This is indeed a TigerVNC bug of sorts. The older server encodes blank cursors using the RFB X11 cursor encoding, but it was sending a non-zero hotspot which, when passed into XCreatePixmapCursor in the TurboVNC Viewer, generated a BadMatch (apparently it's an error to use a non-zero hotspot when you pass an empty Pixmap to that function.) Whenever the failure occurs, the server gets into a bad state somehow and stops sending anything to TurboVNC viewers (but oddly enough, I could connect with a TigerVNC viewer and free it up.) The latest TigerVNC server (1.2) doesn't suffer from this issue.
I worked around the issue by setting the hotspot to 0,0 in the Unix TurboVNC Viewer whenever an empty cursor is received from the server. When using the Windows TurboVNC Viewer, it's also possible to crash the viewer using the same drag 'n' drop technique, assuming that cursor shape updates are not enabled (that is, the cursor is being rendered on the server.) In that case, the server apparently renders the empty cursor and tries to encode that framebuffer update in a way that isn't kosher. Since enabling cursor shape updates works around the issue on Windows, as does upgrading to a newer TigerVNC Server, I'm not going to worry about it further. On 9/26/12 1:39 AM, James Wettenhall wrote: > DRC, > > On 24/09/2012, at 1:01 PM, DRC wrote: > >> Does the same thing happen when using a different viewer? > > No, we can't reproduce the drag and drop problem using TigerVNC viewer and > TigerVNC server > >> Does the same >> thing happen when using the TurboVNC server? > > No, we can't reproduce the drag and drop problem using TurboVNC viewer and > TurboVNC server either. > > And when we switch both, i.e. use TigerVNC viewer with TurboVNC server, we > still can't reproduce the problem. > > We can only reproduce it when using TurboVNC viewer with TigerVNC server. > > Changing browsers (from Firefox to Google Chrome) didn't make a difference. > > Whilst we can't give you login credentials to the webpage in question (within > which we can reproduce the drag and drop crashing problem), we could send you > a saved copy of that webpage. All of the links would be broken because you > wouldn't be properly logged in, but you could still demonstrate dragging one > of the links within that page. I tried running the webpage through the W3C > HTML validator, and it certainly has some HTML errors, (and probably > Javascript and CSS errors too). It is part of a secure portal from an > apparently reputable vendor of firewalls and network infrastructure. > > Or I could give you temporary access to a temporary virtual machine on the > cloud with a public facing IP address on which we can demonstrate the problem > if that helps. > > Dragging and dropping was not required to use the web application, but > Geoffrey accidentally dragged a hyperlink slightly while clicking on it, > which triggered the crash. > > Cheers, > James > >> If the answers to the above are "yes" and "no", then it isn't our bug. >> It's TigerVNC's, and the first thing they'll tell you is "use a newer >> release." Of course, the problem is that Red Hat has frozen their >> supplied version of TigerVNC at 1.1, so newer releases of TigerVNC are >> not supported by Red Hat, but older releases are not supported by The >> TigerVNC Project. > > > > >> >> >> On 9/23/12 9:36 PM, Geoffrey Kong wrote: >>> Hi all, >>> >>> The VNC instances crashed whenever I did a click-and-drag, e.g. from >>> within Firefox, with the following error message. >>> >>> CleanupXErrorHandler called >>> X Error of failed request: BadMatch (invalid parameter attributes) >>> Major opcode of failed request: 93 (X_CreateCursor) >>> Serial number of failed request: 4067 >>> Current serial number in output stream: 4071 >>> >>> We are using TurboVNC 1.1 as client on Mac OS X and TigerVNC 1.0.90 as >>> server on CentOS 6.2 Linux. >>> >>> Would anyone know what the problem is? >>> >>> Thanks, >>> Geoffrey Kong >> >> ------------------------------------------------------------------------------ >> Live Security Virtual Conference >> Exclusive live event will cover all the ways today's security and >> threat landscape has changed and how IT managers can respond. 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