Question about tcp_filter() in tcp_v6_do_rcv()

Question about tcp_filter() in tcp_v6_do_rcv()

[Chenbo Feng]

Hello everybody,

I am testing eBPF programs on ipv6 and I just find out the tcp_filter() 
function (previously named sk_filter()) is called both in tcp_v6_rcv() 
and tcp_v6_do_rcv(). In contrast, it is only called by tcp_v4_rcv() in 
ipv4 layer. I guess this implementation is used to capture some corner 
cases in ipv6 ingress route but I cannot find why. Could I know why we 
need this in two similar places in ipv6 transportation layer?

I have tried to dig into the commit history and the related code path 
but I did not see any obvious reason for doing so. And my problem with 
it is when a eBPF program is attached to a socket or a cgroup in ingress 
side, the filter program will be applied on some packets twice. And it 
affect the accuracy when using eBPF program for traffic accounting.

Thanks!

Chenbo Feng

Re: Question about tcp_filter() in tcp_v6_do_rcv()

[Eric Dumazet]

On Wed, 2017-06-07 at 15:35 -0700, Chenbo Feng wrote:
> Hello everybody,
> 
> I am testing eBPF programs on ipv6 and I just find out the tcp_filter() 
> function (previously named sk_filter()) is called both in tcp_v6_rcv() 
> and tcp_v6_do_rcv(). In contrast, it is only called by tcp_v4_rcv() in 
> ipv4 layer. I guess this implementation is used to capture some corner 
> cases in ipv6 ingress route but I cannot find why. Could I know why we 
> need this in two similar places in ipv6 transportation layer?
> 
> I have tried to dig into the commit history and the related code path 
> but I did not see any obvious reason for doing so. And my problem with 
> it is when a eBPF program is attached to a socket or a cgroup in ingress 
> side, the filter program will be applied on some packets twice. And it 
> affect the accuracy when using eBPF program for traffic accounting.

It seems this was added in this commit

commit 5234b9f7d650fe64975695d835cb9413e1d75f46
Author: James Morris <jmorris@intercode.com.au>
Date:   Thu Feb 6 09:49:40 2003 -0800

    [LSM]: Networking socket SKB receive hook.


You can find the history tree in :

[remote "origin"]
	url = git://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git
	fetch = +refs/heads/*:refs/remotes/origin/*


The call from tcp_v6_do_rcv() should be removed I guess