On Sun, Feb 23, 2025 at 05:59:49PM -0500, Jon Maloy wrote:
> When a local peer sends a UDP message to a non-existing port on an
> existing remote host, that host will return an ICMP message containing
> the error code ICMP_PORT_UNREACH, plus the header and the first eight
> bytes of the original message. If the sender socket has been connected,
> it uses this message to issue a "Connection Refused" event to the user.
> 
> Until now, we have only read such events from the externally facing
> socket, but we don't forward them back to the local sender because
> we cannot read the ICMP message directly to user space. Because of
> this, the local peer will hang and wait for a response that never
> arrives.
> 
> We now fix this for IPv4 by recreating and forwarding a correct ICMP
> message back to the internal sender. We synthesize the message based
> on the information in the extended error structure, plus the returned
> part of the original message body.
> 
> Note that for the sake of completeness, we even produce ICMP messages
> for other error codes. We have noticed that at least ICMP_PROT_UNREACH
> is propagated as an error event back to the user.
> 
> Signed-off-by: Jon Maloy <jmaloy@redhat.com>

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

With the exception of a formatting nit:

> +/**
> + * udp_send_conn_fail_icmp4() - Construct and send ICMP to local peer
> + * @c:	          Execution context
> + * @ee:	  Extended error descriptor
> + * @ref:	  epoll reference
> + * @in:	  First bytes (max 8) of original UDP message body
> + * @dlen:	  Length of the read part of original UDP message body

Many of these function comments are inconsistent on whether the
parameter descriptions are separated by spaces or tabs (it should be
tabs).

-- 
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