Boot fallback, flowtable devices that come and go, healthz, renames

The boot unit fails closed: if ruleset.nft doesn't load, it loads ruleset-fallback.nft (render.Fallback), saved beside it from the same configuration: nothing new in from external zones, established, the ICMPv6 IPv6 needs and DHCPv6 replies let in, the inside left alone and masqueraded, and the unit marked failed with a critical message. housecarld replaces it when it applies; status, the dashboard and /healthz say while it is in force. no_external_zone now also says the fallback closes everything without an external zone. The boot ruleset has no flowtable: nftables on Debian 13's kernel refuses one naming a device that doesn't exist yet (ppp0 before PPPoE), and with it the whole file. internal/linkwatch listens to rtnetlink link messages; housecarld applies again when a flowtable device appears or comes back as a new interface (by ifindex), under the engine's lock. docs/flowtable.md: what it does, when to use it and when not, how. GET /healthz reports firewall (applied, unconfigured, fallback, missing), changes on probation and the machine's warnings, with 503 unless in force, read at most every five seconds. Renaming a zone, set or service changes what names it in the same change (one history entry, one undo); dynamic sets keep their names. The importer keeps a chain's head in order: once a would-be built-in stays a rule, the ones after it do too, so the maintainer's ICMPv6 accepts stay behind the invalid drop as written. hc settings set --flowtable none empties the list. make test (nft 1.1.3) and make e2e (242 checks, with VLAN sub-interfaces, the fallback and the flowtable) pass. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
2026-10-19 23:16:46 +01:00
1 parent 835a9ba2cc
commit 9d766b9823
@@ -0,0 +1,89 @@
+package render
+
+import (
+	"fmt"
+	"strings"
+
+	"housecarl/internal/model"
+)
+
+// FallbackMark starts the comment of every fallback rule ("hc:fallback-…"):
+// how housecarld tells the fallback is in force.
+const FallbackMark = "fallback"
+
+// Fallback builds the ruleset housecarl-ruleset.service loads at boot when
+// the saved one fails to: nothing new gets in from the external zones'
+// interfaces, everything else is let through, and IPv4 leaving an
+// external zone is masqueraded (when any source NAT is configured), so the
+// inside keeps working until housecarld puts the real ruleset back. With
+// no external zone it can't tell which interface faces the internet, and
+// lets nothing but loopback through.
+//
+// It is deliberately small: no sets, flowtable, meters or quotas, and
+// interfaces by name only, so it loads before they exist.
+func Fallback(st *model.State) string {
+	var b strings.Builder
+	line := func(format string, args ...any) {
+		fmt.Fprintf(&b, format, args...)
+		b.WriteByte('\n')
+	}
+	// rule writes a counted rule: what it matches, then its verdict.
+	rule := func(name, match, verdict string) {
+		line("\t\t%s counter %s comment \"hc:%s-%s\"", match, verdict, FallbackMark, name)
+	}
+	ext := st.ExternalInterfaces()
+	line("# Housecarl's fallback: loaded at boot only if ruleset.nft fails to load,")
+	line("# until housecarld starts and puts the real ruleset back.")
+	line("table inet %s {}", Table)
+	line("delete table inet %s", Table)
+	line("table inet %s {", Table)
+	if len(ext) == 0 {
+		// Nothing says which interface faces the internet: close it all.
+		for _, c := range []string{"input", "forward"} {
+			line("\tchain %s {", c)
+			line("\t\ttype filter hook %s priority filter; policy drop;", c)
+			line("\t\tiifname \"lo\" accept")
+			line("\t\tcounter comment \"hc:%s-%s\"", FallbackMark, c)
+			line("\t}")
+		}
+		line("}")
+		return b.String()
+	}
+	e := ifaces(ext)
+	line("\tchain input {")
+	line("\t\ttype filter hook input priority filter; policy accept;")
+	line("\t\tiifname \"lo\" accept")
+	line("\t\tct state established,related accept")
+	rule("icmpv6", fmt.Sprintf("iifname %s icmpv6 type { %s, echo-request, echo-reply }", e, icmpv6Errors), "accept")
+	rule("icmpv6-nd", fmt.Sprintf("iifname %s icmpv6 type { %s } ip6 hoplimit 255", e, icmpv6ND), "accept")
+	rule("icmpv6-mld", fmt.Sprintf("iifname %s ip6 saddr fe80::/10 icmpv6 type { %s }", e, icmpv6MLD), "accept")
+	rule("dhcpv6-client", fmt.Sprintf("iifname %s ip6 saddr fe80::/10 udp dport 546", e), "accept")
+	rule("input", "iifname "+e, "drop")
+	line("\t}")
+	line("\tchain forward {")
+	line("\t\ttype filter hook forward priority filter; policy accept;")
+	if st.Settings.Builtins.MSSClamp {
+		line("\t\toifname %s tcp flags syn tcp option maxseg size set rt mtu", e)
+	}
+	line("\t\tct state established,related accept")
+	rule("forward", "iifname "+e, "drop")
+	line("\t}")
+	if masquerades(st) {
+		line("\tchain srcnat {")
+		line("\t\ttype nat hook postrouting priority srcnat; policy accept;")
+		rule("masquerade", "meta nfproto ipv4 oifname "+e, "masquerade")
+		line("\t}")
+	}
+	line("}")
+	return b.String()
+}
+
+// masquerades reports whether any source NAT is configured.
+func masquerades(st *model.State) bool {
+	for _, x := range st.SNATs {
+		if !x.Disabled {
+			return true
+		}
+	}
+	return false
+}
@@ -0,0 +1,75 @@
+package render
+
+import (
+	"context"
+	"os"
+	"os/exec"
+	"strings"
+	"testing"
+
+	"housecarl/internal/model"
+)
+
+func TestFallback(t *testing.T) {
+	st := router()
+	text := Fallback(st)
+	for _, want := range []string{
+		"delete table inet housecarl",
+		"type filter hook input priority filter; policy accept;",
+		`iifname "wan" counter drop comment "hc:fallback-input"`,
+		`iifname "wan" counter drop comment "hc:fallback-forward"`,
+		`iifname "wan" ip6 saddr fe80::/10 udp dport 546 counter accept`,
+		`ip6 hoplimit 255 counter accept`,
+		`oifname "wan" tcp flags syn tcp option maxseg size set rt mtu`,
+		`meta nfproto ipv4 oifname "wan" counter masquerade comment "hc:fallback-masquerade"`,
+	} {
+		if !strings.Contains(text, want) {
+			t.Errorf("no %q in\n%s", want, text)
+		}
+	}
+	// Nothing that could fail to load before the network is up.
+	for _, not := range []string{"flowtable", "@", "\tset ", "enp2s0", "wg0"} {
+		if strings.Contains(text, not) {
+			t.Errorf("%q in the fallback:\n%s", not, text)
+		}
+	}
+	// Established connections are accepted before the drops.
+	if strings.Index(text, "ct state established,related accept") > strings.Index(text, "hc:fallback-input") {
+		t.Errorf("established after the drop:\n%s", text)
+	}
+
+	// No source NAT: no masquerade.
+	st.SNATs = nil
+	if text := Fallback(st); strings.Contains(text, "masquerade") {
+		t.Errorf("masquerade without source NAT:\n%s", text)
+	}
+
+	// No external zone: everything but loopback is dropped.
+	for _, z := range st.Zones {
+		z.External = false
+	}
+	text = Fallback(st)
+	if strings.Count(text, "policy drop;") != 2 || strings.Contains(text, "policy accept") || strings.Contains(text, "established") {
+		t.Errorf("no external zone:\n%s", text)
+	}
+}
+
+func TestFallbackPassesNft(t *testing.T) {
+	cmd := strings.Fields(os.Getenv("HOUSECARL_NFT"))
+	if len(cmd) == 0 {
+		t.Skip("HOUSECARL_NFT not set")
+	}
+	closed := router()
+	for _, z := range closed.Zones {
+		z.External = false
+	}
+	wild := router()
+	wild.Zones = append(wild.Zones, &model.Zone{ID: 99, Name: "lte", Interfaces: []string{"wwan*"}, External: true})
+	for name, st := range map[string]*model.State{"router": router(), "closed": closed, "wildcard": wild} {
+		c := exec.CommandContext(context.Background(), cmd[0], append(cmd[1:], "-c", "-f", "/dev/stdin")...)
+		c.Stdin = strings.NewReader(Fallback(st))
+		if out, err := c.CombinedOutput(); err != nil {
+			t.Errorf("%s: nft -c: %v\n%s\n%s", name, err, out, Fallback(st))
+		}
+	}
+}
@@ -244,7 +244,15 @@ func TestRenderedRulesetPassesNft(t *testing.T) {
 	}
 	stats := router()
 	stats.Settings.StatsPerDevice = true
-	for name, st := range map[string]*model.State{"router": router(), "empty": model.NewState(), "stats": stats} {
+	// VLAN sub-interfaces: zones of one VLAN, of all of a parent's, and
+	// the flowtable on one.
+	vlan := router()
+	vlan.Zones = append(vlan.Zones, &model.Zone{ID: 900, Name: "iot", Interfaces: []string{"enp2s0.20"}},
+		&model.Zone{ID: 901, Name: "vlans", Interfaces: []string{"enp3s0.*"}})
+	vlan.Rules = append(vlan.Rules, &model.Rule{ID: 902, Chain: model.ChainForward, Position: 99, Action: model.ActionAccept,
+		Match: model.Match{InZones: []string{"iot", "vlans"}, OutZones: []string{"wan"}}})
+	vlan.Settings.FlowtableDevices = []string{"lo", "enp2s0.20"}
+	for name, st := range map[string]*model.State{"router": router(), "empty": model.NewState(), "stats": stats, "vlan": vlan} {
 		q, qs := quotaOptions(st)
 		rs := Render(st, Options{Elements: map[string][]Element{"guests": {{Addr: "10.0.30.5", Timeout: 1700}, {Addr: "2a02:8013:7f3d:30::5"}}}, Quotas: q, QuotaSets: qs,
 			DeviceSets: map[string][]Element{"stats_up_v4": {{Addr: "10.0.10.5", Timeout: 3000, Packets: 7, Bytes: 7000}}, "stats_down_v6": {{Addr: "2001:db8:1:2::", Packets: 1, Bytes: 100}}}})