socat gives error (read(6, 0xf97acc0, 8192): Permission denied)

I'm trying to use socat as a port mapper to map IPv4 connections to my OpenVPN server running behind a DS-Lite IPv6 cable connection.

//editI tried with a non root user and root. But I get the same result with both users.//edit

Goal is to be able to connect from my mobile phone via OpenVPN to my (IPv4) smart home devices.

From the server running socat I can ping6 my router at home. IPv6 port forwarding is enabled as well and forwards 1194/udp to the raspberry running the OpenVPN server at home.

Problem is now that I'm seeing an error from socat as I try to connect OpenVPN from my mobile.

root@scw-31f6c8:~/bin# socat -d -d UDP4-LISTEN:63530,fork UDP6:xxx.dynv6.net:11942017/12/27 13:53:01 socat[15428] N listening on UDP AF=2 0.0.0.0:635302017/12/27 13:53:07 socat[15428] N accepting UDP connection from AF=2 xx.xxx.xxx.xx:13192017/12/27 13:53:07 socat[15428] N forked off child process 154292017/12/27 13:53:07 socat[15428] N listening on UDP AF=2 0.0.0.0:635302017/12/27 13:53:07 socat[15429] N opening connection to AF=10 [2a02:810c:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx]:11942017/12/27 13:53:07 socat[15429] N successfully connected from local address AF=10 [2001:0bc8:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx]:416412017/12/27 13:53:07 socat[15429] N starting data transfer loop with FDs [5,5] and [6,6]2017/12/27 13:53:07 socat[15429] E read(6, 0xf97acc0, 8192): Permission denied2017/12/27 13:53:07 socat[15429] N exit(1)2017/12/27 13:53:07 socat[15428] N childdied(): handling signal 172017/12/27 13:53:07 socat[15428] W waitpid(): child 15429 exited with status 1

On first sight everything looks good until it hits read(6, 0xf97acc0, 8192): Permission denied.

Currently I cannot identify if this is a socat error on the server running it, or if it is related to a communication issue from socat to my IPv6 endpoint at home.

Any pointer on how to find out what's wrong?

//edit

I tried it as well on different machines (uberspace, scaleway) To be sure it is not related to a bad server side configuration. Might be an indicator that something is wrong on my end. But currently I don't see it.