The uinput interface

uinput allows write access to /dev/uinput on the host system for emulating input devices from userspace that can send input events (such as a joystick).

By design, the /dev/uinput device allows for arbitrary input injection and its default permissions are the standard root:root 0660 across Linux distributions.

Third-party software sometimes installs udev rules that change the /dev/uinput device permissions to world-writable permissions (0666) as a shortcut to allow all system users access.

However, snapd considers world-writable permissions for /dev/uinput to be unsafe for most systems because it potentially allows any user with access to the device the ability to inject input events into the kernel.

This means snapd does not install additional udev rules to modify device permissions on behalf of snaps, and consequently, will not interfere with the permissions set by third-party software. As a result, snaps that use this interface will have the same /dev/uinput access as other processes on the system.

See the joystick interface and the raw-usb interface for potential alternatives.

Auto-connect : no

Requires snapd version 2.46+ .

ⓘ This is a snap interface. See Interface management and Supported interfaces for further details on how interfaces are used.

Does that means that, without user intervention, snaps will still be unable to access /dev/uinput even when the interface is connected?

It depends on how the system is setup. If a non-snap can do it, then the snap can do it running as the same user with the uinput interface connected. The point of the comment is that snapd isn’t going to try to guess the right thing to do for the system wrt installing udev rules.

1 Like