Re: [Bridge question] Issue with removing MDB entry after enabling VLAN filtering

[Hangbin Liu <liuhangbin@gmail.com>]

On Wed, Feb 19, 2025 at 11:56:08AM +0200, Nikolay Aleksandrov wrote:
> On 2/19/25 11:43, Hangbin Liu wrote:
> > Hi everyone,
> > 
> > Our QE team reported that after adding an MDB entry, enabling VLAN filtering,
> > and then removing the MDB entry, the removal fails. e.g.
> > 
> > + ip link add dev br0 type bridge
> > + ip link add dev vethin type veth peer name vethout
> > + ip link add dev vethin1 type veth peer name vethout1
> > + ip link set vethout up && ip link set vethout1 up && ip link set vethin up  && ip link set vethin1 up && ip link set br0 up
> > + ip link set vethout master br0
> > + ip link set vethout1 master br0
> > + echo 1 > /sys/class/net/br0/bridge/multicast_snooping
> > + echo 1 > /sys/class/net/br0/bridge/multicast_querier
> > + bridge mdb add dev br0 port vethout1 grp 225.1.1.10 src 192.168.2.1
> > + echo 1 > /sys/class/net/br0/bridge/vlan_filtering
> > + bridge mdb del dev br0 port vethout1 grp  225.1.1.10  src 192.168.2.1
> > RTNETLINK answers: Invalid argument
> > 
> > From reviewing the code in br_mdb_del(), I noticed that it sets the VLAN tag
> > if VLAN filtering is enabled and the VLAN is not specified.
> > 
> > I'm not sure if the QE’s operation is valid under these circumstances.
> > Do we need to disable VLAN filtering before removing the MDB entry if
> > it was added without VLAN filtering?
> > 
> > Thanks
> > Hangbin
> 
> Hi,
> It seems you did not specify a vlan when trying to delete the entry after enabling vlan filtering
> so the bridge code tries to delete it from all vlans on the port and some of them don't have
> that mdb entry so you get the -EINVAL, but it should delete it from any vlans that have
> the entry.
> 
> In this case since the entry was added before vlan filtering was enabled it won't have any
> vlan set making it unreachable for a delete after filtering was enabled. It is a corner case
> for sure and TBH I don't see any value in adding more logic to resolve it (it would require
> some special way to signal the kernel that we want to delete an entry that doesn't have a
> vlan after filtering was enabled), instead you can just disable vlan filtering and
> delete the entry. So IMO it is just wrong config and not worth the extra complexity to be
> able to delete such entries.

Thanks, I agree this is a config issue and does not worth to fix.

Regards
Hangbin