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Re: [Captive-portals] Signals from the network and ICMP

On Thu, May 17, 2018 at 10:00 AM Erik Kline <[email protected]> wrote:

> On Thu, 17 May 2018 at 08:17, Michael Richardson <[email protected]>
> wrote:

> > Erik Kline <[email protected]> wrote:
> >      > In the latter case especially, what becomes clear is that the UE
> needs
> >      > to be able to receive an unsolicited packet.  ICMP is a canonical
> >      > example of receiving and processing an unsolicited packet.  But
> >      > could also be something like a UDP socket listening on a well
> >      > port that receives a 1-byte datagram, which causes the UE to
> >      > (for rate-limiting purposes) a captive API query.

> > On POSIX systems, it's clearly a lot easier to open a UDP socket from an
> > unpriviledged application than to open an ICMP socket.

> > Is this a consideration for you?

> >      >     [3] NetworkMonitor already rate limits requests from
> applications
> >      > to revalidate the network, and these would likely be no different
> (or
> >      > pretty much the same).

> > Or would NetworkMonitor do this anyway, and it has all the priviledges
> > needs anyway?

> The fewer privilege escalation points the better, I suppose.  From that
> perspective a UDP socket may be less concerning, but perhaps not by much.
> NetworkMonitor has the appropriate privileges to do the needful,

I'll start off by admitting that this is a cheap shot, but:

I'm uncomfortable with the "let's have all machines which might possibly
connect to a network with a captive portal have a daemon listening on a
well-known UDP port" idea. Yes, it is very similar to "let's have all
machines which might possibly connect to a network with a captive portal
have a thingie watching for special ICMP messages", but somehow it feels
very different. Yes, I understand the irony of building networks based on
what makes Warren uncomfortable,  but...


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I don't think the execution is relevant when it was obviously a bad idea in
the first place.
This is like putting rabid weasels in your pants, and later expressing
regret at having chosen those particular rabid weasels and that pair of