netdev - Re: [PATCH net v2] packet: on direct_xmit, limit tso and csum to supported devices

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Message-ID: <5810FEEE.2000804@iogearbox.net>
Date:   Wed, 26 Oct 2016 21:07:26 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        netdev@...r.kernel.org
CC:     davem@...emloft.net, Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH net v2] packet: on direct_xmit, limit tso and csum to
 supported devices

On 10/26/2016 05:23 PM, Willem de Bruijn wrote:
> From: Willem de Bruijn <willemb@...gle.com>
>
> When transmitting on a packet socket with PACKET_VNET_HDR and
> PACKET_QDISC_BYPASS, validate device support for features requested
> in vnet_hdr.
>
> Drop TSO packets sent to devices that do not support TSO or have the
> feature disabled. Note that the latter currently do process those
> packets correctly, regardless of not advertising the feature.
>
> Because of SKB_GSO_DODGY, it is not sufficient to test device features
> with netif_needs_gso. Full validate_xmit_skb is needed.
>
> Switch to software checksum for non-TSO packets that request checksum
> offload if that device feature is unsupported or disabled. Note that
> similar to the TSO case, device drivers may perform checksum offload
> correctly even when not advertising it.
>
> When switching to software checksum, packets hit skb_checksum_help,
> which has two BUG_ON checksum not in linear segment. Packet sockets
> always allocate at least up to csum_start + csum_off + 2 as linear.
>
> Tested by running github.com/wdebruij/kerneltools/psock_txring_vnet.c
>
>    ethtool -K eth0 tso off tx on
>    psock_txring_vnet -d $dst -s $src -i eth0 -l 2000 -n 1 -q -v
>    psock_txring_vnet -d $dst -s $src -i eth0 -l 2000 -n 1 -q -v -N
>
>    ethtool -K eth0 tx off
>    psock_txring_vnet -d $dst -s $src -i eth0 -l 1000 -n 1 -q -v -G
>    psock_txring_vnet -d $dst -s $src -i eth0 -l 1000 -n 1 -q -v -G -N
>
> v2:
>    - add EXPORT_SYMBOL_GPL(validate_xmit_skb_list)
>
> Fixes: d346a3fae3ff ("packet: introduce PACKET_QDISC_BYPASS socket option")
> Signed-off-by: Willem de Bruijn <willemb@...gle.com>

Acked-by: Daniel Borkmann <daniel@...earbox.net>