RE: [PATCH net-next v02 1/2] af_packet: allow fanout_add when socket is not RUNNING

[Willem de Bruijn <willemdebruijn.kernel@gmail.com>]

Gur Stavi wrote:
> > Gur Stavi wrote:
> > > >> @@ -1846,21 +1846,21 @@ static int fanout_add(struct sock *sk,
> > struct fanout_args *args)
> > > >>  	err = -EINVAL;
> > > >>
> > > >>  	spin_lock(&po->bind_lock);
> > > >> -	if (packet_sock_flag(po, PACKET_SOCK_RUNNING) &&
> > > >> -	    match->type == type &&
> > > >> +	if (match->type == type &&
> > > >>  	    match->prot_hook.type == po->prot_hook.type &&
> > > >>  	    match->prot_hook.dev == po->prot_hook.dev) {
> > > >
> > > > Remaining unaddressed issue is that the socket can now be added
> > > > before being bound. See comment in v1.
> > >
> > > I extended the psock_fanout test with unbound fanout test.
> > >
> > > As far as I understand, the easiest way to verify bind is to test that
> > > po->prot_hook.dev != NULL, since we are under a bind_lock anyway.
> > > But perhaps a more readable and direct approach to test "bind" would be
> > > to test po->ifindex != -1, as ifindex is commented as "bound device".
> > > However, at the moment ifindex is not initialized to -1, I can add such
> > > initialization, but perhaps I do not fully understand all the logic.
> > >
> > > Any preferences?
> > 
> > prot_hook.dev is not necessarily set if a packet socket is bound.
> > It may be bound to any device. See dev_add_pack and ptype_head.
> > 
> > prot_hook.type, on the other hand, must be set if bound and is only
> > modified with the bind_lock held too.
> > 
> > Well, and in packet_create. But setsockopt PACKET_FANOUT_ADD also
> > succeeds in case bind() was not called explicitly first to bind to
> > a specific device or change ptype.
> 
> Please clarify the last paragraph? When you say "also succeeds" do you
> mean SHOULD succeed or MAY SUCCEED by mistake if "something" happens ???

I mean it succeeds currently. Which behavior must then be maintained.
 
> Do you refer to the following scenario: socket is created with non-zero
> protocol and becomes RUNNING "without bind" for all devices. In that case
> it can be added to FANOUT without bind. Is that considered a bug or does
> the bind requirement for fanout only apply for all-protocol (0) sockets?

I'm beginning to think that this bind requirement is not needed.

All type and dev are valid, even if an ETH_P_NONE fanout group would
be fairly useless.

The type and dev must match that of the fanout group, and once added
to a fanout group can no longer be changed (bind will fail).

I briefy considered the reason might be max_num_members accounting.
Since f->num_members counts running sockets. But that is not used
when tracking membership of the group, sk_ref is. Every packet socket
whose po->rollover is increased increases this refcount.

> What about using ifindex to detect bind? Initialize it to -1 in
> packet_create and ensure that packet_do_bind, on success, sets it
> to device id or 0?
> 
> psock_fanout, should probably be extended with scenarios that test
> "all devices" and all/specific protocols. Any specific scenario
> suggestions?
> 
>