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

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Date:   Thu, 15 Jun 2017 14:33:49 +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 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.

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!