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



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