Destroying lagg interface causes a crash.

[markb_mellanox.com]

Summary

Creating a lagg port attaching i>0 interfaces and then destroying causes a crash

ifconfig lagg destroy

Steps to reproduce:

1. ifconfig mce0 mce0
2. ifconfig lagg0 create
3. ifconfig lagg0 up laggproto lacp laggport mce0
4. ifconfig lagg0 destroy

I believe this is caused by the following flow:

1. lagg_clone_destroy is called
2. we call: lagg_port_destroy(lp, 1); in a loop (going over all sc_ports)
3. SLIST_REMOVE is called and we remove lp from sc_ports
4. when the last interface is removed, inside lagg_port_destroy we enter the if : if (lp == sc->sc_primary) and because sc_ports is empty, lp0 == NULL

6. We call: lagg_port_lladdr(lp0, lladdr); which means: lagg_port_lladdr(NULL, lladdr) and that causes a crash (we deference NULL inside lagg_port_lladdr).

This is a quick fix, I really don't know enough about the lagg module to say if this is the most correct solution.

Mark.

[koobs]

Successful reproduction and confirmation this fix resolves the issue:

https://lists.freebsd.org/pipermail/freebsd-current/2015-October/057803.html

[hrs]

This fix is correct. I will commit it asap.