vde_switch crashes if vlan # 0 is removed

In older versions of vde2 the following switch startup configuration worked like a charm:

vlan/create 1 # isolated w/o real network access
vlan/create 2 # access to local samba server
vlan/create 3 # bridged to hypervisor
port/setvlan 1 1
port/setvlan 2 3
port/create 3
port/setvlan 3 2
vlan/remove 0

In other words, I set up 3 new VLANs and then removed the default VLAN # 0.

I did this because this default VLAN seemed to be special in that it was exempt from VLAN filtering and could therefore see all the traffic. I considered that a security risk and therefore deleted the VLAN.

However, current versions of vde_switch crash when adding new ports after VLAN # 0 has been removed.

Core dump analysis shows the crash happens in line 170 of file src/vde_switch/port.c where the expression

ba_set(vlant[0].table,i)

is evaluated with vlant[0].table containing a null pointer.

Suggested course of action: Either the code should check whether vlant[0].table contains a null pointer and then avoid dereferencing it, or removal of VLAN # 0 should be forbidden because then there will not be a null pointer.

Start in src/vde_switch/port.c at line 170 and reproduce the startup sequence that creates VLANs, removes VLAN 0, and then adds a port. Inspect how vlant[0].table is handled after removal and determine whether the intended behavior is to guard the null pointer or reject VLAN 0 removal. Done means adding a port no longer crashes and the chosen behavior is covered by the relevant project checks.