Messages in this thread | | | Date | Tue, 18 Jul 2006 17:31:20 +0300 | From | Anssi Hannula <> | Subject | Re: input/eventX permissions, force feedback |
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Dmitry Torokhov wrote: > 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...
Yes, it is. I just asked if you had any better idea or if you were strongly opposed to the solutions I proposed, as I want to make a working solution for my distribution (Mandriva).
>> > 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? >
Yes, but afaics there are currently no device privileges given to the console user which would compromise password security. Providing eventX would do that.
-- Anssi Hannula
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