Let a group share the info API too, and serve it on windows

The info API is for other programs on the host, and on unix the only
setting between "the user nebula runs as" and "everyone" was a manual
chgrp that the next bind undid; on windows it was not served at all,
because which accounts a pipe admits had not been decided. The control
socket's `group` decides it, and the info API takes the same key.

- `local_api.info.group`: the socket is handed to the group at 0660
  unless `socket_mode` says otherwise, and a mode that gives a named
  group nothing is refused with the mode that would
- windows: served on a named pipe, the group an ACE on it as on the
  control pipe; the e2e test's helpers dial unix sockets, so it still
  skips there
- a changed group or mode on a reload is applied to the socket in place

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

e2e/info_api_test.go

@@ -27,7 +27,7 @@ import (
 // established with.
 func TestIdentityOverTheInfoAPI(t *testing.T) {
 	if runtime.GOOS == "windows" {
-		t.Skip("the info API is not served on windows")
+		t.Skip("the test's HTTP helpers dial unix sockets; on windows the info API is a named pipe")
 	}
 
 	ca, _, caKey, _ := cert_test.NewTestCaCert(cert.Version2, cert.Curve_CURVE25519, time.Now(), time.Now().Add(10*time.Minute), nil, nil, []string{})

examples/config.yml

@@ -255,7 +255,7 @@ punchy:
     #group: nebula
 
   # The info socket is not made available by default. If you enable it, it makes some
-  # internal state available over HTTP. It's not available on Windows.
+  # internal state available over HTTP.
   #
   # The currently supported HTTP requests are:
   #   GET /v1/identity?address=<vpn addr>[:port]  the host owning the address; the port
@@ -266,10 +266,16 @@ punchy:
   #
   #info:
     #enabled: false
-    # The absolute path to listen on.
+    # The absolute path to listen on, or a full pipe name on Windows.
     #socket: /var/run/nebula/info.sock
-    # Octal mode for the socket, as a quoted string. Defaults to "0600".
-    #socket_mode: "0600"
+    # A group (or account/group/SID on Windows) that should be allowed to access the
+    # socket. On Windows the group may read and write the pipe but not create an
+    # instance of it, so a client in the group must open the pipe asking for read and
+    # write data rather than generic read and write.
+    #group: nebula-info
+    # Octal mode for the socket, as a quoted string. Defaults to "0600" unless a
+    # group is set, in which case it defaults to "0660".
+    #socket_mode: "0660"
 
 # EXPERIMENTAL: relay support for networks that can't establish direct connections.
 relay:

localapi/access_unix_test.go

@@ -4,6 +4,7 @@ package localapi
 
 import (
 	"context"
+	"net/http"
 	"os"
 	"os/user"
 	"strconv"
@@ -139,3 +140,63 @@ func TestControlSocketWithAGroupTrustsTheKernel(t *testing.T) {
 	_, err = (&Client{Path: path}).Describe()
 	require.ErrorContains(t, err, "not permitted")
 }
+
+// TestInfoAccessFromConfig: a group with no mode is 0660; a mode that gives the group
+// nothing is refused, with the mode that would; an explicit mode with group bits is
+// kept as given.
+func TestInfoAccessFromConfig(t *testing.T) {
+	name, gid := ownGroup(t)
+	load := func(body string) (infoConfig, error) {
+		c := config.NewC(test.NewLogger())
+		require.NoError(t, c.LoadString(body))
+		return infoConfigFrom(c)
+	}
+	section := func(extra string) string {
+		return "local_api:\n  info:\n    enabled: true\n    socket: /run/nebula/info.sock\n" + extra
+	}
+
+	cfg, err := load(section("    group: " + name + "\n"))
+	require.NoError(t, err)
+	assert.Equal(t, os.FileMode(0660), cfg.Access.Mode)
+	require.NotNil(t, cfg.Access.Group)
+	assert.Equal(t, gid, cfg.Access.Group.ID)
+
+	cfg, err = load(section("    group: " + name + "\n    socket_mode: \"0664\"\n"))
+	require.NoError(t, err)
+	assert.Equal(t, os.FileMode(0664), cfg.Access.Mode)
+
+	_, err = load(section("    group: " + name + "\n    socket_mode: \"0600\"\n"))
+	require.ErrorContains(t, err, "gives group "+name+" no access")
+	require.ErrorContains(t, err, `"0660"`)
+
+	cfg, err = load(section(""))
+	require.NoError(t, err)
+	assert.Equal(t, os.FileMode(0600), cfg.Access.Mode)
+	assert.Nil(t, cfg.Access.Group)
+}
+
+// TestSocketIsHandedToTheGroup: the socket is created with the group's gid and the
+// mode, and a changed group or mode on a reload is applied to the socket in place.
+func TestSocketIsHandedToTheGroup(t *testing.T) {
+	name, gid := ownGroup(t)
+	group := &Group{Name: name, ID: gid}
+	want, err := strconv.ParseUint(gid, 10, 32)
+	require.NoError(t, err)
+
+	s, path := serveInfo(t, infoRegistry(), 0600)
+	require.NoError(t, s.Rebind(context.Background(), path, Access{Mode: 0660, Group: group}))
+	fi, err := os.Lstat(path)
+	require.NoError(t, err)
+	assert.Equal(t, os.FileMode(0660), fi.Mode().Perm())
+	assert.Equal(t, uint32(want), socketGroup(t, path))
+
+	status, _ := test.HTTPGet(t, path, "/v1/whoami")
+	assert.Equal(t, http.StatusOK, status, "the same listener is still serving")
+
+	// The mode is the operator's to widen further.
+	require.NoError(t, s.Rebind(context.Background(), path, Access{Mode: 0664, Group: group}))
+	fi, err = os.Lstat(path)
+	require.NoError(t, err)
+	assert.Equal(t, os.FileMode(0664), fi.Mode().Perm())
+	assert.Equal(t, path, s.Path())
+}

localapi/info.go

@@ -32,12 +32,13 @@ const (
 	InfoEnabledKey = "local_api.info.enabled"
 	InfoSocketKey  = "local_api.info.socket"
 	InfoModeKey    = "local_api.info.socket_mode"
+	InfoGroupKey   = "local_api.info.group"
 )
 
 const (
-	// defaultInfoMode is the socket's mode when the config names none: the daemon's
-	// user alone, so that enabling the API does not open it to anyone until the operator
-	// says who.
+	// defaultInfoMode is the socket's mode when the config names neither a mode nor a
+	// group: the daemon's user alone, so that enabling the API does not open it to
+	// anyone until the operator says who. Naming a group makes it groupSocketMode.
 	defaultInfoMode os.FileMode = 0600
 
 	// infoMaxConns bounds the connections held open at once. Beyond it the kernel
@@ -407,7 +408,10 @@ type infoConfig struct {
 }
 
 // infoConfigFrom reads the info API section. A disabled section needs nothing else to be
-// right; an enabled one needs a socket path and, if it names a mode, one that parses.
+// right; an enabled one needs a socket path, a group that exists if it names one, and
+// a mode that parses if it names one. A group with no mode means groupSocketMode, and a
+// mode that gives a named group nothing is refused: it would be a group that cannot
+// connect, which is not what naming one asks for.
 func infoConfigFrom(c *config.C) (infoConfig, error) {
 	cfg := infoConfig{Enabled: c.GetBool(InfoEnabledKey, false)}
 	if !cfg.Enabled {
@@ -424,11 +428,23 @@ func infoConfigFrom(c *config.C) (infoConfig, error) {
 	}
 	cfg.Path = path
 
-	mode, err := parseSocketMode(c.Get(InfoModeKey))
+	group, err := groupFromConfig(c, InfoGroupKey)
+	if err != nil {
+		return cfg, err
+	}
+	def := defaultInfoMode
+	if group != nil {
+		def = groupSocketMode
+	}
+
+	mode, err := parseSocketMode(c.Get(InfoModeKey), def)
 	if err != nil {
 		return cfg, fmt.Errorf("%s: %w", InfoModeKey, err)
 	}
-	cfg.Access = Access{Mode: mode}
+	if group != nil && mode&0070 == 0 {
+		return cfg, fmt.Errorf("%s %s gives group %s no access to the socket; use \"%04o\" or leave the mode unset", InfoModeKey, modeString(mode), group.Name, mode|0060)
+	}
+	cfg.Access = Access{Mode: mode, Group: group}
 
 	return cfg, nil
 }
@@ -437,10 +453,10 @@ func infoConfigFrom(c *config.C) (infoConfig, error) {
 // integer, and which integer depends on the parser (octal 432 under YAML 1.1, decimal
 // 660 under 1.2), so a number is refused with the fix rather than quietly applied as
 // whichever mode its digits happen to spell in octal.
-func parseSocketMode(raw any) (os.FileMode, error) {
+func parseSocketMode(raw any, def os.FileMode) (os.FileMode, error) {
 	switch v := raw.(type) {
 	case nil:
-		return defaultInfoMode, nil
+		return def, nil
 	case string:
 		mode, err := strconv.ParseUint(v, 8, 32)
 		if err != nil || mode&^0777 != 0 {

localapi/info_windows_test.go

@@ -4,20 +4,55 @@ package localapi
 
 import (
 	"context"
+	"io"
+	"net"
+	"net/http"
 	"testing"
+	"time"
 
+	"github.com/Microsoft/go-winio"
 	"github.com/slackhq/nebula/commands"
 	"github.com/slackhq/nebula/test"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
+	"golang.org/x/sys/windows"
 )
 
-// TestInfoIsNotServedOnWindows: a pipe has no mode to open to other accounts, so Rebind
-// says so and leaves nothing listening, whatever the config asked for.
-func TestInfoIsNotServedOnWindows(t *testing.T) {
+// TestInfoIsServedOnAPipe: the info API serves HTTP on a named pipe, whose security
+// descriptor is its access control the way a socket's mode is on unix; a group named
+// in the config is admitted by it.
+func TestInfoIsServedOnAPipe(t *testing.T) {
+	users, err := windows.CreateWellKnownSid(windows.WinBuiltinUsersSid)
+	require.NoError(t, err)
+	group := &Group{Name: "Users", ID: users.String()}
+
 	s := NewInfoServer(test.NewLogger(), commands.New())
-	err := s.Rebind(context.Background(), pipePrefix+"nebula-info-test", Access{Mode: 0600})
-	require.ErrorIs(t, err, errInfoUnsupported)
-	assert.Empty(t, s.Path())
-	s.Stop()
+	path := pipePrefix + "nebula-info-test"
+	require.NoError(t, s.Rebind(context.Background(), path, Access{Mode: groupSocketMode, Group: group}))
+	t.Cleanup(s.Stop)
+	assert.Equal(t, path, s.Path())
+
+	client := &http.Client{Transport: &http.Transport{
+		// What a program on the host has to do: ask for the data rights alone, since the
+		// group is granted no more; see pipeClientAccess.
+		DialContext: func(ctx context.Context, _, _ string) (net.Conn, error) {
+			ctx, cancel := context.WithTimeout(ctx, 2*time.Second)
+			defer cancel()
+			return winio.DialPipeAccess(ctx, path, pipeClientAccess)
+		},
+	}}
+	res, err := client.Get("http://nebula/v1")
+	require.NoError(t, err)
+	defer res.Body.Close()
+	body, err := io.ReadAll(res.Body)
+	require.NoError(t, err)
+	assert.Equal(t, http.StatusOK, res.StatusCode)
+	assert.Contains(t, string(body), `"help"`)
+
+	// A change of group means a new pipe under the same name, still serving.
+	require.NoError(t, s.Rebind(context.Background(), path, Access{Mode: groupSocketMode}))
+	res, err = client.Get("http://nebula/v1")
+	require.NoError(t, err)
+	res.Body.Close()
+	assert.Equal(t, http.StatusOK, res.StatusCode)
 }

localapi/platform_windows.go

@@ -46,11 +46,10 @@ func logListening(l *slog.Logger, path string, acc Access) {
 	)
 }
 
-// infoSupported is false here. A pipe has no mode to open to other accounts, and the
-// security descriptor listen builds admits the daemon's account alone, which is the
-// opposite of what the info API is for. Serving it on windows means designing which
-// accounts a pipe admits, and that has not been done.
-const infoSupported = false
+// infoSupported is true here: the pipe's security descriptor is what a mode is on unix,
+// and the group an operator names in the config is the way to open it to other
+// accounts, as it is for the control pipe. The mode itself means nothing to a pipe.
+const infoSupported = true
 
 // listen creates the named pipe at path with a security descriptor that admits the user
 // nebula runs as, SYSTEM and Administrators, and the group acc names, if any, for