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>37.5. Trusted and Untrusted PL/Perl</A
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><P
> Normally, PL/Perl is installed as a <SPAN
CLASS="QUOTE"
>"trusted"</SPAN
> programming
language named <TT
CLASS="LITERAL"
>plperl</TT
>. In this setup, certain Perl
operations are disabled to preserve security. In general, the
operations that are restricted are those that interact with the
environment. This includes file handle operations,
<TT
CLASS="LITERAL"
>require</TT
>, and <TT
CLASS="LITERAL"
>use</TT
> (for
external modules). There is no way to access internals of the
database server process or to gain OS-level access with the
permissions of the server process,
as a C function can do. Thus, any unprivileged database user may
be permitted to use this language.
</P
><P
> Here is an example of a function that will not work because file
system operations are not allowed for security reasons:
</P><PRE
CLASS="PROGRAMLISTING"
>CREATE FUNCTION badfunc() RETURNS integer AS $$
open(TEMP, ">/tmp/badfile");
print TEMP "Gotcha!\n";
return 1;
$$ LANGUAGE plperl;</PRE
><P>
The creation of the function will succeed, but executing it will not.
</P
><P
> Sometimes it is desirable to write Perl functions that are not
restricted. For example, one might want a Perl function that sends
mail. To handle these cases, PL/Perl can also be installed as an
<SPAN
CLASS="QUOTE"
>"untrusted"</SPAN
> language (usually called
<SPAN
CLASS="APPLICATION"
>PL/PerlU</SPAN
><A
NAME="AEN34285"
></A
>).
In this case the full Perl language is available. If the
<TT
CLASS="COMMAND"
>createlang</TT
> program is used to install the
language, the language name <TT
CLASS="LITERAL"
>plperlu</TT
> will select
the untrusted PL/Perl variant.
</P
><P
> The writer of a <SPAN
CLASS="APPLICATION"
>PL/PerlU</SPAN
> function must take care that the function
cannot be used to do anything unwanted, since it will be able to do
anything that could be done by a user logged in as the database
administrator. Note that the database system allows only database
superusers to create functions in untrusted languages.
</P
><P
> If the above function was created by a superuser using the language
<TT
CLASS="LITERAL"
>plperlu</TT
>, execution would succeed.
</P
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