Fall back from ipset at the point of failure and cover route ACLs

client/firewall/iptables/ipset_support_linux.go

@@ -0,0 +1,75 @@
+package iptables
+
+import (
+	"sync"
+
+	log "github.com/sirupsen/logrus"
+)
+
+// ipsetSupport tracks whether ipset-backed firewall rules can be installed.
+//
+// It starts optimistic and latches to unsupported the first time the kernel
+// proves otherwise: either the hash:net set type is missing (ip_set_hash_net) or
+// iptables cannot match against a set (xt_set). Callers then emit per-IP and
+// per-prefix rules instead. Without the fallback, a rule referencing an unusable
+// set is never installed and the catch-all DROP silently blocks traffic the
+// policy permits.
+//
+// One instance is shared by the ACL managers and routers of both address
+// families, because ipset availability is a property of the kernel rather than
+// of any single table.
+type ipsetSupport struct {
+	mu          sync.RWMutex
+	unsupported bool
+}
+
+func newIPSetSupport() *ipsetSupport {
+	return &ipsetSupport{}
+}
+
+func (s *ipsetSupport) supported() bool {
+	s.mu.RLock()
+	defer s.mu.RUnlock()
+
+	return !s.unsupported
+}
+
+// markUnsupported records that ipset cannot be used, logging the reason once.
+func (s *ipsetSupport) markUnsupported(cause error) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	if s.unsupported {
+		return
+	}
+	s.unsupported = true
+
+	log.Warnf("ipset is unavailable (%v); falling back to per-IP firewall rules. "+
+		"Ensure the kernel provides ip_set_hash_net and xt_set; without them rule "+
+		"sets are larger and slower to converge on networks with many peers", cause)
+}
+
+// ipsetUnusableError marks a failure attributable to ipset, so the caller can
+// retry the same rule in its per-IP form before latching the capability off.
+type ipsetUnusableError struct {
+	cause error
+}
+
+func (e *ipsetUnusableError) Error() string { return e.cause.Error() }
+
+func (e *ipsetUnusableError) Unwrap() error { return e.cause }
+
+func ipsetUnusable(cause error) error {
+	return &ipsetUnusableError{cause: cause}
+}
+
+// maybeIPSetUnusable marks an iptables failure as ipset-attributable only when the
+// rule actually carried a set match, since the same call can fail for unrelated
+// reasons on a rule that matches addresses directly.
+func maybeIPSetUnusable(ipsetName string, err error) error {
+	if ipsetName == "" {
+		return err
+	}
+
+	return ipsetUnusable(err)
+}