From: David Miller <davem@davemloft.net>
To: kaber@trash.net
Cc: herbert@gondor.apana.org.au, eric.dumazet@gmail.com,
netdev@vger.kernel.org
Subject: ESP trailer_len calculation
Date: Fri, 24 Sep 2010 14:40:44 -0700 (PDT) [thread overview]
Message-ID: <20100924.144044.179940003.davem@davemloft.net> (raw)
Eric Dumazet and I recently were looking into a strange artifact in
ESP ->trailer_len calculations.
Eric was seeing values like "17" which looked strange.
He foudn that it's because of this line in esp4.c:esp_init_state()
x->props.trailer_len = align + 1 + crypto_aead_authsize(esp->aead);
which comes from commit:
commit c5c2523893747f88a83376abad310c8ad13f7197
Author: Patrick McHardy <kaber@trash.net>
Date: Mon Apr 9 11:47:18 2007 -0700
[XFRM]: Optimize MTU calculation
which is based upon discussion threads:
http://marc.info/?l=linux-netdev&m=115468159401118&w=2
and
http://marc.info/?l=linux-netdev&m=117561805827241&w=2
Even more strange, in the orignal version of this patch the
calcaluation is actually:
x->props.trailer_len = align - 1 + esp->auth.icv_trunc_len;
(ie. 'align - 1' instead of 'align + 1')
It seems that this "- 1 " or "+ 1" term can be completely eliminated,
unless there are some funny semantics wrt. the padding area of ESP.
Patrick and Herbert, what do you guys think?
next reply other threads:[~2010-09-24 21:40 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-09-24 21:40 David Miller [this message]
2010-09-25 6:23 ` ESP trailer_len calculation Herbert Xu
2010-09-27 1:46 ` David Miller
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