From: "Daniel P. Berrangé" <berrange@redhat.com>
To: Laszlo Ersek <lersek@redhat.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>, qemu-devel@nongnu.org
Subject: Re: vnc clipboard support
Date: Fri, 29 Jan 2021 10:02:26 +0000 [thread overview]
Message-ID: <20210129100226.GD4001740@redhat.com> (raw)
In-Reply-To: <e5231182-aee5-a706-a261-1a5bab072402@redhat.com>
On Thu, Jan 28, 2021 at 06:57:24PM +0100, Laszlo Ersek wrote:
> On 01/28/21 18:12, Gerd Hoffmann wrote:
> > Hi folks,
> >
> > I'm looking for a good way to implement cut+paste support for vnc.
> >
> > The vnc core protocol has support for text/plain cut+paste, and there
> > is an extension adding support for other formats. That'll cover one
> > part of the problem, exchanging cut+paste data between vnc client and
> > qemu vnc server.
> >
> > The tricky part is the second: the guest <=> qemu communication.
> > I see basically two possible approaches here:
> >
> > (1) Have some guest agent (spice does it that way).
> > Advantage: more flexible, allows more features.
> > Disadvantage: requires agent in the guest.
> >
> > (2) Send text as key events.
> > Advantage: no guest agent needed.
> > Disadvantage: is translated by guests keyboard map, so qemu
> > needs to know the map for proper char -> key event translation.
> > Only works for text/plain and only for chars you can easily
> > type, anything needing input methods (emoji 😊 for example)
> > isn't going to fly.
> >
> > I think that (1) is clearly the better way. Given that the agent
> > would need to run in user wayland/xorg session context the existing
> > qemu-guest-agent will not work. Also linking against some UI library
> > like gtk3 for clipboard handling is not something we want for the
> > qemu-guest-agent. So we need another one, I'll name it
> > qemu-clipboard-agent for the rest of this mail. And we need a
> > communication channel.
> >
> > I'd tend to model the qemu-clipboard-agent simliar to the
> > qemu-guest-agent, i.e. have some stream as communication path and run
> > some stream protocol over it.
> >
> > Stream options I see are (in order of personal preference):
> >
> > (1) New virtio-serial port. virtio-serial likely is there anyway
> > for the qemu-guest-agent ...
> >
> > (2) Have qemu-clipboard-agent and qemu-guest-agent share the agent
> > channel, i.e. qemu-clipboard-agent will proxy everything through
> > qemu-guest-agent (spice does it that way).
> >
> > Protocol options I see are (not sure yet which to prefer, need to have
> > a closer look at the candidates):
> >
> > (1) Add clipboard commands to QMP and use these.
> >
> > (2) Reuse the clipboard bits of the vnc protocol (forward
> > VNC_MSG_CLIENT_CUT_TEXT messages to the guest agent)
> >
> > (3) Reuse the clipboard bits of the spice-agent protocol.
> >
> > (4) Reuse the clipboard bits of the wayland protocol.
> >
> > Once we have sorted the qemu <-> guest communication path it should be
> > possible to also hook up other UIs (specifically gtk) without too much
> > effort. Which probably makes (2) a rather poor choice.
> >
> > Comments?
> > Suggestions?
> > Other ideas?
>
> Just a random thought: the guest should not be able to sniff, steal, or
> overwrite host-side clipboard (selection) content, without the host user
> explicitly requesting a clipboard operation. I understand this is
> generally a problem between X11 applications (not so on Wayland, if I
> understand correctly), but I assume it becomes graver with
> virtualization -- there shouldn't be an unintended channel between
> host/guest, or even multiple guests. (Analogy: you can "ssh -X -Y" to
> two remote machines at the same time, and assuming "xauth" etc on both
> of those remote machines, you can run "gedit" on each of those remote
> machines, and cut'n'paste will work between them, *even if* you don't
> ask for it -- that's why ssh has a separate option called "-Y".
> Cut'n'paste does not work without "-Y". So I believe this is something
> to consider here.)
Yes, that's a known risk. SPICE lets you disable clipboard synchronization
in QEMU, and any client app should also support doing the same. Basically
only want clipboard sync if you're using a trustworthy guest. eg where
both host and guest admin are the same person, and even then you might
not want it sometimes.
Regards,
Daniel
--
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next prev parent reply other threads:[~2021-01-29 10:03 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-28 17:12 vnc clipboard support Gerd Hoffmann
2021-01-28 17:35 ` Daniel P. Berrangé
2021-01-29 7:59 ` Gerd Hoffmann
2021-01-28 17:38 ` Christophe de Dinechin
2021-01-29 8:03 ` Gerd Hoffmann
2021-01-29 10:50 ` Christophe de Dinechin
2021-01-29 11:08 ` Daniel P. Berrangé
2021-01-29 14:19 ` Christophe de Dinechin
2021-01-29 14:32 ` Daniel P. Berrangé
2021-02-01 15:27 ` Christophe de Dinechin
2021-02-01 15:51 ` Daniel P. Berrangé
2021-02-01 16:31 ` Christophe de Dinechin
2021-02-01 16:56 ` Daniel P. Berrangé
2021-02-01 17:28 ` Christophe de Dinechin
2021-02-01 17:40 ` Daniel P. Berrangé
2021-02-01 18:45 ` BALATON Zoltan
2021-02-02 11:31 ` Gerd Hoffmann
2021-02-02 12:31 ` BALATON Zoltan
2021-02-02 12:38 ` Daniel P. Berrangé
2021-02-02 13:35 ` Gerd Hoffmann
2021-02-02 16:36 ` Gerd Hoffmann
2021-02-02 21:00 ` Marc-André Lureau
2021-02-03 9:40 ` Gerd Hoffmann
2021-02-02 11:10 ` Gerd Hoffmann
2021-02-02 11:17 ` Daniel P. Berrangé
2021-02-02 11:44 ` Gerd Hoffmann
2021-01-29 15:04 ` Gerd Hoffmann
2021-02-01 17:07 ` Christophe de Dinechin
2021-01-29 11:49 ` Gerd Hoffmann
2021-01-29 13:28 ` Christophe de Dinechin
2021-01-28 17:57 ` Laszlo Ersek
2021-01-29 8:09 ` Gerd Hoffmann
2021-01-29 10:02 ` Daniel P. Berrangé [this message]
2021-01-28 20:18 ` Marc-André Lureau
2021-01-28 20:47 ` BALATON Zoltan
2021-01-29 7:59 ` Christophe de Dinechin
2021-01-29 8:27 ` Gerd Hoffmann
2021-01-29 8:34 ` Marc-André Lureau
2021-01-29 10:33 ` Gerd Hoffmann
2021-01-29 11:10 ` Daniel P. Berrangé
2021-01-29 11:24 ` Daniel P. Berrangé
2021-01-29 11:58 ` Marc-André Lureau
2021-01-29 12:21 ` Daniel P. Berrangé
2021-01-29 12:02 ` Gerd Hoffmann
2021-01-29 12:10 ` Marc-André Lureau
[not found] <CWLP265MB5209050A121EB63FE07F9BD5A8689@CWLP265MB5209.GBRP265.PROD.OUTLOOK.COM>
2023-04-30 16:20 ` VNC " Philipp Hahn
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