On Wed, May 31, 2023 at 09:36:22AM +1000, David Gwynne wrote:
> we could export these csum flags as part of the bpf header so we can
> teach tcpdump to shut up in this situation.
Linux does not do that and I want to keep pcap file format compatible.
Also smart tools make debugging real checksum problems harder. I
think people have to live with checksum warning when tcpdump is
called with -v.
> > The question is, does it break corner cases? Please test with pf
> > route-to, IPsec, bridging, IPv6 and other setups where loopback
> > might be involved.
>
> who knows how bridge works? otherwise i think it should be ok.
> hopefully.
No reply from any testers. I think the only way to figure out is
to commit an watch for fallout.
ok?
bluhm
> > Index: net/if.c
> > ===================================================================
> > RCS file: /data/mirror/openbsd/cvs/src/sys/net/if.c,v
> > retrieving revision 1.697
> > diff -u -p -r1.697 if.c
> > --- net/if.c 16 May 2023 14:32:54 -0000 1.697
> > +++ net/if.c 30 May 2023 12:33:42 -0000
> > @@ -778,7 +778,7 @@ if_input(struct ifnet *ifp, struct mbuf_
> > int
> > if_input_local(struct ifnet *ifp, struct mbuf *m, sa_family_t af)
> > {
> > - int keepflags;
> > + int keepflags, keepcksum;
> >
> > #if NBPFILTER > 0
> > /*
> > @@ -796,11 +796,26 @@ if_input_local(struct ifnet *ifp, struct
> > }
> > #endif
> > keepflags = m->m_flags & (M_BCAST|M_MCAST);
> > + /*
> > + * Preserve outgoing checksum flags, in case the packet is
> > + * forwarded to another interface. Then the checksum, which
> > + * is now incorrect, will be calculated before sending.
> > + */
> > + keepcksum = m->m_pkthdr.csum_flags & (M_IPV4_CSUM_OUT |
> > + M_TCP_CSUM_OUT | M_UDP_CSUM_OUT | M_ICMP_CSUM_OUT);
> > m_resethdr(m);
> > m->m_flags |= M_LOOP | keepflags;
> > + m->m_pkthdr.csum_flags = keepcksum;
> > m->m_pkthdr.ph_ifidx = ifp->if_index;
> > m->m_pkthdr.ph_rtableid = ifp->if_rdomain;
> >
> > + if (ISSET(keepcksum, M_TCP_CSUM_OUT))
> > + m->m_pkthdr.csum_flags |= M_TCP_CSUM_IN_OK;
> > + if (ISSET(keepcksum, M_UDP_CSUM_OUT))
> > + m->m_pkthdr.csum_flags |= M_UDP_CSUM_IN_OK;
> > + if (ISSET(keepcksum, M_ICMP_CSUM_OUT))
> > + m->m_pkthdr.csum_flags |= M_ICMP_CSUM_IN_OK;
> > +
> > ifp->if_opackets++;
> > ifp->if_obytes += m->m_pkthdr.len;
> >
> > @@ -809,6 +824,8 @@ if_input_local(struct ifnet *ifp, struct
> >
> > switch (af) {
> > case AF_INET:
> > + if (ISSET(keepcksum, M_IPV4_CSUM_OUT))
> > + m->m_pkthdr.csum_flags |= M_IPV4_CSUM_IN_OK;
> > ipv4_input(ifp, m);
> > break;
> > #ifdef INET6
> > Index: net/if_loop.c
> > ===================================================================
> > RCS file: /data/mirror/openbsd/cvs/src/sys/net/if_loop.c,v
> > retrieving revision 1.93
> > diff -u -p -r1.93 if_loop.c
> > --- net/if_loop.c 21 Oct 2022 14:20:03 -0000 1.93
> > +++ net/if_loop.c 30 May 2023 11:48:55 -0000
> > @@ -173,6 +173,9 @@ loop_clone_create(struct if_clone *ifc,
> > ifp->if_mtu = LOMTU;
> > ifp->if_flags = IFF_LOOPBACK | IFF_MULTICAST;
> > ifp->if_xflags = IFXF_CLONED;
> > + ifp->if_capabilities = IFCAP_CSUM_IPv4 |
> > + IFCAP_CSUM_TCPv4 | IFCAP_CSUM_UDPv4 |
> > + IFCAP_CSUM_TCPv6 | IFCAP_CSUM_UDPv6;
> > ifp->if_rtrequest = lortrequest;
> > ifp->if_ioctl = loioctl;
> > ifp->if_input = loinput;
> >
