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

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Date:   Sat, 29 Oct 2016 15:03:30 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     willemdebruijn.kernel@...il.com
Cc:     netdev@...r.kernel.org, daniel@...earbox.net, willemb@...gle.com
Subject: Re: [PATCH net v2] packet: on direct_xmit, limit tso and csum to
 supported devices

From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
Date: Wed, 26 Oct 2016 11:23:07 -0400

> 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>

Applied and queued up for -stable.