fix: validate that session was issued on the same host

Currently, sessions are valid across all domains.
And our auth tokens are also valid for all pages projects
user has access to.
This means that cookie from one website can be reused on the
another.

Attackers can steal cookies in many different ways.
The easiest way would be to setup a validated custom domain,
then proxy all requests to pages server, but log the cookies.

Once you have a cookie for attackers domain, you can reuse it
on any other pages domain the target user has access to.

This commit saves current domain in the session and validates it
when reading the session.

Changelog: security

3 files changed, 150 insertions, 120 deletions

diff --git a/internal/auth/auth.go b/internal/auth/auth.go
index 98bbf49d..2da28a8a 100644
--- a/internal/auth/auth.go
+++ b/internal/auth/auth.go
@@ -85,41 +85,6 @@ type domain interface {
 	ServeNotFoundAuthFailed(w http.ResponseWriter, r *http.Request)
 }
 
-func (a *Auth) getSessionFromStore(r *http.Request) (*sessions.Session, error) {
-	session, err := a.store.Get(r, "gitlab-pages")
-
-	if session != nil {
-		// Cookie just for this domain
-		session.Options.Path = "/"
-		session.Options.HttpOnly = true
-		session.Options.Secure = request.IsHTTPS(r)
-		session.Options.MaxAge = authSessionMaxAge
-	}
-
-	return session, err
-}
-
-func (a *Auth) checkSession(w http.ResponseWriter, r *http.Request) (*sessions.Session, error) {
-	// Create or get session
-	session, errsession := a.getSessionFromStore(r)
-
-	if errsession != nil {
-		// Save cookie again
-		errsave := session.Save(r, w)
-		if errsave != nil {
-			logRequest(r).WithError(errsave).Error(saveSessionErrMsg)
-			captureErrWithReqAndStackTrace(errsave, r)
-			httperrors.Serve500(w)
-			return nil, errsave
-		}
-
-		http.Redirect(w, r, getRequestAddress(r), http.StatusFound)
-		return nil, errsession
-	}
-
-	return session, nil
-}
-
 // TryAuthenticate tries to authenticate user and fetch access token if request is a callback to /auth?
 func (a *Auth) TryAuthenticate(w http.ResponseWriter, r *http.Request, domains source.Source) bool {
 	if a == nil {
@@ -159,7 +124,7 @@ func (a *Auth) TryAuthenticate(w http.ResponseWriter, r *http.Request, domains s
 	return false
 }
 
-func (a *Auth) checkAuthenticationResponse(session *sessions.Session, w http.ResponseWriter, r *http.Request) {
+func (a *Auth) checkAuthenticationResponse(session *hostSession, w http.ResponseWriter, r *http.Request) {
 	if !validateState(r, session) {
 		// State is NOT ok
 		logRequest(r).Warn("Authentication state did not match expected")
@@ -233,7 +198,7 @@ func (a *Auth) domainAllowed(ctx context.Context, name string, domains source.So
 	return (domain != nil && err == nil)
 }
 
-func (a *Auth) handleProxyingAuth(session *sessions.Session, w http.ResponseWriter, r *http.Request, domains source.Source) bool {
+func (a *Auth) handleProxyingAuth(session *hostSession, w http.ResponseWriter, r *http.Request, domains source.Source) bool {
 	// handle auth callback e.g. https://gitlab.io/auth?domain=domain&state=state
 	if shouldProxyAuthToGitlab(r) {
 		domain := r.URL.Query().Get("domain")
@@ -354,11 +319,11 @@ func shouldProxyAuthToGitlab(r *http.Request) bool {
 	return r.URL.Query().Get("domain") != "" && r.URL.Query().Get("state") != ""
 }
 
-func shouldProxyCallbackToCustomDomain(session *sessions.Session) bool {
+func shouldProxyCallbackToCustomDomain(session *hostSession) bool {
 	return session.Values["proxy_auth_domain"] != nil
 }
 
-func validateState(r *http.Request, session *sessions.Session) bool {
+func validateState(r *http.Request, session *hostSession) bool {
 	state := r.URL.Query().Get("state")
 	if state == "" {
 		// No state param
@@ -424,7 +389,7 @@ func (a *Auth) fetchAccessToken(ctx context.Context, code string) (tokenResponse
 	return token, nil
 }
 
-func (a *Auth) checkSessionIsValid(w http.ResponseWriter, r *http.Request) *sessions.Session {
+func (a *Auth) checkSessionIsValid(w http.ResponseWriter, r *http.Request) *hostSession {
 	session, err := a.checkSession(w, r)
 	if err != nil {
 		return nil
@@ -438,7 +403,7 @@ func (a *Auth) checkSessionIsValid(w http.ResponseWriter, r *http.Request) *sess
 	return session
 }
 
-func (a *Auth) checkTokenExists(session *sessions.Session, w http.ResponseWriter, r *http.Request) bool {
+func (a *Auth) checkTokenExists(session *hostSession, w http.ResponseWriter, r *http.Request) bool {
 	// If no access token redirect to OAuth login page
 	if session.Values["access_token"] == nil {
 		logRequest(r).Debug("No access token exists, redirecting user to OAuth2 login")
@@ -473,7 +438,7 @@ func (a *Auth) getProxyAddress(r *http.Request, state string) string {
 	return fmt.Sprintf(authorizeProxyTemplate, a.redirectURI, getRequestDomain(r), state)
 }
 
-func destroySession(session *sessions.Session, w http.ResponseWriter, r *http.Request) {
+func destroySession(session *hostSession, w http.ResponseWriter, r *http.Request) {
 	logRequest(r).Debug("Destroying session")
 
 	// Invalidate access token and redirect back for refreshing and re-authenticating
@@ -620,7 +585,7 @@ func (a *Auth) CheckResponseForInvalidToken(w http.ResponseWriter, r *http.Reque
 	return false
 }
 
-func checkResponseForInvalidToken(resp *http.Response, session *sessions.Session, w http.ResponseWriter, r *http.Request) bool {
+func checkResponseForInvalidToken(resp *http.Response, session *hostSession, w http.ResponseWriter, r *http.Request) bool {
 	if resp.StatusCode == http.StatusUnauthorized {
 		errResp := errorResponse{}
 
diff --git a/internal/auth/auth_test.go b/internal/auth/auth_test.go
index 47e424c1..28e7c230 100644
--- a/internal/auth/auth_test.go
+++ b/internal/auth/auth_test.go
@@ -8,11 +8,9 @@ import (
 	"net/http"
 	"net/http/httptest"
 	"net/url"
-	"strings"
 	"testing"
 
 	"github.com/golang/mock/gomock"
-	"github.com/gorilla/sessions"
 	"github.com/stretchr/testify/require"
 
 	"gitlab.com/gitlab-org/gitlab-pages/internal/request"
@@ -55,17 +53,18 @@ func (dm *domainMock) ServeNotFoundAuthFailed(w http.ResponseWriter, r *http.Req
 // Which leads to negative side effects: we can't test encryption, and cookie params
 // like max-age and secure are not being properly set
 // To avoid that we use fake request, and set only session cookie without copying context
-func setSessionValues(t *testing.T, r *http.Request, store sessions.Store, values map[interface{}]interface{}) {
+func setSessionValues(t *testing.T, r *http.Request, auth *Auth, values map[interface{}]interface{}) {
 	t.Helper()
 
-	tmpRequest, err := http.NewRequest("GET", "/", nil)
+	tmpRequest, err := http.NewRequest("GET", "http://"+r.Host, nil)
 	require.NoError(t, err)
 
 	result := httptest.NewRecorder()
 
-	session, _ := store.Get(tmpRequest, "gitlab-pages")
+	session, _ := auth.getSessionFromStore(tmpRequest)
 	session.Values = values
-	session.Save(tmpRequest, result)
+	err = session.Save(tmpRequest, result)
+	require.NoError(t, err)
 
 	res := result.Result()
 	defer res.Body.Close()
@@ -111,16 +110,13 @@ func TestTryAuthenticateWithCodeButInvalidState(t *testing.T) {
 	auth := createTestAuth(t, "", "")
 
 	result := httptest.NewRecorder()
-	reqURL, err := url.Parse("/auth?code=1&state=invalid")
-	require.NoError(t, err)
-	reqURL.Scheme = request.SchemeHTTPS
-	r := &http.Request{URL: reqURL}
 
-	session, err := auth.store.Get(r, "gitlab-pages")
+	r, err := http.NewRequest("Get", "https://example.com/auth?code=1&state=invalid", nil)
 	require.NoError(t, err)
 
-	session.Values["state"] = "state"
-	session.Save(r, result)
+	setSessionValues(t, r, auth, map[interface{}]interface{}{
+		"state": "state",
+	})
 
 	mockCtrl := gomock.NewController(t)
 
@@ -133,19 +129,15 @@ func TestTryAuthenticateRemoveTokenFromRedirect(t *testing.T) {
 	auth := createTestAuth(t, "", "")
 
 	result := httptest.NewRecorder()
-	reqURL, err := url.Parse("/auth?code=1&state=state&token=secret")
-	require.NoError(t, err)
 
-	require.Equal(t, reqURL.Query().Get("token"), "secret", "token is present before redirecting")
-	reqURL.Scheme = request.SchemeHTTPS
-	r := &http.Request{URL: reqURL}
-
-	session, err := auth.store.Get(r, "gitlab-pages")
+	r, err := http.NewRequest("Get", "https://example.com/auth?code=1&state=state&token=secret", nil)
+	require.Equal(t, r.URL.Query().Get("token"), "secret", "token is present before redirecting")
 	require.NoError(t, err)
 
-	session.Values["state"] = "state"
-	session.Values["proxy_auth_domain"] = "https://domain.com"
-	session.Save(r, result)
+	setSessionValues(t, r, auth, map[interface{}]interface{}{
+		"state":             "state",
+		"proxy_auth_domain": "https://domain.com",
+	})
 
 	mockCtrl := gomock.NewController(t)
 
@@ -201,15 +193,15 @@ func testTryAuthenticateWithCodeAndState(t *testing.T, https bool) {
 
 	auth := createTestAuth(t, apiServer.URL, "")
 
-	domain := apiServer.URL
+	host := "http://example.com"
 	if https {
-		domain = strings.Replace(apiServer.URL, "http://", "https://", -1)
+		host = "https://example.com"
 	}
 
-	code, err := auth.EncryptAndSignCode(domain, "1")
+	code, err := auth.EncryptAndSignCode(host, "1")
 	require.NoError(t, err)
 
-	r, err := http.NewRequest("GET", "/auth?code="+code+"&state=state", nil)
+	r, err := http.NewRequest("GET", host+"/auth?code="+code+"&state=state", nil)
 	require.NoError(t, err)
 	if https {
 		r.URL.Scheme = request.SchemeHTTPS
@@ -217,9 +209,7 @@ func testTryAuthenticateWithCodeAndState(t *testing.T, https bool) {
 		r.URL.Scheme = request.SchemeHTTP
 	}
 
-	r.Host = strings.TrimPrefix(apiServer.URL, "http://")
-
-	setSessionValues(t, r, auth.store, map[interface{}]interface{}{
+	setSessionValues(t, r, auth, map[interface{}]interface{}{
 		"uri":   "https://pages.gitlab-example.com/project/",
 		"state": "state",
 	})
@@ -267,16 +257,10 @@ func TestCheckAuthenticationWhenAccess(t *testing.T) {
 	auth := createTestAuth(t, apiServer.URL, "")
 
 	result := httptest.NewRecorder()
-	reqURL, err := url.Parse("/auth?code=1&state=state")
-	require.NoError(t, err)
-	reqURL.Scheme = request.SchemeHTTPS
-	r := &http.Request{URL: reqURL}
-
-	session, err := auth.store.Get(r, "gitlab-pages")
+	r, err := http.NewRequest("Get", "https://example.com/", nil)
 	require.NoError(t, err)
 
-	session.Values["access_token"] = "abc"
-	session.Save(r, result)
+	setSessionValues(t, r, auth, map[interface{}]interface{}{"access_token": "abc"})
 	contentServed := auth.CheckAuthentication(result, r, &domainMock{projectID: 1000})
 	require.False(t, contentServed)
 
@@ -304,16 +288,12 @@ func TestCheckAuthenticationWhenNoAccess(t *testing.T) {
 
 	w := httptest.NewRecorder()
 
-	reqURL, err := url.Parse("/auth?code=1&state=state")
-	require.NoError(t, err)
-	reqURL.Scheme = request.SchemeHTTPS
-	r := &http.Request{URL: reqURL}
-
-	session, err := auth.store.Get(r, "gitlab-pages")
+	r, err := http.NewRequest("Get", "https://example.com/auth?code=1&state=state", nil)
 	require.NoError(t, err)
 
-	session.Values["access_token"] = "abc"
-	session.Save(r, w)
+	setSessionValues(t, r, auth, map[interface{}]interface{}{
+		"access_token": "abc",
+	})
 
 	contentServed := auth.CheckAuthentication(w, r, &domainMock{projectID: 1000, notFoundContent: "Generic 404"})
 	require.True(t, contentServed)
@@ -327,6 +307,43 @@ func TestCheckAuthenticationWhenNoAccess(t *testing.T) {
 	require.Equal(t, string(body), "Generic 404")
 }
 
+func TestCheckAuthenticationWithSessionFromDifferentHost(t *testing.T) {
+	apiServer := httptest.NewUnstartedServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		switch r.URL.Path {
+		case "/api/v4/projects/1000/pages_access":
+			require.Equal(t, "Bearer abc", r.Header.Get("Authorization"))
+			w.WriteHeader(http.StatusOK)
+		default:
+			t.Logf("Unexpected r.URL.RawPath: %q", r.URL.Path)
+			w.Header().Set("Content-Type", "text/html; charset=utf-8")
+			w.WriteHeader(http.StatusNotFound)
+		}
+	}))
+
+	apiServer.Start()
+	defer apiServer.Close()
+
+	auth := createTestAuth(t, apiServer.URL, "")
+
+	result := httptest.NewRecorder()
+	r, err := http.NewRequest("Get", "https://different.com/", nil)
+	require.NoError(t, err)
+	setSessionValues(t, r, auth, map[interface{}]interface{}{"access_token": "abc"})
+
+	r, err = http.NewRequest("Get", "https://example.com/", nil)
+	require.NoError(t, err)
+	contentServed := auth.CheckAuthentication(result, r, &domainMock{projectID: 1000})
+	require.True(t, contentServed)
+
+	// should redirect to auth
+	require.Equal(t, http.StatusFound, result.Code)
+	redirectURL, err := url.Parse(result.Header().Get("Location"))
+	require.NoError(t, err)
+	require.Equal(t, "pages.gitlab-example.com", redirectURL.Host)
+	require.Equal(t, "/auth", redirectURL.Path)
+	require.Equal(t, "https://example.com", redirectURL.Query().Get("domain"))
+}
+
 func TestCheckAuthenticationWhenInvalidToken(t *testing.T) {
 	apiServer := httptest.NewUnstartedServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		switch r.URL.Path {
@@ -347,16 +364,13 @@ func TestCheckAuthenticationWhenInvalidToken(t *testing.T) {
 	auth := createTestAuth(t, apiServer.URL, "")
 
 	result := httptest.NewRecorder()
-	reqURL, err := url.Parse("/auth?code=1&state=state")
-	require.NoError(t, err)
-	r := &http.Request{URL: reqURL}
 
-	session, err := auth.store.Get(r, "gitlab-pages")
+	r, err := http.NewRequest("Get", "https://example.com", nil)
 	require.NoError(t, err)
 
-	session.Values["access_token"] = "abc"
-	err = session.Save(r, result)
-	require.NoError(t, err)
+	setSessionValues(t, r, auth, map[interface{}]interface{}{
+		"access_token": "abc",
+	})
 
 	contentServed := auth.CheckAuthentication(result, r, &domainMock{projectID: 1000})
 	require.True(t, contentServed)
@@ -382,16 +396,13 @@ func TestCheckAuthenticationWithoutProject(t *testing.T) {
 	auth := createTestAuth(t, apiServer.URL, "")
 
 	result := httptest.NewRecorder()
-	reqURL, err := url.Parse("/auth?code=1&state=state")
-	require.NoError(t, err)
-	reqURL.Scheme = request.SchemeHTTPS
-	r := &http.Request{URL: reqURL}
 
-	session, err := auth.store.Get(r, "gitlab-pages")
+	r, err := http.NewRequest("Get", "https://example.com/auth?code=1&state=state", nil)
 	require.NoError(t, err)
 
-	session.Values["access_token"] = "abc"
-	session.Save(r, result)
+	setSessionValues(t, r, auth, map[interface{}]interface{}{
+		"access_token": "abc",
+	})
 
 	contentServed := auth.CheckAuthenticationWithoutProject(result, r, &domainMock{projectID: 0})
 	require.False(t, contentServed)
@@ -418,15 +429,13 @@ func TestCheckAuthenticationWithoutProjectWhenInvalidToken(t *testing.T) {
 	auth := createTestAuth(t, apiServer.URL, "")
 
 	result := httptest.NewRecorder()
-	reqURL, err := url.Parse("/auth?code=1&state=state")
-	require.NoError(t, err)
-	r := &http.Request{URL: reqURL}
 
-	session, err := auth.store.Get(r, "gitlab-pages")
+	r, err := http.NewRequest("Get", "https://example.com/", nil)
 	require.NoError(t, err)
 
-	session.Values["access_token"] = "abc"
-	session.Save(r, result)
+	setSessionValues(t, r, auth, map[interface{}]interface{}{
+		"access_token": "abc",
+	})
 
 	contentServed := auth.CheckAuthenticationWithoutProject(result, r, &domainMock{projectID: 0})
 	require.True(t, contentServed)
@@ -451,15 +460,13 @@ func TestGetTokenIfExistsWhenTokenExists(t *testing.T) {
 	auth := createTestAuth(t, "", "")
 
 	result := httptest.NewRecorder()
-	reqURL, err := url.Parse("/")
-	require.NoError(t, err)
-	r := &http.Request{URL: reqURL}
 
-	session, err := auth.store.Get(r, "gitlab-pages")
+	r, err := http.NewRequest("Get", "https://example.com", nil)
 	require.NoError(t, err)
 
-	session.Values["access_token"] = "abc"
-	session.Save(r, result)
+	setSessionValues(t, r, auth, map[interface{}]interface{}{
+		"access_token": "abc",
+	})
 
 	token, err := auth.GetTokenIfExists(result, r)
 	require.NoError(t, err)
@@ -470,14 +477,11 @@ func TestGetTokenIfExistsWhenTokenDoesNotExist(t *testing.T) {
 	auth := createTestAuth(t, "", "")
 
 	result := httptest.NewRecorder()
-	reqURL, err := url.Parse("http://pages.gitlab-example.com/test")
-	require.NoError(t, err)
-	r := &http.Request{URL: reqURL, Host: "pages.gitlab-example.com", RequestURI: "/test"}
 
-	session, err := auth.store.Get(r, "gitlab-pages")
+	r, err := http.NewRequest("Get", "https://example.com", nil)
 	require.NoError(t, err)
 
-	session.Save(r, result)
+	setSessionValues(t, r, auth, map[interface{}]interface{}{})
 
 	token, err := auth.GetTokenIfExists(result, r)
 	require.Equal(t, "", token)
diff --git a/internal/auth/session.go b/internal/auth/session.go
new file mode 100644
index 00000000..40ab6467
--- /dev/null
+++ b/internal/auth/session.go
@@ -0,0 +1,61 @@
+package auth
+
+import (
+	"net/http"
+
+	"github.com/gorilla/sessions"
+
+	"gitlab.com/gitlab-org/gitlab-pages/internal/httperrors"
+	"gitlab.com/gitlab-org/gitlab-pages/internal/request"
+)
+
+type hostSession struct {
+	*sessions.Session
+}
+
+const sessionHostKey = "_session_host"
+
+func (s *hostSession) Save(r *http.Request, w http.ResponseWriter) error {
+	s.Session.Values[sessionHostKey] = r.Host
+
+	return s.Session.Save(r, w)
+}
+
+func (a *Auth) getSessionFromStore(r *http.Request) (*hostSession, error) {
+	session, err := a.store.Get(r, "gitlab-pages")
+
+	if session != nil {
+		// Cookie just for this domain
+		session.Options.Path = "/"
+		session.Options.HttpOnly = true
+		session.Options.Secure = request.IsHTTPS(r)
+		session.Options.MaxAge = authSessionMaxAge
+
+		if session.Values[sessionHostKey] == nil || session.Values[sessionHostKey] != r.Host {
+			session.Values = make(map[interface{}]interface{})
+		}
+	}
+
+	return &hostSession{session}, err
+}
+
+func (a *Auth) checkSession(w http.ResponseWriter, r *http.Request) (*hostSession, error) {
+	// Create or get session
+	session, errsession := a.getSessionFromStore(r)
+
+	if errsession != nil {
+		// Save cookie again
+		errsave := session.Save(r, w)
+		if errsave != nil {
+			logRequest(r).WithError(errsave).Error(saveSessionErrMsg)
+			captureErrWithReqAndStackTrace(errsave, r)
+			httperrors.Serve500(w)
+			return nil, errsave
+		}
+
+		http.Redirect(w, r, getRequestAddress(r), http.StatusFound)
+		return nil, errsession
+	}
+
+	return session, nil
+}