From: Florian Westphal <fw@strlen.de>
To: Florian Westphal <fw@strlen.de>,
Pablo Neira Ayuso <pablo@netfilter.org>,
netfilter-devel@vger.kernel.org, davem@davemloft.net,
netdev@vger.kernel.org
Subject: Re: [PATCH 01/12] netfilter: avoid get_random_bytes calls
Date: Mon, 6 Jan 2014 14:04:51 +0100 [thread overview]
Message-ID: <20140106130451.GF28854@breakpoint.cc> (raw)
In-Reply-To: <20140106124340.GC4611@order.stressinduktion.org>
Hannes Frederic Sowa <hannes@stressinduktion.org> wrote:
> On Mon, Jan 06, 2014 at 12:54:36PM +0100, Florian Westphal wrote:
> > Hannes Frederic Sowa <hannes@stressinduktion.org> wrote:
> > Can you elaborate? If entropy estimate is really really low
> > (because we're booting up), why would get_random_bytes() be a better
> > choice [ i understand net_get_random_once() is for delaying
> > the actual random_bytes call until a later point in time where we've
> > hopefully collected more entropy ]
[..]
> On some of my small virtual machines (amd64) I even see this message while
> login on the console (small iptables set also loaded before). In the mean
> time prandom_u32() is still seeded with maybe 3 bits (I once measured it)
> at the beginning and won't get a refresh until the nonblocking pool is
> fully initialized.
I see. In this case it indeed could be a problem; I was doing this
change with the assumption that prandom is useable at ->checkenty time.
> > I specifically did not use net_get_random_once once because checkentry is
> > not a hotpath.
> >
> > I don't see why get_random_bytes use increases the security margin, especially
> > considering none of these hashes have periodic run-time rehashing?
> >
> > But sure, if you think this change is a problem, Pablo can just revert it.
>
> I don't know if it is a real problem. Most of the time the initial seed
> should be enough, but I guess get_random_bytes would still be a more
> defensive choice. I would have used it. ;)
Alright. Given that this went into -next, I think we have a few weeks to
investigate.
I will check if the specific hash uses are problematic in their own right
(due to lack of reseed) or if they are weakened by this change only.
I'll follow up on this.
Pablo/David, if you think this needs to be fixed RIGHT NOW then please
just issue a revert for a42b99a6e329654d376b330de057eff87686d890.
Thanks!
next prev parent reply other threads:[~2014-01-06 13:04 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-01-05 23:12 [PATCH 00/12] netfilter updates for net-next Pablo Neira Ayuso
2014-01-05 23:12 ` [PATCH 01/12] netfilter: avoid get_random_bytes calls Pablo Neira Ayuso
2014-01-05 23:41 ` Hannes Frederic Sowa
2014-01-06 11:54 ` Florian Westphal
2014-01-06 12:43 ` Hannes Frederic Sowa
2014-01-06 12:58 ` Pablo Neira Ayuso
2014-01-06 13:04 ` Florian Westphal [this message]
2014-01-06 13:06 ` Pablo Neira Ayuso
2014-01-06 13:07 ` Florian Westphal
2014-01-05 23:12 ` [PATCH 02/12] netfilter: ctnetlink: honor CTA_MARK_MASK when setting ctmark Pablo Neira Ayuso
2014-01-05 23:12 ` [PATCH 03/12] netfilter: nfnetlink_queue: enable UID/GID socket info retrieval Pablo Neira Ayuso
2014-01-06 15:32 ` Eric Dumazet
2014-01-06 16:36 ` Pablo Neira Ayuso
2014-01-06 18:36 ` David Miller
2014-01-05 23:12 ` [PATCH 04/12] netfilter: add IPv4/6 IPComp extension match support Pablo Neira Ayuso
2014-01-05 23:12 ` [PATCH 05/12] ipvs: Remove unused variable ret from sync_thread_master() Pablo Neira Ayuso
2014-01-05 23:13 ` [PATCH 06/12] netfilter: nf_nat: add full port randomization support Pablo Neira Ayuso
2014-01-05 23:13 ` [PATCH 07/12] netfilter: ipset: remove unused code Pablo Neira Ayuso
2014-01-05 23:13 ` [PATCH 08/12] netfilter: nf_conntrack: remove dead code Pablo Neira Ayuso
2014-01-05 23:13 ` [PATCH 09/12] netfilter: xt_CT: fix error value in xt_ct_tg_check() Pablo Neira Ayuso
2014-01-05 23:13 ` [PATCH 10/12] net: net_cls: move cgroupfs classid handling into core Pablo Neira Ayuso
2014-01-05 23:13 ` [PATCH 11/12] net: netprio: rename config to be more consistent with cgroup configs Pablo Neira Ayuso
2014-01-05 23:13 ` [PATCH 12/12] netfilter: x_tables: lightweight process control group matching Pablo Neira Ayuso
-- strict thread matches above, loose matches on Subject: below --
2014-01-05 23:09 [PATCH 00/12] netfilter/IPVS updates for net-next Pablo Neira Ayuso
2014-01-05 23:09 ` [PATCH 01/12] netfilter: avoid get_random_bytes calls Pablo Neira Ayuso
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