ipn/ipnlocal, etc: require file sharing capability to send/recv files

tailscale/corp#1582

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

4 files changed, 44 insertions, 2 deletions

diff --git a/ipn/ipnlocal/local.go b/ipn/ipnlocal/local.go
index 51761bc19..18d8b310f 100644
--- a/ipn/ipnlocal/local.go
+++ b/ipn/ipnlocal/local.go
@@ -2215,12 +2215,36 @@ func (b *LocalBackend) OpenFile(name string) (rc io.ReadCloser, size int64, err
 	return apiSrv.OpenFile(name)
 }
 
+// hasCapFileSharing reports whether the current node has the file
+// sharing capability enabled.
+func (b *LocalBackend) hasCapFileSharing() bool {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	return b.hasCapFileSharingLocked()
+}
+
+func (b *LocalBackend) hasCapFileSharingLocked() bool {
+	nm := b.netMap
+	if nm == nil || nm.SelfNode == nil {
+		return false
+	}
+	for _, c := range nm.SelfNode.Capabilities {
+		if c == tailcfg.CapabilityFileSharing {
+			return true
+		}
+	}
+	return false
+}
+
 // FileTargets lists nodes that the current node can send files to.
 func (b *LocalBackend) FileTargets() ([]*apitype.FileTarget, error) {
 	var ret []*apitype.FileTarget
 
 	b.mu.Lock()
 	defer b.mu.Unlock()
+	if !b.hasCapFileSharingLocked() {
+		return nil, errors.New("file sharing not enabled by Tailscale admin")
+	}
 	nm := b.netMap
 	if b.state != ipn.Running || nm == nil {
 		return nil, errors.New("not connected")
diff --git a/ipn/ipnlocal/peerapi.go b/ipn/ipnlocal/peerapi.go
index 2af91f234..b1a43b3c2 100644
--- a/ipn/ipnlocal/peerapi.go
+++ b/ipn/ipnlocal/peerapi.go
@@ -410,6 +410,10 @@ func (h *peerAPIHandler) put(w http.ResponseWriter, r *http.Request) {
 		http.Error(w, "not owner", http.StatusForbidden)
 		return
 	}
+	if !h.ps.b.hasCapFileSharing() {
+		http.Error(w, "file sharing not enabled by Tailscale admin", http.StatusForbidden)
+		return
+	}
 	if r.Method != "PUT" {
 		http.Error(w, "not method PUT", http.StatusMethodNotAllowed)
 		return
diff --git a/ipn/ipnstate/ipnstate.go b/ipn/ipnstate/ipnstate.go
index a748f3271..cbc3413ca 100644
--- a/ipn/ipnstate/ipnstate.go
+++ b/ipn/ipnstate/ipnstate.go
@@ -88,7 +88,8 @@ type PeerStatus struct {
 	KeepAlive     bool
 	ExitNode      bool // true if this is the currently selected exit node.
 
-	PeerAPIURL []string
+	PeerAPIURL   []string
+	Capabilities []string `json:",omitempty"`
 
 	// ShareeNode indicates this node exists in the netmap because
 	// it's owned by a shared-to user and that node might connect
diff --git a/ipn/localapi/localapi.go b/ipn/localapi/localapi.go
index 8e57f85e1..f8adb188b 100644
--- a/ipn/localapi/localapi.go
+++ b/ipn/localapi/localapi.go
@@ -9,6 +9,7 @@ import (
 	"crypto/rand"
 	"encoding/hex"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"io"
 	"net"
@@ -299,6 +300,18 @@ func (h *Handler) serveFiles(w http.ResponseWriter, r *http.Request) {
 	io.Copy(w, rc)
 }
 
+func writeErrorJSON(w http.ResponseWriter, err error) {
+	if err == nil {
+		err = errors.New("unexpected nil error")
+	}
+	w.Header().Set("Content-Type", "application/json")
+	w.WriteHeader(500)
+	type E struct {
+		Error string `json:"error"`
+	}
+	json.NewEncoder(w).Encode(E{err.Error()})
+}
+
 func (h *Handler) serveFileTargets(w http.ResponseWriter, r *http.Request) {
 	if !h.PermitRead {
 		http.Error(w, "access denied", http.StatusForbidden)
@@ -310,7 +323,7 @@ func (h *Handler) serveFileTargets(w http.ResponseWriter, r *http.Request) {
 	}
 	fts, err := h.b.FileTargets()
 	if err != nil {
-		http.Error(w, err.Error(), 500)
+		writeErrorJSON(w, err)
 		return
 	}
 	makeNonNil(&fts)