On Thu, Nov 30, 2006 at 05:38:16PM +0100, Daniel Lezcano wrote:
> Vlad Yasevich wrote:
> > Daniel Lezcano wrote:
> >> Brian Haley wrote:
> >>> Eric W. Biederman wrote:
> >>>> I think for cases across network socket namespaces it should
> >>>> be a matter for the rules, to decide if the connection should
> >>>> happen and what error code to return if the connection does not
> >>>> happen.
> >>>>
> >>>> There is a potential in this to have an ambiguous case where two
> >>>> applications can be listening for connections on the same socket
> >>>> on the same port and both will allow the connection.  If that
> >>>> is the case I believe the proper definition is the first socket
> >>>> that we find that will accept the connection gets the connection.
> >> No. If you try to connect, the destination IP address is assigned to a
> >> network namespace. This network namespace is used to leave the listening
> >> socket ambiguity.
> >>> Wouldn't you want to catch this at bind() and/or configuration time and
> >>> fail?  Having overlapping namespaces/rules seems undesirable, since as
> >>> Herbert said, can get you "unexpected behaviour".
> >> Overlapping is not a problem, you can have several sockets binded on the
> >> same INADDR_ANY/port without ambiguity because the network namespace
> >> pointer is added as a new key for sockets lookup, (src addr, src port,
> >> dst addr, dst port, net ns pointer). The bind should not be forced to a
> >> specific address because you will not be able to connect via 127.0.0.1.
> > 
> > So, all this leads to me ask, how to handle 127.0.0.1?
> > 
> > For L2 it seems easy.  Each namespace gets a tagged lo device.
> > How do you propose to do it for L3, because disabling access to loopback is
> > not a valid option, IMO.
> 
> There are 2 options:
> 
> 1 - Dmitry Mishin proposed to use the l2 mechanism and reinstantiate a 
> new loopback device, I didn't tested that yet, perhaps there are issues 
> with non-127.0.0.1 loopback traffic and routes creation, I don't know.
> 
> 2 - add the pointer of the network namespace who has originated the 
> packet into the skbuff when the traffic is for 127.0.0.1, so when the 
> packet arrive to IP, it has the namespace destination information 
> because source == destination. I tested it and it works fine without 
> noticeable overhead and this can be done with a very few lines of code.

there is a third option, which is a little 'hacky' but
works quite fine too:

 use different loopback addresses for each 'guest' e.g.
 127.x.y.z and 'map' them to 127.0.0.1 (or the other
 way round) whenever appropriate

advantages:
 - doesn't require any skb tagging
 - doesn't change the routing in any way
 - allows isolated loopback connections

disadvantages:
 - blocks those special addresses (127.x.y.z)
 - requires the mapping at bind/receive

best,
Herbert
 
>    -- Daniel
> 
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