Re: [PATCH] time: Validate the usec before covert to nsec in do_adjtimex

[Richard Cochran]

On Mon, Jul 08, 2019 at 03:55:04PM +0800, ZhangXiaoxu wrote:
> When covert the usec to nsec, it will multiple 1000, it maybe
> overflow and lead an undefined behavior.
> 
> For example, users may input an negative tv_usec values when
> call adjtimex syscall, then multiple 1000 maybe overflow it
> to a positive and legal number.
> 
> So, we should validate the usec before coverted it to nsec.
> 
> Signed-off-by: ZhangXiaoxu <zhangxiaoxu5@xxxxxxxxxx>
> ---
>  kernel/time/timekeeping.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
> index 44b726b..e5c1d00 100644
> --- a/kernel/time/timekeeping.c
> +++ b/kernel/time/timekeeping.c
> @@ -1272,9 +1272,6 @@ static int timekeeping_inject_offset(const struct timespec64 *ts)
>  	struct timespec64 tmp;
>  	int ret = 0;
>  
> -	if (ts->tv_nsec < 0 || ts->tv_nsec >= NSEC_PER_SEC)
> -		return -EINVAL;
> -
>  	raw_spin_lock_irqsave(&timekeeper_lock, flags);
>  	write_seqcount_begin(&tk_core.seq);
>  
> @@ -2321,6 +2318,9 @@ int do_adjtimex(struct __kernel_timex *txc)
>  
>  	if (txc->modes & ADJ_SETOFFSET) {
>  		struct timespec64 delta;
> +
> +		if (txc->time.tv_usec < 0 || txc->time.tv_usec >= USEC_PER_SEC)
> +			return -EINVAL;

This test is wrong.  If the tv_usec field is in nanoseconds, then the
value can easily be greater than USEC_PER_SEC.

>  		delta.tv_sec  = txc->time.tv_sec;
>  		delta.tv_nsec = txc->time.tv_usec;
>  		if (!(txc->modes & ADJ_NANO))
> -- 
> 2.7.4
> 

Thanks,
Richard