From: Patrick McHardy <kaber@trash•net>
To: Changli Gao <xiaosuo@gmail•com>
Cc: hawk@comx•dk, Eric Dumazet <eric.dumazet@gmail•com>,
Linux Kernel Network Hackers <netdev@vger•kernel.org>,
netfilter-devel@vger•kernel.org,
Paul E McKenney <paulmck@linux•vnet.ibm.com>
Subject: Re: DDoS attack causing bad effect on conntrack searches
Date: Thu, 22 Apr 2010 15:17:40 +0200 [thread overview]
Message-ID: <4BD04C74.9020402@trash.net> (raw)
In-Reply-To: <q2h412e6f7f1004220613m488c2ee4r6d24a8d1e65997d4@mail.gmail.com>
Changli Gao wrote:
> On Thu, Apr 22, 2010 at 8:58 PM, Jesper Dangaard Brouer <hawk@comx•dk> wrote:
>> At an unnamed ISP, we experienced a DDoS attack against one of our
>> customers. This attack also caused problems for one of our Linux
>> based routers.
>>
>> The attack was "only" generating 300 kpps (packets per sec), which
>> usually isn't a problem for this (fairly old) Linux Router. But the
>> conntracking system chocked and reduced pps processing power to
>> 40kpps.
>>
>> I do extensive RRD/graph monitoring of the machines. The IP conntrack
>> searches in the period exploded, to a stunning 700.000 searches per
>> sec.
>>
>> http://people.netfilter.org/hawk/DDoS/2010-04-12__001/conntrack_searches001.png
>>
>> First I though it might be caused by bad hashing, but after reading
>> the kernel code (func: __nf_conntrack_find()), I think its caused by
>> the loop restart (goto begin) of the conntrack search, running under
>> local_bh_disable(). These RCU changes to conntrack were introduced in
>> ea781f19 by Eric Dumazet.
>>
>> Code: net/netfilter/nf_conntrack_core.c
>> Func: __nf_conntrack_find()
>>
>> struct nf_conntrack_tuple_hash *
>> __nf_conntrack_find(struct net *net, const struct nf_conntrack_tuple *tuple)
>> {
>> struct nf_conntrack_tuple_hash *h;
>> struct hlist_nulls_node *n;
>> unsigned int hash = hash_conntrack(tuple);
>>
>> /* Disable BHs the entire time since we normally need to disable them
>> * at least once for the stats anyway.
>> */
>> local_bh_disable();
>> begin:
>> hlist_nulls_for_each_entry_rcu(h, n, &net->ct.hash[hash], hnnode) {
>> if (nf_ct_tuple_equal(tuple, &h->tuple)) {
>> NF_CT_STAT_INC(net, found);
>> local_bh_enable();
>> return h;
>> }
>> NF_CT_STAT_INC(net, searched);
>> }
>> /*
>> * if the nulls value we got at the end of this lookup is
>> * not the expected one, we must restart lookup.
>> * We probably met an item that was moved to another chain.
>> */
>> if (get_nulls_value(n) != hash)
>> goto begin;
>> local_bh_enable();
>>
>
> We should add a retry limit there.
We can't do that since that would allow false negatives.
next prev parent reply other threads:[~2010-04-22 13:17 UTC|newest]
Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-04-22 12:58 DDoS attack causing bad effect on conntrack searches Jesper Dangaard Brouer
2010-04-22 13:13 ` Changli Gao
2010-04-22 13:17 ` Patrick McHardy [this message]
2010-04-22 14:36 ` Eric Dumazet
2010-04-22 14:53 ` Eric Dumazet
2010-04-22 15:51 ` Paul E. McKenney
2010-04-22 16:02 ` Eric Dumazet
2010-04-22 16:34 ` Paul E. McKenney
2010-04-22 20:38 ` Jesper Dangaard Brouer
2010-04-22 21:03 ` Eric Dumazet
2010-04-22 21:14 ` Eric Dumazet
2010-04-22 23:44 ` David Miller
2010-04-23 5:44 ` Eric Dumazet
2010-04-23 8:13 ` David Miller
2010-04-23 8:18 ` David Miller
2010-04-23 8:40 ` Jesper Dangaard Brouer
2010-04-23 10:36 ` Patrick McHardy
2010-04-23 11:06 ` Eric Dumazet
2010-04-22 21:28 ` Jesper Dangaard Brouer
2010-04-23 7:23 ` Jan Engelhardt
2010-04-23 7:46 ` Eric Dumazet
2010-04-23 7:55 ` Jan Engelhardt
2010-04-23 9:23 ` Eric Dumazet
2010-04-23 10:55 ` Patrick McHardy
2010-04-23 11:05 ` Eric Dumazet
2010-04-23 11:06 ` Patrick McHardy
2010-04-23 20:57 ` Eric Dumazet
2010-04-24 11:11 ` Jesper Dangaard Brouer
2010-04-24 20:11 ` Eric Dumazet
2010-04-26 14:36 ` Jesper Dangaard Brouer
2010-05-31 21:21 ` Eric Dumazet
2010-06-01 0:28 ` Changli Gao
2010-06-01 5:05 ` Eric Dumazet
2010-06-01 5:48 ` Changli Gao
2010-06-01 10:18 ` Patrick McHardy
2010-06-01 10:31 ` Eric Dumazet
2010-06-01 10:41 ` Patrick McHardy
2010-06-01 16:20 ` [RFC nf-next-2.6] conntrack: per cpu nf_conntrack_untracked Eric Dumazet
2010-06-04 11:40 ` Patrick McHardy
2010-06-04 12:10 ` Changli Gao
2010-06-04 12:29 ` Patrick McHardy
2010-06-04 12:36 ` Eric Dumazet
2010-06-04 16:25 ` [PATCH nf-next-2.6] conntrack: IPS_UNTRACKED bit Eric Dumazet
2010-06-04 20:15 ` [PATCH nf-next-2.6 2/2] conntrack: per_cpu untracking Eric Dumazet
2010-06-08 14:29 ` Patrick McHardy
2010-06-08 14:52 ` Eric Dumazet
2010-06-08 15:12 ` Eric Dumazet
2010-06-09 12:45 ` Patrick McHardy
2010-06-08 14:12 ` [PATCH nf-next-2.6] conntrack: IPS_UNTRACKED bit Patrick McHardy
2010-04-23 10:56 ` DDoS attack causing bad effect on conntrack searches Patrick McHardy
2010-04-23 12:45 ` Jesper Dangaard Brouer
2010-04-23 13:57 ` Patrick McHardy
2010-04-22 13:31 ` Jesper Dangaard Brouer
2010-04-23 10:35 ` Patrick McHardy
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=4BD04C74.9020402@trash.net \
--to=kaber@trash$(echo .)net \
--cc=eric.dumazet@gmail$(echo .)com \
--cc=hawk@comx$(echo .)dk \
--cc=netdev@vger$(echo .)kernel.org \
--cc=netfilter-devel@vger$(echo .)kernel.org \
--cc=paulmck@linux$(echo .)vnet.ibm.com \
--cc=xiaosuo@gmail$(echo .)com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox