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- Normally, PL/Perl is installed as a <span class="quote">“<span class="quote">trusted</span>”</span> programming
- language named <code class="literal">plperl</code>. 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,
- <code class="literal">require</code>, and <code class="literal">use</code> (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 can
- 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 $$
- my $tmpfile = "/tmp/badfile";
- open my $fh, '>', $tmpfile
- or elog(ERROR, qq{could not open the file "$tmpfile": $!});
- print $fh "Testing writing to a file\n";
- close $fh or elog(ERROR, qq{could not close the file "$tmpfile": $!});
- return 1;
- $$ LANGUAGE plperl;
- </pre><p>
- The creation of this function will fail as its use of a forbidden
- operation will be caught by the validator.
- </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">“<span class="quote">untrusted</span>”</span> language (usually called
- <span class="application">PL/PerlU</span><a id="id-1.8.10.13.5.3" class="indexterm"></a>).
- In this case the full Perl language is available. When installing the
- language, the language name <code class="literal">plperlu</code> 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
- <code class="literal">plperlu</code>, execution would succeed.
- </p><p>
- In the same way, anonymous code blocks written in Perl can use
- restricted operations if the language is specified as
- <code class="literal">plperlu</code> rather than <code class="literal">plperl</code>, but the caller
- must be a superuser.
- </p><div class="note"><h3 class="title">Note</h3><p>
- While <span class="application">PL/Perl</span> functions run in a separate Perl
- interpreter for each SQL role, all <span class="application">PL/PerlU</span> functions
- executed in a given session run in a single Perl interpreter (which is
- not any of the ones used for <span class="application">PL/Perl</span> functions).
- This allows <span class="application">PL/PerlU</span> functions to share data freely,
- but no communication can occur between <span class="application">PL/Perl</span> and
- <span class="application">PL/PerlU</span> functions.
- </p></div><div class="note"><h3 class="title">Note</h3><p>
- Perl cannot support multiple interpreters within one process unless
- it was built with the appropriate flags, namely either
- <code class="literal">usemultiplicity</code> or <code class="literal">useithreads</code>.
- (<code class="literal">usemultiplicity</code> is preferred unless you actually need
- to use threads. For more details, see the
- <span class="citerefentry"><span class="refentrytitle">perlembed</span></span> man page.)
- If <span class="application">PL/Perl</span> is used with a copy of Perl that was not built
- this way, then it is only possible to have one Perl interpreter per
- session, and so any one session can only execute either
- <span class="application">PL/PerlU</span> functions, or <span class="application">PL/Perl</span> functions
- that are all called by the same SQL role.
- </p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="plperl-global.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="plperl.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="plperl-triggers.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">44.4. Global Values in PL/Perl </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> 44.6. PL/Perl Triggers</td></tr></table></div></body></html>
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