netdev - RE: [PATCH nf v3 1/1] netfilter: snmp: Fix one possible panic when snmp_trap

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Date:   Fri, 24 Mar 2017 20:42:07 +0800
From:   "Gao Feng" <gfree.wind@...mail.com>
To:     "'Pablo Neira Ayuso'" <pablo@...filter.org>, <fgao@...ai8.com>
Cc:     <davem@...emloft.net>, <jolsa@...hat.com>,
        <netfilter-devel@...r.kernel.org>, <netdev@...r.kernel.org>,
        <gfree.wind@...il.com>
Subject: RE: [PATCH nf v3 1/1] netfilter: snmp: Fix one possible panic when snmp_trap_helper fail to register

Hi Pablo,

> -----Original Message-----
> From: netfilter-devel-owner@...r.kernel.org
> [mailto:netfilter-devel-owner@...r.kernel.org] On Behalf Of Pablo Neira
Ayuso
> Sent: Friday, March 24, 2017 8:23 PM
> To: fgao@...ai8.com
> Cc: davem@...emloft.net; jolsa@...hat.com;
netfilter-devel@...r.kernel.org;
> netdev@...r.kernel.org; gfree.wind@...il.com
> Subject: Re: [PATCH nf v3 1/1] netfilter: snmp: Fix one possible panic
when
> snmp_trap_helper fail to register
> 
> On Fri, Mar 24, 2017 at 01:21:30PM +0100, Pablo Neira Ayuso wrote:
> > On Tue, Mar 21, 2017 at 08:22:29AM +0800, fgao@...ai8.com wrote:
> > > From: Gao Feng <fgao@...ai8.com>
> > >
> > > In the commit 93557f53e1fb ("netfilter: nf_conntrack: nf_conntrack
> > > snmp helper"), the snmp_helper is replaced by nf_nat_snmp_hook. So
> > > the snmp_helper is never registered. But it still tries to
> > > unregister the snmp_helper, it could cause the panic.
> >
> > This patch looks correct to me.
> >
> > But probably for some reason I don't manage to trigger, how do you
> > reproduce this?
> 
> I'm refering to the panic.
[高峰] 
It is got by reviewing the codes.
When nf_conntrack_helper_unregister(&snmp_helper), but snmp_helper didn't
register actually.
And snmp_helper. hnode is not initialized, it would trigger the issue when
hlist_del_rcu in nf_conntrack_helper_unregister.

Best Regards
Feng


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