netdev - Re: [PATCH] net: Do not include padding in TCP GRO checksum

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Date:	Thu, 14 Nov 2013 17:26:48 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Alexander Duyck <alexander.h.duyck@...el.com>
Cc:	davem@...emloft.net, netdev@...r.kernel.org, edumazet@...gle.com,
	herbert@...dor.apana.org
Subject: Re: [PATCH] net: Do not include padding in TCP GRO checksum

On Thu, 2013-11-14 at 17:18 -0800, Alexander Duyck wrote:
> In some recent tests where I was generating invalid frames I found that
> the checksum was being treated as valid for certain frames that computed
> the checksum with padding included.  On closer inspection I found the
> issue was that GRO was using the skb->len instead of the length recorded in
> the IP/IPv6 header to determine the number of bytes to checksum.  As such
> padded frames that actually had invalid checksums generated by adding the
> padding to the checksum were being incorrectly tagged as valid.
> 
> This change corrects that by using the tot_len from IPv4 headers and the
> payload_len from IPv6 headers to compute the total number of bytes to be
> included in the checksum.
> 
> Signed-off-by: Alexander Duyck <alexander.h.duyck@...el.com>
> ---
> 
> I haven't had a chance to test this much yet and I am not that familiar
> some of this GRO code so any review of this would be greatly appreciated.
> I will try to get this tested by end-of-day tomorrow to verify it resolves
> the issues I saw with invalid padded frames being marked as valid and
> doesn't introduce any new issues.
> 
>  net/ipv4/tcp_offload.c   |   13 ++++++++-----
>  net/ipv6/tcpv6_offload.c |   11 +++++++----
>  2 files changed, 15 insertions(+), 9 deletions(-)
> 
> diff --git a/net/ipv4/tcp_offload.c b/net/ipv4/tcp_offload.c
> index a2b68a1..3dabb76 100644
> --- a/net/ipv4/tcp_offload.c
> +++ b/net/ipv4/tcp_offload.c
> @@ -273,13 +273,16 @@ static int tcp_v4_gso_send_check(struct sk_buff *skb)
>  static struct sk_buff **tcp4_gro_receive(struct sk_buff **head, struct sk_buff *skb)
>  {
>  	const struct iphdr *iph = skb_gro_network_header(skb);
> +	int length = iph->tot_len;

Well, you probably should test this on x86 for example ;)


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