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Question: `channel 2: open failed: unknown channel type: unsupported channel type` Enabling local (-L) and dynamic (-D) forwarding in addition to reverse (-R)
Hi, sorry if this isn't the right place to put this but I'm stumped. Additionally I'm a bit of a Go newbie, so if this is painfully obvious to everyone else I apologize again.
I'm trying to make an SSH application that supports SSH tunneling for forward (-L), reverse (-R), and dynamic / socks (-D).
The example from _examples/ssh-remoteforward/portforward.go works like a champ for setting up reverse tunnels but forward tunnels and dynamic tunnels keep failing as channel 2: open failed: unknown channel type: unsupported channel type. Below is an example of what happens. I'm using the example and a regular SSH client to cut out any extraneous details.
# go run _examples/ssh-remoteforward/portforward.go &
[1] 2314
# 2021/08/26 11:29:51 starting ssh server on port 2222...
# ssh -p 2222 -Nf localhost -R1234:127.0.0.1:4321
The authenticity of host '[localhost]:2222 ([::1]:2222)' can't be established.
RSA key fingerprint is SHA256:n9/o3zJo5iw4blSjOarZAVGt20/KUuT238Z5G6tz90Y.
Are you sure you want to continue connecting (yes/no/[fingerprint])? yes
Warning: Permanently added '[localhost]:2222' (RSA) to the list of known hosts.
2021/08/26 11:30:53 attempt to bind localhost 1234 granted
# nc -lvnp 4321 &
[2] 2408
# listening on [any] 4321 ...
# echo test | nc -nv 127.0.0.1 1234
(UNKNOWN) [127.0.0.1] 1234 (?) open
connect to [127.0.0.1] from (UNKNOWN) [127.0.0.1] 48602
test
^C
[2]+ Stopped nc -lvnp 4321
# pkill ssh
# netstat -antp | grep LIST
tcp6 0 0 :::2222 :::* LISTEN 2373/portforward
# ssh -p 2222 -Nf localhost -L5678:127.0.0.1:8765
# netstat -antp | grep LIST
tcp 0 0 127.0.0.1:5678 0.0.0.0:* LISTEN 2423/ssh
tcp6 0 0 ::1:5678 :::* LISTEN 2423/ssh
tcp6 0 0 :::2222 :::* LISTEN 2373/portforward
#
# nc -lvnp 8765 &
[3] 2428
# listening on [any] 8765 ...
# nc -nv 127.0.0.1 5678
(UNKNOWN) [127.0.0.1] 5678 (?) open
channel 2: open failed: unknown channel type: unsupported channel type
# pkill ssh
# ssh -p 2222 -Nf localhost -D1080
# curl -I http://google.com
curl: (52) Empty reply from server
HTTP/1.1 301 Moved Permanently
Location: http://www.google.com/
Content-Type: text/html; charset=UTF-8
Date: Thu, 26 Aug 2021 15:37:05 GMT
Expires: Sat, 25 Sep 2021 15:37:05 GMT
Cache-Control: public, max-age=2592000
Server: gws
Content-Length: 219
X-XSS-Protection: 0
X-Frame-Options: SAMEORIGIN
# curl -I --socks5-hostname localhost:1080 http://google.com
channel 2: open failed: unknown channel type: unsupported channel type
curl: (97) connection to proxy closed
The "direct-tcpip" channel handler seems to be missing from the example. Try adding ssh.DirectTCPIPHandler to ChannelHandlers to get local and dynamic forwarding working:
server := ssh.Server{
...
ChannelHandlers: map[string]ssh.ChannelHandler{
"direct-tcpip": ssh.DirectTCPIPHandler,
"session": ssh.DefaultSessionHandler,
},
...
}
