netdev - Re: [RFC PATCH net-next 2/2] net: Reset forwarded skb->tstamp before delivering to user space

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Date:   Fri, 10 Dec 2021 02:19:17 -0800
From:   Eric Dumazet <edumazet@...gle.com>
To:     Martin KaFai Lau <kafai@...com>
Cc:     Daniel Borkmann <daniel@...earbox.net>,
        Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        netdev@...r.kernel.org, Alexei Starovoitov <ast@...nel.org>,
        David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, Kernel-team@...com
Subject: Re: [RFC PATCH net-next 2/2] net: Reset forwarded skb->tstamp before
 delivering to user space

On Wed, Dec 8, 2021 at 12:48 PM Martin KaFai Lau <kafai@...com> wrote:
>
> On Wed, Dec 08, 2021 at 10:27:51AM -0800, Eric Dumazet wrote:
> > On Wed, Dec 8, 2021 at 12:30 AM Martin KaFai Lau <kafai@...com> wrote:
> >
> > > For non bpf ingress, hmmm.... yeah, not sure if it is indeed an issue :/
> > > may be save the tx tstamp first and then temporarily restamp with __net_timestamp()
> >
> > Martin, have you looked at time namespaces (CLONE_NEWTIME) ?
> >
> > Perhaps we need to have more than one bit to describe time bases.
> My noob understanding is it only affects the time returning
> to the user in the syscall.  Could you explain how that
> may affect the time in skb->tstamp?

I would think it should affect timestamps (rx/tx network ones),
otherwise user applications would be broken ?