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

1 files changed, 61 insertions, 0 deletions

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
+}