netdev - Re: [PATCH net-next] ipv4: Add support to disable icmp timestamp

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Date:   Mon, 13 May 2019 20:26:18 +0800
From:   Weilong Chen <chenweilong@...wei.com>
To:     Michal Kubecek <mkubecek@...e.cz>, <netdev@...r.kernel.org>
CC:     <davem@...emloft.net>, <kuznet@....inr.ac.ru>,
        <yoshfuji@...ux-ipv6.org>
Subject: Re: [PATCH net-next] ipv4: Add support to disable icmp timestamp

On 2019/5/13 20:11, Michal Kubecek wrote:
> On Mon, May 13, 2019 at 08:06:37PM +0800, Weilong Chen wrote:
>> On 2019/5/13 19:49, Michal Kubecek wrote:
>>> One idea is that there may be applications using current time as a seed
>>> for random number generator - but then such application is the real
>>> problem, not having correct time.
>>>
>> Yes, the target computer responded to an ICMP timestamp request. By
>> accurately determining the target's clock state, an attacker can more
>> effectively attack certain time-based pseudorandom number generators (PRNGs)
>> and the authentication systems that rely on them.
>>
>> So, the 'time' may become sensitive information. The OS should not leak it
>> out.
>
> So you are effectively saying that having correct time is a security
> vulnerability?
No, I mean that a server should not provide time to others if not necessary.

>
> I'm sorry but I cannot agree with that. Seeding PRNG with current time
> is known to be a bad practice and if some application does it, the
> solution is to fix the application, not obfuscating system time.
>
As I said, users can use Firewall to achieve the purpose. This patch 
just provide a simple way.

I can resubmit this patch and set default to 1, preserving current 
behaviour by default. Does that OK for you?

> Michal Kubecek
>
> .
>