linux-kernel - Re: [v2] time: Validate the usec before covert to nsec in do

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Message-ID: <5fcccfec-cd51-02d5-d096-5a14675c2132@huawei.com>
Date:   Mon, 8 Jul 2019 21:33:50 +0800
From:   "zhangxiaoxu (A)" <zhangxiaoxu5@...wei.com>
To:     Thomas Gleixner <tglx@...utronix.de>
CC:     <john.stultz@...aro.org>, <sboyd@...nel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [v2] time: Validate the usec before covert to nsec in do_adjtimex



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
> 
> 
> 
> .
>