ipn/ipnlocal: add some validation to PeerAPI

Updates tailscale/corp#7948

Signed-off-by: Maisem Ali <maisem@tailscale.com>

ipn/ipnlocal/peerapi.go

@@ -32,6 +32,7 @@
 	"unicode/utf8"
 
 	"github.com/kortschak/wol"
+	"golang.org/x/exp/slices"
 	"golang.org/x/net/dns/dnsmessage"
 	"tailscale.com/client/tailscale/apitype"
 	"tailscale.com/envknob"
@@ -542,7 +543,37 @@ func (h *peerAPIHandler) logf(format string, a ...any) {
 	h.ps.b.logf("peerapi: "+format, a...)
 }
 
+func (h *peerAPIHandler) validateHost(r *http.Request) error {
+	if r.Host == "peer" {
+		return nil
+	}
+	ap, err := netip.ParseAddrPort(r.Host)
+	if err != nil {
+		return err
+	}
+	hostIPPfx := netip.PrefixFrom(ap.Addr(), ap.Addr().BitLen())
+	if !slices.Contains(h.ps.selfNode.Addresses, hostIPPfx) {
+		return fmt.Errorf("%v not found in self addresses", hostIPPfx)
+	}
+	return nil
+}
+
+func (h *peerAPIHandler) validatePeerAPIRequest(r *http.Request) error {
+	if r.Referer() != "" {
+		return errors.New("unexpected Referer")
+	}
+	if r.Header.Get("Origin") != "" {
+		return errors.New("unexpected Origin")
+	}
+	return h.validateHost(r)
+}
+
 func (h *peerAPIHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	if err := h.validatePeerAPIRequest(r); err != nil {
+		h.logf("invalid request from %v: %v", h.remoteAddr, err)
+		http.Error(w, "invalid peerapi request", http.StatusForbidden)
+		return
+	}
 	if strings.HasPrefix(r.URL.Path, "/v0/put/") {
 		h.handlePeerPut(w, r)
 		return

ipn/ipnlocal/peerapi_test.go

@@ -108,6 +108,7 @@ func hexAll(v string) string {
 }
 
 func TestHandlePeerAPI(t *testing.T) {
+	const nodeFQDN = "self-node.tail-scale.ts.net."
 	tests := []struct {
 		name       string
 		isSelf     bool // the peer sending the request is owned by us
@@ -402,6 +403,30 @@ func TestHandlePeerAPI(t *testing.T) {
 				bodyContains("bad filename"),
 			),
 		},
+		{
+			name:   "host-val/bad-ip",
+			isSelf: true,
+			req:    httptest.NewRequest("GET", "http://12.23.45.66:1234/v0/env", nil),
+			checks: checks(
+				httpStatus(403),
+			),
+		},
+		{
+			name:   "host-val/no-port",
+			isSelf: true,
+			req:    httptest.NewRequest("GET", "http://100.100.100.101/v0/env", nil),
+			checks: checks(
+				httpStatus(403),
+			),
+		},
+		{
+			name:   "host-val/peer",
+			isSelf: true,
+			req:    httptest.NewRequest("GET", "http://peer/v0/env", nil),
+			checks: checks(
+				httpStatus(200),
+			),
+		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
@@ -417,6 +442,11 @@ func TestHandlePeerAPI(t *testing.T) {
 				},
 				ps: &peerAPIServer{
 					b: lb,
+					selfNode: &tailcfg.Node{
+						Addresses: []netip.Prefix{
+							netip.MustParsePrefix("100.100.100.101/32"),
+						},
+					},
 				},
 			}
 			var rootDir string
@@ -425,6 +455,9 @@ func TestHandlePeerAPI(t *testing.T) {
 				e.ph.ps.rootDir = rootDir
 			}
 			e.rr = httptest.NewRecorder()
+			if tt.req.Host == "example.com" {
+				tt.req.Host = "100.100.100.101:12345"
+			}
 			e.ph.ServeHTTP(e.rr, tt.req)
 			for _, f := range tt.checks {
 				f(t, &e)
@@ -455,6 +488,9 @@ func TestFileDeleteRace(t *testing.T) {
 			logf:           t.Logf,
 			capFileSharing: true,
 		},
+		selfNode: &tailcfg.Node{
+			Addresses: []netip.Prefix{netip.MustParsePrefix("100.100.100.101/32")},
+		},
 		rootDir: dir,
 	}
 	ph := &peerAPIHandler{
@@ -467,7 +503,7 @@ func TestFileDeleteRace(t *testing.T) {
 	buf := make([]byte, 2<<20)
 	for i := 0; i < 30; i++ {
 		rr := httptest.NewRecorder()
-		ph.ServeHTTP(rr, httptest.NewRequest("PUT", "/v0/put/foo.txt", bytes.NewReader(buf[:rand.Intn(len(buf))])))
+		ph.ServeHTTP(rr, httptest.NewRequest("PUT", "http://100.100.100.101:123/v0/put/foo.txt", bytes.NewReader(buf[:rand.Intn(len(buf))])))
 		if res := rr.Result(); res.StatusCode != 200 {
 			t.Fatal(res.Status)
 		}