On Tue, Jul 11, 2023 at 04:54:15PM -0700, 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 show an error when enabling STP in netns.
>
> # unshare -n
> # ip link add br0 type bridge
> # ip link set br0 type bridge stp_state 1
> Error: bridge: STP can't be enabled 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@xxxxxxxxxxxxxxxxx>
I'm not sure that's accurate. I read his response in the link below and
he says "I'd rather be warned than blocked" and "But better warned and
awaiting a fix than blocked", which I agree with. The patch has the
potential to cause a lot of regressions, but without actually fixing the
problem.
How about simply removing the error [1]? Since iproute2 commit
844c37b42373 ("libnetlink: Handle extack messages for non-error case"),
it can print extack warnings and not only errors. With the diff below:
# unshare -n
# ip link add name br0 type bridge
# ip link set dev br0 type bridge stp_state 1
Warning: bridge: STP can't be enabled in non-root netns.
# echo $?
0
[1]
diff --git a/net/bridge/br_stp_if.c b/net/bridge/br_stp_if.c
index a807996ac56b..b5143de37938 100644
--- a/net/bridge/br_stp_if.c
+++ b/net/bridge/br_stp_if.c
@@ -201,10 +201,8 @@ int br_stp_set_enabled(struct net_bridge *br, unsigned long val,
{
ASSERT_RTNL();
- if (!net_eq(dev_net(br->dev), &init_net)) {
+ if (!net_eq(dev_net(br->dev), &init_net))
NL_SET_ERR_MSG_MOD(extack, "STP can't be enabled in non-root netns");
- return -EINVAL;
- }
if (br_mrp_enabled(br)) {
NL_SET_ERR_MSG_MOD(extack,
> Link: https://lore.kernel.org/netdev/0f531295-e289-022d-5add-5ceffa0df9bc@xxxxxxxxxxxxxxxxx/
> Signed-off-by: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>
> ---
> net/bridge/br_stp_if.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/net/bridge/br_stp_if.c b/net/bridge/br_stp_if.c
> index 75204d36d7f9..a807996ac56b 100644
> --- a/net/bridge/br_stp_if.c
> +++ b/net/bridge/br_stp_if.c
> @@ -201,6 +201,11 @@ 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 can't be enabled in non-root netns");
> + return -EINVAL;
> + }
> +
> if (br_mrp_enabled(br)) {
> NL_SET_ERR_MSG_MOD(extack,
> "STP can't be enabled if MRP is already enabled");
> --
> 2.30.2
>
>
