Switch to Referrer-Policy header (#149)

Use of the Content-Security-Policy header to specify a referrer policy
was deprecated in favor of a [new
header](fc55d917be).
This change changes the existing referrer policy directives to use this
header and adds corresponding config options/command line flags.

README.md

@@ -47,8 +47,10 @@ allowhotlink = true
 - ```-maxsize 4294967296``` -- maximum upload file size in bytes (default 4GB)
 - ```-maxexpiry 86400``` -- maximum expiration time in seconds (default is 0, which is no expiry)
 - ```-allowhotlink``` -- Allow file hotlinking
-- ```-contentsecuritypolicy "..."``` -- Content-Security-Policy header for pages (default is "default-src 'self'; img-src 'self' data:; style-src 'self' 'unsafe-inline'; frame-ancestors 'self'; referrer origin;")
+- ```-contentsecuritypolicy "..."``` -- Content-Security-Policy header for pages (default is "default-src 'self'; img-src 'self' data:; style-src 'self' 'unsafe-inline'; frame-ancestors 'self';")
-- ```-filecontentsecuritypolicy "..."``` -- Content-Security-Policy header for files (default is "default-src 'none'; img-src 'self'; object-src 'self'; media-src 'self'; style-src 'self' 'unsafe-inline'; frame-ancestors 'self'; referrer origin;")
+- ```-filecontentsecuritypolicy "..."``` -- Content-Security-Policy header for files (default is "default-src 'none'; img-src 'self'; object-src 'self'; media-src 'self'; style-src 'self' 'unsafe-inline'; frame-ancestors 'self';")
+- ```-refererpolicy "..."``` -- Referrer-Policy header for pages (default is "same-origin")
+- ```-filereferrerpolicy "..."``` -- Referrer-Policy header for files (default is "same-origin")
 - ```-xframeoptions "..." ``` -- X-Frame-Options header (default is "SAMEORIGIN")
 - ```-remoteuploads``` -- (optionally) enable remote uploads (/upload?url=https://...) 
 - ```-nologs``` -- (optionally) disable request logs in stdout

csp.go

@@ -6,6 +6,7 @@ import (
 
 const (
 	cspHeader          = "Content-Security-Policy"
+	rpHeader           = "Referrer-Policy"
 	frameOptionsHeader = "X-Frame-Options"
 )
 
@@ -16,6 +17,7 @@ type csp struct {
 
 type CSPOptions struct {
 	policy         string
+	referrerPolicy string
 	frame          string
 }
 
@@ -25,6 +27,11 @@ func (c csp) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		w.Header().Add(cspHeader, c.opts.policy)
 	}
 
+	// only add a Referrer Policy if one is not already set
+	if existing := w.Header().Get(rpHeader); existing == "" {
+		w.Header().Add(rpHeader, c.opts.referrerPolicy)
+	}
+
 	w.Header().Set(frameOptionsHeader, c.opts.frame)
 
 	c.h.ServeHTTP(w, r)

csp_test.go

@@ -12,6 +12,7 @@ import (
 
 var testCSPHeaders = map[string]string{
 	"Content-Security-Policy": "default-src 'none'; style-src 'self';",
+	"Referrer-Policy":         "strict-origin-when-cross-origin",
 	"X-Frame-Options":         "SAMEORIGIN",
 }
 
@@ -22,8 +23,9 @@ func TestContentSecurityPolicy(t *testing.T) {
 	Config.maxSize = 1024 * 1024 * 1024
 	Config.noLogs = true
 	Config.siteName = "linx"
-	Config.contentSecurityPolicy = "default-src 'none'; style-src 'self';"
+	Config.contentSecurityPolicy = testCSPHeaders["Content-Security-Policy"]
-	Config.xFrameOptions = "SAMEORIGIN"
+	Config.referrerPolicy = testCSPHeaders["Referrer-Policy"]
+	Config.xFrameOptions = testCSPHeaders["X-Frame-Options"]
 	mux := setup()
 
 	w := httptest.NewRecorder()
@@ -35,6 +37,7 @@ func TestContentSecurityPolicy(t *testing.T) {
 
 	goji.Use(ContentSecurityPolicy(CSPOptions{
 		policy:         testCSPHeaders["Content-Security-Policy"],
+		referrerPolicy: testCSPHeaders["Referrer-Policy"],
 		frame:          testCSPHeaders["X-Frame-Options"],
 	}))
 

fileserve.go

@@ -32,6 +32,7 @@ func fileServeHandler(c web.C, w http.ResponseWriter, r *http.Request) {
 	}
 
 	w.Header().Set("Content-Security-Policy", Config.fileContentSecurityPolicy)
+	w.Header().Set("Referrer-Policy", Config.fileReferrerPolicy)
 
 	fileBackend.ServeFile(fileName, w, r)
 }

server.go

@@ -46,6 +46,8 @@ var Config struct {
 	keyFile                   string
 	contentSecurityPolicy     string
 	fileContentSecurityPolicy string
+	referrerPolicy            string
+	fileReferrerPolicy        string
 	xFrameOptions             string
 	maxSize                   int64
 	maxExpiry                 uint64
@@ -89,6 +91,7 @@ func setup() *web.Mux {
 	mux.Use(middleware.AutomaticOptions)
 	mux.Use(ContentSecurityPolicy(CSPOptions{
 		policy:         Config.contentSecurityPolicy,
+		referrerPolicy: Config.referrerPolicy,
 		frame:          Config.xFrameOptions,
 	}))
 	mux.Use(AddHeaders(Config.addHeaders))
@@ -233,11 +236,17 @@ func main() {
 	flag.StringVar(&Config.remoteAuthFile, "remoteauthfile", "",
 		"path to a file containing newline-separated scrypted auth keys for remote uploads")
 	flag.StringVar(&Config.contentSecurityPolicy, "contentsecuritypolicy",
-		"default-src 'self'; img-src 'self' data:; style-src 'self' 'unsafe-inline'; frame-ancestors 'self'; referrer origin;",
+		"default-src 'self'; img-src 'self' data:; style-src 'self' 'unsafe-inline'; frame-ancestors 'self';",
 		"value of default Content-Security-Policy header")
 	flag.StringVar(&Config.fileContentSecurityPolicy, "filecontentsecuritypolicy",
-		"default-src 'none'; img-src 'self'; object-src 'self'; media-src 'self'; style-src 'self' 'unsafe-inline'; frame-ancestors 'self'; referrer origin;",
+		"default-src 'none'; img-src 'self'; object-src 'self'; media-src 'self'; style-src 'self' 'unsafe-inline'; frame-ancestors 'self';",
 		"value of Content-Security-Policy header for file access")
+	flag.StringVar(&Config.referrerPolicy, "referrerpolicy",
+		"same-origin",
+		"value of default Referrer-Policy header")
+	flag.StringVar(&Config.fileReferrerPolicy, "filereferrerpolicy",
+		"same-origin",
+		"value of Referrer-Policy header for file access")
 	flag.StringVar(&Config.xFrameOptions, "xframeoptions", "SAMEORIGIN",
 		"value of X-Frame-Options header")
 	flag.Var(&Config.addHeaders, "addheader",