diff --git a/sys/netpfil/ipfilter/netinet/fil.c b/sys/netpfil/ipfilter/netinet/fil.c
--- a/sys/netpfil/ipfilter/netinet/fil.c
+++ b/sys/netpfil/ipfilter/netinet/fil.c
@@ -9951,3 +9951,37 @@
 	ASSERT(mtab->imt6_max >= 0);
 }
 #endif
+
+/* ------------------------------------------------------------------------ */
+/* Function:    ipf_frname_vfy                                              */
+/* Returns:     char *   - 0    == FRNAME                                   */
+/*                       - NULL ==                                          */
+/*                              fr_ifnames index is < 0                     */
+/*                              fr_name exceeds MAX_IFNAME_LENGTH           */
+/*                              fr_name string exceeds fr_namelen           */
+/* Parameters:  fr(I)    - pointer to filter rule                           */
+/*              i        - index                                            */
+/*                                                                          */
+/* Bounds-check all indices into fr_names. Return a verified FRNAME.        */
+/* ------------------------------------------------------------------------ */
+char *
+ipf_frname_vfy(frentry_t *fr, int i)
+{
+	size_t namelen;
+	char *name;
+
+	/*
+	 * We assume the caller has already ensured fr_namelen is acceptable:
+	 * if (fr->fr_namelen > MAX_IFNAME_LENGTH))
+	 *	then error
+	 */
+
+	if (fr->fr_ifnames[i] < 0)
+		return (NULL);
+	name = FR_NAME(fr, fr_ifnames[i]);
+	if ((namelen = strnlen(name ,LIFNAMSIZ + 1)) > LIFNAMSIZ)
+		return (NULL);
+	if (namelen > fr->fr_namelen)
+		return (NULL);
+	return (name);
+}
diff --git a/sys/netpfil/ipfilter/netinet/ip_fil.h b/sys/netpfil/ipfilter/netinet/ip_fil.h
--- a/sys/netpfil/ipfilter/netinet/ip_fil.h
+++ b/sys/netpfil/ipfilter/netinet/ip_fil.h
@@ -1693,6 +1693,7 @@
 extern	int	ipf_matcharray_load(ipf_main_softc_t *, caddr_t,
 					 ipfobj_t *, int **);
 extern	int	ipf_matcharray_verify(int *, int);
+extern	char	*ipf_frname_vfy(frentry_t *, int);
 extern	int	ipf_outobj(ipf_main_softc_t *, void *, void *, int);
 extern	int	ipf_outobjk(ipf_main_softc_t *, ipfobj_t *, void *);
 extern	int	ipf_outobjsz(ipf_main_softc_t *, void *, void *,