netdev - Re: [PATCH RESEND bpf 2/4] bpf, sockmap: Fix missing BPF_F_INGRESS flag when using apply

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Date:   Tue, 29 Nov 2022 20:16:44 +0100
From:   Jakub Sitnicki <jakub@...udflare.com>
To:     John Fastabend <john.fastabend@...il.com>
Cc:     Pengcheng Yang <yangpc@...gsu.com>, bpf@...r.kernel.org,
        netdev@...r.kernel.org, 'Daniel Borkmann' <daniel@...earbox.net>,
        'Lorenz Bauer' <lmb@...udflare.com>
Subject: Re: [PATCH RESEND bpf 2/4] bpf, sockmap: Fix missing BPF_F_INGRESS
 flag when using apply_bytes


On Mon, Nov 28, 2022 at 10:18 AM -08, John Fastabend wrote:
> Jakub Sitnicki wrote:
>> On Wed, Nov 23, 2022 at 02:01 PM +08, Pengcheng Yang wrote:
>> > John Fastabend <john.fastabend@...il.com> wrote:

[...]

>> >> Now that we have a psock->flags we should clera that as
>> >> well right?
>> >
>> > According to my understanding, it is not necessary (but can) to clear
>> > psock->flags here, because psock->flags will be overwritten by msg->flags
>> > at the beginning of each redirection (in sk_psock_msg_verdict()).
>> 
>> 1. We should at least document that psock->flags value can be garbage
>>    (undefined) if psock->sk_redir is null.
>
> Per v2 I think we should not have garbage flags. Just zero the flags
> field no point in saving a single insn here IMO.

It would make sense to me if zero was not a valid value here. But since
it signifies "redirect to egress", we won't be able to tell if it has
been reset anyway.