Pull request: home: don't allow all origins

Merge in DNS/adguard-home from 2484-access-control to master

Updates #2484.

Squashed commit of the following:

commit 4f0c6ddae35b55a9251f4d5e14c4d92fd2107443
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Fri Feb 5 12:42:22 2021 +0300

    home: don't allow all origins

CHANGELOG.md

@@ -43,6 +43,8 @@ and this project adheres to
 
 ### Changed
 
+- `Access-Control-Allow-Origin` is now only set to the same origin as the
+  domain, but with an HTTP scheme as opposed to `*` ([#2484]).
 - `workDir` now supports symlinks.
 - Stopped mounting together the directories `/opt/adguardhome/conf` and
   `/opt/adguardhome/work` in our Docker images ([#2589]).
@@ -67,6 +69,7 @@ and this project adheres to
 [#2358]: https://github.com/AdguardTeam/AdGuardHome/issues/2358
 [#2391]: https://github.com/AdguardTeam/AdGuardHome/issues/2391
 [#2394]: https://github.com/AdguardTeam/AdGuardHome/issues/2394
+[#2484]: https://github.com/AdguardTeam/AdGuardHome/issues/2484
 [#2509]: https://github.com/AdguardTeam/AdGuardHome/issues/2509
 [#2552]: https://github.com/AdguardTeam/AdGuardHome/issues/2552
 [#2589]: https://github.com/AdguardTeam/AdGuardHome/issues/2589

internal/home/control.go

@@ -2,6 +2,7 @@ package home
 
 import (
 	"encoding/json"
+	"errors"
 	"fmt"
 	"net"
 	"net/http"
@@ -202,37 +203,81 @@ func preInstallHandler(handler http.Handler) http.Handler {
 	return &preInstallHandlerStruct{handler}
 }
 
-// postInstall lets the handler run only if firstRun is false, and redirects to /install.html otherwise
-// it also enforces HTTPS if it is enabled and configured
+const defaultHTTPSPort = 443
+
+// handleHTTPSRedirect redirects the request to HTTPS, if needed.  If ok is
+// true, the middleware must continue handling the request.
+func handleHTTPSRedirect(w http.ResponseWriter, r *http.Request) (ok bool) {
+	web := Context.web
+	if web.httpsServer.server == nil {
+		return true
+	}
+
+	host, _, err := net.SplitHostPort(r.Host)
+	if err != nil {
+		// Check for the missing port error.  If it is that error, just
+		// use the host as is.
+		//
+		// See the source code for net.SplitHostPort.
+		const missingPort = "missing port in address"
+
+		addrErr := &net.AddrError{}
+		if !errors.As(err, &addrErr) || addrErr.Err != missingPort {
+			httpError(w, http.StatusBadRequest, "bad host: %s", err)
+
+			return false
+		}
+
+		host = r.Host
+	}
+
+	if r.TLS == nil && web.forceHTTPS {
+		hostPort := host
+		if port := web.conf.PortHTTPS; port != defaultHTTPSPort {
+			portStr := strconv.Itoa(port)
+			hostPort = net.JoinHostPort(host, portStr)
+		}
+
+		httpsURL := &url.URL{
+			Scheme:   "https",
+			Host:     hostPort,
+			Path:     r.URL.Path,
+			RawQuery: r.URL.RawQuery,
+		}
+		http.Redirect(w, r, httpsURL.String(), http.StatusTemporaryRedirect)
+
+		return false
+	}
+
+	// Allow the frontend from the HTTP origin to send requests to the HTTPS
+	// server.  This can happen when the user has just set up HTTPS with
+	// redirects.
+	originURL := &url.URL{
+		Scheme: "http",
+		Host:   r.Host,
+	}
+	w.Header().Set("Access-Control-Allow-Origin", originURL.String())
+
+	return true
+}
+
+// postInstall lets the handler to run only if firstRun is false.  Otherwise, it
+// redirects to /install.html.  It also enforces HTTPS if it is enabled and
+// configured and sets appropriate access control headers.
 func postInstall(handler func(http.ResponseWriter, *http.Request)) func(http.ResponseWriter, *http.Request) {
 	return func(w http.ResponseWriter, r *http.Request) {
-		if Context.firstRun &&
-			!strings.HasPrefix(r.URL.Path, "/install.") &&
-			!strings.HasPrefix(r.URL.Path, "/assets/") {
+		path := r.URL.Path
+		if Context.firstRun && !strings.HasPrefix(path, "/install.") &&
+			!strings.HasPrefix(path, "/assets/") {
 			http.Redirect(w, r, "/install.html", http.StatusFound)
+
 			return
 		}
 
-		// enforce https?
-		if r.TLS == nil && Context.web.forceHTTPS && Context.web.httpsServer.server != nil {
-			// yes, and we want host from host:port
-			host, _, err := net.SplitHostPort(r.Host)
-			if err != nil {
-				// no port in host
-				host = r.Host
-			}
-			// construct new URL to redirect to
-			newURL := url.URL{
-				Scheme:   "https",
-				Host:     net.JoinHostPort(host, strconv.Itoa(Context.web.conf.PortHTTPS)),
-				Path:     r.URL.Path,
-				RawQuery: r.URL.RawQuery,
-			}
-			http.Redirect(w, r, newURL.String(), http.StatusTemporaryRedirect)
+		if !handleHTTPSRedirect(w, r) {
 			return
 		}
 
-		w.Header().Set("Access-Control-Allow-Origin", "*")
 		handler(w, r)
 	}
 }

internal/home/home_test.go

@@ -133,7 +133,7 @@ func TestHome(t *testing.T) {
 	h := http.Client{}
 	for i := 0; i != 50; i++ {
 		resp, err = h.Get("http://127.0.0.1:3000/")
-		if err == nil && resp.StatusCode != 404 {
+		if err == nil && resp.StatusCode != http.StatusNotFound {
 			break
 		}
 		time.Sleep(100 * time.Millisecond)