BGP: Implement flowspec validation procedure

Implement flowspec validation procedure as described in RFC 8955 sec. 6
and RFC 9117. The Validation procedure enforces that only routers in the
forwarding path for a network can originate flowspec rules for that
network.

The patch adds new mechanism for tracking inter-table dependencies, which
is necessary as the flowspec validation depends on IP routes, and flowspec
rules must be revalidated when best IP routes change.

The validation procedure is disabled by default and requires that
relevant IP table uses trie, as it uses interval queries for subnets.

1 files changed, 27 insertions, 1 deletions

diff --git a/doc/bird.sgml b/doc/bird.sgml
index 39dadaf2..d1d2bdae 100644
--- a/doc/bird.sgml
+++ b/doc/bird.sgml
@@ -2274,6 +2274,7 @@ avoid routing loops.
 <item> <rfc id="8092"> - BGP Large Communities Attribute
 <item> <rfc id="8203"> - BGP Administrative Shutdown Communication
 <item> <rfc id="8212"> - Default EBGP Route Propagation Behavior without Policies
+<item> <rfc id="9117"> - Revised Validation Procedure for BGP Flow Specifications
 </itemize>
 
 <sect1>Route selection rules
@@ -2659,7 +2660,7 @@ using the following configuration parameters:
 
 	<tag><label id="bgp-error-wait-time">error wait time <m/number/,<m/number/</tag>
 	Minimum and maximum delay in seconds between a protocol failure (either
-	local or reported by the peer) and automatic restart. Doesn't apply
+	local or reported by the peer) and automatic restart. Doesn not apply
 	when <cf/disable after error/ is configured. If consecutive errors
 	happen, the delay is increased exponentially until it reaches the
 	maximum. Default: 60, 300.
@@ -2837,6 +2838,31 @@ be used in explicit configuration.
 	explicitly (to conserve memory). This option requires that the connected
 	routing table is <ref id="dsc-table-sorted" name="sorted">. Default: off.
 
+	<tag><label id="bgp-validate">validate <m/switch/</tag>
+	Apply flowspec validation procedure as described in <rfc id="8955">
+	section 6 and <rfc id="9117">. The Validation procedure enforces that
+	only routers in the forwarding path for a network can originate flowspec
+	rules for that network. The validation procedure should be used for EBGP
+	to prevent injection of malicious flowspec rules from outside, but it
+	should also be used for IBGP to ensure that selected flowspec rules are
+	consistent with selected IP routes. The validation procedure uses an IP
+	routing table (<ref id="bgp-base-table" name="base table">, see below)
+	against which flowspec rules are validated. This option is limited to
+	flowspec channels. Default: off (for compatibility reasons).
+
+	Note that currently the flowspec validation does not work reliably
+	together with <ref id="bgp-import-table" name="import table"> option
+	enabled on flowspec channels.
+
+	<tag><label id="bgp-base-table">base table <m/name/</tag>
+	Specifies an IP table used for the flowspec validation procedure. The
+	table must have enabled <cf/trie/ option, otherwise the validation
+	procedure would not work. The type of the table must be <cf/ipv4/ for
+	<cf/flow4/ channels and <cf/ipv6/ for <cf/flow6/ channels. This option
+	is limited to flowspec channels. Default: the main table of the
+	<cf/ipv4/ / <cf/ipv6/ channel of the same BGP instance, or the
+	<cf/master4/ / <cf/master6/ table if there is no such channel.
+
 	<tag><label id="bgp-extended-next-hop">extended next hop <m/switch/</tag>
 	BGP expects that announced next hops have the same address family as
 	associated network prefixes. This option provides an extension to use