Re: llc needs namespace awareness asap, was Re: Patch fixing STP if bridge in non-default namespace.

[Kuniyuki Iwashima <kuniyu@amazon.com>]

From: Harry Coin <hcoin@quietfountain.com>
Date: Tue, 11 Jul 2023 12:08:15 -0500
> On 7/10/23 22:22, Kuniyuki Iwashima wrote:
> > From: Harry Coin <hcoin@quietfountain.com>
> > Date: Mon, 10 Jul 2023 08:35:08 -0500
> >> Notice without access to link-level multicast address 01:80:C2:00:00:00,
> >> the STP loop-avoidance feature of bridges fails silently, leading to
> >> packet storms if loops exist in the related L2.  The Linux kernel's
> >> latest code silently drops BPDU STP packets if the bridge is in a
> >> non-default namespace.
> >>
> >> The current llc_rcv.c around line 166 in net/llc/llc_input.c  has
> >>
> >>          if (!net_eq(dev_net(dev), &init_net))
> >>                  goto drop;
> >>
> >> Which, when commented out, fixes this bug.  A search on &init_net may
> >> reveal many similar artifacts left over from the early days of namespace
> >> implementation.
> > I think just removing the part is not sufficient and will introduce a bug
> > in another place.
> >
> > As you found, llc has the same test in another place.  For example, when
> > you create an AF_LLC socket, it has to be in the root netns.  But if you
> > remove the test in llc_rcv() only, it seems llc_recv() would put a skb for
> > a child netns into sk's recv queue that is in the default netns.
> >
> >    - llc_rcv
> >      - if (net_eq(dev_net(dev), &init_net))
> >        - goto drop
> >      - sap_handler / llc_sap_handler
> >        - sk = llc_lookup_dgram
> >        - llc_sap_rcv
> >          - llc_sap_state_process
> > 	  - sock_queue_rcv_skb
> >
> > So, we need to namespacify the whole llc infra.
> 
> Agreed.  Probably sooner rather than later since IP4 and IP6 multicast, 
> GARP and more as well as STP depends on llc multicast delivery.   I 
> suspect the authors who added the 'drop unless default namespace' code 
> commented out above knew this, and were just buying some time.  Well, 
> the time has come.
> 
> Now all bridges in a namespace will always -- and silently -- think of 
> itself as the 'root bridge' as it can't get packets informing it 
> otherwise.  This leads to packet storms at line-level speeds bringing 
> whole infrastructures down in a self-inflicted event worse than a DDOS 
> attack.
> 
> I think whoever does 'advisories' ought to warn the community that ipv6 
> ndp (if using multicast), ipv4 arp (if using multicast), bridges with 
> STP, lldp, GARP, ipv6 multicast and ipv4 mulitcast for sockets in the 
> non-default namespace will not get RX traffic as it gets dropped in the 
> kernel before other modules or user code has a chance to see it.  
> Outcomes range from local seeming disconnection to kernel induced 
> site-crippling packet storms.
> 
> Is there a way to track this llc namespace awareness effort?  I'm new to 
> this particular dev community.  It's on a critical path for my project.

AFAIK, there is no ongoing work for this.  I can spend some cycles on
this, but note that the patches might not be backported to stable as
it would be invasive.