netdev - Re: [Intel-wired-lan] [PATCH net-next 1/2] igc: AF_XDP zero-copy metadata adjust breaks SKBs on XDP

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Date:   Fri, 26 Nov 2021 16:54:08 +0100
From:   Alexander Lobakin <alexandr.lobakin@...el.com>
To:     Jesper Dangaard Brouer <jbrouer@...hat.com>
Cc:     Alexander Lobakin <alexandr.lobakin@...el.com>,
        Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
        brouer@...hat.com, netdev@...r.kernel.org,
        intel-wired-lan@...ts.osuosl.org, bjorn@...nel.org,
        Jakub Kicinski <kuba@...nel.org>, bpf@...r.kernel.org,
        Daniel Borkmann <borkmann@...earbox.net>,
        "David S. Miller" <davem@...emloft.net>, magnus.karlsson@...el.com
Subject: Re: [Intel-wired-lan] [PATCH net-next 1/2] igc: AF_XDP zero-copy metadata adjust breaks SKBs on XDP_PASS

From: Jesper Dangaard Brouer <jbrouer@...hat.com>
Date: Fri, 26 Nov 2021 16:32:47 +0100

> On 26/11/2021 16.25, Maciej Fijalkowski wrote:
> > On Mon, Nov 15, 2021 at 09:36:25PM +0100, Jesper Dangaard Brouer wrote:
> >> Driver already implicitly supports XDP metadata access in AF_XDP
> >> zero-copy mode, as xsk_buff_pool's xp_alloc() naturally set xdp_buff
> >> data_meta equal data.
> >>
> >> This works fine for XDP and AF_XDP, but if a BPF-prog adjust via
> >> bpf_xdp_adjust_meta() and choose to call XDP_PASS, then igc function
> >> igc_construct_skb_zc() will construct an invalid SKB packet. The
> >> function correctly include the xdp->data_meta area in the memcpy, but
> >> forgot to pull header to take metasize into account.
> >>
> >> Fixes: fc9df2a0b520 ("igc: Enable RX via AF_XDP zero-copy")
> >> Signed-off-by: Jesper Dangaard Brouer<brouer@...hat.com>
> > Acked-by: Maciej Fijalkowski<maciej.fijalkowski@...el.com>
> > 
> > Great catch. Will take a look at other ZC enabled Intel drivers if they
> > are affected as well.

They are. We'll cover them in a separate series, much thanks for
revealing that (:

> Thanks a lot for taking this task!!! :-)
> --Jesper

Al