Problem: Has anyone thought about a mechanism to limit/remove an access to a device during an application runtime? Meaning we have an application that has an open file descriptor to some /dev/node and depending on *something* it gains or looses the access to it gracefully (with or without a notification, but without any fatal consequences).

Example: LXC. Imagine we have 2 separate containers. Both running full operating systems. Specifically with 2 X servers. Both running concurrently of

course. Both need the same input devices (e.g. we have just one mouse). This creates a security problem when we want to have completely separate environments. One container is active (being displayed on a monitor and controlled with a mouse) while the other container runs evtest /dev/input/something and grabs the secret password user typed in the other.

Solutions: The complete solution would comprise of 2 parts: - a mechanism that would allow to temporally "hide" a device from an open file descriptor. - a mechanism for deciding whether application/process/namespace should have an access to a specific device at a specific moment

>> Problem: >> Has anyone thought about a mechanism to limit/remove an access to a >> device during an application runtime? Meaning we have an >> application that has an open file descriptor to some /dev/node and >> depending on *something* it gains or looses the access to it >> gracefully (with or without a notification, but without any fatal >> consequences). > > logind can mute input devices as sessions are switched, to enable > unpriviliged X11 and wayland compositors. Would you please elaborate on this? Where is this mechanism? How does it work without kernel space support? Is there some kernel space support I’m not aware of?

> Before you think about doing something like this, you need to fix the > kernel to provide namespaced devices (good luck!) Precisly! That’s the generic idea. I’m not for implementing it though at this moment. I just wanted to know whether anybody actually though about it or maybe someone is interested in starting such a work, etc.

> logind can do this for you between sessions. But such a container setup > will never work without proper device namespacing. So how can it do it when there is no kernel support? You mean it could be doing this if the support were there?

Problem: Has anyone thought about a mechanism to limit/remove an access to a device during an application runtime? Meaning we have an application that has an open file descriptor to some /dev/node and depending on *something* it gains or looses the access to it gracefully (with or without a notification, but without any fatal consequences). Example: LXC. Imagine we have 2 separate containers. Both running full operating systems. Specifically with 2 X servers. Both running concurrently of course. Both need the same input devices (e.g. we have just one mouse). This creates a security problem when we want to have completely separate environments. One container is active (being displayed on a monitor and controlled with a mouse) while the other container runs evtest /dev/input/something and grabs the secret password user typed in the other. Solutions: The complete solution would comprise of 2 parts: - a mechanism that would allow to temporally "hide" a device from an open file descriptor. - a mechanism for deciding whether application/process/namespace should have an access to a specific device at a specific moment Let's focus on the first problem only, as it would need to be solved first anyway. I haven't found anything that would allow me to do it. There are a lot mechanisms that make it possible to restrict an access during open(): - DAC - ACL (controlled by hand or with uaccess) - LSM (in general) - device cgroups But all of those can't do a thing when the device is already opened and an application has a file descriptor. I don't see such mechanism in kernel sources either. I do imagine that it would not be possible for every device to handle such a thing (dri comes to mind) without breaking something (graphics card state in dri example). But there is class of simple input/output devices that would handle this without problems. I did implement some proof-of-concept solution for an evdev driver by allowing or disallowing events that go to evdev_client structure using some arbitrary condition. But this is far from a generic solution. My proof-of-concept is somewhat similar to this (I just found it): http://www.spinics.net/lists/linux-input/msg25547.html Though a little bit wider in scope. But neither is flawless nor generic. Has anyone had any thoughts about a similar problem?