netdev - Re: [PATCH net] openvswitch: take into account de-fragmentation in execute_check_pkt

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Message-ID: <20200622204651.GE27892@localhost.localdomain>
Date:   Mon, 22 Jun 2020 22:46:51 +0200
From:   Lorenzo Bianconi <lorenzo.bianconi@...hat.com>
To:     Pravin Shelar <pravin.ovn@...il.com>
Cc:     Lorenzo Bianconi <lorenzo@...nel.org>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Numan Siddique <nusiddiq@...hat.com>,
        Greg Rose <gvrose8192@...il.com>, ovs dev <dev@...nvswitch.org>
Subject: Re: [PATCH net] openvswitch: take into account de-fragmentation in
 execute_check_pkt_len

> On Mon, Jun 22, 2020 at 5:02 AM Lorenzo Bianconi <lorenzo@...nel.org> wrote:
> >
> > > On Fri, Jun 19, 2020 at 4:48 AM Lorenzo Bianconi <lorenzo@...nel.org> wrote:
> > > >
> > > > ovs connection tracking module performs de-fragmentation on incoming
> > > > fragmented traffic. Take info account if traffic has been de-fragmented
> > > > in execute_check_pkt_len action otherwise we will perform the wrong
> > > > nested action considering the original packet size. This issue typically
> > > > occurs if ovs-vswitchd adds a rule in the pipeline that requires connection
> > > > tracking (e.g. OVN stateful ACLs) before execute_check_pkt_len action.
> > > >
> > > > Fixes: 4d5ec89fc8d14 ("net: openvswitch: Add a new action check_pkt_len")
> > > > Signed-off-by: Lorenzo Bianconi <lorenzo@...nel.org>
> > > > ---
> > > >  net/openvswitch/actions.c | 6 ++++--
> > > >  1 file changed, 4 insertions(+), 2 deletions(-)
> > > >
> > > > diff --git a/net/openvswitch/actions.c b/net/openvswitch/actions.c
> > > > index fc0efd8833c8..9f4dd64e53bb 100644
> > > > --- a/net/openvswitch/actions.c
> > > > +++ b/net/openvswitch/actions.c
> > > > @@ -1169,9 +1169,10 @@ static int execute_check_pkt_len(struct datapath *dp, struct sk_buff *skb,
> > > >                                  struct sw_flow_key *key,
> > > >                                  const struct nlattr *attr, bool last)
> > > >  {
> > > > +       struct ovs_skb_cb *ovs_cb = OVS_CB(skb);
> > > >         const struct nlattr *actions, *cpl_arg;
> > > >         const struct check_pkt_len_arg *arg;
> > > > -       int rem = nla_len(attr);
> > > > +       int len, rem = nla_len(attr);
> > > >         bool clone_flow_key;
> > > >
> > > >         /* The first netlink attribute in 'attr' is always
> > > > @@ -1180,7 +1181,8 @@ static int execute_check_pkt_len(struct datapath *dp, struct sk_buff *skb,
> > > >         cpl_arg = nla_data(attr);
> > > >         arg = nla_data(cpl_arg);
> > > >
> > > > -       if (skb->len <= arg->pkt_len) {
> > > > +       len = ovs_cb->mru ? ovs_cb->mru : skb->len;
> > > > +       if (len <= arg->pkt_len) {
> > >
> > > We could also check for the segmented packet and use  segment length
> > > for this check.
> >
> > Hi Pravin,
> >
> > thx for review.
> > By 'segmented packet' and 'segment length', do you mean 'fragment' and
> > 'fragment length'?
> 
> I am actually talking about GSO packets.

ack. IIUC you mean to add a check for gso packets as well taking into account
gso_size. I will fix in v2.

Regards,
Lorenzo

> 
> Thanks.
> 
> > If so I guess we can't retrieve the original fragment length if we exec
> > OVS_ACTION_ATTR_CT before OVS_ACTION_ATTR_CHECK_PKT_LEN (e.g if we have a
> > stateful ACL in the ingress pipeline) since handle_fragments() will reconstruct
> > the whole IP datagram and it will store frag_max_size in OVS_CB(skb)->mru.
> > Am I missing something?
> >
> > Regards,
> > Lorenzo
> >
> 

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