Don't write more data than the protocol can grok or the server will

be confused. This comes without a test because the server needs to be
a non-community one with closed source PAM plugin loaded.

ext/mysqlnd/mysqlnd_wireprotocol.c

@@ -496,6 +496,14 @@ size_t php_mysqlnd_auth_write(void * _packet, MYSQLND_CONN_DATA * conn TSRMLS_DC
 		if (packet->auth_data == NULL) {
 			packet->auth_data_len = 0;
 		}
+		if (packet->auth_data_len > 0xFF) {
+			const char * const msg = "Authentication data too long. "
+				"Won't fit into the buffer and will be truncated. Authentication will thus fail";
+			SET_CLIENT_ERROR(*conn->error_info, CR_UNKNOWN_ERROR, UNKNOWN_SQLSTATE, msg);
+			php_error_docref(NULL TSRMLS_CC, E_WARNING, msg);
+			DBG_RETURN(0);
+		}		
+		
 		int1store(p, packet->auth_data_len);
 		++p;
 /*!!!!! is the buffer big enough ??? */