From: Eric Dumazet <eric.dumazet@gmail.com>
To: Jesper Dangaard Brouer <brouer@redhat.com>
Cc: "David S. Miller" <davem@davemloft.net>,
Hannes Frederic Sowa <hannes@stressinduktion.org>,
netdev@vger.kernel.org
Subject: Re: [net-next PATCH 1/4] Revert "inet: limit length of fragment queue hash table bucket lists"
Date: Thu, 02 May 2013 08:16:41 -0700 [thread overview]
Message-ID: <1367507801.29805.12.camel@edumazet-glaptop> (raw)
In-Reply-To: <20130502095955.1ea082fb@redhat.com>
On Thu, 2013-05-02 at 09:59 +0200, Jesper Dangaard Brouer wrote:
> On Wed, 24 Apr 2013 17:00:30 -0700 Eric Dumazet <eric.dumazet@gmail.com> wrote:
>
> > On Wed, 2013-04-24 at 17:48 +0200, Jesper Dangaard Brouer wrote:
> > > This reverts commit 5a3da1fe9561828d0ca7eca664b16ec2b9bf0055.
> > >
> > > The problem with commit 5a3da1fe (inet: limit length of fragment
> > > queue hash table bucket lists) is that, once we hit the hash depth
> > > limit (of 128), the we *keep* the existing frag queues, not
> > > allowing new frag queues to be created. Thus, an attacker can
> > > effectivly block handling of fragments for 30 sec (as each frag
> > > queue have a timeout of 30 sec)
> > >
> >
> > I do not think its good to revert this patch. It was a step in right
> > direction.
>
> We need a revert, because we are too close to the merge window, and
> cannot complete the needed "steps" to make this patch safe, sorry.
Again, a limit of 128 is totally OK. Its in fact too big.
128 cache misses consume 5 us
Allowing a chain being non limited is a more severe bug.
Reverting will allow an attacker to consume all your cpu cycles.
We changed INETFRAGS_HASHSZ to 1024, so 128*1024 max frags is already a
very big limit.
No matter what we do, we need to limit both :
- Memory consumption
- Cpu consumption
For people willing to allow more memory to be used, the only way is to
resize hash table, or using a bigger INETFRAGS_HASHSZ
I do not think there is a hurry, current defrag code is already better
than what we had years ago.
next prev parent reply other threads:[~2013-05-02 15:16 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-04-24 15:47 [net-next PATCH 0/4] net: frag patchset for fixing LRU scalability issue Jesper Dangaard Brouer
2013-04-24 15:48 ` [net-next PATCH 1/4] Revert "inet: limit length of fragment queue hash table bucket lists" Jesper Dangaard Brouer
2013-04-25 0:00 ` Eric Dumazet
2013-04-25 13:10 ` Jesper Dangaard Brouer
2013-04-25 13:58 ` David Laight
2013-05-02 7:59 ` Jesper Dangaard Brouer
2013-05-02 15:16 ` Eric Dumazet [this message]
2013-05-03 9:15 ` Jesper Dangaard Brouer
2013-04-24 15:48 ` [net-next PATCH 2/4] net: increase frag hash size Jesper Dangaard Brouer
2013-04-24 22:09 ` Sergei Shtylyov
2013-04-25 10:13 ` Jesper Dangaard Brouer
2013-04-25 12:13 ` Sergei Shtylyov
2013-04-25 19:11 ` David Miller
2013-04-24 23:48 ` Eric Dumazet
2013-04-25 3:26 ` Hannes Frederic Sowa
2013-04-25 19:52 ` [net-next PATCH V2] " Jesper Dangaard Brouer
2013-04-29 17:44 ` David Miller
2013-04-24 15:48 ` [net-next PATCH 3/4] net: avoid false perf interpretations in frag code Jesper Dangaard Brouer
2013-04-24 23:48 ` Eric Dumazet
2013-04-24 23:54 ` David Miller
2013-04-25 10:57 ` Jesper Dangaard Brouer
2013-04-25 19:13 ` David Miller
2013-04-24 15:48 ` [net-next PATCH 4/4] net: frag LRU list per CPU Jesper Dangaard Brouer
2013-04-25 0:25 ` Eric Dumazet
2013-04-25 2:05 ` Eric Dumazet
2013-04-25 14:06 ` Jesper Dangaard Brouer
2013-04-25 14:37 ` Eric Dumazet
2013-04-25 13:59 ` Jesper Dangaard Brouer
2013-04-25 14:10 ` Eric Dumazet
2013-04-25 14:18 ` Eric Dumazet
2013-04-25 19:15 ` Jesper Dangaard Brouer
2013-04-25 19:22 ` Eric Dumazet
2013-04-24 16:21 ` [net-next PATCH 0/4] net: frag patchset for fixing LRU scalabilityissue David Laight
2013-04-25 11:39 ` Jesper Dangaard Brouer
2013-04-25 12:57 ` David Laight
2013-04-24 17:27 ` [net-next PATCH 0/4] net: frag patchset for fixing LRU scalability issue Hannes Frederic Sowa
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