From: ebiederm@xmission•com (Eric W. Biederman)
To: Florian Westphal <fw@strlen•de>
Cc: Pablo Neira Ayuso <pablo@netfilter•org>,
netfilter-devel@vger•kernel.org, dale.4d@gmail•com,
netdev@vger•kernel.org
Subject: Re: [PATCH nf V2] netfilter: fix oops in nfqueue during netns error unwinding
Date: Sat, 14 May 2016 22:00:09 -0500 [thread overview]
Message-ID: <87h9e0do06.fsf@x220.int.ebiederm.org> (raw)
In-Reply-To: <20160514103309.GD29941@breakpoint.cc> (Florian Westphal's message of "Sat, 14 May 2016 12:33:09 +0200")
Florian Westphal <fw@strlen•de> writes:
> Eric W. Biederman <ebiederm@xmission•com> wrote:
>> Florian Westphal <fw@strlen•de> writes:
>>
>> > Eric W. Biederman <ebiederm@xmission•com> wrote:
>> >> Florian could you test and verify this patch fixes your issues?
>> >
>> > Yes, this seems to work.
>> >
>> > Pablo, I'm fine with this patch going into -nf/stable but I do not think
>> > making the pointers per netns is a desireable option in the long term.
>> >
>> >> Unlike the other possibilities that have been discussed this also
>> >> addresses the nf_queue path as well as the nf_queue_hook_drop path.
>> >
>> > The nf_queue path should have been fine, no?
>> >
>> > Or putting it differently: can we start processing skbs before a netns
>> > is fully initialized?
>>
>> The practical case that worries me is what happens when someone does
>> "rmmod nfnetlink_queue" while the system is running. It appears to me
>> that today we could free the per netns data during the rcu grace period
>> and cause a similar issue in nfnl_queue_pernet.
>>
>> That looks like it could affect both the nf_queue path and the
>> nf_queue_nf_hook_drop path.
>
> OK, I'll check this again but I seem to recall this was fine (the
> nfqueue module exit path sets the handler to NULL before doing anything
> else).
Good point.
Yes, the nfnetlink_queue module calls nf_unregister_queue_handler()
in the module fini method before it does anything else. That does
set queue_handler to NULL and calls synchronize_rcu() before anything
else.
So in practice that is not a problem, but being disconnected from
everything else that is not immediately apparent. Sigh.
> The normal netns exit path should be fine too as exit and free happens
> in two distinct loops, i.e. while (without your change) we can have
> calls to nf_queue_hook_drop after the nfqueue netns exit function was
> called, these calls will always happen before the pernets data is
> freed.
Ouch. That is a little scary. Today we only have remove_proc_entry
in nfnl_queue_net_exit. If we had something more substantial those
calls after .exit (without my change) we could get into nasty to find
oopses. So I guess I did prevent a possible future issue with my patch.
I am half wondering if we could make everything simpler by simply not
allowing nfnetlink_queue be a module.
Eric
next prev parent reply other threads:[~2016-05-15 3:00 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-11 15:41 [PATCH nf V2] netfilter: fix oops in nfqueue during netns error unwinding Florian Westphal
2016-05-12 9:47 ` Pablo Neira Ayuso
2016-05-12 16:15 ` Eric W. Biederman
2016-05-12 16:40 ` Florian Westphal
2016-05-13 19:40 ` Eric W. Biederman
2016-05-13 20:04 ` Florian Westphal
2016-05-13 20:26 ` Eric W. Biederman
2016-05-13 21:07 ` Florian Westphal
2016-05-13 20:44 ` Eric W. Biederman
2016-05-13 21:20 ` Florian Westphal
2016-05-14 0:58 ` Eric W. Biederman
2016-05-14 10:33 ` Florian Westphal
2016-05-15 3:00 ` Eric W. Biederman [this message]
2016-05-14 2:18 ` [PATCH] nf_queue: Make the queue_handler pernet Eric W. Biederman
2016-05-30 9:31 ` Pablo Neira Ayuso
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