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:
> 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
