New: BNEP multicast filter is filtering multicast addresses in default case although differently specified

https://bugzilla.kernel.org/show_bug.cgi?id=106691

            Bug ID: 106691
           Summary: BNEP multicast filter is filtering multicast addresses
                    in default case although differently specified
           Product: Drivers
           Version: 2.5
    Kernel Version: 4.0.4
          Hardware: All
                OS: Linux
              Tree: Mainline
            Status: NEW
          Severity: high
          Priority: P1
         Component: Bluetooth
          Assignee: [email protected]
          Reporter: [email protected]
        Regression: No

A Linux PC is connected with another device over Bluetooth PAN using a BNEP interface.

Whenever a packet is tried to be sent over the BNEP interface, the function "bnep_net_xmit()" in "net/bluetooth/bnep/netdev.c" is called. This function calls "bnep_net_mc_filter()", which checks (if the destination address is multicast) if the address is set in a certain multicast filter (&s->mc_filter). If it is not, then it is not sent out.

This filter is only changed in two other functions, found in net/bluetooth/bnep/core.c": in "bnep_ctrl_set_mc_filter()", which is only called if a message of type "BNEP_FILTER_MULTI_ADDR_SET" is received. Otherwise, it is set in "bnep_add_connection()", where it is set to a default value which only adds the broadcast address to the filter:

set_bit(bnep_mc_hash(dev->broadcast), (ulong *) &s->mc_filter);

To sum up, if the BNEP interface does not receive any message of type "BNEP_FILTER_MULTI_ADDR_SET", it will not send out any messages with multicast destination addresses except for broadcast.

However, in the BNEP specification (page 27 in
http://grouper.ieee.org/groups/802/15/Bluetooth/BNEP.pdf), it is said that per default, all multicast addresses should not be filtered, i.e. the BNEP interface should be able to send packets with any multicast destination address.

It seems that the default case is wrong: the multicast filter should not block almost all multicast addresses, but should not filter out any.

This leads to the problem that e.g. Neighbor Solicitation messages sent with Bluetooth PAN over the BNEP interface to a multicast destination address other than broadcast are blocked and not sent out.

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https://bugzilla.kernel.org/show_bug.cgi?id=106691

Johan Hedberg <[email protected]> changed:

What |Removed |Added
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CC| |[email protected]

--- Comment #1 from Johan Hedberg <[email protected]> --- Looks like you've analyzed and understood the issue fairly well! The next step would be to send a patch proposal to the linux-bluetooth list. Would you be able to do that?

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