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Date: Fri, 9 Feb 2024 11:00:09 -0800
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Subject: Re: [PATCH] net: remove check before __cgroup_bpf_run_filter_skb
From: Stanislav Fomichev <sdf@google.com>
To: Oliver Crumrine <ozlinuxc@gmail.com>
Cc: bpf@vger.kernel.org, linux-kernel@vger.kernel.org, thinker.li@gmail.com
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On 02/08, Oliver Crumrine wrote:
> On Thu, Feb 08, 2024 at 04:43:06PM -0800, Stanislav Fomichev wrote:
> > The check is here to make sure we only run this hook on non-req sockets.
> > Dropping it would mean we'd be running the hook on the listeners
> > instead. I don't think we want that.
> 
> You are correct that we don't want to run the code on listeners. However
> the check for that is in the function this macro calls,
> __cgroup_bpf_run_filter_skb (the check is on line 1367 of
> kernel/bpf/cgroup.c, for 6.8.0-rc3). The check doesn't need to be done
> twice, so it can be removed in this macro. 

Maybe we should instead remove "(!sk || !sk_fullsock(sk))" check from
__cgroup_bpf_run_filter_skb? BPF_CGROUP_RUN_PROG_INET_EGRESS makes
care of all those corner conditions. We just need to add those checks to
BPF_CGROUP_RUN_PROG_INET_INGRESS.

Let me also CC Kui-Feng, he was touching this part recently in commit
223f5f79f2ce ("bpf, net: Check skb ownership against full socket.").