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

tailscale/corp#1582

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

client/tailscale/tailscale.go

@@ -66,6 +66,20 @@ func DoLocalRequest(req *http.Request) (*http.Response, error) {
 	return tsClient.Do(req)
 }
 
+type errorJSON struct {
+	Error string
+}
+
+// bestError returns either err, or if body contains a valid JSON
+// object of type errorJSON, its non-empty error body.
+func bestError(err error, body []byte) error {
+	var j errorJSON
+	if err := json.Unmarshal(body, &j); err == nil && j.Error != "" {
+		return errors.New(j.Error)
+	}
+	return err
+}
+
 func send(ctx context.Context, method, path string, wantStatus int, body io.Reader) ([]byte, error) {
 	req, err := http.NewRequestWithContext(ctx, method, "http://local-tailscaled.sock"+path, body)
 	if err != nil {
@@ -81,7 +95,8 @@ func send(ctx context.Context, method, path string, wantStatus int, body io.Read
 		return nil, err
 	}
 	if res.StatusCode != wantStatus {
-		return nil, fmt.Errorf("HTTP %s: %s (expected %v)", res.Status, slurp, wantStatus)
+		err := fmt.Errorf("HTTP %s: %s (expected %v)", res.Status, slurp, wantStatus)
+		return nil, bestError(err, slurp)
 	}
 	return slurp, nil
 }

control/controlclient/direct.go

@@ -829,6 +829,9 @@ func (c *Direct) sendMapRequest(ctx context.Context, maxPolls int, cb func(*netm
 				p.Endpoints = []string{"127.9.9.9:456"}
 			}
 		}
+		if Debug.StripCaps {
+			resp.Node.Capabilities = nil
+		}
 
 		if pf := resp.PacketFilter; pf != nil {
 			lastParsedPacketFilter = c.parsePacketFilter(pf)
@@ -1072,6 +1075,7 @@ type debug struct {
 	OnlyDisco      bool
 	Disco          bool
 	StripEndpoints bool // strip endpoints from control (only use disco messages)
+	StripCaps      bool // strip all local node's control-provided capabilities
 }
 
 func initDebug() debug {
@@ -1080,6 +1084,7 @@ func initDebug() debug {
 		NetMap:         envBool("TS_DEBUG_NETMAP"),
 		ProxyDNS:       envBool("TS_DEBUG_PROXY_DNS"),
 		StripEndpoints: envBool("TS_DEBUG_STRIP_ENDPOINTS"),
+		StripCaps:      envBool("TS_DEBUG_STRIP_CAPS"),
 		OnlyDisco:      use == "only",
 		Disco:          use == "only" || use == "" || envBool("TS_DEBUG_USE_DISCO"),
 	}

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")

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

ipn/ipnstate/ipnstate.go

@@ -89,6 +89,7 @@ type PeerStatus struct {
 	ExitNode      bool // true if this is the currently selected exit node.
 
 	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

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)

tailcfg/tailcfg.go

@@ -177,7 +177,7 @@ type Node struct {
 	// They're free-form strings, but should be in the form of URLs/URIs
 	// such as:
 	//    "https://tailscale.com/cap/is-admin"
-	//    "https://tailscale.com/cap/recv-file"
+	//    "https://tailscale.com/cap/file-sharing"
 	Capabilities []string `json:",omitempty"`
 
 	// The following three computed fields hold the various names that can
@@ -1140,3 +1140,8 @@ type Oauth2Token struct {
 	// mechanisms for that TokenSource will not be used.
 	Expiry time.Time `json:"expiry,omitempty"`
 }
+
+const (
+	CapabilityFileSharing = "https://tailscale.com/cap/file-sharing"
+	CapabilityAdmin       = "https://tailscale.com/cap/is-admin"
+)

wgengine/magicsock/magicsock.go

@@ -2984,6 +2984,11 @@ func (c *Conn) UpdateStatus(sb *ipnstate.StatusBuilder) {
 			ss.HostName = c.netMap.Hostinfo.Hostname
 			ss.DNSName = c.netMap.Name
 			ss.UserID = c.netMap.User
+			if c.netMap.SelfNode != nil {
+				if c := c.netMap.SelfNode.Capabilities; len(c) > 0 {
+					ss.Capabilities = append([]string(nil), c...)
+				}
+			}
 		} else {
 			ss.HostName, _ = os.Hostname()
 		}