netdev - Re: [PATCH net] packet: copy user buffers before orphan or clone

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Message-ID: <CAF=yD-JwAomiTdUz1UA9Nerz9VuPFDsxDZahun6Fc-sFa01niw@mail.gmail.com>
Date:   Fri, 23 Nov 2018 17:32:38 -0500
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     David Miller <davem@...emloft.net>
Cc:     Network Development <netdev@...r.kernel.org>,
        johann.baudy@...-log.net,
        "Anand H. Krishnan" <anandhkrishnan@...il.com>,
        Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH net] packet: copy user buffers before orphan or clone

On Fri, Nov 23, 2018 at 2:09 PM David Miller <davem@...emloft.net> wrote:
>
> From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
> Date: Tue, 20 Nov 2018 13:00:18 -0500
>
> > From: Willem de Bruijn <willemb@...gle.com>
> >
> > tpacket_snd sends packets with user pages linked into skb frags. It
> > notifies that pages can be reused when the skb is released by setting
> > skb->destructor to tpacket_destruct_skb.
> >
> > This can cause data corruption if the skb is orphaned (e.g., on
> > transmit through veth) or cloned (e.g., on mirror to another psock).
> >
> > Create a kernel-private copy of data in these cases, same as tun/tap
> > zerocopy transmission. Reuse that infrastructure: mark the skb as
> > SKBTX_ZEROCOPY_FRAG, which will trigger copy in skb_orphan_frags(_rx).
> >
> > Unlike other zerocopy packets, do not set shinfo destructor_arg to
> > struct ubuf_info. tpacket_destruct_skb already uses that ptr to notify
> > when the original skb is released and a timestamp is recorded. Do not
> > change this timestamp behavior. The ubuf_info->callback is not needed
> > anyway, as no zerocopy notification is expected.
> >
> > Mark destructor_arg as not-a-uarg by setting the lower bit to 1. The
> > resulting value is not a valid ubuf_info pointer, nor a valid
> > tpacket_snd frame address. Add skb_zcopy_.._nouarg helpers for this.
> >
> > The fix relies on features introduced in commit 52267790ef52 ("sock:
> > add MSG_ZEROCOPY"), so can be backported as is only to 4.14.
> >
> > Tested with from `./in_netns.sh ./txring_overwrite` from
> > http://github.com/wdebruij/kerneltools/tests
> >
> > Fixes: 69e3c75f4d54 ("net: TX_RING and packet mmap")
> > Reported-by: Anand H. Krishnan <anandhkrishnan@...il.com>
> > Signed-off-by: Willem de Bruijn <willemb@...gle.com>
>
> Applied, and queued up for -stable.  Thanks for the backporting notes.
>
> Any chance those tests from your kerneltools repo can make their way
> into selftests?

Absolutely. I'll send it to net-next once it has the fix.