Re: [PATCH v5 net 1/2] net: udp: fix UDP header access on Fast/frag0 UDP GRO

[Willem de Bruijn]

On Wed, Nov 11, 2020 at 3:45 PM Alexander Lobakin <alobakin@xxxxx> wrote:
>
> UDP GRO uses udp_hdr(skb) in its .gro_receive() callback. While it's
> probably OK for non-frag0 paths (when all headers or even the entire
> frame are already in skb head), this inline points to junk when
> using Fast GRO (napi_gro_frags() or napi_gro_receive() with only
> Ethernet header in skb head and all the rest in the frags) and breaks
> GRO packet compilation and the packet flow itself.
> To support both modes, skb_gro_header_fast() + skb_gro_header_slow()
> are typically used. UDP even has an inline helper that makes use of
> them, udp_gro_udphdr(). Use that instead of troublemaking udp_hdr()
> to get rid of the out-of-order delivers.
>
> Present since the introduction of plain UDP GRO in 5.0-rc1.
>
> Fixes: e20cf8d3f1f7 ("udp: implement GRO for plain UDP sockets.")
> Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
> Cc: Jakub Kicinski <kuba@xxxxxxxxxx>
> Cc: Willem de Bruijn <willemb@xxxxxxxxxx>
> Signed-off-by: Alexander Lobakin <alobakin@xxxxx>

Acked-by: Willem de Bruijn <willemb@xxxxxxxxxx>