netdev - Re: [bpf-next PATCH v3 08/18] bpf: sk_msg program helper bpf_sk_msg_pull

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Date:   Sun, 18 Mar 2018 16:31:10 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     john.fastabend@...il.com
Cc:     davejwatson@...com, daniel@...earbox.net, ast@...nel.org,
        netdev@...r.kernel.org
Subject: Re: [bpf-next PATCH v3 08/18] bpf: sk_msg program helper
 bpf_sk_msg_pull_data

From: John Fastabend <john.fastabend@...il.com>
Date: Sun, 18 Mar 2018 12:57:25 -0700

> Currently, if a bpf sk msg program is run the program
> can only parse data that the (start,end) pointers already
> consumed. For sendmsg hooks this is likely the first
> scatterlist element. For sendpage this will be the range
> (0,0) because the data is shared with userspace and by
> default we want to avoid allowing userspace to modify
> data while (or after) BPF verdict is being decided.
> 
> To support pulling in additional bytes for parsing use
> a new helper bpf_sk_msg_pull(start, end, flags) which
> works similar to cls tc logic. This helper will attempt
> to point the data start pointer at 'start' bytes offest
> into msg and data end pointer at 'end' bytes offset into
> message.
 ...
> Signed-off-by: John Fastabend <john.fastabend@...il.com>

Acked-by: David S. Miller <davem@...emloft.net>