svn commit: r304436 - in head: . sys/netinet

[Bruce Simpson]

On 20/08/16 19:09, Adrian Chadd wrote:
> On 20 August 2016 at 11:02, Ryan Stone <rysto32 at gmail.com> wrote:
>> On Sat, Aug 20, 2016 at 1:30 PM, Slawa Olhovchenkov <slw at zxy.spb.ru> wrote:
>>> For host enought have [hidden] alias with broadcsts bits.
>>> Anyway, don't should relay on the L2 information, you can recive L3
>>> unicast addressed packets (with alien dst IP address) in L2 broadcas
>>> packet.
>>
>> This is still handled correctly.  The new code only checks for L3 broadcast
>> addresses on L2 broadcast packets, but we still check the L3 address before
>> treating it as a broadcast. The problem is that I assumed that all paths
>> into the IP stack would set M_BCAST, but as Bruce has pointed out there are
>> cases like PPP which do not.
>
> So why not fix those paths?

Because it would involve doing something similar to what if_ethersubr.c 
does right now: a direct comparison with FF:FF:FF:FF:FF:FF. Doing so 
outside of Ethernet would be invasive and one of those 'bad' layer 
crossings.

This is tricky to get right. NetBSD introduced the M_PROMISC flag to 
cover situations which can occur when Ethernet can be re-entered by 
layers 'above' its original invocation. (I merged it here.)

Ryan proposes slipping the definition of M_BCAST to include the network 
layer, inside ip_input() itself. That would not strictly violate 
layering, but bends the original meaning of the flag somewhat.

That may work, provided it doesn't tread on the toes of anything above 
it. However the situation is somewhat similar to that of M_PROMISC.