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

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Date:   Mon, 13 May 2019 14:22:00 +0200
From:   Florian Westphal <fw@...len.de>
To:     Weilong Chen <chenweilong@...wei.com>
Cc:     Michal Kubecek <mkubecek@...e.cz>, netdev@...r.kernel.org,
        davem@...emloft.net, kuznet@....inr.ac.ru, yoshfuji@...ux-ipv6.org
Subject: Re: [PATCH net-next] ipv4: Add support to disable icmp timestamp

Weilong Chen <chenweilong@...wei.com> wrote:
> On 2019/5/13 15:49, Michal Kubecek wrote:
> > On Mon, May 13, 2019 at 09:33:13AM +0800, Weilong Chen wrote:
> > > The remote host answers to an ICMP timestamp request.
> > > This allows an attacker to know the time and date on your host.
> > 
> > Why is that a problem? If it is, does it also mean that it is a security
> > problem to have your time in sync (because then the attacker doesn't
> > even need ICMP timestamps to know the time and date on your host)?
> > 
> It's a low risk vulnerability(CVE-1999-0524). TCP has
> net.ipv4.tcp_timestamps = 0 to disable it.

These are not the same.

TCP timestamps (before pseudo-randomized offset were added) used to leaked
system uptime.

ICMP timestamps "leak" milliseconds since midnight. Don't see how thats
a problem.