netdev - Re: [PATCHv4 net-next 16/16] sctp: enable udp tunneling socks

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Message-ID: <20201020211108.GF11030@localhost.localdomain>
Date:   Tue, 20 Oct 2020 18:11:08 -0300
From:   Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
To:     Xin Long <lucien.xin@...il.com>
Cc:     network dev <netdev@...r.kernel.org>, linux-sctp@...r.kernel.org,
        Neil Horman <nhorman@...driver.com>,
        Michael Tuexen <tuexen@...muenster.de>,
        davem <davem@...emloft.net>, Guillaume Nault <gnault@...hat.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Willem de Bruijn <willemdebruijn.kernel@...il.com>
Subject: Re: [PATCHv4 net-next 16/16] sctp: enable udp tunneling socks

On Tue, Oct 20, 2020 at 05:12:06PM +0800, Xin Long wrote:
> On Tue, Oct 20, 2020 at 6:15 AM Marcelo Ricardo Leitner
> <marcelo.leitner@...il.com> wrote:
> >
> > On Mon, Oct 19, 2020 at 08:25:33PM +0800, Xin Long wrote:
> > > --- a/Documentation/networking/ip-sysctl.rst
> > > +++ b/Documentation/networking/ip-sysctl.rst
> > > @@ -2640,6 +2640,12 @@ addr_scope_policy - INTEGER
> > >
> > >       Default: 1
> > >
> > > +udp_port - INTEGER
> >
> > Need to be more verbose here, and also mention the RFC.
> >
> > > +     The listening port for the local UDP tunneling sock.
> >         , shared by all applications in the same net namespace.
> > > +     UDP encapsulation will be disabled when it's set to 0.
> >
> >         "Note, however, that setting just this is not enough to actually
> >         use it. ..."
> When it's a client, yes,  but when it's a server, the encap_port can
> be got from the incoming packet.
> 
> >
> > > +
> > > +     Default: 9899
> > > +
> > >  encap_port - INTEGER
> > >       The default remote UDP encapsalution port.
> > >       When UDP tunneling is enabled, this global value is used to set
> >
> > When is it enabled, which conditions are needed? Maybe it can be
> > explained only in the one above.
> Thanks!
> pls check if this one will be better:

It is. Verbose enough now, thx.
(one other comment below)

> 
> udp_port - INTEGER
> 
> The listening port for the local UDP tunneling sock.
> 
> This UDP sock is used for processing the incoming UDP-encapsulated
> SCTP packets (from RFC6951), and shared by all applications in the
> same net namespace. This UDP sock will be closed when the value is
> set to 0.
> 
> The value will also be used to set the src port of the UDP header
> for the outgoing UDP-encapsulated SCTP packets. For the dest port,
> please refer to 'encap_port' below.
> 
> Default: 9899

I'm now wondering if this is the right default. I mean, it is the
standard port for it, yes, but at the same time, it means loading SCTP
module will steal/use that UDP port on all net namespaces and can lead
to conflicts with other apps. A more conservative approach here is to
document the standard port, but set the default to 0 and require the
user to set it in if it is expected to be used.

Did FreeBSD enable it by default too?