kern/53562: bridge(4) breaks segmentation / TX checksum offloading

[rokuyama%rk.phys.keio.ac.jp@localhost]

>Number:         53562
>Category:       kern
>Synopsis:       bridge(4) breaks segmentation / TX checksum offloading
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Thu Aug 30 09:25:00 +0000 2018
>Originator:     Rin Okuyama
>Release:        8.99.24
>Organization:
School of Science and Technology, Meiji University
>Environment:
NetBSD rpi3b 8.99.24 NetBSD 8.99.24 (RPI3-64) #24: Thu Aug 30 17:39:24 JST 2018  rin@latipes:/var/build/src/sys/arch/evbarm/compile/RPI3-64 evbarm aarch64
>Description:
If a network interface is added to bridge(4), segmentation or TX
checksum offloading do not work. This is because csum_flags are
cleared in bridge_enqueue():

https://nxr.netbsd.org/xref/src/sys/net/if_bridge.c#1401

  1391  void
  1392  bridge_enqueue(struct bridge_softc *sc, struct ifnet *dst_ifp, struct mbuf *m,
  1393      int runfilt)
  1394  {
  ....
  1398          /*
  1399           * Clear any in-bound checksum flags for this packet.
  1400           */
  1401          m->m_pkthdr.csum_flags = 0;
>How-To-Repeat:
Enable segmentation or TX checksum offloading for a network interface,
and add it to bridge(4). Then, data transmission starts to fail.
>Fix:
Not known.