netdev - Re: [PATCH net-next 1/2] bpf: enable non-root eBPF programs

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Date:	Tue, 06 Oct 2015 10:56:00 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Alexei Starovoitov <ast@...mgrid.com>
Cc:	Daniel Borkmann <daniel@...earbox.net>,
	Ingo Molnar <mingo@...nel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Andy Lutomirski <luto@...capital.net>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	Eric Dumazet <edumazet@...gle.com>,
	Kees Cook <keescook@...omium.org>, linux-api@...r.kernel.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 1/2] bpf: enable non-root eBPF programs

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.


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