netdev - Re: [PATCH net-next 0/3] ipmr/ip6mr: add Netlink notifications on cache reports

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Date:   Thu, 15 Jun 2017 14:44:40 +0300
From:   Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
To:     Julien Gomes <julien@...sta.com>, davem@...emloft.net
Cc:     Netdev <netdev@...r.kernel.org>,
        Donald Sharp <sharpd@...ulusnetworks.com>
Subject: Re: [PATCH net-next 0/3] ipmr/ip6mr: add Netlink notifications on
 cache reports

On 15/06/17 14:33, Nikolay Aleksandrov wrote:
> On 15/06/17 00:51, Julien Gomes wrote:
>> Hi Nikolay,
>>
>> On 06/14/2017 05:04 AM, Nikolay Aleksandrov wrote:
>>
>>> This has been on our todo list and I'm definitely interested in the implementation.
>>> A few things that need careful consideration from my POV. First are the security
>>> implications - this sends rtnl multicast messages but the rtnl socket has
>>> the NL_CFG_F_NONROOT_RECV flag thus allowing any user on the system to listen in.
>>> This would allow them to see the full packets and all reports (granted they can see
>>> the notifications even now), but the full packet is like giving them the opportunity
>>> to tcpdump the PIM traffic.
>>
>> I definitely see how this can be an issue.
>> From what I see, this means that either the packet should be
>> transmitted another way, or another Netlink family should be used.
>>
>> NETLINK_ROUTE looks to be the logical family to choose though,
>> but then I do not see a proper other way to handle this.
> 
> Right, currently me neither, unless it provides a bind callback when registering
> the kernel socket.
> 
>>
>> However I may just not be looking into the right direction,
>> maybe you currently have another approach in mind?
> 
> I haven't gotten around to make (or even try) them but I was thinking about 2 options
> ending up with a similar result:
> 
> 1) genetlink
>  It also has the NONROOT_RECV flag, but it also allows for a callback - mcast_bind()
>  which can be used to filter.
> 
> or
> 
> 2) Providing a bind callback to the NETLINK_ROUTE socket.
> 

Ah nevermind, these cannot be used for filtering currently, so it seems
the netlink interface would need to be extended too if going down this road.

> I haven't checked in detail how feasible each option is. To me 2) seems like the
> cleaner/proper way to do it but it requires extending the rtnetlink api.
> 
> It would be nice to get feedback and comments from more people on this.
> 
>>
>>> My second (more fixable and minor) concern is about the packet itself, how do you
>>> know that the packet is all linear so you can directly copy it ?
>>
>> Indeed, I overlooked this possibility in this version.
>> I will improve that.
>>
> 
> Thanks!
>