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Subject: Re: [PATCH net-next 1/2] bpf: enable non-root eBPF programs
From: Eric Dumazet <eric.dumazet@gmail.com>
To: Alexei Starovoitov <ast@plumgrid.com>
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Date: Tue, 06 Oct 2015 10:56:00 -0700
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On Tue, 2015-10-06 at 10:50 -0700, Alexei Starovoitov wrote:

> was also thinking that we can do it only in paths that actually
> have multiple protocol layers, since today bpf is mainly used with
> tcpdump(raw_socket) and new af_packet fanout both have cb cleared
> on RX, because it just came out of alloc_skb and no layers were called,
> and on TX we can clear 20 bytes in dev_queue_xmit_nit().
> af_unix/netlink also have clean skb. Need to analyze tun and sctp...
> but it feels overly fragile to save a branch in sk_filter,
> so planning to go with
> if(unlikely(prog->cb_access)) memset in sk_filter().
> 

This will break TCP use of sk_filter().
skb->cb[] contains useful data in TCP layer.