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 đ 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 -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
