Re: [PATCH net-next v2 3/5] mpls: Differentiate implicit-null and unlabeled neighbours
From: Eric W. Biederman <hidden>
Date: 2015-03-22 19:53:22
Robert Shearman [off-list ref] writes:
The control plane can advertise labels for neighbours that don't have an outgoing label. RFC 3032 s3.22 states that either the remaining labels should be popped (if the control plane can determine that it's safe to do so, which in light of MPLS-VPN, RFC 4364, is never the case now) or that the packet should be discarded.
I can not figure out what you are referring to. There is no section 3.2 in RFC3022.
Therefore, if the peer is unlabeled and the last label wasn't popped then drop the packet. The peer being unlabeled is signalled by an empty label stack. However, implicit-null still needs to be supported (i.e. penultimate hop popping) where the incoming label is popped and no labels are put on and the packet can still go out labeled with the unpopped part of the stack. This is achieved by the control plane specifying a label stack consisting of the single special implicit-null value.
As I understand it you want to handle the case for a label for which there is no next hop, and the packet should be black-holed. In struct mpls_route such routes are currently represented by routes that have no network device. And in rtnetlink should be represented with routes of type RTN_BLACKHOLE which I do not currently support parsing. But that should be simple enough to correc.t With respect to Implicit NULL it should be an error to accept a route that has an RTA_NEWDST that includes an implicit NULL. The rtnetlink is not ldp nor should it have ldp semantics and be made complicated by those semantics. The semantics of RTA_NEWDST are the labels to push on after the top most label has been popped off. I see no reason to include other mechanisms into that processing when it is easy enough to add or tweak other attributes to have those semantics. Certainly it is not something that I think is worth special casing on the fast path in mpls_forward.
quoted hunk ↗ jump to hunk
Cc: "Eric W. Biederman" <redacted> Signed-off-by: Robert Shearman <redacted> --- net/mpls/af_mpls.c | 21 +++++++++++++++++---- 1 file changed, 17 insertions(+), 4 deletions(-)diff --git a/net/mpls/af_mpls.c b/net/mpls/af_mpls.c index bf3459a..e3586a7 100644 --- a/net/mpls/af_mpls.c +++ b/net/mpls/af_mpls.c@@ -28,7 +28,8 @@ struct mpls_route { /* next hop label forwarding entry */ struct rcu_head rt_rcu; u32 rt_label[MAX_NEW_LABELS]; u8 rt_protocol; /* routing protocol that set this entry */ - u8 rt_labels; + u8 rt_unlabeled : 1; + u8 rt_labels : 7; u8 rt_via_alen; u8 rt_via_table; u8 rt_via[0];@@ -201,6 +202,11 @@ static int mpls_forward(struct sk_buff *skb, struct net_device *dev, if (unlikely(!new_header_size && dec.bos)) { if (!mpls_egress(rt, skb, dec)) goto drop; + } else if (rt->rt_unlabeled) { + /* Labeled traffic destined to unlabeled peer should + * be discarded + */ + goto drop; } else { bool bos; int i;@@ -385,9 +391,16 @@ static int mpls_route_add(struct mpls_route_config *cfg) if (!rt) goto errout; - rt->rt_labels = cfg->rc_output_labels; - for (i = 0; i < rt->rt_labels; i++) - rt->rt_label[i] = cfg->rc_output_label[i]; + if (cfg->rc_output_labels == 1 && + cfg->rc_output_label[0] == LABEL_IMPLICIT_NULL) { + rt->rt_labels = 0; + } else { + rt->rt_labels = cfg->rc_output_labels; + for (i = 0; i < rt->rt_labels; i++) + rt->rt_label[i] = cfg->rc_output_label[i]; + if (!rt->rt_labels) + rt->rt_unlabeled = true; + } rt->rt_protocol = cfg->rc_protocol; RCU_INIT_POINTER(rt->rt_dev, dev); rt->rt_via_table = cfg->rc_via_table;