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    SubjectRe: input/eventX permissions, force feedback
    On 7/18/06, Anssi Hannula <anssi.hannula@gmail.com> wrote:
    > Dmitry Torokhov wrote:
    > > Hi Anssi,
    > >
    > > On 7/18/06, Anssi Hannula <anssi.hannula@gmail.com> wrote:
    > >
    > >> Currently most distributions have /dev/input/event* strictly as 0600
    > >> root:root or 0640 root:root. The user logged in will not have rights to
    > >> the device, unlike /dev/input/js*, as he could read all passwords from
    > >> the keyboard device.
    > >>
    > >> This is a problem, because /dev/input/event* is used for force feedback
    > >> and should therefore be user-accessible.
    > >>
    > >> I can think of the following solutions to this problem:
    > >>
    > >> 1. Some creative udev rule to chmod /dev/input/event* less strictly when
    > >> it has a /dev/input/js* and is thus a gaming device.
    > >>
    > >> 2. Some creative udev rule to chmod /dev/input/event* more strictly when
    > >> it is a keyboard.
    > >>
    > >> 3. Have another force feedback interface also in /dev/input/js*.
    > >>
    > >
    > > You can do it in udev looking either at MODALIAS or at EV and ABS
    > > environment variables. I think it is pretty safe to say that a device
    > > with EV_ABS, EV_FF, ABS_X and ABS_Y is a force-feedback joystick-type
    > > device and not a keyboard.
    >
    > Okay, thanks. But I think it'd be more consistant if all devices that
    > have js* entries would have the relaxed perms in event*. Looking at
    > joydev.c, that seems to be devices where EV_ABS && (ABS_X || ABS_WHEEL
    > || ABS_THROTTLE) && !(EV_KEY && BTN_TOUCH).
    >

    OK, you can do that too.

    > There's another problem, too:
    > Some distros (Fedora, Mandriva...) don't use groups with /dev/input/jsX,
    > they use pam_console to chmod the device to the console owner.
    > Unfortunately, it allows to specify the permissions based on device file
    > names only.
    >
    > To solve this problem, I see two solutions:
    >
    > 1. Have the pam_console_apply program extended so that it can perform
    > more complex matches (but what kind of matches would those be?).
    >
    > 2. Have udev create symlinks like the following case:
    > /dev/input/event3
    > /dev/input/js0
    > /dev/input/jsevent0 => event3
    > Then pam_console_apply could match jsevent[0-9]* and it would follow the
    > symlink, thus chowning event3 to the wanted user.
    >
    > Unfortunately neither look too good to me. Do you have any other ideas?
    >

    I think this is really up to particular destribution to decide how
    they want to handle security/granting access. One could even imagine
    writing SELinux policies...

    > > Another solution would be to relax permissions if user is also console
    > > owner (home box installation).
    >
    > I thought of that too, but I thought it's too big a security risk, as
    > it's not guaranteed that somebody else won't temporarily login on
    > another terminal.
    >

    That is what you are doing with pam_console_apply, don't you?

    --
    Dmitry
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