netdev - Re: [PATCH net-next] ila: Fix checksum neutral mapping

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Message-Id: <20160615.214402.1975081304384066829.davem@davemloft.net>
Date:	Wed, 15 Jun 2016 21:44:02 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	tom@...bertland.com
Cc:	netdev@...r.kernel.org, kernel-team@...com, haoxuany@...com
Subject: Re: [PATCH net-next] ila: Fix checksum neutral mapping

From: Tom Herbert <tom@...bertland.com>
Date: Tue, 14 Jun 2016 16:29:15 -0700

> The algorithm for checksum neutral mapping is incorrect. This problem
> was being hidden since we were previously always performing checksum
> offload on the translated addresses and only with IPv6 HW csum.
> Enabling an ILA router shows the issue.
> 
> Corrected algorithm:
> 
> old_loc is the original locator in the packet, new_loc is the value
> to overwrite with and is found in the lookup table. old_flag is
> the old flag value (zero of CSUM_NEUTRAL_FLAG) and new_flag is
> then (old_flag ^ CSUM_NEUTRAL_FLAG) & CSUM_NEUTRAL_FLAG.
> 
> Need SUM(new_id + new_flag + diff) == SUM(old_id + old_flag) for
> checksum neutral translation.
> 
> Solving for diff gives:
> 
> diff = (old_id - new_id) + (old_flag - new_flag)
> 
> compute_csum_diff8(new_id, old_id) gives old_id - new_id
> 
> If old_flag is set
>    old_flag - new_flag = old_flag = CSUM_NEUTRAL_FLAG
> Else
>    old_flag - new_flag = -new_flag = ~CSUM_NEUTRAL_FLAG
> 
> Tested:
>   - Implemented a user space program that creates random addresses
>     and random locators to overwrite. Compares the checksum over
>     the address before and after translation (must always be equal)
>   - Enabled ILA router and showed proper operation.
> 
> Signed-off-by: Tom Herbert <tom@...bertland.com>

Applied.