Index: sys/netinet/ip_reass.c
===================================================================
--- sys/netinet/ip_reass.c
+++ sys/netinet/ip_reass.c
@@ -225,8 +225,19 @@
 		m->m_flags |= M_IP_FRAG;
 	} else
 		m->m_flags &= ~M_IP_FRAG;
+
 	ip->ip_off = htons(ntohs(ip->ip_off) << 3);
 
+	/*
+	 * Make sure the fragment lies within a packet of valid size.
+	 */
+	if (ntohs(ip->ip_len) + ntohs(ip->ip_off) > IP_MAXPACKET) {
+		IPSTAT_INC(ips_toolong);
+		IPSTAT_INC(ips_fragdropped);
+		m_freem(m);
+		return (NULL);
+	}
+
 	/*
 	 * Attempt reassembly; if it succeeds, proceed.
 	 * ip_reass() will return a different mbuf.