netdev - Re: [PATCH] netlink: Add netns check on taps

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Date:   Wed, 6 Dec 2017 21:51:44 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     David Miller <davem@...emloft.net>, cernekee@...omium.org
Cc:     johannes.berg@...el.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] netlink: Add netns check on taps

On 12/06/2017 08:40 PM, David Miller wrote:
> From: Kevin Cernekee <cernekee@...omium.org>
> Date: Tue,  5 Dec 2017 14:46:22 -0800
> 
>> Currently, a nlmon link inside a child namespace can observe systemwide
>> netlink activity.  Filter the traffic so that in a non-init netns,
>> nlmon can only sniff netlink messages from its own netns.
>>
>> Test case:
>>
>>     vpnns -- bash -c "ip link add nlmon0 type nlmon; \
>>                       ip link set nlmon0 up; \
>>                       tcpdump -i nlmon0 -q -w /tmp/nlmon.pcap -U" &
>>     sudo ip xfrm state add src 10.1.1.1 dst 10.1.1.2 proto esp \
>>         spi 0x1 mode transport \
>>         auth sha1 0x6162633132330000000000000000000000000000 \
>>         enc aes 0x00000000000000000000000000000000
>>     grep abc123 /tmp/nlmon.pcap
>>
>> Signed-off-by: Kevin Cernekee <cernekee@...omium.org>
> 
> Daniel, what behavior did you intend this to have?
> 
> Taps can see their own namespace only, or init_net is special
> and can see all netlink activity.
> 
> I think letting init_net see everything could be confusing,
> because there is no way to distinguish netlink events by
> namespace just by looking at the messages that arrive at
> the tap right?

Yeah, only snooping from own netns makes sense, lets limit
it to this.