Re: [PATCH v2 net] bridge: Add extack warning when enabling STP in netns.

[Nikolay Aleksandrov <razor@blackwall.org>]

On 12/07/2023 18:44, Kuniyuki Iwashima wrote:
> When we create an L2 loop on a bridge in netns, we will see packets storm
> even if STP is enabled.
> 
>   # unshare -n
>   # ip link add br0 type bridge
>   # ip link add veth0 type veth peer name veth1
>   # ip link set veth0 master br0 up
>   # ip link set veth1 master br0 up
>   # ip link set br0 type bridge stp_state 1
>   # ip link set br0 up
>   # sleep 30
>   # ip -s link show br0
>   2: br0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP mode DEFAULT group default qlen 1000
>       link/ether b6:61:98:1c:1c:b5 brd ff:ff:ff:ff:ff:ff
>       RX: bytes  packets  errors  dropped missed  mcast
>       956553768  12861249 0       0       0       12861249  <-. Keep
>       TX: bytes  packets  errors  dropped carrier collsns     |  increasing
>       1027834    11951    0       0       0       0         <-'   rapidly
> 
> This is because llc_rcv() drops all packets in non-root netns and BPDU
> is dropped.
> 
> Let's add extack warning when enabling STP in netns.
> 
>   # unshare -n
>   # ip link add br0 type bridge
>   # ip link set br0 type bridge stp_state 1
>   Warning: bridge: STP does not work in non-root netns.
> 
> Note this commit will be reverted later when we namespacify the whole LLC
> infra.
> 
> Fixes: e730c15519d0 ("[NET]: Make packet reception network namespace safe")
> Suggested-by: Harry Coin <hcoin@quietfountain.com>
> Link: https://lore.kernel.org/netdev/0f531295-e289-022d-5add-5ceffa0df9bc@quietfountain.com/
> Suggested-by: Ido Schimmel <idosch@idosch.org>
> Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
> ---
> v2:
>   - Just add extack instead of returning error (Ido Schimmel)
> 
> v1: https://lore.kernel.org/netdev/20230711235415.92166-1-kuniyu@amazon.com/
> ---
>  net/bridge/br_stp_if.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/net/bridge/br_stp_if.c b/net/bridge/br_stp_if.c
> index 75204d36d7f9..b65962682771 100644
> --- a/net/bridge/br_stp_if.c
> +++ b/net/bridge/br_stp_if.c
> @@ -201,6 +201,9 @@ int br_stp_set_enabled(struct net_bridge *br, unsigned long val,
>  {
>  	ASSERT_RTNL();
>  
> +	if (!net_eq(dev_net(br->dev), &init_net))
> +		NL_SET_ERR_MSG_MOD(extack, "STP does not work in non-root netns");
> +
>  	if (br_mrp_enabled(br)) {
>  		NL_SET_ERR_MSG_MOD(extack,
>  				   "STP can't be enabled if MRP is already enabled");

Thanks,
Acked-by: Nikolay Aleksandrov <razor@blackwall.org>