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Date:   Mon, 13 May 2019 19:38:37 +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 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.

>> 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.
>
Firewall is not applied to all scenarios.

> Michal Kubecek
>
> .
>

thanks.

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