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

Thomas Gleixner
2011-03-11T19:47:17Z

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