Re: [PATCH] Do not filter multicast addresses by default

[Johan Hedberg <johan.hedberg@gmail.com>]

Hi,

On Mon, Dec 07, 2015, Marcel Holtmann wrote:
> > 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.
> > 
> > Therefore, in the default case, we set the mc_filter to ~0LL to not filter out any multicast addresses.
> > ---
> > net/bluetooth/bnep/core.c | 8 ++++++--
> > 1 file changed, 6 insertions(+), 2 deletions(-)
> > 
> > diff --git a/net/bluetooth/bnep/core.c b/net/bluetooth/bnep/core.c
> > index 1641367..8e02289 100644
> > --- a/net/bluetooth/bnep/core.c
> > +++ b/net/bluetooth/bnep/core.c
> > @@ -608,8 +608,12 @@ int bnep_add_connection(struct bnep_connadd_req *req, struct socket *sock)
> > 	s->msg.msg_flags = MSG_NOSIGNAL;
> > 
> > #ifdef CONFIG_BT_BNEP_MC_FILTER
> > -	/* Set default mc filter */
> > -	set_bit(bnep_mc_hash(dev->broadcast), (ulong *) &s->mc_filter);
> > +	/* 
> > +	 * Set default mc filter to not filter out any mc addresses
> > +	 * as defined in the BNEP specification (revision 0.95a)
> > +	 * http://grouper.ieee.org/groups/802/15/Bluetooth/BNEP.pdf
> > +	 */
> > +	s->mc_filter = ~0LL;
> > #endif
> > 
> 
> Applying: Do not filter multicast addresses by default
> /data/kernel/maintainer-bluetooth-next/.git/rebase-apply/patch:15: trailing whitespace.
> 	/* 
> fatal: 1 line adds whitespace errors.
> Patch failed at 0001 Do not filter multicast addresses by default
> 
> And please prefix the subject line with Bluetooth:

There's also a missing Signed-off-by and the lines should be wrapped at
some 74 characters (right now it's basically a single line per
paragraph).

Johan