From: Alexander Duyck <adu...@mirantis.com> Date: Thu, 25 Feb 2016 19:10:59 -0800
> This change makes it so that we only use a 16 bit length field instead of a > 32 bit length field when computing a UDP checksum for IPv6. > > This fixes an issue found with UDP tunnels over IPv6 where the total size > exceeded 65536 for a frame that was to be segmented. As a result the > checksum being computed didn't match the frame data so we ended up being > off by 1 for the final checksum value since we didn't cancel out the upper > 16 bits of the length. > > The reasoning behind this is that RFC2460 states that for protocols such as > UDP that carry their own length field we should use that when computing the > checksum for the pseudo-header. As such we should be using a 16 bit value, > not a 32 bit as is currently occurring when computing the UDP checksum for > IPv6. > > Signed-off-by: Alexander Duyck <adu...@mirantis.com> What a can of worms. :-/ Reading RFC2460 over a few times, indeed using the truncated 16-bit length is the thing to do for the pseudo-header checksum. We have this mistake in a few places, for example ip6_compute_pseudo() unconditionally uses skb->len, yet is used by UDP on receive. Can you do a little audit and fix as many of these cases as you can find and wrap them all into this patch? Thanks!
