ANNOUNCE: gtk-vnc 0.7.0 release including 2 security fixes

Posted: February 10th, 2017 | Filed under: Fedora, Gtk-Vnc, libvirt, Security, Virt Tools | No Comments »

I’m pleased to announce a new release of GTK-VNC, vesion 0.7.0. The release focus is on bug fixing and includes fixes for two publically reported security bugs which allow a malicious server to exploit the client. Similar bugs were recently reported & fixed in other common VNC clients too.

  • CVE-2017-5884 – fix bounds checking for RRE, hextile and copyrect encodings
  • CVE-2017-5885 – fix color map index bounds checking
  • Add API to allow smooth scaling to be disabled
  • Workaround to help SPICE servers quickly drop VNC clients which mistakenly connect, by sending “RFB ” signature bytes early
  • Don’t accept color map entries for true-color pixel formats
  • Add missing vala .deps files for gvnc & gvncpulse
  • Avoid crash if host/port is NULL
  • Add precondition checks to some public APIs
  • Fix link to home page in README file
  • Fix misc memory leaks
  • Clamp cursor hot-pixel to within cursor region

Thanks to all those who reported bugs and provides patches that went into this new release.

The libvirt & virtualization tools software development platform

In the five years since the libvirt project started, alot has changed. The size of the libvirt API has increased dramatically; the number of languages you can access the API from has likewise grown to cover most important targets; libvirt has been translated to fit into several other object models; plugins have been developed to bind libvirt to other tools. At the same time many other libraries have grown up alongside libvirt, not least libguestfs, gtk-vnc and more recently spice-gtk. Together all these pieces provide a rich software development platform for people building virtualization management applications. A picture is worth 1000 words, so to keep this blog post short, here is the way I visualize the pieces in the virtualization tools platform, and a selection of the applications built on it (click to enlarge the image)

The libvirt & virtualization tools software development platform

The base layer

  • libvirt: the core hypervisor agnostic management API, coring virtual machines, host devices, networking, storage, security and more
  • libvirt-qemu: a small set of QEMU specific APIs, such as the ability to talk to the QEMU monitor, or attach to externally launched QEMU guests. This library builds on top libvirt.
  • libguestfs: the library for manipulating and accessing the contents of guest filesystem images. This uses libvirt for some actions internally. libguestfs has its own huge set of language bindings which are not shown in the diagram, for the sake of clarity. It will also soon be gaining a mapping into the GObject type system, which will help it play nicely with other GObject based APIs here.

Language bindings

The language bindings for libvirt aim to be a 1-for-1 export of the libvirt C API into the corresponding language. They generally don’t attempt to change the way the libvirt API looks or is structured. There is generally completely interoperability between all language bindings, so you can trivially have part of your application written in Perl and another part written in Java and play nicely together.

  • libvirt-ocaml: a binding into the OCaml functional language
  • libvirt-php: a binding into the PHP scripting language
  • libvirt-perl: a binding into the Perl scripting language
  • libvirt-python: a binding into the Python scripting language, which comes as a standard part of the libvirt package
  • libvirt-java: a binding into the Java object language
  • libvirt-ruby: a binding into the Ruby scripting language
  • libvirt-csharp: a binding into the C# object language

Object mappings

The object mappings are distinct from language bindings, because they will often significantly change the structure of the libvirt API to fit in the requirement of the object system being targeted. Depending on the object systems involved, this translation might be lossless, thus an application generally has to pick one object system & stick with it. It is not a good idea to do a mixture of SNMP and QMF calls from the same application.

  • libvirt-snmp: an agent for SNMP that translates from an SNMP MIB to libvirt API calls.
  • libvirt-cim: an agent for CIM the translates from the DMTF virtualization schema to the libvirt API
  • libvirt-qmf: an agent for Matahari that translates from a QMF schema to the libvirt API

Infrastructure plugins

Many common infrastructure applications can be extended by adding plugins for new functionality.  This particularly common with network monitoring or performance collection applications. libvirt can of course be used to create plugins for such applications

  • libvirt-collectd: a plugin for collectd that reports statistics on virtual machines
  • libvirt-munin: a plugin for collectd that reports statistics on virtual machines
  • libvirt-nagios: a plugin for nagious that reports where virtual machines are running
  • fence-virt: a plugin for clustering software to allow virtual machines to be “fenced”

GObject layer

The development of a set of GObject based libraries came about after noticing that many users of the basic libvirt API were having to solve similar problems over & over. For example, every application wanted some programmatic way to extract info from XML documents. Many applications wanted libvirt translated into GObjects. Many applications needed a way to determine optimal hardware configuration for operating systems. The primary reasons for choosing to use GObject as the basis for these APIs was first to facilitate development of graphical desktop applications. With the advent of GObject Introspection, the even more compelling reason is that you get language bindings to all GObject libraries for free. Contrary to popular understanding, GObject is not solely for GTK based desktop applications. It is entirely independent of GTK and can be easily used from any conceivable application. If libvirt were to be started from scratch again today, it would probably go straight for GObject as  the basis for the primary C library. It is that compelling.

  • libosinfo: an API for managing metadata related to operating systems. It includes a database of operating systems with details such as common download URLs, magic byte sequences to identify ISO images, lists of supported hardware. In addition there is a database of hypervisors and their supported hardware. The API allows applications to determine the optimal virtual hardware configuration for deployment of an operating system on a particular hypervisor.
  • gvnc: an API providing a client for the RFB protocol, used for VNC servers. The API facilitates the creation of new VNC client applications.
  • spiceglib: an API providing a client for the SPICE protocol, used for SPICE servers. The API facilitates the creation of new SPICE client applications.
  • libvirt-glib: an API binding the libvirt event loop into the GLib main loop, and translating libvirt errors into GLib errors.
  • libvirt-gconfig: an API for generating and manipulating libvirt XML documents. It removes the need for application programmers to directly deal with raw XML themselves.
  • libvirt-gobject: an API which translates the libvirt object model, also integrating them with the lbivirt-gconfig APIs.
  • libvirt-sandbox: an API for building application sandboxes using virtualization technology.

GTK layer

  • gtk-vnc: an API building on gvnc providing a GTK widget which acts as a VNC client. This is used in both virt-manager & virt-viewer
  • spice-gtk: an API building on spice-glib providing a GTK widget which acts as a SPICE client. This is used in both virt-manager & virt-viewer


  • python-virtinst: provides the original python virt-install command line tool, as well as a python API which is leveraged by virt-manager. The python-virtinst internal API was the motivation behind the libosinfo library and libvirt-gconfig library
  • virt-manager: provides a general purpose desktop application for interacting with libvirt managed virtualization hosts. The virt-manager internal API was the motivation behind the libvirt-gobject library
  • oVirt: the umbrella project for building an open source virtualized data center management application. Its VDSM component uses the libvirt python language bindings for managing KVM hosts
  • OpenStack: the umbrella project for building an open source cloud management application. Its Nova component uses the libvirt python language bindings for managing KVM, Xen and LXC hosts.
  • GNOME Boxes: the new GNOME desktop application for running virtual machines and accessing remote desktops. It uses libirt-gobject, libosinfo, gtk-vnc & spice-gtk via automatically generated vala bindings.

The Future

  • Get oVirt, OpenStack, python-virtinst and virt-manager using the libosinfo library to centralize definitions of what hardware config to use for deploying operating systems
  • Get oVirt & OpenStack using the libvirt-gconfig library to generate configuration, instead of building XML documents up through string concatenation
  • Convert python-virtinst & virt-manager to use the libvirt-gconfig, libvirt-gobject libraries instead of their private internal equivalents
  • Create a remote-viewer library which pulls in both gtk-vnc and spice-gtk in a higher level framework. This is essentially pulling the commonality out of virt-viewer, virt-manager and GNOME boxes use of gtk-vnc and spice-gtk.
  • Create a libvirt-install library which provides APIs for provisioning operating systems. This would be pulling out commonality between the way python-virtinst, GNOME boxes and other applications deploy new operating systems. This would be a bridge layer between libosinfo and libvirt-gobject

There is undoubtably plenty of stuff I left out of this diagram & description. For example there are many other data center & cloud management projects that are based on libvirt, which I left out for clarity.  There are plenty more libvirt plugins for other applications too, many I will never have heard about. No doubt our future plans will change too, as we adapt to new information.  This should have given a good overview of how broad the open source virtualization tools software development ecosystem has become.

A “Hello World” like example for GTK-VNC in Perl, Python and JavaScript

Posted: November 4th, 2011 | Filed under: Coding Tips, Fedora, Gtk-Vnc, Virt Tools | Tags: , , , | No Comments »

I have written before about what a great benefit GObject Introspection is, by removing the need to write dynamic language bindings for C libraries. When I ported GTK-VNC to optionally build with GTK3, I did not bother to update the previous manually created Python binding. Instead application developers are now instructed to use GObject Introspection if they ever want to use GTK-VNC from non-C languages. As a nice demo of the capabilities I have written the bare minimum “Hello World” like example for GTK-VNC in Perl, Python and JavaScript. The only significant difference between these examples is syntax for actually importing a particular library. The Perl binding is the most verbose for importing libraries, which is a surprise, since Perl is normally a very concise language. Hopefully they will invent a more concise syntax for importing soon.

Perl “hello world” VNC client


use Gtk3 -init;
Glib::Object::Introspection->setup(basename => 'GtkVnc', version => '2.0', package => 'GtkVnc');
Glib::Object::Introspection->setup(basename => 'GVnc', version => '1.0', package => 'GVnc');


my $win = Gtk3::Window->new ('toplevel');
my $dpy = GtkVnc::Display->new();

$win->set_title("GTK-VNC with Perl");
$dpy->open_host("localhost", "5900");

Python “hello world” VNC client


from gi.repository import Gtk;
from gi.repository import GVnc;
from gi.repository import GtkVnc;


win = Gtk.Window()
dpy = GtkVnc.Display()

win.set_title("GTK-VNC with Python")
dpy.open_host("localhost", "5900")

JavaScript “hello world” VNC client


const Vnc =;
const GVnc =;
const Gtk =;

Gtk.init(0, null);

var win = new Gtk.Window();
var dpy = new Vnc.Display();

win.set_title("GTK-VNC with JavaScript");
dpy.open_host("localhost", "5900");

Injecting fake keyboard events to KVM guests via libvirt

Posted: September 23rd, 2011 | Filed under: Fedora, Gtk-Vnc, libvirt, Virt Tools | 3 Comments »

I’ve written before about how virtualization causes pain wrt keyboard handling and about the huge number of scancode/keycode sets you have to worry about. Following on from that investigative work I completely rewrote GTK-VNC’s keycode handling, so it is able to correctly translate the keycodes it receives from GTK on Linux, Win32 and OS-X, even when running against a remote X11 server on a different platform. In doing so I made sure that the tables used for doing conversions between keycode sets were not just big arrays of magic numbers in the code, as is common practice across the kernel or QEMU codebase. Instead GTK-VNC now has a CSV file containing the unadulterated mapping data along with a simple script to split out mapping tables. This data file and script has already been reused to solve the same keycode mapping problem in SPICE-GTK.

Fast-forward a year and a libvirt developer from Fujitsu is working on a patch to wire up QEMU’s “sendkey” monitor command to a formal libvirt API. The first design question is how should the API accept the list of keys to be injected to the guest. The QEMU monitor command accepts a list of keycode names as strings, or as keycode values as hex-encoded strings. The QEMU keycode values come from what I term the “RFB” codeset, which is just the XT codeset with a slightly unusual encoding of extended keycodes. VirtualBox meanwhile has an API which wants integer keycode values, from the regular XT codeset.

One of the problems with the XT codeset is that no one can ever quite agree on what is the official way to encode extended keycodes, or whether it is even possible to encode certain types of key. There is also a usability problem with having the API require a lowlevel hardware oriented keycode set as input, in that as an application developer you might know what Win32 virtual keycode you want to generate, but have no idea what the corresponding XT keycode is. It would be preferable if you could simply directly inject a Win32 keycode to a Windows guest, or directly inject a Linux keycode to a Linux guest, etc.

After a little bit of discussion we came to the conclusion that the libvirt API should accept an array of integer keycodes, along with a enum parameter specifying what keycode set they belong to. Internally libvirt would then translate from whatever keycode set the application used, to the  keycode set required by the hypervisor’s own API. Thus we got an API that looks like:

typedef enum {
   VIR_KEYCODE_SET_LINUX          = 0,
   VIR_KEYCODE_SET_XT             = 1,
   VIR_KEYCODE_SET_ATSET1         = 2,
   VIR_KEYCODE_SET_ATSET2         = 3,
   VIR_KEYCODE_SET_ATSET3         = 4,
   VIR_KEYCODE_SET_OSX            = 5,
   VIR_KEYCODE_SET_XT_KBD         = 6,
   VIR_KEYCODE_SET_USB            = 7,
   VIR_KEYCODE_SET_WIN32          = 8,
   VIR_KEYCODE_SET_RFB          = 9,

} virKeycodeSet;

int virDomainSendKey(virDomainPtr domain,
                     unsigned int codeset,
                     unsigned int holdtime,
                     unsigned int *keycodes,
                     int nkeycodes,
                     unsigned int flags);

As with all libvirt APIs, this is also exposed in the virsh command line tool, via a new “send-key” command. As you might expect, this accepts a list of integer keycodes as parameters, along with a keycode set name. If the keycode set is omitted, we are assuming use of the Linux keycode set by default. To be slightly more user friendly though, for the Linux, Win32 & OS-X keycode sets, we also support symbolic keycode names as an alternative to the integer values. These names are simply the name of the #define constant from corresponding header file.

Some examples of how to use the new virsh command are

# send three strokes 'k', 'e', 'y', using xt codeset
virsh send-key dom --codeset xt 37 18 21

# send one stroke 'right-ctrl+C'
virsh send-key dom KEY_RIGHTCTRL KEY_C

# send a tab, held for 1 second
virsh send-key --holdtime 1000 0xf

So when interacting with virtual guests you now have a choice of how to send fake keycodes. If you have a VNC or SPICE connection directly to the guest in question, you can inject keycodes over that channel, while if you have a libvirt connection to the hypervisor you can inject keycodes over that channel.

A summary of scan code & key codes sets used in the PC virtualization stack

Posted: July 4th, 2010 | Filed under: Gtk-Vnc, Virt Tools | Tags: , | 1 Comment »

In learning about virtual keyboard handling for my previous post, I spent alot of time researching just what scan code & key code sets are used at each point in the stack. I trawled across many websites and source code trees to discover this information, so I figure I should write it down in case I forget it all in 12 months time when I next get a keyboard handling bug report. I can’t guarantee I’ve got all the details here correct, so if you  spot mistakes, leave a comment.

IBM XT keyboard

In the beginning the PC was invented. This has made a lot of people very angry and has been widely regarded as a bad move. The IBM XT scan codes are first set encountered. Most of the scan codes were a  just a single byte, with the high bit clear for a make event and set for a break event. The keycodes don’t correspond at all to ASCII values, rather they were assigned incrementally across rows. As an example, the key in the 4th row, second column (labelled A on a us layout) has value 0x1e for make code and 0x9e for break code.  Keys on the numeric keypad would generate multi-byte sequences, where the leading byte is “0xe0” (sometimes referred to as the grey code, I guess because the keypad was a darker grey plastic)

IBM AT & PS/2 keyboards

The IBM AT keyboard was incompatible with the XT at a wire protocol level. In terms of scan codes though, it can support upto 3 sets. The first set is the original XT scan codes. The second set is a new AT scan codes. The third set is so called PS/2 scan codes. In all cases though, the second set is the default and the first & third sets may not even be supported. There is no resemblance between AT and XT scan codes. The use of the high bit for break code was abandoned. The same scan code is used by make and break, but in the break case it is prefixed by a byte 0xf0. As an example, the key in the 4th row, second column (labelled A on a us layout) has the value 0x1c. Again the keys on the numeric keyboard generated multi-byte sequences with a leading “0xe0”.

For added fun, regardless of what scan code set the keyboard is generating the i8042 keyboard controller will, by default, provide the OS with XT scan codes unless told otherwise. This was for backwards compatible with software which only knows about the previous XT scan code set.

Over time Microsoft introduced the Windows keys, then Internet keys arrived followed by all sorts of other function keys on laptops. The extended 0xe0 (“grey code”) sequence space was used for these new scan codes. Of course these keys needed scan codes in both the XT and AT sets to be defined. So for example, the left Windows key got the XT make/break scan codes 0xe0+0x5c and 0xe0+0xdc and the AT make/break scan codes 0xe0+0x27 and 0xe0+0xf0+0x27.

USB keyboards

The introduction of USB input devices, allowed for a clean break with the past, so XT/AT scan codes are no more in the USB world. The USB HID spec defines a standard 16 bit scan code set for all compliant keyboards to use. The USB HID spec gives scan codes names based on the US ASCII key cap labels. Thus the US ASCII key labelled ‘A’ has HID page ID 0x07 and HID usage ID 0x04. Where both the XT/AT sets and USB HID sets support a common key it is possible to perform a lossless mapping in either direction. There are, however, some keys in the USB HID scan code set for which there isn’t a XT/AT scan code.

Linux internals

The Linux internal event subsystem has defined a standard set of key codes that are hardware independant, able to represent any scan code from any type of keyboard whether AT, XT or USB. There are names assigned to the key codes based on the common US ASCII key cap labels. The key codes are defined in /usr/include/linux/input.h. For an example ‘#define KEY_A 30’. For convenience, key codes 0-88 map directly to XT scan codes 0-88. All the low level hardware drivers for AT, XT, USB keyboards, etc have to translate from scan codes to the Linux key codes when queueing key events for dispatch by the input subsystem. In “struct input_event”, the “code” field contains the key code while the “value” field indicates the state (press/release). Mouse buttons are also represented as key codes in this set.

Linux console

The Linux console (eg /dev/console or /dev/tty*) can operate in several different modes.

  • RAW: turns linux keycodes back into XT scancodes
  • MEDIUMRAW: an encoding of the linux key codes. key codes < 127 generated directly, with high bit set for a release event. key codes >= 127 are generated as multi-byte sequences. The leading byte is 0x0 or 0x1 depending on whether a key press or release. The second byte contains the low 7 bits and third byte contains the high 7 bits. Both second and third bytes always have the 8th bit set. This allows room for future expansion upto 16384 different key codes
  • ASCII: the ascii value associated with the key code + current modifiers, according to the loaded keymap
  • UNICODE: the UTF-8 byte sequence associated with the key code + current modifiers, according to the loaded keymap

The state of the current console can be seen and changed using the “kbd_mode” command line tool. Changing the mode is not recommended except to switch between ASCII & UNICODE modes

Linux evdev

The evdev driver is a new way of exposing input events to userspace, bypassing the traditional console/tty devices. The “struct input_event” data is provided directly to userspace without any magic encodings. Thus apps using evdev will always be operating with the Linux key code set initially. They can of course convert this into the XT scan codes if desired, in exactly the same way that the console device already does when in RAW mode.

Xorg XKB

In modern Xorg servers, XKB is in charge of all keyboard event handling. Unusually, XKB does not actually define any standard key code set. At least not numerically. In the XKB configuration files there are logical names for every key, based on their position. Some names may be obvious ‘<TAB>’, while others are purely reflecting a physical row/column location ‘<AE01>’. Each Xorg keyboard driver is free to define whatever key code set it desires. The driver must provide a mapping from its key code values to the XKB key code names (in /usr/share/X11/xkb/keycodes/). There is then a mapping from XKB key code names to key symbols (in /usr/share/X11/xkb/keysyms). The problem with this is that the key code seen in the XKeyEvent can come from an arbitrary set of which the application is not explicitly aware. Three common key code sets from Xorg will now be mentioned.

Xorg kbd driver

The traditional “kbd” driver uses the traditional Linux console/tty devices for receiving input, configuring the devices in RAW mode. Thus it is accepting XT scan codes initially. The kdb keycodes are defined in its source code at src/atKeynames.h  For scan codes below 89, a key code is formed simply by adding 8. Scan codes above that have a set of re-mapping rules that can’t be quickly illustrated here. The mapping is reverseable though, given a suitable mapping table.

Xorg evdev driver

The new “evdev” driver of course uses the new Linux evdev devices for receiving input, as Linux key codes. It forms its scan codes simply by adding 8 to the Linux key code. This is trivially reverseable.

Xorg XQuartz driver

The Xorg build for OS-X, known as XQuartz, does not use either of the previously mentioned drivers. Instead it has a OS-X specific keyboard driver that receives input directly from the OS-X graphical toolkit. It receives OS-X virtual key codes and produces X key codes simply by adding 8. This is again trivially reversable.

RFB protocol extended key event

The RFB protocol extension defined by GTK-VNC and QEMU allows for providing a key code in addition to the key symbol for all keypress/release events sent over the wire. The key codes are defined to be based on a simple encoding of XT scan code set. Single byte XT scan codes 0-127 are sent directly. Two-byte scan codes with the grey code (0xe0) are sent as single bytes with the high bit set. eg 0x1e is sent as 0x1e, while 0xe0+0x1e is sent as 0x9e (ie 0x1e | 0x80). The press/release state is sent as a separate value.

QEMU internals

QEMU’s internal input subsystem for keyboard events uses raw XT scan codes directly. The hardware device emulation maps to other scan code sets as required. It is no coincidence that the RFB protocol extension for sending key codes is a trivial mapping to QEMU scan codes.

Microsoft Windows

The Windows GDI defines a standard set of virtual key codes that are independent of any particular keyboard hardware.

Apple OS-X

OS-X defines a standard set of virtual key codes that are based on the original Apple extended keyboard scan codes.


The SDL_KeyboardEvent struct contains a “scancode” field. This provides the operating system dependant key code corresponding to the key event. This is easily interpreted on OS-X/Windows, but on Linux X11 this requires knowledge of what keyboard driver is used by Xorg.


The GDKKeyEvent struct contains a “hardware_keycode” field. This provides the operating system dependant key code corresponding to the key event. This is easily interpreted on OS-X/Windows, but on Linux X11 this requires knowledge of what keyboard driver is used by Xorg.

Future ideas

The number of different scan code and key code sets is really impressive / depressing / horrific. The good news is that given the right information, it is possible to map between them all fairly easily, in a lossless fashion. The bad news is that the data for performing such mappings is hidden across many web pages and many, many source trees. It would be great to have a single point of reference providing all the scan/key code sets, along with a tool that can generate the mapping tables & example code to convert between any 2 sets.