[Spice-devel] [spice-gtk v3 3/3] gtk-session: clipboard: x11: do not request data while on focus

[Victor Toso]

Hi,

On Thu, Jan 10, 2019 at 07:01:59PM +0400, Marc-André Lureau wrote:
> Hi
> 
> On Thu, Jan 10, 2019 at 5:50 PM Victor Toso <victortoso at redhat.com> wrote:
> >
> > On Thu, Jan 10, 2019 at 05:25:21PM +0400, Marc-André Lureau wrote:
> > > Hi
> > >
> > > On Thu, Jan 10, 2019 at 4:47 PM Victor Toso <victortoso at redhat.com> wrote:
> > > >
> > > > From: Victor Toso <me at victortoso.com>
> > > >
> > > > If SpiceGtkSession is holding the keyboard, that's huge indication
> > > > that the client should not be requesting guest's clipboard data yet.
> > > >
> > > > This patch adds a check in clipboard_get() callback, to avoid such
> > > > requests. In Linux, this only happens with X11 backend.
> > > >
> > > > This patch helps to handle a possible state race between who owns the
> > > > grab between client and agent which could lead to agent clipboard
> > > > failing or getting stuck, see:
> > >
> > > hmm
> > >
> > > > The way to reproduce the race might depend on guest system and
> > > > applications but it is connected to amount of VDAGENTD_CLIPBOARD_GRAB
> > > > sent by the agent which depends on the amount of clipboard changes in
> > > > the guest. Simple example is on RHEL 6.10, with Gedit, select a text
> > > > char by char; Client receives VDAGENTD_CLIPBOARD_GRAB every time a new
> > > > char is selected instead of once when the full message is selected.
> > >
> > > Sorry, you get a lot of clipboard-grab from the remote, but where is
> > > the problem?
> >
> > Problem is, why fetch data that no other application is
> > requesting.
> >
> > Situations like the one below happens due state changing fast +
> > idle callbacks for clear/request clipboard data...
> >
> >     https://gitlab.freedesktop.org/spice/win32/vd_agent/issues/6#note_85246
> 
> Sorry, I don't understand the problem, yes I try :)

I don't follow. You try to reproduce and failed?

I could erase the mentioning of the bugs and etc and just leave
it as..

  | Problem is, why fetch data that no other application is
  | requesting.

.. and would be enough for me.

> > > > v2 -> v3:
> > > > * Split the fix in two patches while adding some info in a 3rd patch;
> > > > * Kept the "clipboard_clear" as it was (Jakub)
> > > > * Added a "clipboard_grab" log in clipboard_grab() function;
> > > >
> > > > Related: https://gitlab.freedesktop.org/spice/win32/vd_agent/issues/6
> > > > Related: https://gitlab.freedesktop.org/spice/linux/vd_agent/issues/9
> > > > Related: https://bugzilla.redhat.com/show_bug.cgi?id=1594876
> > > >
> > > > Signed-off-by: Victor Toso <victortoso at redhat.com>
> > > > ---
> > > >  src/spice-gtk-session.c | 15 +++++++++++++++
> > > >  1 file changed, 15 insertions(+)
> > > >
> > > > diff --git a/src/spice-gtk-session.c b/src/spice-gtk-session.c
> > > > index 85d5880..f5959f7 100644
> > > > --- a/src/spice-gtk-session.c
> > > > +++ b/src/spice-gtk-session.c
> > > > @@ -763,6 +763,19 @@ static void clipboard_get(GtkClipboard *clipboard,
> > > >
> > > >      SPICE_DEBUG("clipboard get");
> > > >
> > > > +#ifdef GDK_WINDOWING_X11
> > > > +    /* Do not request clipboard data while we are still interacting with the
> > > > +     * Guest; Clipboard data could change shortly and this request would just
> > > > +     * be wasteful. */
> > >
> > > I don't think there is anything preventing another app the
> > > clipboard data while spice-gtk has the focus. In fact, that's
> > > how clipboard manager work afaik.
> >
> > That means that another application in Client OS might get remote
> > clipboard data while the user is interacting with remote VM.
> > That's pretty much a security concern as well. This does not
> > happen on Wayland and I would rather that we avoid it with X11
> > too, even if it breaks ClipboardManagers that don't request our
> > clipboard after we focus-out
> 
> I think it could happen on wayland as well, for example with
> https://extensions.gnome.org/extension/779/clipboard-indicator/.

I could not install it to test it, sadly. Any other app in mind?

If the problem is having this that we should have this not only
on x11 but on wayland too, let me know.
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