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

[Jon Maloy <jmaloy@redhat.com>]

On 2025-02-25 09:19, Stefano Brivio wrote:
> 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.
> 

For some reason I never receive a confirmation email when trying to 
create an account, nor any reset email in case I have one (not sure.)
Anyway, I´ll try to introduce some of this. The 1280 byte IPCv6 returned
data should be the easiest one.


///jon