Subject: Re: [RFC net-next 3/6] net: Introduce VRF device driver - v2

From: David Ahern <[email-masked]>
Date: Thu, 09 Jul 2015 22:20:36 -0600

On 7/9/15 9:55 PM, Eric W. Biederman wrote:
>> IP addresses are per interface and interfaces are uniquely assigned to
>> a VRF so why do you think IP addresses are not per VRF?
>
> I have read large swaths of the linux networking code over the years.
>
> Further I was thinking more about non-local addresses ip addresses, but
> I would not be surprised if there are also issues with local addresses.

Well, if someone has a specific example I'll take a look.

>
>>>   Which means things like packet fragmentation reassembly
>>> can easily do the wrong thing.  Similarly things like the xfrm for ipsec
>>> tunnels are not hooked into this mix.
>>>
>>> So I really do not see how this VRF/MRF thing as designed can support
>>> general purpose sockets.  I am not certain it can correctly support any
>>> kind of socket except perhaps SOCK_RAW.
>>
>> Sockets bound to the VRF device work properly. Why do you think they won't?
>
> Because there are many locations in the network stack (like fragment
> reassembly) that make the assumption that ip addresses are unique and
> do not bother looking at network device or anything else.  If fragments
> manage to come into play I don't expect it would be hard to poision a
> connections with fragments from another routing domain with overlapping
> ip addresses.

If that is true it is a problem with the networking stack today and is 
completely independent of this VRF proposal.

> I guess if we are talking about SO_BINDTODEVICE which requires
> CAP_NET_RAW we aren't really talking ordinary applications so there is
> already a big helping of buyer beware.
>
> Still a blanket statement that sockets just work and there is nothing
> to be concerned about is just wrong.

If you have examples of something that does not work I will be happy to 
look into it. As it stands I have a growing suite of test cases where my 
comment is true.

David