netdev - Re: Oops in nf_nat_core.c:find_appropriate

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Date:	Sat, 07 Jun 2008 17:14:29 +0200
From:	Patrick McHardy <kaber@...sh.net>
To:	Chuck Ebbert <cebbert@...hat.com>
CC:	Netdev <netdev@...r.kernel.org>,
	Netfilter Development Mailinglist 
	<netfilter-devel@...r.kernel.org>
Subject: Re: Oops in nf_nat_core.c:find_appropriate_src(), kernel 2.6.25.4

Patrick McHardy wrote:
> Chuck Ebbert wrote:
>> Reported at https://bugzilla.redhat.com/show_bug.cgi?id=449315
>>
>> In find_appropriate_src():
>>
>>         hlist_for_each_entry_rcu(nat, n, &bysource[h], bysource) {
>>                 ct = nat->ct;
>>                 if (same_src(ct, tuple)) {
>>
>> Dereference of ct in same_src() causes the oops. This only seems to
>> happen on heavily loaded firewall machines. Kernel 2.6.24.7 works.
>>
>> The reporter identifies commit 4d354c5782dc352cec187845d17eedc2c2bfcf67
>> ("[NETFILTER]: nf_nat: use RCU for bysource hash") as a possible cause
>> of the problem.
> 
> We have a similar looking report, but that one also affects 2.6.24:
> 
> http://bugzilla.kernel.org/show_bug.cgi?id=10875
> 
> Anyways, does this patch help? When reallocating storage
> for a conntrack, it is replaced in the list before assigning
> the nat->ct pointer.


I'm afraid we also need this one on top - when reallocating
an extension, we must not free the old storage since it may
still be used in a RCU read side.



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