[lwip-devel] [bug #49662] UDP layer should filter incoming multicast datagrams against the bound IP address

[Sam Kearney]

URL:
  <http://savannah.nongnu.org/bugs/?49662>

                 Summary: UDP layer should filter incoming multicast datagrams
against the bound IP address
                 Project: lwIP - A Lightweight TCP/IP stack
            Submitted by: skearney
            Submitted on: Mon 21 Nov 2016 04:43:57 PM GMT
                Category: UDP
                Severity: 3 - Normal
              Item Group: Change Request
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
         Planned Release: None
            lwIP version: Other

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Details:

Hi,

First a disclaimer: I'm not sure if this is the right place to register this
gripe; I couldn't find a forum where someone could tell me if I'm being stupid
or missing a compile-time option to change this behavior. So, sorry in advance
if that's the case.

I am attempting to use lwIP 2.0.0 through the sockets API to support a
higher-level protocol that makes heavy use of UDP multicast and unicast
traffic on the same port. I'm finding that if I bind a socket to the specific
interface IP address (rather than INADDR_ANY), that socket will still receive
datagrams addressed to its port and a multicast address to which some other
socket has subscribed. This seems to be due to the logic in
udp_input_local_match(), which lets through any datagram addressed to a
multicast address.

We have existing ports of our protocol for Windows, Mac OSX, Debian Linux and
VxWorks, and all of those platforms filter incoming multicast datagrams
against a socket's bound address in addition to the port. I hope this is
sufficient justification to change this behavior, since standardization of
multicast at the transport layer seems to be light.

It's difficult to add application-layer filtering to deal with this, since the
lwIP sockets API doesn't seem to provide a way  to get the
<em>destination</em> address of an incoming datagram (this is possible in BSD
sockets with the recvmsg function).




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