netdev - Re: [PATCH net-next v4 3/4] bpf: BPF for lightweight tunnel infrastructure

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Date:   Wed, 30 Nov 2016 15:43:54 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Thomas Graf <tgraf@...g.ch>
Cc:     davem@...emloft.net, netdev@...r.kernel.org, daniel@...earbox.net,
        tom@...bertland.com, roopa@...ulusnetworks.com,
        hannes@...essinduktion.org
Subject: Re: [PATCH net-next v4 3/4] bpf: BPF for lightweight tunnel
 infrastructure

On Wed, Nov 30, 2016 at 05:10:10PM +0100, Thomas Graf wrote:
> Registers new BPF program types which correspond to the LWT hooks:
>   - BPF_PROG_TYPE_LWT_IN   => dst_input()
>   - BPF_PROG_TYPE_LWT_OUT  => dst_output()
>   - BPF_PROG_TYPE_LWT_XMIT => lwtunnel_xmit()
> 
> The separate program types are required to differentiate between the
> capabilities each LWT hook allows:
> 
>  * Programs attached to dst_input() or dst_output() are restricted and
>    may only read the data of an skb. This prevent modification and
>    possible invalidation of already validated packet headers on receive
>    and the construction of illegal headers while the IP headers are
>    still being assembled.
> 
>  * Programs attached to lwtunnel_xmit() are allowed to modify packet
>    content as well as prepending an L2 header via a newly introduced
>    helper bpf_skb_change_head(). This is safe as lwtunnel_xmit() is
>    invoked after the IP header has been assembled completely.
> 
> All BPF programs receive an skb with L3 headers attached and may return
> one of the following error codes:
> 
>  BPF_OK - Continue routing as per nexthop
>  BPF_DROP - Drop skb and return EPERM
>  BPF_REDIRECT - Redirect skb to device as per redirect() helper.
>                 (Only valid in lwtunnel_xmit() context)
> 
> The return codes are binary compatible with their TC_ACT_
> relatives to ease compatibility.
> 
> Signed-off-by: Thomas Graf <tgraf@...g.ch>

Looks great.

Acked-by: Alexei Starovoitov <ast@...nel.org>