bgpd: fix Prefix-SID parsing failure case

Prefix-SID path attribute Label-index TLV (type-1) is
used by SR-MPLS. And Label-index TLV MUST ignored
if that path attribute is append on non-Labeled-unicast
UPDATE message described on [ref1].
There is a problem case exist arround this implementation.
This commit fix that.

Before this commit,
unfortunally, setting Label-Index value is skipped at somecases.
because, Label-Index TLV implementation check the AFI/SAFI pair.
by mp_update variable that is set by bgp_mp_reach_parse function.
if MP_REACH_NLRI is present after PREFIX_SID, bgp_attr_psid_sub
function can't understand AFI/SAFI pair. and the order of each
path attributes is never no-deterministic thing for receiver.[ref2]

In this commit,
I re-located checking code of AFI/SAFI pair after path-attr loop.

[ref1](https://tools.ietf.org/html/draft-ietf-idr-bgp-prefix-sid-27#section-3.2)
> The Originator SRGB TLV may only appear in a BGP Prefix-SID attribute
> attached to IPv4/IPv6 Labeled Unicast prefixes ([RFC8277]).  It MUST
> be ignored when received for other BGP AFI/SAFI combinations.

[ref2](https://tools.ietf.org/html/rfc4271#section-5)
> The sender of an UPDATE message SHOULD order path attributes within
> the UPDATE message in ascending order of attribute type.  The
> receiver of an UPDATE message MUST be prepared to handle path
> attributes within UPDATE messages that are out of order.

Signed-off-by: Hiroki Shirokura <slank.dev@gmail.com>

diff --git a/bgpd/bgp_attr.c b/bgpd/bgp_attr.c
index 2bbcade8e8ef7436a9f010a4310ef84cc99974ce..316cc957c9d710d8e01eb825e47d9997f7b4a901 100644 (file)
--- a/bgpd/bgp_attr.c
+++ b/bgpd/bgp_attr.c
@@ -2382,15 +2382,6 @@ static bgp_attr_parse_ret_t bgp_attr_psid_sub(uint8_t type, uint16_t length,
                /* Store label index; subsequently, we'll check on
                 * address-family */
                attr->label_index = label_index;
-
-               /*
-                * Ignore the Label index attribute unless received for
-                * labeled-unicast
-                * SAFI.
-                */
-               if (!mp_update->length
-                   || mp_update->safi != SAFI_LABELED_UNICAST)
-                       attr->label_index = BGP_INVALID_LABEL_INDEX;
        }
 
        /* Placeholder code for the IPv6 SID type */
@@ -3078,6 +3069,17 @@ bgp_attr_parse_ret_t bgp_attr_parse(struct peer *peer, struct attr *attr,
                }
        }
 
+       /*
+        * draft-ietf-idr-bgp-prefix-sid-27#section-3:
+        * About Prefix-SID path attribute,
+        * Label-Index TLV(type1) and The Originator SRGB TLV(type-3)
+        * may only appear in a BGP Prefix-SID attribute attached to
+        * IPv4/IPv6 Labeled Unicast prefixes ([RFC8277]).
+        * It MUST be ignored when received for other BGP AFI/SAFI combinations.
+        */
+       if (!attr->mp_nexthop_len || mp_update->safi != SAFI_LABELED_UNICAST)
+               attr->label_index = BGP_INVALID_LABEL_INDEX;
+
        /* Check final read pointer is same as end pointer. */
        if (BGP_INPUT_PNT(peer) != endp) {
                flog_warn(EC_BGP_ATTRIBUTES_MISMATCH,