rpyc zerodeploy EOF during classic_connect (linux only)

[dweesy]

Hello! I would like to control a remote Linux server from my Mac using rpyc zerodeploy. However, rpyc zerodeploy appears to not work correctly on the linux machine. I tested this by writing a script (based on an rpyc test) that would ssh to localhost and print something. First, I ensured that ssh localhost worked password-free. On Mac (python 3.11.7, rpyc 5.3.1) the script worked, but on Linux (python 3.11.5 and 3.10.13, rpyc 5.3.1) it failed.

from rpyc.utils.zerodeploy import DeployedServer
from plumbum import SshMachine

rem = SshMachine("localhost")
with DeployedServer(rem) as dep:
    conn = dep.classic_connect()
    print(conn.modules.sys)
    func = conn.modules.os.getcwd
    print(func())
    conn.close()

I expect this to print something like:

<module 'sys' (built-in)>
/home/user/

However, when run on this Linux host, instead I observe an EOFError, indicating the sshd terminated the connection:

[user@host rpc_prototype]$ uname
Linux
[user@host rpc_prototype]$ uname -r
3.10.0-962.3.2.lve1.5.81.el7.x86_64

[user@host rpc_prototype]$ python3 rpyc_local.py 
Traceback (most recent call last):
  File "/home/user/rpyc_prototype/rpyc.py", line 10, in <module>
    conn = dep.classic_connect()
           ^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/.local/lib/python3.11/site-packages/rpyc/utils/zerodeploy.py", line 211, in classic_connect
    return rpyc.utils.classic.connect_stream(
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/.local/lib/python3.11/site-packages/rpyc/utils/classic.py", line 42, in connect_stream
    return factory.connect_stream(stream, SlaveService)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/.local/lib/python3.11/site-packages/rpyc/utils/factory.py", line 60, in connect_stream
    return connect_channel(Channel(stream), service=service, config=config)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/.local/lib/python3.11/site-packages/rpyc/utils/factory.py", line 48, in connect_channel
    return service._connect(channel, config)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/.local/lib/python3.11/site-packages/rpyc/core/service.py", line 106, in _connect
    self.on_connect(conn)
  File "/home/user/.local/lib/python3.11/site-packages/rpyc/core/service.py", line 215, in on_connect
    self._install(conn, conn.root)
                        ^^^^^^^^^
  File "/home/user/.local/lib/python3.11/site-packages/rpyc/core/protocol.py", line 751, in root
    self._remote_root = self.sync_request(consts.HANDLE_GETROOT)
                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/.local/lib/python3.11/site-packages/rpyc/core/protocol.py", line 718, in sync_request
    return _async_res.value
           ^^^^^^^^^^^^^^^^
  File "/home/user/.local/lib/python3.11/site-packages/rpyc/core/async_.py", line 106, in value
    self.wait()
  File "/home/user/.local/lib/python3.11/site-packages/rpyc/core/async_.py", line 51, in wait
    self._conn.serve(self._ttl)
  File "/home/user/.local/lib/python3.11/site-packages/rpyc/core/protocol.py", line 438, in serve
    data = self._channel.poll(timeout) and self._channel.recv()
                                           ^^^^^^^^^^^^^^^^^^^^
  File "/home/user/.local/lib/python3.11/site-packages/rpyc/core/channel.py", line 55, in recv
    header = self.stream.read(self.FRAME_HEADER.size)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/.local/lib/python3.11/site-packages/rpyc/core/stream.py", line 280, in read
    raise EOFError("connection closed by peer")
EOFError: connection closed by peer

I am certain that ssh localhost works correctly, same as on my Mac:

# Prove that passwordless login works on Linux host:
[user@host rpc_prototype]$ ssh localhost
[user@host ~]$ exit
logout
Connection to localhost closed.
[user@host rpc_prototype]$ 

Though the OpenSSL version seems old, it has been patched with security fixes up to 2023.

Here is ssh -v localhost:

[user@host ~]$ ssh -v localhost
OpenSSH_7.4p1, OpenSSL 1.0.2k-fips  26 Jan 2017
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 58: Applying options for *
debug1: Connecting to localhost [127.0.0.1] port 22.
debug1: Connection established.
debug1: identity file /home/user/.ssh/id_rsa type 1
debug1: key_load_public: No such file or directory
debug1: identity file /home/user/.ssh/id_rsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/user/.ssh/id_dsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/user/.ssh/id_dsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/user/.ssh/id_ecdsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/user/.ssh/id_ecdsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/user/.ssh/id_ed25519 type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/user/.ssh/id_ed25519-cert type -1
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_7.4
debug1: Remote protocol version 2.0, remote software version OpenSSH_7.4
debug1: match: OpenSSH_7.4 pat OpenSSH* compat 0x04000000
debug1: Authenticating to localhost:22 as 'user'
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: algorithm: curve25519-sha256
debug1: kex: host key algorithm: ecdsa-sha2-nistp256
debug1: kex: server->client cipher: [email protected] MAC: <implicit> compression: none
debug1: kex: client->server cipher: [email protected] MAC: <implicit> compression: none
debug1: kex: curve25519-sha256 need=64 dh_need=64
debug1: kex: curve25519-sha256 need=64 dh_need=64
debug1: expecting SSH2_MSG_KEX_ECDH_REPLY
debug1: Server host key: ecdsa-sha2-nistp256 SHA256:...
debug1: Host 'localhost' is known and matches the ECDSA host key.
debug1: Found key in /home/user/.ssh/known_hosts:1
debug1: rekey after 134217728 blocks
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: SSH2_MSG_NEWKEYS received
debug1: rekey after 134217728 blocks
debug1: SSH2_MSG_EXT_INFO received
debug1: kex_input_ext_info: server-sig-algs=<rsa-sha2-256,rsa-sha2-512>
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug1: Authentications that can continue: publickey,gssapi-keyex,gssapi-with-mic,password
debug1: Next authentication method: gssapi-keyex
debug1: No valid Key exchange context
debug1: Next authentication method: gssapi-with-mic
debug1: Unspecified GSS failure.  Minor code may provide more information
No Kerberos credentials available (default cache: FILE:/tmp/krb5cc_2212)

debug1: Unspecified GSS failure.  Minor code may provide more information
No Kerberos credentials available (default cache: FILE:/tmp/krb5cc_2212)

debug1: Next authentication method: publickey
debug1: Offering RSA public key: /home/user/.ssh/id_rsa
debug1: Server accepts key: pkalg rsa-sha2-512 blen 279
debug1: Authentication succeeded (publickey).
Authenticated to localhost ([127.0.0.1]:22).
debug1: channel 0: new [client-session]
debug1: Requesting [email protected]
debug1: Entering interactive session.
debug1: pledge: network
debug1: client_input_global_request: rtype [email protected] want_reply 0
debug1: Sending environment.
debug1: Sending env LANG = en_US.UTF-8