From mboxrd@z Thu Jan  1 00:00:00 1970
From: Alexei Starovoitov <ast@plumgrid.com>
Subject: Re: [PATCH net-next 1/2] bpf: enable non-root eBPF programs
Date: Tue, 6 Oct 2015 12:26:53 -0700
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To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>, Ingo Molnar <mingo@kernel.org>, "David S. Miller" <davem@davemloft.net>, Andy Lutomirski <luto@amacapital.net>, Hannes Frederic Sowa <hannes@stressinduktion.org>, Eric Dumazet <edumazet@google.com>, Kees Cook <keescook@chromium.org>, linux-api@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org
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On 10/6/15 10:56 AM, Eric Dumazet wrote:
> 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.

oops. thanks for catching. In case of sk_filter on top of tcp sock,
it shouldn't be looking at cb at all.
I'm thinking to send a patch to get rid of cb access for socket filters
all together until better solution found.