netdev - Re: [PATCH v2] net: introduce ip_local_unbindable

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Message-ID: <20191212180459.687adf9c@cakuba.netronome.com>
Date:   Thu, 12 Dec 2019 18:04:59 -0800
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     subashab@...eaurora.org
Cc:     Lorenzo Colitti <lorenzo@...gle.com>,
        Maciej Żenczykowski 
        <zenczykowski@...il.com>, "David S . Miller" <davem@...emloft.net>,
        Linux Network Development Mailing List 
        <netdev@...r.kernel.org>,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        Sean Tranchetti <stranche@...eaurora.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Linux SCTP <linux-sctp@...r.kernel.org>
Subject: Re: [PATCH v2] net: introduce ip_local_unbindable_ports sysctl

On Thu, 12 Dec 2019 18:53:19 -0700, subashab@...eaurora.org wrote:
> On 2019-12-12 17:57, Lorenzo Colitti wrote:
> > On Fri, Dec 13, 2019 at 9:47 AM Jakub Kicinski wrote:  
> >> How are the ports which get reserved communicated between the baseband
> >> and the AP? Is this part of the standard? Is the driver that talks to
> >> the base band in the user space and it knows which ports to reserve
> >> statically? Or does the modem dynamically request ports to
> >> reserve/inform the host of ports in use?  
> > 
> > I'm not an expert in that part of the system, but my understanding is
> > that the primary way this is used is to pre-allocate a block of ports
> > to be used by the modem on boot, before other applications can bind to
> > ports. Subash, do you have more details?  
> 
> AFAIK these ports are randomly picked and not from a standard.
> Userspace gets this information through qrtr during boot.
> 
> Atleast in our case, there cannot be any existing user of these ports
> since these ports are blocked prior to mobile connection establishment.

Not even a listening socket?

> We could call SOCK_DIAG_DESTROY on these ports from userspace as a
> precaution as applications would gracefully handle the socket errors.

Right, or kernel could walk them, since presumably every application
using this functionality should do it, anyway? But no strong feeling 
on this if nobody else feels this is needed.