[GUACAMOLE-1717] Cursor Improperly Initialized when Connecting to Gnome Remote Desktop via RDP

• Type: Bug
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 1.4.0
• Fix Version/s: 1.5.2
• Component/s: RDP

Language

C

• Assignee: Mike Jumper
• Reporter: Mike Powers
• Created: 21/Nov/22 01:13
• Updated: 07/Jun/23 19:26
• Resolved: 09/May/23 16:28

Description

When connecting to a Gnome Remote Desktop RDP instance the mouse cursor is created but the image data is never copied into the cursor's pixel buffer resulting in a garbled bitmap containing uninitialized data:

This appears to happen because of this guard condition in src/protocols/rdp/pointer.c (line 49):

if (pointer->andMaskData && pointer->xorMaskData) 

 

It appears when Gnome Remote Desktop initializes cursors when starting the session it sets `andMaskData` to NULL with a length of zero:

      pointer_color->lengthAndMask = 0;
      pointer_color->lengthXorMask = xor_mask_length;
      pointer_color->andMaskData = NULL; 

This causes the guard condition in the RDP plugin to fail to copy bitmap data from the server. It appears as if FreeRDP correctly handles the image data in freerdp_image_copy_from_pointer_data() if lengthAndMask == 0:

    if (andMask)
    {
        if (andStep * nHeight > andMaskLength)
            return FALSE;
    }

I believe this guard condition is probably not necessary; removing it resolves the issue for me. I tested against both Gnome Remote Desktop and a Windows 11 Professional instance.

Please let me know if you'd like any additional information or testing done. This was tested with Guacamole 1.4.0 from Docker Hub (guacamole/guacamole:1.4.0 and guacamole/guacd:1.4.0). Testing against a fresh install of Fedora 37/Gnome 43.

Issue Links

• causes: GUACAMOLE-1802 Regression: Fix for GUACAMOLE-1717 causes guacd segfault