[PATCH] Check net->nfnl for NULL in ctnetlink_conntrack_event to, avoid Oops on container destroy

[PATCH] Check net->nfnl for NULL in ctnetlink_conntrack_event to, avoid Oops on container destroy

[Tim Gardner]

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Patrick,

I received this patch from a developer that uses lxc and network name 
spaces. I don't know the locking semantics well enough for CT to judge 
whether this fix is sufficient. Bug info can be found at 
http://bugs.launchpad.net/bugs/843892 . See comment #7 for his analysis.

rtg
-- 
Tim Gardner tim.gardner@canonical.com

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>From dcb64e27c7daaf4affe5b1a617b45a9a0364b4ad Mon Sep 17 00:00:00 2001
From: Alex Bligh <alex@alex.org.uk>
Date: Sat, 10 Sep 2011 13:29:12 +0100
Subject: [PATCH] Check net->nfnl for NULL in ctnetlink_conntrack_event to
 avoid Oops on container destroy


Signed-off-by: Alex Bligh <alex@alex.org.uk>
---
 net/netfilter/nf_conntrack_netlink.c |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)

diff --git a/net/netfilter/nf_conntrack_netlink.c b/net/netfilter/nf_conntrack_netlink.c
index 482e90c..0790d0a 100644
--- a/net/netfilter/nf_conntrack_netlink.c
+++ b/net/netfilter/nf_conntrack_netlink.c
@@ -570,6 +570,11 @@ ctnetlink_conntrack_event(unsigned int events, struct nf_ct_event *item)
 		return 0;
 
 	net = nf_ct_net(ct);
+
+	/* container deinit, netlink may have died before death_by_timeout */
+	if (!net->nfnl)
+		return 0;
+
 	if (!item->report && !nfnetlink_has_listeners(net, group))
 		return 0;
 
-- 
1.7.5.4

Re: [PATCH] Check net->nfnl for NULL in ctnetlink_conntrack_event to, avoid Oops on container destroy

[Tim Gardner]

On 09/12/2011 12:03 PM, Tim Gardner wrote:
> Patrick,
>
> I received this patch from a developer that uses lxc and network name
> spaces. I don't know the locking semantics well enough for CT to judge
> whether this fix is sufficient. Bug info can be found at
> http://bugs.launchpad.net/bugs/843892 . See comment #7 for his analysis.
>
> rtg

Never mind. Looks like Alex already sent this patch on Sept 10 with the 
subject 'Fix repeatable Oops on container destroy with conntrack'.

rtg

-- 
Tim Gardner tim.gardner@canonical.com

Re: [PATCH] Check net->nfnl for NULL in ctnetlink_conntrack_event to, avoid Oops on container destroy

[Julian Anastasov]

	Hello,

On Mon, 12 Sep 2011, Tim Gardner wrote:

> Patrick,
> 
> I received this patch from a developer that uses lxc and network name spaces.
> I don't know the locking semantics well enough for CT to judge whether this
> fix is sufficient. Bug info can be found at
> http://bugs.launchpad.net/bugs/843892 . See comment #7 for his analysis.

	We found same problems triggered by IPVS during
subsys cleanup:

http://marc.info/?l=netfilter-devel&m=130765388528399&w=2

	It is a general problem for modules that register
callbacks to the netfilter core. nfnetlink is such example
with a mix of global (ctnl_notifier) and per-net (nfnetlink_net_ops) 
registrations. During net cleanup the module must be prepared
to be called by core because the core cleanup happens later.

	So, may be rcu_dereference under rcu lock is needed for
some functions (nfnetlink_has_listeners, nfnetlink_send) but
such changes should be audited by nfnetlink developers.
Using rcu_assign_pointer for net->nfnl without corresponding 
rcu_dereference looks like a problem.

Regards

--
Julian Anastasov <ja@ssi.bg>

Re: [PATCH] Check net->nfnl for NULL in ctnetlink_conntrack_event to, avoid Oops on container destroy

[Pablo Neira Ayuso]

On Mon, Sep 12, 2011 at 12:03:13PM -0600, Tim Gardner wrote:
> Patrick,
> 
> I received this patch from a developer that uses lxc and network
> name spaces. I don't know the locking semantics well enough for CT
> to judge whether this fix is sufficient. Bug info can be found at
> http://bugs.launchpad.net/bugs/843892 . See comment #7 for his
> analysis.

We're still discussing a better solution for it.