What to do on Warning: Tainted filename for search '/etc/exim4/virtual/some.domain?

Let’s suppose that once upon a time you had set up your aliases for virtual domains like this:

    # cat /etc/exim4/conf.d/router/350_exim4-config_vdom_aliases
    [...]
    vdom_aliases:
          driver = redirect
          allow_defer
          allow_fail
          domains = dsearch;/etc/exim4/virtual
          data = ${expand:${lookup{$local_part}lsearch*@{/etc/exim4/virtual/$domain}}}
          retry_use_local_part
          pipe_transport   = address_pipe
          file_transport   = address_file
    [...]

Upon upgrading your machine from Debian buster to Debian bullseye, following the upgrade release documentation you find out that this lookup will complain about tainted filename lookups:

# grep -i taint /var/log/exim4/*log
[...]
[...] Warning: Tainted filename for search '/etc/exim4/virtual/some.domain
[...]

What to do? Use the untainted variable $domain_data instead of $domain! Thus:

    # cat /etc/exim4/conf.d/router/350_exim4-config_vdom_aliases
    [...]
    vdom_aliases:
          [...]
          data = ${expand:${lookup{$local_part}lsearch*@{/etc/exim4/virtual/$domain_data}}}
          [...]

VoilĂ !