linux-kernel - Re: RTC wakealarm write-only, still has 644 permissions

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Message-ID: <20071202113609.GA1796@elf.ucw.cz>
Date:	Sun, 2 Dec 2007 12:36:09 +0100
From:	Pavel Machek <pavel@....cz>
To:	David Brownell <david-b@...bell.net>
Cc:	rtc-linux@...glegroups.com,
	kernel list <linux-kernel@...r.kernel.org>,
	Alessandro Zummo <alessandro.zummo@...ertech.it>
Subject: Re: RTC wakealarm write-only, still has 644 permissions

Hi!

> > > It's not an issue of accidental writes, it's an issue of there being
> > > no other synchronization for setting those alarms.  Remember that both
> > > RTC_WKALM_SET and RTC_ALM_SET ioctls can set that same alarm, and so
> > > could a different userspace activity ...
> > 
> > We have 3 interfaces to one hardware resource. I do not think kernel
> > should try to arbitrate it here. There's just one alarm clock with
> > three interfaces.
> 
> Having three interfaces is bad enough ... ensuring that none of
> them can ever be used safely would be stupid.

They can be used safely. You just have to pick one and stay with
it. (And no, no-clobber hack does not help here. Or do you have
specific application where no-clobber hack helps?)

Anyway, with wildcarded dates, no-clobber is a problem -- because you
need to kill the alarm after you waken up, or it will repeat.
								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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