Re: [PATCH v6 4/4] udp: create and send ICMPv6 to local peer when applicable

[Stefano Brivio <sbrivio@redhat.com>]

On Mon, 24 Feb 2025 14:24:47 -0500
Jon Maloy <jmaloy@redhat.com> 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 IPv6 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.

Have a look at https://bugs.passt.top/show_bug.cgi?id=63#c1 if you
haven't (I didn't really go through it).

While bug #63 is beyond the scope of this series, if you register an
account on the bug tracker you can be Cc'ed on comments.

-- 
Stefano