Re: Patch fixing STP if bridge in non-default namespace.

From: Harry Coin <redacted>
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.