netdev - Re: [net PATCH 1/2] bpf: bpf_compute_data uses incorrect cb structure

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Date:   Fri, 27 Oct 2017 12:43:30 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     John Fastabend <john.fastabend@...il.com>
Cc:     davem@...emloft.net, netdev@...r.kernel.org, edumazet@...gle.com,
        daniel@...earbox.net
Subject: Re: [net PATCH 1/2] bpf: bpf_compute_data uses incorrect cb structure

On Fri, Oct 27, 2017 at 09:45:34AM -0700, John Fastabend wrote:
> SK_SKB program types use bpf_compute_data to store the end of the
> packet data. However, bpf_compute_data assumes the cb is stored in the
> qdisc layer format. But, for SK_SKB this is the wrong layer of the
> stack for this type.
> 
> It happens to work (sort of!) because in most cases nothing happens
> to be overwritten today. This is very fragile and error prone.
> Fortunately, we have another hole in tcp_skb_cb we can use so lets
> put the data_end value there.
> 
> Note, SK_SKB program types do not use data_meta, they are failed by
> sk_skb_is_valid_access().
> 
> Signed-off-by: John Fastabend <john.fastabend@...il.com>

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