Source: https://blogs.msdn.microsoft.com/commandline/2018/01/12/chmod-chown-wsl-improvements/

sudo umount /mnt/c
sudo mount -t drvfs C: /mnt/c -o metadata
 
sudo chmod 600 .ssh/id_rsa
sudo chowin $USER .ssh/id_rsa

Source: https://www.jetbrains.com/help/pycharm/configuring-remote-interpreters-via-wsl.html

Modern Windows installations may have built-in SSH server that has to be stopped, because it prevents OpenSSH from listening to port 22.

For example, from the elevated powershell one may run:

Get-Service -Name ssh* | Stop-Service -Force
Get-Service -Name ssh* | Set-Service -StartupType Disabled

If you get a message “Could not load host key: /etc/ssh/ssh_host_rsa_key”, you may need to regenerate keys. In bash prompt type

sudo ssh-keygen -A