svn commit: r347063 - head/sys/kern

[Warner Losh]

On Mon, May 6, 2019 at 3:11 PM John Baldwin <jhb at freebsd.org> wrote:

> On 5/6/19 1:57 PM, Mark Johnston wrote:
> > On Mon, May 06, 2019 at 01:40:19PM -0700, John Baldwin wrote:
> >> On 5/6/19 11:45 AM, Mark Johnston wrote:
> >>> 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.
> >>
> >> Ok, thanks.  A few things I didn't see anyone else note in the review
> then:
> >>
> >> 1) This subtraction is actually not done for all rtc drivers, so it
> seems
> >>    like we might block small times for RTC clocks that set
> >>    CLOCKF_GETTIME_NO_ADJ.
> >
> > The drivers that set NO_ADJ still account for the offset in their
> > individual settime methods.  I don't see how it can be correct for any
> > driver to ignore adjkerntz?
> >
> >> 2) utc_offset can be negative for machines using local time in timezones
> >>    "before" UTC.
> >
> > Hmm, I believe the patch still handles this case?
>
> Yes, it's just redundant as the earlier 'tv_sec < 0' check means we'll
> never see a value < utc_offset.  One thought I had was similar to what
> Warner suggested of just using the max value of '24 * 60 * 60', though
> I suppose the maximal utc_offset is more like '12 * 60 * 60'?  utc_offset
> is probably good enough as is.
>

The maximum UTC offset is closer to 15 hours due to that crazy
international date line and different groups of islands wanting to be on
one side or the other of the international date line. that's why I
suggested 24 hours (if you read carefully, I typed * 2 for bogus reasons).

Warner