netdev - Re: [PATCH] xen-netfront: reset skb transport header before checksum

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Date:	Mon, 11 May 2015 18:51:33 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Venkat Venkatsubra <venkat.x.venkatsubra@...cle.com>
Cc:	netdev@...r.kernel.org, xen-devel@...ts.xenproject.org,
	davem@...emloft.net, david.vrabel@...rix.com,
	konrad.wilk@...cle.com, boris.ostrovsky@...cle.com,
	wei.liu2@...rix.com, paul.durrant@...rix.com
Subject: Re: [PATCH] xen-netfront: reset skb transport header before checksum

On Mon, 2015-05-11 at 18:34 -0700, Venkat Venkatsubra wrote:
> In ed1f50c3a ("net: add skb_checksum_setup") some checksum functions
> were introduced in core. Subsequent change b5cf66cd1 ("xen-netfront:
> use new skb_checksum_setup function") made use of those functions to
> replace its own implementation. With that change ip_hdr() and tcp_hdr()
> were not pointing at the right place. d554f73df ("xen-netfront: reset
> skb network header before checksum") fixed the ip_hdr().
> 
> This patch fixes tcp_hdr().
> 
> We saw this problem when LRO was enabled on the host and it results in
> netfront setting skb->ip_summed to CHECKSUM_UNNECESSARY.
> 
> Signed-off-by: Venkat Venkatsubra <venkat.x.venkatsubra@...cle.com>
> ---
>  drivers/net/xen-netfront.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
> index 3f45afd..ed5c242 100644
> --- a/drivers/net/xen-netfront.c
> +++ b/drivers/net/xen-netfront.c
> @@ -889,6 +889,7 @@ static int handle_incoming_queue(struct netfront_queue *queue,
>  		/* Ethernet work: Delayed to here as it peeks the header. */
>  		skb->protocol = eth_type_trans(skb, queue->info->netdev);
>  		skb_reset_network_header(skb);
> +		skb_set_transport_header(skb, ip_hdrlen(skb));
>  
>  		if (checksum_setup(queue->info->netdev, skb)) {
>  			kfree_skb(skb);

This looks bogus for IPv6.

I would rather fix skb_checksum_setup_ip() and
skb_checksum_setup_ipv6(), since you already use correctly
skb_maybe_pull_tail() there.

In general, setting network and transport header at this point seems
extra work.



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