Re: [PATCH v3 0/2] Reconstruct ICMP headers for failed UDP connect

[David Gibson <david@gibson.dropbear.id.au>]

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On Thu, Feb 20, 2025 at 11:08:28AM -0500, Jon Maloy wrote:
> 
> 
> On 2025-02-19 22:47, David Gibson wrote:
> > On Wed, Feb 19, 2025 at 02:30:05PM -0500, Jon Maloy wrote:
> > > Reconstruct incoming ICMP headers for failed UDP connect and forward back
> > > to local peer.
> > > 
> > > v2: - Added patch breaking out udp header creation from function
> > >        tap_udp4_send().
> > >      - Updated the ICMP creation by using the new function.
> > >      - Added logics to find correct flow, depending on origin.
> > >      - All done after feedback from David Gibson.
> > > v3: - More changes after feedback from David Gibson.
> > 
> 
> [...]
> 
> > "listening" socket.
> > 
> > The only way I can see to fix this would be to create connect()ed
> > sockets for both ends of a flow when we establish it.  I _think_ we can
> > have the listening and connected socket concurrently (at least with
> > REUSEADDR) with the connect()ed socket taking priority when it
> > matches.
> > 
> > However, it does have a complication: there's a brief time window
> > between bind() and connect() on the new socket, when it might pick up
> > packets that should go to the original listening socket.  We'd need to
> > decide what to do with that case.
> > 
> > In any case, it kind of looks like there's not much point trying to
> > handle error events on the listening socket (beyond a debug()
> > message), since I'm not sure such events are ever delivered.
> > 
> 
> I eliminated the handling of listener sockets ICMPs in my latest
> version.

I think that makes sense for now.

> I can create a separate connected socket in a separate patch,
> if you agree that is the way to go.

That's reasonable.  Fwiw someone momentarily popped up on the IRC and
suggested trying to read MSG_ERRQUEUE for the listening sockets on
EPOLLIN events.  I don't know if that will do anything useful, but you
could try.

-- 
David Gibson (he or they)	| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you, not the other way
				| around.
http://www.ozlabs.org/~dgibson

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