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

[Marc-André Lureau]

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 :)

>
> > > 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/.

>
> Thanks for reviewing,
> Victor
>
> >
> > > +    if (GDK_IS_X11_DISPLAY(gdk_display_get_default()) &&
> > > +        spice_gtk_session_get_keyboard_has_focus(self)) {
> > > +        SPICE_DEBUG("clipboard get: not requesting data while holding focus");
> > > +        return;
> > > +    }
> > > +#endif
> > > +    SPICE_DEBUG("clipboard get: has-foucus=%d",
> > > +                spice_gtk_session_get_keyboard_has_focus(self));
> > > +
> > >      selection = get_selection_from_clipboard(s, clipboard);
> > >      g_return_if_fail(selection != -1);
> > >      g_return_if_fail(info < SPICE_N_ELEMENTS(atom2agent));
> > > @@ -818,6 +831,8 @@ static gboolean clipboard_grab(SpiceMainChannel *main, guint selection,
> > >                                 guint32* types, guint32 ntypes,
> > >                                 gpointer user_data)
> > >  {
> > > +    SPICE_DEBUG("clipboard_grab");
> > > +
> > >      g_return_val_if_fail(SPICE_IS_GTK_SESSION(user_data), FALSE);
> > >
> > >      SpiceGtkSession *self = user_data;
> > > --
> > > 2.20.1
> > >
> > > _______________________________________________
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> > > Spice-devel at lists.freedesktop.org
> > > https://lists.freedesktop.org/mailman/listinfo/spice-devel
> >
> >
> >
> > --
> > Marc-André Lureau



-- 
Marc-André Lureau