linux-kernel - Re: [PATCH 3/3] Check for write permission on FD based posix-clocks

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Date:	Fri, 11 Mar 2011 20:46:57 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Richard Cochran <richardcochran@...il.com>
cc:	Torben Hohn <torbenh@....de>, linux-kernel@...r.kernel.org,
	richard.cochran@...cron.at, johnstul@...ibm.com
Subject: Re: [PATCH 3/3] Check for write permission on FD based
 posix-clocks

On Fri, 4 Mar 2011, Richard Cochran wrote:

> On Thu, Mar 03, 2011 at 06:26:14PM +0100, Torben Hohn wrote:
> > pc_clock_settime() and pc_clock_adjtime() did not check
> > whether the fd was opened in write mode.
> > 
> > It was possible to set a clock, when we only had read
> > permissions.
> > 
> > for completeness, we would also need to check for Read permissions
> > on the read operations. but that would be a bit paranoid, probably.
> 
> I have no objection to this form of clock access control, but I would
> like to get agreement about it from the list.

Acked-by-me
 
> > diff --git a/kernel/time/posix-clock.c b/kernel/time/posix-clock.c
> > index 04498cb..25028dd 100644
> > --- a/kernel/time/posix-clock.c
> > +++ b/kernel/time/posix-clock.c
> > @@ -287,11 +287,16 @@ static int pc_clock_adjtime(clockid_t id, struct timex *tx)
> >  	if (err)
> >  		return err;
> >  
> > +	if ((cd.fp->f_mode & FMODE_WRITE) == 0) {
> > +		err = -EACCES;
> 
> Looks like clock_settime and adjtimex are supposed to return EPERM in
> this case.

As Arnd already said -EACCES is sensible for file permission checks
while -EPERM means that you have no permission at all.

Thanks,

	tglx
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