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From: David Miller <davem@davemloft.net>
Subject: Re: [PATCH] ip : take care of last fragment in ip_append_data
Date: Tue, 21 Sep 2010 21:53:37 -0700 (PDT)
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From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Wed, 22 Sep 2010 06:44:06 +0200

> The "17" (instead of probable 16 need) comes from :
> 
> net/ipv4/esp4.c line 599 :
> 
> x->props.trailer_len = align + 1 + crypto_aead_authsize(esp->aead);
> 
> In my Nick ipsec script case, 
> crypto_aead_blocksize(aead) = 16, 
> crypto_aead_authsize(esp->aead) = 0
> 
> -> align = 16
> trailer_len = 16 + 1 + 0;
> 
> I am not sure we need the "+ 1", but I know nothing about this stuff.
> 
> Same in net/ipv6/esp6.c ?

I think the author of this code thought that the alignment was
expressed as "N - 1" instead of plain "N".

I'll do some research. :-)

Thanks Eric.