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

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Message-ID: <20190513121145.GE22349@unicorn.suse.cz>
Date:   Mon, 13 May 2019 14:11:45 +0200
From:   Michal Kubecek <mkubecek@...e.cz>
To:     netdev@...r.kernel.org
Cc:     Weilong Chen <chenweilong@...wei.com>, davem@...emloft.net,
        kuznet@....inr.ac.ru, yoshfuji@...ux-ipv6.org
Subject: Re: [PATCH net-next] ipv4: Add support to disable icmp timestamp

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?

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.

Michal Kubecek