Re: [RFC] Input: implement sysrq as an input handler

From: Pavel Machek
Date: Sun Apr 04 2010 - 09:27:55 EST


> > If userspace disables sysrq during normal operation, that makes it
> > useless.
> >
> > If normal user could do that, that's a security problem.
> >
> Yes, and...? This patch does not change the way one enables, disables,
> intercepts, etc. SysRq and SAK compared to how it was handled when SysRq
> was part of keyboard _input handler_. The only thisng this patch does is
> moving the code into a _separate_ input handler.

Yep, that was just a note.

> > > The problem is that device does not know what SysRq and especially SAK are.
> > > User can reassign key codes and key symbols easily.
> >
> > That was not case in original implementation; it had hardcoded keymap.
> The earth was also flat back then and the only keyboard was AT one. SAK
> was always part of keymap so could be reassinged at any time.

Well, there are two SAKs.

One SAK -- in keymap, is remappable and always was.

Second, sysrq-saK -- is (was?) hardcoded and not affected by
keymap. Please don't change that.

> > > I don't think we had any issues like this since 2.5 so I would not worry
> > > about userspace too much. If anything we just need to review what stuff
> > > we run as root (we do that anyway, right?).
> >
> > Hehe. If X can break sysrq, that's both X and sysrq problem.
> Root can disable Sysrq... News at 11.

Root *does* disable sysrq is indeed news ... and problem.
(cesky, pictures)
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