--- a/svr-authpasswd.c	Wed Mar 21 00:52:02 2018 +0800
+++ b/svr-authpasswd.c	Thu Mar 21 00:14:38 2019 +0800
@@ -48,22 +48,14 @@
 
 /* Process a password auth request, sending success or failure messages as
  * appropriate */
-void svr_auth_password() {
+void svr_auth_password(int valid_user) {
 	
 	char * passwdcrypt = NULL; /* the crypt from /etc/passwd or /etc/shadow */
 	char * testcrypt = NULL; /* crypt generated from the user's password sent */
-	char * password;
+	char * password = NULL;
 	unsigned int passwordlen;
-
 	unsigned int changepw;
 
-	passwdcrypt = ses.authstate.pw_passwd;
-
-#ifdef DEBUG_HACKCRYPT
-	/* debugging crypt for non-root testing with shadows */
-	passwdcrypt = DEBUG_HACKCRYPT;
-#endif
-
 	/* check if client wants to change password */
 	changepw = buf_getbool(ses.payload);
 	if (changepw) {
@@ -73,12 +65,30 @@
 	}
 
 	password = buf_getstring(ses.payload, &passwordlen);
-
-	/* the first bytes of passwdcrypt are the salt */
-	testcrypt = crypt(password, passwdcrypt);
+	if (valid_user && passwordlen <= DROPBEAR_MAX_PASSWORD_LEN) {
+		/* the first bytes of passwdcrypt are the salt */
+		passwdcrypt = ses.authstate.pw_passwd;
+		testcrypt = crypt(password, passwdcrypt);
+	}
 	m_burn(password, passwordlen);
 	m_free(password);
 
+	/* After we have got the payload contents we can exit if the username
+	is invalid. Invalid users have already been logged. */
+	if (!valid_user) {
+		send_msg_userauth_failure(0, 1);
+		return;
+	}
+
+	if (passwordlen > DROPBEAR_MAX_PASSWORD_LEN) {
+		dropbear_log(LOG_WARNING,
+				"Too-long password attempt for '%s' from %s",
+				ses.authstate.pw_name,
+				svr_ses.addrstring);
+		send_msg_userauth_failure(0, 1);
+		return;
+	}
+
 	if (testcrypt == NULL) {
 		/* crypt() with an invalid salt like "!!" */
 		dropbear_log(LOG_WARNING, "User account '%s' is locked",