ipn/ipnlocal: apply the new AcceptRoutesFilter to all peer routes

Signed-off-by: James Tucker <james@tailscale.com>

ipn/ipnlocal/local.go

@@ -2775,18 +2775,67 @@ func ipPrefixLess(ri, rj netip.Prefix) bool {
 	return ri.Addr().Less(rj.Addr())
 }
 
+func (b *LocalBackend) parseAcceptRoutesFilter(acceptFilter string) (*netipx.IPSet, error) {
+	var acceptFilterBuilder netipx.IPSetBuilder
+	for _, af := range strings.Split(acceptFilter, ",") {
+		af = strings.TrimSpace(af)
+		if af == "" {
+			continue
+		}
+		includeRange := true
+		if strings.HasPrefix(af, "-") {
+			includeRange = false
+			af = af[1:]
+		}
+		pfx, err := netip.ParsePrefix(af)
+		if err != nil {
+			b.logf("accept routes filter: invalid prefix %q will be ignored: %v (check accept-routes flag)", af, err)
+			continue
+		}
+		if includeRange {
+			acceptFilterBuilder.AddPrefix(pfx)
+		} else {
+			acceptFilterBuilder.RemovePrefix(pfx)
+		}
+	}
+	return acceptFilterBuilder.IPSet()
+}
+
+func (b *LocalBackend) filterRoutes(routes []netip.Prefix, acceptFilter *netipx.IPSet) []netip.Prefix {
+	if acceptFilter == nil {
+		return routes
+	}
+	var builder netipx.IPSetBuilder
+	for _, r := range routes {
+		builder.AddPrefix(r)
+	}
+	builder.Intersect(acceptFilter)
+	set, err := builder.IPSet()
+	if err != nil {
+		b.logf("accept routes filter: failed to build filtered set, all routes will be accepted: %v (check accept-routes flag)", err)
+		return routes
+	}
+	return set.Prefixes()
+}
+
 // routerConfig produces a router.Config from a wireguard config and IPN prefs.
 func (b *LocalBackend) routerConfig(cfg *wgcfg.Config, prefs *ipn.Prefs, oneCGNATRoute bool) *router.Config {
 	singleRouteThreshold := 10_000
 	if oneCGNATRoute {
 		singleRouteThreshold = 1
 	}
+
+	acceptRoutesFilterSet, err := b.parseAcceptRoutesFilter(prefs.AcceptRoutesFilter)
+	if err != nil {
+		b.logf("accept routes filter: failed to build filter set: %v", err)
+	}
+
 	rs := &router.Config{
 		LocalAddrs:       unmapIPPrefixes(cfg.Addresses),
 		SubnetRoutes:     unmapIPPrefixes(prefs.AdvertiseRoutes),
 		SNATSubnetRoutes: !prefs.NoSNAT,
 		NetfilterMode:    prefs.NetfilterMode,
-		Routes:           peerRoutes(cfg.Peers, singleRouteThreshold),
+		Routes:           b.filterRoutes(peerRoutes(cfg.Peers, singleRouteThreshold), acceptRoutesFilterSet),
 	}
 
 	if distro.Get() == distro.Synology {