• Willem de Bruijn's avatar
    net: accept UFO datagrams from tuntap and packet · 0c19f846
    Willem de Bruijn authored
    Tuntap and similar devices can inject GSO packets. Accept type
    VIRTIO_NET_HDR_GSO_UDP, even though not generating UFO natively.
    Processes are expected to use feature negotiation such as TUNSETOFFLOAD
    to detect supported offload types and refrain from injecting other
    packets. This process breaks down with live migration: guest kernels
    do not renegotiate flags, so destination hosts need to expose all
    features that the source host does.
    Partially revert the UFO removal from 182e0b6b~1..d9d30adf.
    This patch introduces nearly(*) no new code to simplify verification.
    It brings back verbatim tuntap UFO negotiation, VIRTIO_NET_HDR_GSO_UDP
    insertion and software UFO segmentation.
    It does not reinstate protocol stack support, hardware offload
    (NETIF_F_UFO), SKB_GSO_UDP tunneling in SKB_GSO_SOFTWARE or reception
    of VIRTIO_NET_HDR_GSO_UDP packets in tuntap.
    To support SKB_GSO_UDP reappearing in the stack, also reinstate
    logic in act_csum and openvswitch. Achieve equivalence with v4.13 HEAD
    by squashing in commit 93991221 ("net: skb_needs_check() removes
    CHECKSUM_UNNECESSARY check for tx.") and reverting commit 8d63bee6
    ("net: avoid skb_warn_bad_offload false positives on UFO").
    (*) To avoid having to bring back skb_shinfo(skb)->ip6_frag_id,
    ipv6_proxy_select_ident is changed to return a __be32 and this is
    assigned directly to the frag_hdr. Also, SKB_GSO_UDP is inserted
    at the end of the enum to minimize code churn.
      Booted a v4.13 guest kernel with QEMU. On a host kernel before this
      patch `ethtool -k eth0` shows UFO disabled. After the patch, it is
      enabled, same as on a v4.13 host kernel.
      A UFO packet sent from the guest appears on the tap device:
          nc -l -p -u 8000 &
          tcpdump -n -i tap0
          dd if=/dev/zero of=payload.txt bs=1 count=2000
          nc -u 8000 < payload.txt
      Direct tap to tap transmission of VIRTIO_NET_HDR_GSO_UDP succeeds,
      packets arriving fragmented:
        ./with_tap_pair.sh ./tap_send_ufo tap0 tap1
        (from https://github.com/wdebruij/kerneltools/tree/master/tests)
      v1 -> v2
        - simplified set_offload change (review comment)
        - documented test procedure
    Link: http://lkml.kernel.org/r/<CAF=yD-LuUeDuL9YWPJD9ykOZ0QCjNeznPDr6whqZ9NGMNF12Mw@mail.gmail.com>
    Fixes: fb652fdf ("macvlan/macvtap: Remove NETIF_F_UFO advertisement.")
    Reported-by: default avatarMichal Kubecek <mkubecek@suse.cz>
    Signed-off-by: default avatarWillem de Bruijn <willemb@google.com>
    Acked-by: default avatarJason Wang <jasowang@redhat.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
output_core.c 4.28 KB