Messages in this thread | | | Date | Tue, 18 Sep 2018 04:58:37 +0200 | From | Dominique Martinet <> | Subject | Re: [PATCH v2] kcm: remove any offset before parsing messages |
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David Miller wrote on Mon, Sep 17, 2018: > > 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)
Dave defined one himself ; for a simple protocol where the offset is in the first four bytes of the message.
The whole bpf program could look like this:
------ struct kcm_rx_msg { int full_len; int offset; }; static inline struct kcm_rx_msg *kcm_rx_msg(struct __sk_buff *skb) { return (struct kcm_rx_msg *)skb->cb; } int decode_framing(struct __sk_buff *skb) { return load_word(skb, kcm_rx_msg(skb)->offset); } ------
If we go towards documenting it, adding a helper would be useful yes; buf if we pull that becomes unnecessary. (I'll add the example program in the commit message anyway at your suggestion)
-- Dominique Martinet
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