Date: Mon, 6 May 2019 13:35:03 -0700 (PDT) From: "Rodney W. Grimes" <freebsd@gndrsh.dnsmgr.net> To: Mark Johnston <markj@freebsd.org> Cc: John Baldwin <jhb@freebsd.org>, src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r347063 - head/sys/kern Message-ID: <201905062035.x46KZ37X008317@gndrsh.dnsmgr.net> In-Reply-To: <20190506184502.GA35464@raichu>
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> 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@freebsd.org
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