netdev - Re: [PATCH] net: implement emergency route cache rebulds when gc

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <48E2662A.6030104@cosmosbay.com>
Date:	Tue, 30 Sep 2008 19:47:22 +0200
From:	Eric Dumazet <dada1@...mosbay.com>
To:	David Miller <davem@...emloft.net>
Cc:	nhorman@...driver.com, netdev@...r.kernel.org,
	kuznet@....inr.ac.ru, pekkas@...core.fi, jmorris@...ei.org,
	yoshfuji@...ux-ipv6.org, kaber@...sh.net
Subject: Re: [PATCH] net: implement emergency route cache rebulds when gc_elasticity
 is exceeded

David Miller a écrit :
> From: Neil Horman <nhorman@...driver.com>
> Date: Mon, 29 Sep 2008 15:12:54 -0400
> 
>> 	We currently have the ability to disable our route cache secret interval
>> rebuild timer (by setting it to zero), but if we do that its possible for an
>> attacker (if they guess our route cache hash secret, to fill our system with
>> routes that all hash to the same bucket, destroying our performance.  This patch
>> provides a backstop for that issues.  In the event that our rebuild interval is
>> disabled (or very large), if any hash chain exceeds ip_rt_gc_elasticity, we do
>> an emergency hash rebuild.  During the hash rebuild we:
>> 1) warn the user of the emergency
>> 2) disable the rebuild timer
>> 3) invalidate the route caches
>> 4) re-enable the rebuild timer with its old value
> 
> I just want to clarify what my intentions were when I spoke
> with Neil about this stuff last week.
> 
> The idea is that we can by default not rebuild the secret
> at all.
> 
> And only when we notice that chains are growing larger than
> "(NUM_RTCACHE_ENTRIES / NUM_HASH_CHAINS) * N", only then
> do we do this secret rebuild and flush.  Where N is some
> constant of configurable value, the GC elasticity is some
> example.
> 
> Normally this whole hash secret business is totally unnecessary and
> there is zero reason to do it until we notice there is actually some
> kind of deep hash chain growth problem.
> 
> It's expensive, we flush the whole routing cache, so doing it
> every so often by default makes no sense and it is causing
> performance problems for people.

Intentions are very good, thanks for clarifying and letting us know.




--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html