Avoid overwriting modified DNS upon restore

[elias-pap]

In openvpn_disconnect(), "modify_dns revert_to_backup" is called to
restore DNS to the value backed-up by openvpn_connect(). However,
DNS might change after the backup and before a --disconnect is issued.
In that case, --disconnect causes a needless overwrite of DNS with an
old value, that might as well break the internet connection.

Use case:

• Client connects to protonvpn.
• Client changes access point. Internet connection breaks.
• Client issues a --disconnect to restore internet connection.
• Internet connection remains broken due to DNS overwrite.
  New --connect attempts will fail.

[Tamaranch]

There is a mistake at line 370 (Custom DNS). To avoid this and make the code more readable, both echo -e… should be replaced by cp "/etc/resolv.conf" "$(get_protonvpn_cli_home)/.resolv.conf.protonvpn_applied_backup"

[elias-pap]

There is a mistake at line 370 (Custom DNS).

Thanks for pointing that out.

To avoid this and make the code more readable, both echo -e… should be replaced by cp "/etc/resolv.conf" "$(get_protonvpn_cli_home)/.resolv.conf.protonvpn_applied_backup"

Not really, because someone might change the resolv.conf in between (although it is quite unlikely to happen). I guess tee is the best/cleaner solution.

[Tamaranch]

Yes, you're right! :)