[GitHub] [guacamole-server] trengri commented on a change in pull request #274: GUACAMOLE-1059: Use FreeRDP function for verifying Stream length

[GitBox <gi...@apache.org>]

trengri commented on a change in pull request #274:
URL: https://github.com/apache/guacamole-server/pull/274#discussion_r419534959



##########
File path: src/protocols/rdp/channels/rdpsnd/rdpsnd.c
##########
@@ -35,11 +35,23 @@ void guac_rdpsnd_process_receive(guac_rdp_common_svc* svc,
     guac_rdpsnd* rdpsnd = (guac_rdpsnd*) svc->data;
     guac_rdpsnd_pdu_header header;
 
+    /* Check that we at least have a header. */
+    if (Stream_GetRemainingLength(input_stream) < 4)
+        return;
+    
     /* Read RDPSND PDU header */
     Stream_Read_UINT8(input_stream, header.message_type);
     Stream_Seek_UINT8(input_stream);
     Stream_Read_UINT16(input_stream, header.body_size);
-
+    
+    if (Stream_GetRemainingLength(input_stream) < header.body_size) {
+        guac_client_log(svc->client, GUAC_LOG_DEBUG, "Not enough bytes in stream."
+                "  Remaining: %d, Body size: %d",
+                Stream_GetRemainingLength(input_stream),
+                header.body_size);
+        return;
+    }

Review comment:
       I'm not a RDP expert. It's just a guess, based on reading the comments in the source code.
   It looks like some PDUs like do not have headers, so there is little sense in inspecting header.body_size for them...
   Maybe you need to move this check a few lines lower (i.e. put it after the following piece of code)?
   https://github.com/apache/guacamole-server/blob/9c37fc56171d55b8fa838949d7fd40db85506857/src/protocols/rdp/channels/rdpsnd/rdpsnd.c#L43-L50




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