Date: Mon, 6 May 2019 16:57:43 -0400 From: Mark Johnston <markj@freebsd.org> To: John Baldwin <jhb@freebsd.org> Cc: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r347063 - head/sys/kern Message-ID: <20190506205743.GA65083@raichu> In-Reply-To: <52484f6b-fdae-565b-6c03-37a63d56ad30@FreeBSD.org> References: <201905032126.x43LQilu092655@repo.freebsd.org> <335d828e-ac61-bc59-bac3-f80f27b951c7@FreeBSD.org> <20190506184502.GA35464@raichu> <52484f6b-fdae-565b-6c03-37a63d56ad30@FreeBSD.org>
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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? > I suppose we don't think any FreeBSD machines actually need to set the > running clock to 0 anyway so fixing it here rather than rejecting invalid > values only for RTCs that can't handle it is probably ok, but the > connection doesn't feel obvious that we are rejecting times that might > be non-representable in RTCs. I can add a comment explaining where the comment comes from, assuming there are no objections to keeping the existing change. The placement of the check was motivated by the placement of the pre-existing bounds check, and the fact that we have no good way to signal an error after setting the clock.
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