Subject: Re: [PATCH net-next] Change in Openvswitch to support MPLS label depth of 3 in ingress direction

From: Martin Varghese <[email-masked]>
Date: Thu, 10 Oct 2019 10:01:01 +0530

On Wed, Oct 09, 2019 at 08:29:51AM -0700, Pravin Shelar wrote:
> On Mon, Oct 7, 2019 at 9:41 PM Martin Varghese
> <[email-masked]> wrote:
> >
> > From: Martin Varghese <[email-masked]>
> >
> > The openvswitch was supporting a MPLS label depth of 1 in the ingress
> > direction though the userspace OVS supports a max depth of 3 labels.
> > This change enables openvswitch module to support a max depth of
> > 3 labels in the ingress.
> >
> > Signed-off-by: Martin Varghese <[email-masked]>
> > ---
> >  net/openvswitch/actions.c      | 10 +++++++-
> >  net/openvswitch/flow.c         | 20 ++++++++++-----
> >  net/openvswitch/flow.h         |  9 ++++---
> >  net/openvswitch/flow_netlink.c | 55 +++++++++++++++++++++++++++++++++---------
> >  4 files changed, 72 insertions(+), 22 deletions(-)
> >
> > diff --git a/net/openvswitch/actions.c b/net/openvswitch/actions.c
> > index 3572e11..eb5bed5 100644
> > --- a/net/openvswitch/actions.c
> > +++ b/net/openvswitch/actions.c
> > @@ -178,10 +178,14 @@ static int pop_mpls(struct sk_buff *skb, struct sw_flow_key *key,
> >  {
> >         int err;
> >
> > +       if (!key->mpls.num_labels_mask)
> > +               return -EINVAL;
> > +
> >         err = skb_mpls_pop(skb, ethertype);
> >         if (err)
> >                 return err;
> >
> > +       key->mpls.num_labels_mask >>= 1;
> >         invalidate_flow_key(key);
> Since this key is immediately invalidated, what is point of updating
> the label count?
> 

The num_labels_mask is being checked in the pop_mpls action to see if anymore
label present to pop.

if (!key->mpls.num_labels_mask)
	return -EINVAL:

> >         return 0;
> >  }
> What about checks in OVS_ACTION_ATTR_PUSH_MPLS?
>
The change does not have any impact to the PUSH_MPLS actions.
It should work as before.

> > @@ -192,6 +196,7 @@ static int set_mpls(struct sk_buff *skb, struct sw_flow_key *flow_key,
> >         struct mpls_shim_hdr *stack;
> >         __be32 lse;
> >         int err;
> > +       u32 i = 0;
> >
> >         stack = mpls_hdr(skb);
> >         lse = OVS_MASKED(stack->label_stack_entry, *mpls_lse, *mask);
> > @@ -199,7 +204,10 @@ static int set_mpls(struct sk_buff *skb, struct sw_flow_key *flow_key,
> >         if (err)
> >                 return err;
> >
> > -       flow_key->mpls.top_lse = lse;
> > +       for (i = MPLS_LABEL_DEPTH - 1; i > 0; i--)
> > +               flow_key->mpls.lse[i] = flow_key->mpls.lse[i - 1];
> > +
> > +       flow_key->mpls.lse[i] = *mpls_lse;
> This is changing semantic of mpls-set action. It is looking like
> mpls-push. Lets keep the MPLS set that sets one or more MPLS lebels.
> 
> >         return 0;
> >  }

Not sure if I got your comment correct.
Just as before, the new code updates the top most label in the flow_key.
> >
> > diff --git a/net/openvswitch/flow.c b/net/openvswitch/flow.c
> > index dca3b1e..c101355 100644
> > --- a/net/openvswitch/flow.c
> > +++ b/net/openvswitch/flow.c
> > @@ -699,27 +699,35 @@ static int key_extract(struct sk_buff *skb, struct sw_flow_key *key)
> >                         memset(&key->ipv4, 0, sizeof(key->ipv4));
> >                 }
> >         } else if (eth_p_mpls(key->eth.type)) {
> > -               size_t stack_len = MPLS_HLEN;
> > +               u8 label_count = 1;
> >
> > +               memset(&key->mpls, 0, sizeof(key->mpls));
> >                 skb_set_inner_network_header(skb, skb->mac_len);
> >                 while (1) {
> >                         __be32 lse;
> >
> > -                       error = check_header(skb, skb->mac_len + stack_len);
> > +                       error = check_header(skb, skb->mac_len +
> > +                                            label_count * MPLS_HLEN);
> I do not think this is right. This way OVS can copy into MPLS labels
> from next header beyond MPLS. You need parse MPLS header and determine
> end of MPLS labels.
> 
The MPLS labels are parsed and then the label count is updated.
Did i miss anything ?
> >                         if (unlikely(error))
> >                                 return 0;
> >
> >                         memcpy(&lse, skb_inner_network_header(skb), MPLS_HLEN);
> >
> > -                       if (stack_len == MPLS_HLEN)
> > -                               memcpy(&key->mpls.top_lse, &lse, MPLS_HLEN);
> > +                       if (label_count <= MPLS_LABEL_DEPTH)
> > +                               memcpy(&key->mpls.lse[label_count - 1], &lse,
> > +                                      MPLS_HLEN);
> >
> > -                       skb_set_inner_network_header(skb, skb->mac_len + stack_len);
> > +                       skb_set_inner_network_header(skb, skb->mac_len +
> > +                                                    label_count * MPLS_HLEN);
> >                         if (lse & htonl(MPLS_LS_S_MASK))
> >                                 break;
> >
> > -                       stack_len += MPLS_HLEN;
> > +                       label_count++;
> >                 }
> > +               if (label_count > MPLS_LABEL_DEPTH)
> > +                       label_count = MPLS_LABEL_DEPTH;
> > +
> > +               key->mpls.num_labels_mask = GENMASK(label_count - 1, 0);
> >         } else if (key->eth.type == htons(ETH_P_IPV6)) {
> >                 int nh_len;             /* IPv6 Header + Extensions */
> >
> ...
> ...
> > diff --git a/net/openvswitch/flow_netlink.c b/net/openvswitch/flow_netlink.c
> > index d7559c6..4eb04e9 100644
> > --- a/net/openvswitch/flow_netlink.c
> > +++ b/net/openvswitch/flow_netlink.c
> > @@ -424,7 +424,7 @@ size_t ovs_key_attr_size(void)
> >         [OVS_KEY_ATTR_DP_HASH]   = { .len = sizeof(u32) },
> >         [OVS_KEY_ATTR_TUNNEL]    = { .len = OVS_ATTR_NESTED,
> >                                      .next = ovs_tunnel_key_lens, },
> > -       [OVS_KEY_ATTR_MPLS]      = { .len = sizeof(struct ovs_key_mpls) },
> > +       [OVS_KEY_ATTR_MPLS]      = { .len = OVS_ATTR_VARIABLE },
> >         [OVS_KEY_ATTR_CT_STATE]  = { .len = sizeof(u32) },
> >         [OVS_KEY_ATTR_CT_ZONE]   = { .len = sizeof(u16) },
> >         [OVS_KEY_ATTR_CT_MARK]   = { .len = sizeof(u32) },
> > @@ -1628,10 +1628,26 @@ static int ovs_key_from_nlattrs(struct net *net, struct sw_flow_match *match,
> >
> >         if (attrs & (1 << OVS_KEY_ATTR_MPLS)) {
> >                 const struct ovs_key_mpls *mpls_key;
> > +               u32 hdr_len = 0;
> > +               u32 label_count = 0, i = 0;
> > +               u32 label_count_mask = 0;
> No need to initialize these values.

> >
> >                 mpls_key = nla_data(a[OVS_KEY_ATTR_MPLS]);
> > -               SW_FLOW_KEY_PUT(match, mpls.top_lse,
> > -                               mpls_key->mpls_lse, is_mask);
> > +               hdr_len = nla_len(a[OVS_KEY_ATTR_MPLS]);
> > +               label_count = hdr_len / sizeof(struct ovs_key_mpls);
> > +
> > +               if (label_count == 0 || label_count > MPLS_LABEL_DEPTH ||
> > +                   hdr_len % sizeof(struct ovs_key_mpls))
> > +                       return -EINVAL;
> > +
> > +               label_count_mask =  GENMASK(label_count - 1, 0);
> > +
> > +               for (i = 0 ; i < label_count; i++)
> > +                       SW_FLOW_KEY_PUT(match, mpls.lse[i],
> > +                                       mpls_key[i].mpls_lse, is_mask);
> > +
> > +               SW_FLOW_KEY_PUT(match, mpls.num_labels_mask,
> > +                               label_count_mask, is_mask);
> >
> >                 attrs &= ~(1 << OVS_KEY_ATTR_MPLS);
> >          }
> > @@ -2114,13 +2130,22 @@ static int __ovs_nla_put_key(const struct sw_flow_key *swkey,
> >                 ether_addr_copy(arp_key->arp_sha, output->ipv4.arp.sha);
> >                 ether_addr_copy(arp_key->arp_tha, output->ipv4.arp.tha);
> >         } else if (eth_p_mpls(swkey->eth.type)) {
> > +               u8 i = 0;
> > +               u8 num_labels;
> >                 struct ovs_key_mpls *mpls_key;
> >
> > -               nla = nla_reserve(skb, OVS_KEY_ATTR_MPLS, sizeof(*mpls_key));
> > +               num_labels = hweight_long(output->mpls.num_labels_mask);
> > +               if (num_labels >= MPLS_LABEL_DEPTH)
> > +                       num_labels = MPLS_LABEL_DEPTH;
> I do not see need for this check. We can copy the value directly from key.
> 

> > +
> > +               nla = nla_reserve(skb, OVS_KEY_ATTR_MPLS,
> > +                                 num_labels * sizeof(*mpls_key));
> >                 if (!nla)
> >                         goto nla_put_failure;
> > +
> >                 mpls_key = nla_data(nla);
> > -               mpls_key->mpls_lse = output->mpls.top_lse;
> > +               for (i = 0; i < num_labels; i++)
> > +                       mpls_key[i].mpls_lse = output->mpls.lse[i];
> >         }
> >
> >         if ((swkey->eth.type == htons(ETH_P_IP) ||
> > @@ -3068,22 +3093,28 @@ static int __ovs_nla_copy_actions(struct net *net, const struct nlattr *attr,
> >                         break;
> >                 }
> >
> > -               case OVS_ACTION_ATTR_POP_MPLS:
> > +               case OVS_ACTION_ATTR_POP_MPLS: {
> > +                       __be16  proto;
> >                         if (vlan_tci & htons(VLAN_CFI_MASK) ||
> >                             !eth_p_mpls(eth_type))
> >                                 return -EINVAL;
> >
> Since this patch is adding support for multiple labels, we need to
> track depth of the MPLS label stack in MPLS push and pop actions
> validation to avoid checks in fastpath.
>
As mentioned before this change has no impact to the push.
As before, there is no restriction on the number of pushes we can make.

For the pop_mpls, we coud add a local variable to count the number of pops
and validate that against MPLS_LABEL_DEPTH ?
> > -                       /* Disallow subsequent L2.5+ set and mpls_pop actions
> > -                        * as there is no check here to ensure that the new
> > -                        * eth_type is valid and thus set actions could
> > -                        * write off the end of the packet or otherwise
> > -                        * corrupt it.
> > +                       /* Disallow subsequent L2.5+ set actions as there is
> > +                        * no check here to ensure that the new eth type is
> > +                        * valid and thus set actions could write off the
> > +                        * end of the packet or otherwise corrupt it.
> >                          *
> >                          * Support for these actions is planned using packet
> >                          * recirculation.
> >                          */
> > -                       eth_type = htons(0);
> > +
> > +                       proto = nla_get_be16(a);
> > +                       if (!eth_p_mpls(proto))
> > +                               eth_type = htons(0);
> > +                       else
> > +                               eth_type =  proto;
> 
> I do not see any point of changing this validation logic. OVS can not
> parse beyond MPLS, so lets keep this as it it.
> 
> 
unlike before, we can have multiple pop actions now.so we need to update
the eth_type properly if the proto is MPLS.
> >                         break;
> > +               }
> >
> >                 case OVS_ACTION_ATTR_SET:
> >                         err = validate_set(a, key, sfa,
> 
> I would also like to see patch that adds multi label MPLS unit test in
> system-traffic.at along with this patch.