Re: [v2] time: Validate the usec before covert to nsec in do_adjtimex

[zhangxiaoxu (A)]

在 2019/7/8 21:04, Thomas Gleixner 写道:
> On Mon, 8 Jul 2019, 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.
>
> Looking deeper before applying it. That change is wrong for two reasons:
>
>   1) The value is already validated in timekeeping_validate_timex()
>
>   2) The tv_usec value can legitimately be >= USEC_PER_SEC if the ADJ_NANO
>      mode bit is set. See timekeeping_validate_timex() and the code you
>      actually modified:
Yes, you are right.
This actually found in an old version, and doesn't check more detail on mainline.
Thank you very much.
> >   	if (txc->modes & ADJ_SETOFFSET) {
> >   		struct timespec64 delta;
> > +
> > +		if (txc->time.tv_usec < 0 || txc->time.tv_usec >= USEC_PER_SEC)
> > +			return -EINVAL;
> >   		delta.tv_sec  = txc->time.tv_sec;
> >   		delta.tv_nsec = txc->time.tv_usec;
> >   		if (!(txc->modes & ADJ_NANO))
> 			delta.tv_nsec *= 1000;
>
>      	The multiplication is conditional ....
>
> Thanks,
>
> 	tglx
>
>
>
> .