[client] Authorize daemon IPC callers by their local identity (#6967)

client/internal/daemonaddr/pipe.go

@@ -0,0 +1,103 @@
+package daemonaddr
+
+import (
+	"context"
+	"net"
+	"runtime"
+	"strings"
+
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/credentials/insecure"
+)
+
+const (
+	// WindowsPipeAddr is the default daemon address on Windows. A named pipe
+	// carries the connecting process's token, which loopback TCP does not, so
+	// it is the only Windows transport on which the daemon can tell who is
+	// calling it.
+	WindowsPipeAddr = "npipe://netbird"
+
+	// legacyWindowsAddr is the loopback-TCP address the Windows daemon used
+	// before named-pipe support.
+	legacyWindowsAddr = "tcp://127.0.0.1:41731"
+
+	pipeScheme = "npipe://"
+
+	// protectedPrefix is the NPFS namespace in which only LocalSystem and
+	// members of BUILTIN\Administrators may create a pipe. A daemon running as
+	// the service account creates its pipe there so that an unprivileged process
+	// cannot pre-create the name, which would keep the daemon from starting and
+	// leave callers talking to the squatter. Opening such a pipe needs no
+	// privilege, so unprivileged clients still reach the daemon.
+	protectedPrefix = `ProtectedPrefix\Administrators\`
+)
+
+// DialTarget returns the gRPC dial target and transport options for a daemon
+// address. The npipe scheme needs a context dialer because gRPC has no
+// named-pipe resolver; unix and tcp are handled by gRPC itself.
+func DialTarget(addr string) (string, []grpc.DialOption) {
+	opts := []grpc.DialOption{grpc.WithTransportCredentials(insecure.NewCredentials())}
+
+	if name, ok := strings.CutPrefix(addr, pipeScheme); ok {
+		paths := PipePaths(name)
+		opts = append(opts, grpc.WithContextDialer(func(ctx context.Context, _ string) (net.Conn, error) {
+			return dialPipePaths(ctx, paths)
+		}))
+		return "passthrough:///netbird-daemon-pipe", opts
+	}
+
+	return strings.TrimPrefix(addr, "tcp://"), opts
+}
+
+// PipePath maps an npipe address name ("netbird", from "npipe://netbird") to a
+// Windows named-pipe path (\\.\pipe\netbird). A fully qualified path is left as
+// is.
+func PipePath(name string) string {
+	if strings.HasPrefix(name, `\\`) {
+		return name
+	}
+	return `\\.\pipe\` + name
+}
+
+// PipePaths returns the paths a daemon control pipe may live at for an npipe
+// address name, in the order both sides must try them: the protected name first,
+// then the plain one.
+//
+// The daemon serves the first it can create, which is the protected name when it
+// runs as the service account and the plain one when it runs as an ordinary user,
+// as it does in netstack mode. Clients therefore have to try both, and because a
+// client cannot tell from the name alone who created the pipe, the plain name is
+// only usable once the server's identity has been checked: see
+// verifyPipeServer.
+//
+// A fully qualified path is what the operator asked for and is used as is.
+func PipePaths(name string) []string {
+	if strings.HasPrefix(name, `\\`) {
+		return []string{name}
+	}
+	return []string{PipePath(protectedPrefix + name), PipePath(name)}
+}
+
+// IsProtectedPipePath reports whether a pipe path is in the namespace only an
+// administrator or LocalSystem can create in, which is what lets a client trust
+// such a pipe from its name alone.
+func IsProtectedPipePath(path string) bool {
+	return strings.HasPrefix(path, `\\.\pipe\`+protectedPrefix)
+}
+
+// MigrateLegacy upgrades the pre-named-pipe Windows daemon address to the named
+// pipe, reporting whether it rewrote the address. Existing installs persist the
+// daemon address, so without this an upgraded daemon would keep listening on
+// loopback TCP, where callers carry no identity and privileged operations would
+// have to be refused for everyone. Only the exact legacy default is rewritten:
+// a deliberately chosen custom address is left alone.
+func MigrateLegacy(addr string) (string, bool) {
+	return migrateLegacyForOS(runtime.GOOS, addr)
+}
+
+func migrateLegacyForOS(goos, addr string) (string, bool) {
+	if goos == "windows" && addr == legacyWindowsAddr {
+		return WindowsPipeAddr, true
+	}
+	return addr, false
+}