netdev - Re: [PATCH net v2] openvswitch: Fix conntrack cache with timeout

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Message-ID: <CAG1aQhLkrvVADEtAFcdO+GX03SGx7GMW1YyLVTGrPjiCz1HMyQ@mail.gmail.com>
Date:   Fri, 23 Aug 2019 09:40:34 -0700
From:   Yi-Hung Wei <yihung.wei@...il.com>
To:     Pravin Shelar <pshelar@....org>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [PATCH net v2] openvswitch: Fix conntrack cache with timeout

On Thu, Aug 22, 2019 at 11:51 PM Pravin Shelar <pshelar@....org> wrote:
>
> On Thu, Aug 22, 2019 at 1:28 PM Yi-Hung Wei <yihung.wei@...il.com> wrote:
> >
> > This patch addresses a conntrack cache issue with timeout policy.
> > Currently, we do not check if the timeout extension is set properly in the
> > cached conntrack entry.  Thus, after packet recirculate from conntrack
> > action, the timeout policy is not applied properly.  This patch fixes the
> > aforementioned issue.
> >
> > Fixes: 06bd2bdf19d2 ("openvswitch: Add timeout support to ct action")
> > Reported-by: kbuild test robot <lkp@...el.com>
> > Signed-off-by: Yi-Hung Wei <yihung.wei@...il.com>
> > ---
> > v1->v2: Fix rcu dereference issue reported by kbuild test robot.
> > ---
> >  net/openvswitch/conntrack.c | 13 +++++++++++++
> >  1 file changed, 13 insertions(+)
> >
> > diff --git a/net/openvswitch/conntrack.c b/net/openvswitch/conntrack.c
> > index 848c6eb55064..4d7896135e73 100644
> > --- a/net/openvswitch/conntrack.c
> > +++ b/net/openvswitch/conntrack.c
> > @@ -1657,6 +1666,10 @@ int ovs_ct_copy_action(struct net *net, const struct nlattr *attr,
> >                                       ct_info.timeout))
> >                         pr_info_ratelimited("Failed to associated timeout "
> >                                             "policy `%s'\n", ct_info.timeout);
> > +               else
> > +                       ct_info.nf_ct_timeout = rcu_dereference(
> > +                               nf_ct_timeout_find(ct_info.ct)->timeout);
> Is this dereference safe from NULL pointer?

Hi Pravin,

Thanks for your review.  I am not sure if
nf_ct_timeout_find(ct_info.ct) will return NULL in this case.

We only run into this statement when ct_info.timeout[0] is set, and it
is only set in parse_ct() when CONFIG_NF_CONNTRACK_TIMEOUT is
configured.  Also, in this else condition the timeout extension is
supposed to be set properly by nf_ct_set_timeout().

Am I missing something?

Thanks,

-Yi-Hung