svn commit: r347063 - head/sys/kern

[John Baldwin]

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.

-- 
John Baldwin