pfSense

When creating a bridge, it is possible to create multiple bridges which contain the same interface(s), which is invalid.

For example, with OPT3 (em3), OPT4 (em4), and OPT5 (em5) I am able to create two bridges in the GUI: OPT3+OPT4, OPT4+OPT5, but in the OS the second bridge is missing OPT4 since it cannot be on two bridges at once:

: ifconfig -a
[...]
bridge0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
    ether 02:fb:d1:bb:af:00
    nd6 options=1<PERFORMNUD>
    id 00:00:00:00:00:00 priority 32768 hellotime 2 fwddelay 15
    maxage 20 holdcnt 6 proto rstp maxaddr 2000 timeout 1200
    root id 00:00:00:00:00:00 priority 32768 ifcost 0 port 0
    member: em4 flags=143<LEARNING,DISCOVER,AUTOEDGE,AUTOPTP>
            ifmaxaddr 0 port 5 priority 128 path cost 20000
    member: em3 flags=143<LEARNING,DISCOVER,AUTOEDGE,AUTOPTP>
            ifmaxaddr 0 port 4 priority 128 path cost 20000
bridge1: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
    ether 02:fb:d1:bb:af:01
    nd6 options=1<PERFORMNUD>
    id 00:00:00:00:00:00 priority 32768 hellotime 2 fwddelay 15
    maxage 20 holdcnt 6 proto rstp maxaddr 2000 timeout 1200
    root id 00:00:00:00:00:00 priority 32768 ifcost 0 port 0
    member: em5 flags=143<LEARNING,DISCOVER,AUTOEDGE,AUTOPTP>
            ifmaxaddr 0 port 6 priority 128 path cost 20000

: ifconfig bridge1 addm em4
ifconfig: BRDGADD em4: Device busy

The bridge "Member interfaces" list in the GUI should either remove or disable entries for interfaces that are already on other bridges, and present an error if a bridge is saved that somehow contains overlapping interfaces.