netdev - Re: [PATCH v2 net] tcp: randomize timestamps on syncookies

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Date:   Fri, 5 May 2017 11:36:30 +0200
From:   Florian Westphal <fw@...len.de>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     Florian Westphal <fw@...len.de>,
        David Miller <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Yuchung Cheng <ycheng@...gle.com>
Subject: Re: [PATCH v2 net] tcp: randomize timestamps on syncookies

Eric Dumazet <eric.dumazet@...il.com> wrote:
> From: Eric Dumazet <edumazet@...gle.com>
> 
> Whole point of randomization was to hide server uptime, but an attacker
> can simply start a syn flood and TCP generates 'old style' timestamps,
> directly revealing server jiffies value.
> 
> Also, TSval sent by the server to a particular remote address vary
> depending on syncookies being sent or not, potentially triggering PAWS
> drops for innocent clients.
> 
> Lets implement proper randomization, including for SYNcookies.


Thanks a lot Eric, this works for me (I also tested ipv6 this time ;) )

Minor nit:
net/ipv4/tcp_ipv4.c:154:6: warning: unused variable 'seq' [-Wunused-variable]

Other than this:
Reviewed-by: Florian Westphal <fw@...len.de>
Tested-by: Florian Westphal <fw@...len.de>