[Xen-devel] Re: [PATCH] xen: netfront: Drop GSO SKBs which do not have csum_blank.

[Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>]

Hi David,

http://patchwork.ozlabs.org/patch/77593/ tells me this patch is "Not
Applicable". Is this scenario not worth worrying about for some reason?

The error would be due to a buggy peer (i.e. netback) so I guess this
frontend fix is really just a belt-and-braces thing.

However The equivalent netback patch (which is not upstream yet but I'm
working on cleaning it up for a first post soon) is more critical since
it could allow a malicious guest to spam the domain 0 syslog (via the
WARN_ON in skb_gso_segment) so I just wanted to check if I was also
missing some reason why the netback patch would be non-applicable too.

Thanks,
Ian.

On Wed, 2011-01-05 at 13:23 +0000, Ian Campbell wrote:
> The Linux network stack expects all GSO SKBs to have ip_summed ==
> CHECKSUM_PARTIAL (which implies that the frame contains a partial
> checksum) and the Xen network ring protocol similarly expects an SKB
> which has GSO set to also have NETRX_csum_blank (which also implies a
> partial checksum). Therefore drop such frames on receive otherwise
> they will trigger the warning in skb_gso_segment.
> 
> Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
> Cc: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
> Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
> Cc: netdev@xxxxxxxxxxxxxxx
> ---
>  drivers/net/xen-netfront.c |    5 +++++
>  1 files changed, 5 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
> index cdbeec9..8b8c480 100644
> --- a/drivers/net/xen-netfront.c
> +++ b/drivers/net/xen-netfront.c
> @@ -836,6 +836,11 @@ static int handle_incoming_queue(struct net_device *dev,
>                               dev->stats.rx_errors++;
>                               continue;
>                       }
> +             } else if (skb_is_gso(skb)) {
> +                     kfree_skb(skb);
> +                     packets_dropped++;
> +                     dev->stats.rx_errors++;
> +                     continue;
>               }
>  
>               dev->stats.rx_packets++;



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