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

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Message-ID: <20190513074928.GC22349@unicorn.suse.cz>
Date:   Mon, 13 May 2019 09:49:28 +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 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)?

> This path is an another way contrast to iptables rules:
> iptables -A input -p icmp --icmp-type timestamp-request -j DROP
> iptables -A output -p icmp --icmp-type timestamp-reply -j DROP
> 
> Default is disabled to improve security.

If we need a sysctl for this (and I'm not convinced we do), I would
prefer preserving current behaviour by default.

Michal Kubecek