cmd/mesh-host/main.go

@@ -1421,7 +1421,7 @@ func applyAndKeep(ctx context.Context, opts options, raw []byte, signed *store.D
 	// (novox/hq ADR 0140). Reported whatever the node's mode: a converged node's filter needs it,
 	// and an adopted one becomes converged without a further round trip. A machine that cannot read
 	// its own routing table says nothing rather than guessing, and is sent no filter.
-	if links, err := outward.Links(""); err != nil {
+	if links, err := outward.Links("", ""); err != nil {
 		fmt.Fprintf(os.Stderr, "mesh-host: applied, and could not read which links face outside: %v\n", err)
 	} else {
 		report.Outward = links

internal/outward/links.go

@@ -29,17 +29,32 @@ import (
 // routing table without one.
 const ProcNet = "/proc/net"
 
-// Links are the interfaces carrying a default route, for both address families, sorted and without
+// SysClassNet is where the kernel lists the machine's network interfaces, one directory each. A
-// repeats.
+// parameter for the same reason.
+const SysClassNet = "/sys/class/net"
+
+// Links are the interfaces carrying a default route, for both address families, and every interface
+// backed by a physical device, sorted and without repeats.
+//
+// **A physical link faces outside whether or not it is up** (novox/hq issue 197). The filter accepts
+// whatever did not arrive on a link named here, so a link left out of this list is not filtered at
+// all. A cable unplugged when the machine last reported carries no default route, and was left out:
+// plugged in, everything arriving on it was accepted until the next report and the next push — and a
+// second physical link that never carries the default route was never filtered. A physical device is
+// read from the kernel's own list, where it has a `device` entry; a bridge, a veth, the tunnel and the
+// loopback have none, and stay what they are, this machine's own.
 //
 // A machine may have more than one: a laptop with a cable and a radio has two, and both face
 // outside. A machine with none — no route off itself — returns nothing, and the mesh refuses to
 // compose a filter for it rather than writing a rule around a link with no name, which would be a
 // rule set that does not load and a machine filtering nothing while its unit reports success.
-func Links(procNet string) ([]string, error) {
+func Links(procNet, sysClassNet string) ([]string, error) {
 	if procNet == "" {
 		procNet = ProcNet
 	}
+	if sysClassNet == "" {
+		sysClassNet = SysClassNet
+	}
 	seen := map[string]bool{}
 
 	four, err := defaultsV4(filepath.Join(procNet, "route"))
@@ -50,7 +65,11 @@ func Links(procNet string) ([]string, error) {
 	if err != nil {
 		return nil, err
 	}
-	for _, name := range append(four, six...) {
+	devices, err := physical(sysClassNet)
+	if err != nil {
+		return nil, err
+	}
+	for _, name := range append(append(four, six...), devices...) {
 		if name != "" && name != "lo" {
 			seen[name] = true
 		}
@@ -64,6 +83,25 @@ func Links(procNet string) ([]string, error) {
 	return out, nil
 }
 
+// physical is every interface the kernel lists with a device behind it. A list that is not there is
+// not an error — a machine without sysfs mounted reports what its routing table says, as before.
+func physical(sysClassNet string) ([]string, error) {
+	entries, err := os.ReadDir(sysClassNet)
+	if os.IsNotExist(err) {
+		return nil, nil
+	}
+	if err != nil {
+		return nil, err
+	}
+	var out []string
+	for _, e := range entries {
+		if _, err := os.Stat(filepath.Join(sysClassNet, e.Name(), "device")); err == nil {
+			out = append(out, e.Name())
+		}
+	}
+	return out, nil
+}
+
 // defaultsV4 reads /proc/net/route, whose columns are
 //
 //	Iface Destination Gateway Flags RefCnt Use Metric Mask ...

internal/outward/links_test.go

@@ -32,7 +32,7 @@ func TestLinksAreTheOnesCarryingADefaultRoute(t *testing.T) {
 	write(t, dir, "route", routeV4)
 	write(t, dir, "ipv6_route", routeV6)
 
-	got, err := Links(dir)
+	got, err := Links(dir, t.TempDir())
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -52,7 +52,7 @@ func TestAZeroDestinationWithAMaskIsNotADefaultRoute(t *testing.T) {
 	write(t, dir, "route", `Iface	Destination	Gateway 	Flags	RefCnt	Use	Metric	Mask		MTU	Window	IRTT
 br-abc	00000000	00000000	0001	0	0	0	00FFFFFF	0	0	0
 `)
-	got, err := Links(dir)
+	got, err := Links(dir, t.TempDir())
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -67,7 +67,7 @@ br-abc	00000000	00000000	0001	0	0	0	00FFFFFF	0	0	0
 func TestNoDefaultRouteIsNoLinks(t *testing.T) {
 	dir := t.TempDir()
 	write(t, dir, "route", "Iface\tDestination\tGateway \tFlags\tRefCnt\tUse\tMetric\tMask\t\tMTU\tWindow\tIRTT\n")
-	got, err := Links(dir)
+	got, err := Links(dir, t.TempDir())
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -81,7 +81,7 @@ func TestNoDefaultRouteIsNoLinks(t *testing.T) {
 func TestAMissingTableIsNotAFailure(t *testing.T) {
 	dir := t.TempDir()
 	write(t, dir, "route", routeV4)
-	got, err := Links(dir)
+	got, err := Links(dir, t.TempDir())
 	if err != nil {
 		t.Fatalf("a missing v6 table should not fail: %v", err)
 	}
@@ -97,7 +97,7 @@ func TestALinkIsReportedOnce(t *testing.T) {
 	write(t, dir, "ipv6_route",
 		"00000000000000000000000000000000 00 00000000000000000000000000000000 00 "+
 			"fe800000000000000000000000000001 00000400 00000001 00000000 00000003     enp9s0\n")
-	got, err := Links(dir)
+	got, err := Links(dir, t.TempDir())
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -109,7 +109,7 @@ func TestALinkIsReportedOnce(t *testing.T) {
 // Against this machine's own routing table, so the parse is held to what the kernel actually writes
 // and not only to a fixture written to agree with it.
 func TestAgainstThisMachinesOwnTable(t *testing.T) {
-	got, err := Links("")
+	got, err := Links("", "")
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -118,3 +118,39 @@ func TestAgainstThisMachinesOwnTable(t *testing.T) {
 	}
 	t.Logf("this machine's outward links: %v", got)
 }
+
+// sysNet is a /sys/class/net: each name a directory, with a `device` entry when a device backs it.
+func sysNet(t *testing.T, physical []string, virtual []string) string {
+	t.Helper()
+	dir := t.TempDir()
+	for _, name := range physical {
+		if err := os.MkdirAll(filepath.Join(dir, name, "device"), 0o755); err != nil {
+			t.Fatal(err)
+		}
+	}
+	for _, name := range virtual {
+		if err := os.MkdirAll(filepath.Join(dir, name), 0o755); err != nil {
+			t.Fatal(err)
+		}
+	}
+	return dir
+}
+
+// **A physical link faces outside whether or not it carries the default route** (novox/hq issue
+// 197). A machine on its radio with its cable unplugged reported only the radio, and the filter then
+// accepted everything arriving on the cable the moment it was plugged in. Bridges, veths, the tunnel
+// and the loopback have no device behind them and stay this machine's own.
+func TestEveryPhysicalLinkFacesOutsideUpOrDown(t *testing.T) {
+	proc := t.TempDir()
+	write(t, proc, "route", `Iface	Destination	Gateway 	Flags	RefCnt	Use	Metric	Mask		MTU	Window	IRTT
+wlp5s0	00000000	01FEA8C0	0003	0	0	600	00000000	0	0	0
+`)
+	sys := sysNet(t, []string{"wlp5s0", "enp6s0"}, []string{"lo", "docker0", "br-0123456789ab", "veth1", "mesh0"})
+	got, err := Links(proc, sys)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if want := []string{"enp6s0", "wlp5s0"}; !reflect.DeepEqual(got, want) {
+		t.Fatalf("outward links are %v, want %v", got, want)
+	}
+}