Do not dump corrupted packets on loopback bpf.

lo(4) used to dump to bpf only for output.  It seems that when
if_bpf_mtap() was introduced, this changed and lo(4) dumps an
additional truncated packet.  The default bpf_mtap_ether() is not
suitable for lo(4).

Install a dummy lo_bpf_mtap() to suppress bpf on input.

OK mvs@

diff --git a/sys/net/if_loop.c b/sys/net/if_loop.c
index 7610ac6..1c771d1 100644 (file)
--- a/sys/net/if_loop.c
+++ b/sys/net/if_loop.c
@@ -1,4 +1,4 @@
-/*     $OpenBSD: if_loop.c,v 1.96 2023/07/18 16:01:20 bluhm Exp $      */
+/*     $OpenBSD: if_loop.c,v 1.97 2023/07/21 22:24:41 bluhm Exp $      */
 /*     $NetBSD: if_loop.c,v 1.15 1996/05/07 02:40:33 thorpej Exp $     */
 
 /*
@@ -146,6 +146,7 @@ void        lortrequest(struct ifnet *, int, struct rtentry *);
 void   loinput(struct ifnet *, struct mbuf *);
 int    looutput(struct ifnet *,
            struct mbuf *, struct sockaddr *, struct rtentry *);
+int    lo_bpf_mtap(caddr_t, const struct mbuf *, u_int);
 
 int    loop_clone_create(struct if_clone *, int);
 int    loop_clone_destroy(struct ifnet *);
@@ -177,6 +178,7 @@ loop_clone_create(struct if_clone *ifc, int unit)
            IFCAP_CSUM_TCPv4 | IFCAP_CSUM_UDPv4 |
            IFCAP_CSUM_TCPv6 | IFCAP_CSUM_UDPv6 |
            IFCAP_LRO | IFCAP_TSOv4 | IFCAP_TSOv6;
+       ifp->if_bpf_mtap = lo_bpf_mtap;
        ifp->if_rtrequest = lortrequest;
        ifp->if_ioctl = loioctl;
        ifp->if_input = loinput;
@@ -231,6 +233,13 @@ loop_clone_destroy(struct ifnet *ifp)
        return (0);
 }
 
+int
+lo_bpf_mtap(caddr_t if_bpf, const struct mbuf *m, u_int dir)
+{
+       /* loopback dumps on output, disable input bpf */
+       return (0);
+}
+
 void
 loinput(struct ifnet *ifp, struct mbuf *m)
 {