netdev - Re: Query regarding sk

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Date:	Fri, 9 Jan 2015 16:51:46 -0800
From:	Alexei Starovoitov <alexei.starovoitov@...il.com>
To:	Kumar Sanghvi <kumaras@...lsio.com>
Cc:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: Query regarding sk_filter

On Fri, Jan 9, 2015 at 3:23 AM, Kumar Sanghvi <kumaras@...lsio.com> wrote:
> Hi netdev team,
>
> I have a query regarding sk_filter call in tcp receive path:
>
> In 'tcp_v4_rcv' function, if sk is found by __inet_lookup_skb then,
> down the line, there is a call to sk_filter to ensure if the incoming packet
> is allowed to be processed for that sk.
>
> However, in 'tcp_v4_hnd_req' function, if nsk is found by inet_lookup_established
> then, later, there does not seem to be a sk_filter call for that nsk in the receive
> path processing.
>
> I am wondering shouldn't there be a sk_filter call on nsk found in 'tcp_v4_hnd_req'
> function ? Or, probably I am missing something.

hmm. I'm not sure what you're seeing.
tcp_v4_hnd_req() is called from tcp_v4_do_rcv() which is called
after sk_filter() check is done in tcp_v4_rcv() (either directly
or via prequeue/backlog)

> I am running some high rate syn-flood tests and trying to understand
> the sk_filter behaviour in this case.

are you saying not all of syn packets are reaching filter?
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