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

[Lorenzo Bianconi <lorenzo@kernel.org>]

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> On Fri, Jun 19, 2020 at 4:48 AM Lorenzo Bianconi <lorenzo@kernel.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@kernel.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'?
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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