {
+		if (*(struct ifnet **)(mtag + 1) == ifp) {
+			log(LOG_NOTICE, "Loop detected on %s\n", ifp->if_xname);
+			m_freem(m);
+			return (EDEADLK);
+		}
+	}
+	mtag = m_tag_alloc(MTAG_NGIF, MTAG_NGIF_CALLED, sizeof(struct ifnet *),
+	    M_NOWAIT);
+	if (mtag == NULL) {
+		m_freem(m);
+		return (ENOMEM);
+	}
+	*(struct ifnet **)(mtag + 1) = ifp;
+	m_tag_prepend(m, mtag);
+
 	/* BPF writes need to be handled specially. */
 	if (dst->sa_family == AF_UNSPEC) {
 		bcopy(dst->sa_data, &af, sizeof(af));
diff --git a/sys/netgraph/ng_iface.h b/sys/netgraph/ng_iface.h
index 54dfa8c78690..58fb44230582 100644
--- a/sys/netgraph/ng_iface.h
+++ b/sys/netgraph/ng_iface.h
@@ -72,4 +72,7 @@ enum {
 	NGM_IFACE_GET_IFINDEX,
 };
 
+#define	MTAG_NGIF			NGM_IFACE_COOKIE
+#define	MTAG_NGIF_CALLED		0 | MTAG_PERSISTENT
+
 #endif /* _NETGRAPH_NG_IFACE_H_ */