Re: [PATCH net] net: accept UFO datagrams from tuntap and packet

[Jason Wang <jasowang@redhat.com>]

On 2017年11月18日 06:59, Willem de Bruijn wrote:
> From: Willem de Bruijn<willemb@google.com>
>
> 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 182e0b6b5846~1..d9d30adf5677.
> 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 939912216fa8 ("net: skb_needs_check() removes
> CHECKSUM_UNNECESSARY check for tx.") and reverting commit 8d63bee643f1
> ("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, which is
> assigned directly to the frag_hdr. Also, SKB_GSO_UDP is inserted
> at the end of the enum to minimize code churn.
>
> Link:http://lkml.kernel.org/r/<CAF=yD-LuUeDuL9YWPJD9ykOZ0QCjNeznPDr6whqZ9NGMNF12Mw@mail.gmail.com>
> Fixes: fb652fdfe837 ("macvlan/macvtap: Remove NETIF_F_UFO advertisement.")
> Reported-by: Michal Kubecek<mkubecek@suse.cz>
> Signed-off-by: Willem de Bruijn<willemb@google.com>

Looks good to me. The only concern is that whether or not stable can 
accept this patch:

stable-kernel-rules.rst said:

"
- It cannot be bigger than 100 lines, with context.
"

Otherwise we may consider the things like doing segmentation in 
tun_get_user() mentioned in another thread by you.

Thanks