BGP: Handle flowspec rules without dst part

The RFC 5575 does not explicitly reject flowspec rules without dst part,
it just requires dst part in validation procedure for feasibility, which
we do not implement anyway. Thus flow without dst prefix is syntactically
valid, but unfeasible (if feasibilty testing is done).

Thanks to Alex D. for the bugreport.

1 files changed, 14 insertions, 14 deletions

diff --git a/proto/bgp/packets.c b/proto/bgp/packets.c
index ed878e41..ee031c05 100644
--- a/proto/bgp/packets.c
+++ b/proto/bgp/packets.c
@@ -1824,15 +1824,15 @@ bgp_decode_nlri_flow4(struct bgp_parse_state *s, byte *pos, uint len, rta *a)
       bgp_parse_error(s, 1);
     }
 
-    if (data[0] != FLOW_TYPE_DST_PREFIX)
-    {
-      log(L_REMOTE "%s: No dst prefix at first pos", s->proto->p.name);
-      bgp_parse_error(s, 1);
-    }
+    ip4_addr px = IP4_NONE;
+    uint pxlen = 0;
 
     /* Decode dst prefix */
-    ip4_addr px = flow_read_ip4_part(data);
-    uint pxlen = data[1];
+    if (data[0] == FLOW_TYPE_DST_PREFIX)
+    {
+      px = flow_read_ip4_part(data);
+      pxlen = flow_read_pxlen(data);
+    }
 
     /* Prepare the flow */
     net_addr *n = alloca(sizeof(struct net_addr_flow4) + flen);
@@ -1912,15 +1912,15 @@ bgp_decode_nlri_flow6(struct bgp_parse_state *s, byte *pos, uint len, rta *a)
       bgp_parse_error(s, 1);
     }
 
-    if (data[0] != FLOW_TYPE_DST_PREFIX)
-    {
-      log(L_REMOTE "%s: No dst prefix at first pos", s->proto->p.name);
-      bgp_parse_error(s, 1);
-    }
+    ip6_addr px = IP6_NONE;
+    uint pxlen = 0;
 
     /* Decode dst prefix */
-    ip6_addr px = flow_read_ip6_part(data);
-    uint pxlen = data[1];
+    if (data[0] == FLOW_TYPE_DST_PREFIX)
+    {
+      px = flow_read_ip6_part(data);
+      pxlen = flow_read_pxlen(data);
+    }
 
     /* Prepare the flow */
     net_addr *n = alloca(sizeof(struct net_addr_flow6) + flen);