reject wrong email in SMTP MAIL(), reject impersonation attempts

bot/access.go

@@ -125,7 +125,7 @@ func (b *Bot) Ban(addr net.Addr) {
 }
 
 // AllowAuth check if SMTP login (email) and password are valid
-func (b *Bot) AllowAuth(email, password string) bool {
+func (b *Bot) AllowAuth(email, password string) (id.RoomID, bool) {
 	var suffix bool
 	for _, domain := range b.domains {
 		if strings.HasSuffix(email, "@"+domain) {
@@ -134,22 +134,27 @@ func (b *Bot) AllowAuth(email, password string) bool {
 		}
 	}
 	if !suffix {
-		return false
+		return "", false
 	}
 
 	roomID, ok := b.getMapping(utils.Mailbox(email))
 	if !ok {
-		return false
+		return "", false
 	}
 	cfg, err := b.getRoomSettings(roomID)
 	if err != nil {
 		b.log.Error("failed to retrieve settings: %v", err)
-		return false
+		return "", false
+	}
+
+	if cfg.NoSend() {
+		b.log.Warn("trying to send email from %q (%q), but it's receive-only", email, roomID)
+		return "", false
 	}
 
 	allow, err := argon2pw.CompareHashWithPassword(cfg.Password(), password)
 	if err != nil {
 		b.log.Warn("Password for %s is not valid: %v", email, err)
 	}
-	return allow
+	return roomID, allow
 }

smtp/manager.go

@@ -40,7 +40,7 @@ type Manager struct {
 }
 
 type matrixbot interface {
-	AllowAuth(string, string) bool
+	AllowAuth(string, string) (id.RoomID, bool)
 	IsGreylisted(net.Addr) bool
 	IsBanned(net.Addr) bool
 	Ban(net.Addr)

smtp/server.go

@@ -47,7 +47,8 @@ func (m *mailServer) Login(state *smtp.ConnectionState, username, password strin
 		return nil, ErrBanned
 	}
 
-	if !m.bot.AllowAuth(username, password) {
+	roomID, allow := m.bot.AllowAuth(username, password)
+	if !allow {
 		m.log.Debug("username=%s or password=<redacted> is invalid", username)
 		m.bot.Ban(state.RemoteAddr)
 		return nil, ErrBanned
@@ -60,6 +61,8 @@ func (m *mailServer) Login(state *smtp.ConnectionState, username, password strin
 		from:      username,
 		log:       m.log,
 		domains:   m.domains,
+		getRoomID: m.bot.GetMapping,
+		fromRoom:  roomID,
 		tos:       []string{},
 	}, nil
 }

smtp/session.go

@@ -48,9 +48,10 @@ func (s *incomingSession) Mail(from string, opts smtp.MailOptions) error {
 func (s *incomingSession) Rcpt(to string) error {
 	sentry.GetHubFromContext(s.ctx).Scope().SetTag("to", to)
 	s.tos = append(s.tos, to)
+	hostname := utils.Hostname(to)
 	var domainok bool
 	for _, domain := range s.domains {
-		if utils.Hostname(to) == domain {
+		if hostname == domain {
 			domainok = true
 			break
 		}
@@ -109,10 +110,12 @@ type outgoingSession struct {
 	sendmail  func(string, string, string) error
 	privkey   string
 	domains   []string
+	getRoomID func(string) (id.RoomID, bool)
 
 	ctx      context.Context
 	tos      []string
 	from     string
+	fromRoom id.RoomID
 }
 
 func (s *outgoingSession) Mail(from string, opts smtp.MailOptions) error {
@@ -120,6 +123,28 @@ func (s *outgoingSession) Mail(from string, opts smtp.MailOptions) error {
 	if !email.AddressValid(from) {
 		return errors.New("please, provide email address")
 	}
+	hostname := utils.Hostname(from)
+	var domainok bool
+	for _, domain := range s.domains {
+		if hostname == domain {
+			domainok = true
+			break
+		}
+	}
+	if !domainok {
+		s.log.Debug("wrong domain of %s", from)
+		return ErrNoUser
+	}
+
+	roomID, ok := s.getRoomID(utils.Mailbox(from))
+	if !ok {
+		s.log.Debug("mapping for %s not found", from)
+		return ErrNoUser
+	}
+	if s.fromRoom != roomID {
+		s.log.Warn("sender from %q tries to impersonate %q", s.fromRoom, roomID)
+		return ErrNoUser
+	}
 	return nil
 }