bgpd: Flowspec overflow issue

According to the flowspec RFC 8955 a flowspec nlri is <length, <nlri data>>
Specifying 0 as a length makes BGP get all warm on the inside.  Which
in this case is not a good thing at all.  Prevent warmth, stay cold
on the inside.

Reported-by: Iggy Frankovic <iggyfran@amazon.com>
Signed-off-by: Donald Sharp <sharpd@nvidia.com>

diff --git a/bgpd/bgp_flowspec.c b/bgpd/bgp_flowspec.c
index 8d5ca5e77779516a573ba07c1ac840959dbc9bb7..f9debe43cd45b350defdc326defe5f9c7bad42df 100644 (file)
--- a/bgpd/bgp_flowspec.c
+++ b/bgpd/bgp_flowspec.c
@@ -127,6 +127,13 @@ int bgp_nlri_parse_flowspec(struct peer *peer, struct attr *attr,
                                psize);
                        return BGP_NLRI_PARSE_ERROR_PACKET_OVERFLOW;
                }
+
+               if (psize == 0) {
+                       flog_err(EC_BGP_FLOWSPEC_PACKET,
+                                "Flowspec NLRI length 0 which makes no sense");
+                       return BGP_NLRI_PARSE_ERROR_PACKET_OVERFLOW;
+               }
+
                if (bgp_fs_nlri_validate(pnt, psize, afi) < 0) {
                        flog_err(
                                EC_BGP_FLOWSPEC_PACKET,