From: David Miller <davem@davemloft.net>
To: fw@strlen.de
Cc: netdev@vger.kernel.org, jbohac@suse.cz
Subject: Re: [PATCH 1/2] tcp: syncookies: reduce cookie lifetime to 128 seconds
Date: Wed, 28 Aug 2013 18:20:48 -0400 (EDT) [thread overview]
Message-ID: <20130828.182048.371311612380335945.davem@davemloft.net> (raw)
In-Reply-To: <1377453242-4773-1-git-send-email-fw@strlen.de>
From: Florian Westphal <fw@strlen.de>
Date: Sun, 25 Aug 2013 19:54:01 +0200
> We currently accept cookies that were created less than 4 minutes ago
> (ie, cookies with counter delta 0-3). Combined with the 8 mss table
> values, this yields 32 possible values (out of 2**32) that will be valid.
>
> Reducing the lifetime to < 2 minutes halves the guessing chance while
> still providing a large enough period (possible cookies are
> only validated if last synqueue overflow was less than 3 seconds ago).
>
> While at it, get rid of jiffies value -- they overflow too quickly on
> 32 bit platforms.
>
> getnstimeofday is used to create a counter that increments every 64s.
>
> Reported-by: Jakob Lell <jakob@jakoblell.com>
> Signed-off-by: Florian Westphal <fw@strlen.de>
Moving from jiffies as a time seed to getnstimeofday() obviously will
have some performance impact, can you talk a little bit about that?
> +#define MAX_SYNCOOKIE_AGE 2 /* 128 seconds */
I'm sure you understand how 2 translates into 128 seconds in this syncookie
code, but I sure don't and the next person who reads this patch or this
code after I apply it may not either.
Could you in some way expose the calculation? Thanks.
prev parent reply other threads:[~2013-08-28 22:20 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-08-25 17:54 [PATCH 1/2] tcp: syncookies: reduce cookie lifetime to 128 seconds Florian Westphal
2013-08-25 17:54 ` [PATCH 2/2] tcp: syncookies: reduce mss table to four values Florian Westphal
2013-08-28 22:22 ` David Miller
2013-08-28 22:20 ` David Miller [this message]
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