[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <4A3A67B5.1060909@netfilter.org>
Date: Thu, 18 Jun 2009 18:13:41 +0200
From: Pablo Neira Ayuso <pablo@...filter.org>
To: Patrick McHardy <kaber@...sh.net>
CC: Eric Dumazet <eric.dumazet@...il.com>, Ingo Molnar <mingo@...e.hu>,
David Miller <davem@...emloft.net>,
Thomas Gleixner <tglx@...utronix.de>,
torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [bug] __nf_ct_refresh_acct(): WARNING: at lib/list_debug.c:30
__list_add+0x7d/0xad()
Patrick McHardy wrote:
> Eric Dumazet wrote:
>> In my own analysis, I found death_by_timeout() might be problematic,
>> with RCU and lockless lookups.
>>
>> static void death_by_timeout(unsigned long ul_conntrack)
>> {
>> struct nf_conn *ct = (void *)ul_conntrack;
>>
>> if (!test_bit(IPS_DYING_BIT, &ct->status) &&
>> unlikely(nf_conntrack_event(IPCT_DESTROY, ct) < 0)) {
>> /* destroy event was not delivered */
>> nf_ct_delete_from_lists(ct);
>> << HERE >>
>>
>> nf_ct_insert_dying_list(ct);
>> return;
>> }
>> set_bit(IPS_DYING_BIT, &ct->status);
>> nf_ct_delete_from_lists(ct);
>> nf_ct_put(ct);
>> }
>>
>>
>> We delete ct from a list and insert it in a new list.
>>
>> I believe a reader could "*catch*" ct while doing a lookup and miss
>> the end
>> of its chain. (nulls algo check the null value at the end of lookup
>> and can
>> decide to restart the lookup if the null value is not the expected one)
>>
>> We need to change nf_conntrack_init_net() and use a different "null"
>> value,
>> guaranteed not being used in regular lists
>
> Good catch. This is a new bug, but it shouldn't matter in this case
> since nf_conntrack_event() can't fail unless you have a userspace
> listener that makes use of reliable delivery, which I think hasn't
> even been released yet.
Indeed. I didn't include user-space support for this yet in my tree, so
this should not be the problem. Thanks for the catch anyway!
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists