netdev - Re: [PATCH v2] kcm: remove any offset before parsing messages

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Message-Id: <20180917.195150.315319338322641005.davem@davemloft.net>
Date:   Mon, 17 Sep 2018 19:51:50 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     asmadeus@...ewreck.org
Cc:     doronrk@...com, tom@...ntonium.net, davejwatson@...com,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] kcm: remove any offset before parsing messages

From: Dominique Martinet <asmadeus@...ewreck.org>
Date: Tue, 18 Sep 2018 04:45:36 +0200

> David Miller wrote on Mon, Sep 17, 2018:
>> Remind me, is there actually any way for the bpf programs run in this
>> situation to even _see_ strp_msg(skb)->offset at all?
> 
> No, they can see it, so it's possible to make a KCM program that works
> right now if you are careful (I'm not sure why the offset within bpf is
> different from the offset in the kernel though, it looks like the bpf
> program skips the qos part of the control buffer)

What helper is used in the BPF program to get this offset value?

(also good info to add to the commit message)