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Date: Fri, 15 Nov 2013 12:20:58 +0800 From: Herbert Xu <herbert@...dor.apana.org.au> 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, Nov 14, 2013 at 05:18:18PM -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> Good catch. > + /* adjust for any offsets */ > + length += skb_network_offset(skb) - skb_gro_offset(skb); Since skb->csum includes your padding, you'll need to adjust that as well. Also this is not the only place where we use skb_gro_len to measure the packet length. So rather than changing each one of them, I think we could just do a pskb_trim_rcsum at the point where we obtain the network packet length, i.e., in ipv4/ipv6. We should then fix pskb_trim_rcsum to adjust CHECKSUM_COMPLETE checksums as otherwise your NIC's RX checksum offload feature will be useless. Thanks, -- Email: Herbert Xu <herbert@...dor.apana.org.au> Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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