[PATCH v1 net] bridge: Return an error when enabling STP in netns.

[PATCH v1 net] bridge: Return an error when enabling STP in netns.

[Kuniyuki Iwashima]

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@quietfountain.com>
Link: https://lore.kernel.org/netdev/0f531295-e289-022d-5add-5ceffa0df9bc@quietfountain.com/
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
---
 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

Re: [PATCH v1 net] bridge: Return an error when enabling STP in netns.

[Nikolay Aleksandrov]

On 12/07/2023 02:54, 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@quietfountain.com>
> Link: https://lore.kernel.org/netdev/0f531295-e289-022d-5add-5ceffa0df9bc@quietfountain.com/
> Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
> ---
>  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");

Oh well, I guess this should do for now. Hopefully we don't break scripts that rely
on configuring the bridge without any errors. Thanks for the patch,

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

Re: [PATCH v1 net] bridge: Return an error when enabling STP in netns.

[Ido Schimmel]

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@quietfountain.com>

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@quietfountain.com/
> Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
> ---
>  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
> 
> 

Re: [PATCH v1 net] bridge: Return an error when enabling STP in netns.

[Nikolay Aleksandrov]

On 12/07/2023 17:48, Ido Schimmel wrote:
> 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@quietfountain.com>
> 
> 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,
> 

I'd prefer this approach to changing user-visible behaviour and potential regressions.
Just change the warning message.

Thanks,
 Nik

Re: [PATCH v1 net] bridge: Return an error when enabling STP in netns.

[Ido Schimmel]

On Wed, Jul 12, 2023 at 05:52:09PM +0300, Nikolay Aleksandrov wrote:
> I'd prefer this approach to changing user-visible behaviour and potential regressions.
> Just change the warning message.

Yea, I noticed after sending that the message no longer fits :)

Re: [PATCH v1 net] bridge: Return an error when enabling STP in netns.

[Harry Coin]

On 7/12/23 09:52, Nikolay Aleksandrov wrote:
> On 12/07/2023 17:48, Ido Schimmel wrote:
>> 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@quietfountain.com>
>> 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,
>>
> I'd prefer this approach to changing user-visible behaviour and potential regressions.
> Just change the warning message.
>
> Thanks,
>   Nik

Remember, the only way it's honest to 'warn but not block' STP in netns 
is trust in the Kuniyuki's assertion that the llc will be 
'namespacified' in a near term frame.   As STP is not only 
non-functional in a netns, but will in fact bring down every connected 
system in a packet storm should a L2 loop exist the situation is much 
worse than a merely inaccessible extra feature. This as the only reason 
STP exists is to avoid crashing sites owing to packet storms arising 
from L2 loops.    I think as this bug is a potential 'site killer' 
(which in fact happened to me!) The Linux dev community has an 
obligation to either hard block this or commit to a fix time frame and 
merely warn.

Thanks

Harry Coin

Re: [PATCH v1 net] bridge: Return an error when enabling STP in netns.

[Kuniyuki Iwashima]

From: Ido Schimmel <idosch@idosch.org>
Date: Wed, 12 Jul 2023 17:48:20 +0300
> 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@quietfountain.com>
> 
> 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:

This is good to know and I also prefer this approach!
I'll post v2.

Thanks!


> 
>  # 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@quietfountain.com/
> > Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
> > ---
> >  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