NULL pointer dereference bug triggered by netmap

[Luiz Otavio O Souza]

On 5 July 2017 at 08:05, Marius Strobl wrote:
> On Mon, Jul 03, 2017 at 05:08:09PM +0200, Vincenzo Maffione wrote:
>> Details here:
>>
>> https://github.com/luigirizzo/netmap/issues/322
>>
>> Is it acceptable to commit the proposed patch?
>
> As suggested by hselasky@, the outliner problem at hand is better solved
> by a dummy if_start method in order to not hurt the fast-path. Thus, if
> anything at all, a KASSERT(ifp->if_start != NULL, "no if_start method")
> should be added to if_handoff() and if_start().

As noted by ae@, if_transmit() is not supported on the loopback
interface.  In any case, the loopback interface could provide a dummy
if_transmit() method to not queue the packets, not call if_start() and
print a warning/panic.

Luiz