svn commit: r347063 - head/sys/kern

[Rodney W. Grimes]

> On Mon, May 06, 2019 at 11:07:18AM -0700, John Baldwin wrote:
> > On 5/3/19 2:26 PM, Mark Johnston wrote:
> > > Author: markj
> > > Date: Fri May  3 21:26:44 2019
> > > New Revision: 347063
> > > URL: https://svnweb.freebsd.org/changeset/base/347063
> > > 
> > > Log:
> > >   Disallow excessively small times of day in clock_settime(2).
> > >   
> > >   Reported by:	syzkaller
> > >   Reviewed by:	cem, kib
> > >   MFC after:	1 week
> > >   Sponsored by:	The FreeBSD Foundation
> > >   Differential Revision:	https://reviews.freebsd.org/D20151
> > > 
> > > Modified:
> > >   head/sys/kern/kern_time.c
> > > 
> > > Modified: head/sys/kern/kern_time.c
> > > ==============================================================================
> > > --- head/sys/kern/kern_time.c	Fri May  3 21:13:09 2019	(r347062)
> > > +++ head/sys/kern/kern_time.c	Fri May  3 21:26:44 2019	(r347063)
> > > @@ -412,7 +412,9 @@ kern_clock_settime(struct thread *td, clockid_t clock_
> > >  	if (ats->tv_nsec < 0 || ats->tv_nsec >= 1000000000 ||
> > >  	    ats->tv_sec < 0)
> > >  		return (EINVAL);
> > > -	if (!allow_insane_settime && ats->tv_sec > 8000ULL * 365 * 24 * 60 * 60)
> > > +	if (!allow_insane_settime &&
> > > +	    (ats->tv_sec > 8000ULL * 365 * 24 * 60 * 60 ||
> > > +	    ats->tv_sec < utc_offset()))
> > >  		return (EINVAL);
> > >  	/* XXX Don't convert nsec->usec and back */
> > >  	TIMESPEC_TO_TIMEVAL(&atv, ats);
> > 
> > Pardon my ignorance, but I can't see why you are checking against utc_offset()
> > vs some small constant?  None of the discussion in the review mentioned the
> > reason for using this particular value, and I didn't see any comparisons
> > against utc_offset or kernadjtz in kern_clock_setttime() or settime() that
> > would have underflowed or panicked.  Can you give a bit more detail on why
> > utc_offset() is the lower bound?  Thanks.
> 
> I chose it because we subtract utc_offset() from the time passed in to
> clock_settime(); see settime_task_func().  That subtraction caused the
> underflow that later caused the observed panics.

If the above conditional stays could the above go in a block comment
near this check please?

Doesn't this underflow actually indicate the settime is in the prior
day and other stuff needs adjusted?


-- 
Rod Grimes                                                 rgrimes at freebsd.org