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

David Miller
2018-03-18T20:31:11Z

From: John Fastabend <john.fastabend@gmail.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@gmail.com>