Michael Raskin <7c6f434c@mail.ru> writes:
One of the benefits that Wayland is supposed to have over X11 is security. A Wayland application isn't supposed to be able to record the screen without user permission, for example. But in most compositors, it can, with no restrictions. Existing Wayland compositors are
… and theoretically, an X server could feed empty capture to a client it does not like …
(of course with literal decades of actual backwards compatibility, X11 protocol has accumulated enough extensions that assigning permissions to all of them might be somewhat painful)
Considering that the world has convered on a single X server implementation, and it's apparently pretty horrible to maintain, I'm not sure I feel very positive about the idea of a custom one! And yeah, with Wayland clients are already expecting to have to ask for permission. (I've just learned that this is actually done over DBus, so the proxy would have to implement that as well, ugh.) I suspect X11 clients wouldn't be very happy if it took them seconds to get the result of their attempted screen capture, and users wouldn't be very happy if screen sharing was just a blank box by default, rather than a permission request. (I'm not sure which of those would be possible with X11.)
monolithic, and each one would have to implement its own access controls. (Mutter already does this to some extent, at least for screen sharing, I believe.) The popular Wayland compositors are largely focused on being feature-complete reimplementations of their X11 equivalents, and so taking advantage of the security features and access controls the Wayland protocol makes possible hasn't been a priority for
… unsurprisingly, as these are typically WM teams who are now deprived of what Xorg server did for everyone.
Only the ones that don't use wlroots, I think. wlroots has its own problems, but in large part those are the problems we're trying to mitigate here.
To solve these problems, I propose a proxy program that sits between Wayland clients and the compositor, in the same privelege domain as the compositor. The proxy would decode and re-encode every Wayland request (client->compositor message), and would discard any request it didn't understand. This would mitigate the problem of a large, privileged program written in a memory-unsafe language being exposed to untrusted
Presumably, also validating that the shared memory buffers passed around have the same size and protection as promised?
Aren't shared memory buffers usually handed out by the compositor, to the client? IIRC this was the reason virtio wayland can work when it only supports shared memory that was allocated by the host.
inputs. Additionally, the proxy would support a plugin interface, through which the user of the proxy (or their distributor) could configure custom behaviour. This could be used to prompt the user for confirmation before allowing a screen capture request, or even to implement a similar thing for e.g. clipboard access, for which there is no support in the Wayland protocol. It could even be used to modify surfaces, to implement things like Qubes-style unspoofable coloured window borders.
I am tempted to ask how close it will be to providing a socket for WM and window decorator implementation (with some suitably limited compositor as the backend behind the proxy).
(So basically, defining a scope will be hard, and defining a scope in a usefully extensible way might be even harder)
I don't understand this point. Can you rephrase / expand?
This approach would allow permissions systems and other custom Wayland behaviour to be implemented in a compositor-independent manner. Distributions which suppor tseveral compositors could implement customisations in a single place, and users of compositors which lack security features and the assurances memory-safety can provide against untrusted input would gain access to those things.
That surely sounds good…