Block environment variable mutations from trusted PL/Perl.

Many process environment variables (e.g. PATH), bypass the containment
expected of a trusted PL.  Hence, trusted PLs must not offer features
that achieve setenv().  Otherwise, an attacker having USAGE privilege on
the language often can achieve arbitrary code execution, even if the
attacker lacks a database server operating system user.

To fix PL/Perl, replace trusted PL/Perl %ENV with a tied hash that just
replaces each modification attempt with a warning.  Sites that reach
these warnings should evaluate the application-specific implications of
proceeding without the environment modification:

  Can the application reasonably proceed without the modification?

    If no, switch to plperlu or another approach.

    If yes, the application should change the code to stop attempting
    environment modifications.  If that's too difficult, add "untie
    %main::ENV" in any code executed before the warning.  For example,
    one might add it to the start of the affected function or even to
    the plperl.on_plperl_init setting.

In passing, link to Perl's guidance about the Perl features behind the
security posture of PL/Perl.

Back-patch to v12 (all supported versions).

Andrew Dunstan and Noah Misch

Security: CVE-2024-10979

diff --git a/doc/src/sgml/plperl.sgml b/doc/src/sgml/plperl.sgml
index 25b1077ad73823657325cce36e6b2ded90e156bd..8007261d0224c84420abb9e19b64541fa301c2b6 100644 (file)
--- a/doc/src/sgml/plperl.sgml
+++ b/doc/src/sgml/plperl.sgml
@@ -1093,6 +1093,19 @@ $$ LANGUAGE plperl;
    be permitted to use this language.
   </para>
 
+  <warning>
+   <para>
+    Trusted PL/Perl relies on the Perl <literal>Opcode</literal> module to
+    preserve security.
+    Perl
+    <ulink url="https://perldoc.perl.org/Opcode#WARNING">documents</ulink>
+    that the module is not effective for the trusted PL/Perl use case.  If
+    your security needs are incompatible with the uncertainty in that warning,
+    consider executing <literal>REVOKE USAGE ON LANGUAGE plperl FROM
+    PUBLIC</literal>.
+   </para>
+  </warning>
+
   <para>
    Here is an example of a function that will not work because file
    system operations are not allowed for security reasons:

diff --git a/src/pl/plperl/GNUmakefile b/src/pl/plperl/GNUmakefile
index 3a6954ce60e504b8b783bc98628a5c62fffdf614..01588d016a0637a24c78c3ad8df5aa1e294e53b5 100644 (file)
--- a/src/pl/plperl/GNUmakefile
+++ b/src/pl/plperl/GNUmakefile
@@ -55,10 +55,10 @@ endif # win32
 
 SHLIB_LINK = $(perl_embed_ldflags)
 
-REGRESS_OPTS = --dbname=$(PL_TESTDB)
+REGRESS_OPTS = --dbname=$(PL_TESTDB) --dlpath=$(top_builddir)/src/test/regress
 REGRESS = plperl_setup plperl plperl_lc plperl_trigger plperl_shared \
        plperl_elog plperl_util plperl_init plperlu plperl_array \
-       plperl_call plperl_transaction
+       plperl_call plperl_transaction plperl_env
 # if Perl can support two interpreters in one backend,
 # test plperl-and-plperlu cases
 ifneq ($(PERL),)

diff --git a/src/pl/plperl/expected/plperl_env.out b/src/pl/plperl/expected/plperl_env.out
new file mode 100644 (file)
index 0000000..328a536
--- /dev/null
+++ b/src/pl/plperl/expected/plperl_env.out
@@ -0,0 +1,53 @@
+--
+-- Test the environment setting
+--
+-- directory path and dlsuffix are passed to us in environment variables
+\getenv libdir PG_LIBDIR
+\getenv dlsuffix PG_DLSUFFIX
+\set regresslib :libdir '/regress' :dlsuffix
+CREATE FUNCTION get_environ()
+   RETURNS text[]
+   AS :'regresslib', 'get_environ'
+   LANGUAGE C STRICT;
+-- fetch the process environment
+CREATE FUNCTION process_env () RETURNS text[]
+LANGUAGE plpgsql AS
+$$
+
+declare
+   res text[];
+   tmp text[];
+   f record;
+begin
+    for f in select unnest(get_environ()) as t loop
+         tmp := regexp_split_to_array(f.t, '=');
+         if array_length(tmp, 1) = 2 then
+            res := res || tmp;
+         end if;
+    end loop;
+    return res;
+end
+
+$$;
+-- plperl should not be able to affect the process environment
+DO
+$$
+   $ENV{TEST_PLPERL_ENV_FOO} = "shouldfail";
+   untie %ENV;
+   $ENV{TEST_PLPERL_ENV_FOO} = "testval";
+   my $penv = spi_exec_query("select unnest(process_env()) as pe");
+   my %received;
+   for (my $f = 0; $f < $penv->{processed}; $f += 2)
+   {
+      my $k = $penv->{rows}[$f]->{pe};
+      my $v = $penv->{rows}[$f+1]->{pe};
+      $received{$k} = $v;
+   }
+   unless (exists $received{TEST_PLPERL_ENV_FOO})
+   {
+      elog(NOTICE, "environ unaffected")
+   }
+
+$$ LANGUAGE plperl;
+WARNING:  attempted alteration of $ENV{TEST_PLPERL_ENV_FOO} at line 12.
+NOTICE:  environ unaffected

diff --git a/src/pl/plperl/plc_trusted.pl b/src/pl/plperl/plc_trusted.pl
index 41b9b6a3530d694e30d73d2d9008abaf5a5fcf38..cf7b4d9cea9f900feb08f318d04ae89537a8e4e6 100644 (file)
--- a/src/pl/plperl/plc_trusted.pl
+++ b/src/pl/plperl/plc_trusted.pl
@@ -30,3 +30,27 @@ require Carp;
 require Carp::Heavy;
 require warnings;
 require feature if $] >= 5.010000;
+
+#<<< protect next line from perltidy so perlcritic annotation works
+package PostgreSQL::InServer::WarnEnv; ## no critic (RequireFilenameMatchesPackage)
+#>>>
+
+use strict;
+use warnings;
+use Tie::Hash;
+our @ISA = qw(Tie::StdHash);
+
+sub STORE  { warn "attempted alteration of \$ENV{$_[1]}"; }
+sub DELETE { warn "attempted deletion of \$ENV{$_[1]}"; }
+sub CLEAR  { warn "attempted clearance of ENV hash"; }
+
+# Remove magic property of %ENV. Changes to this will now not be reflected in
+# the process environment.
+*main::ENV = {%ENV};
+
+# Block %ENV changes from trusted PL/Perl, and warn. We changed %ENV to just a
+# normal hash, yet the application may be expecting the usual Perl %ENV
+# magic. Blocking and warning avoids silent application breakage. The user can
+# untie or otherwise disable this, e.g. if the lost mutation is unimportant
+# and modifying the code to stop that mutation would be onerous.
+tie %main::ENV, 'PostgreSQL::InServer::WarnEnv', %ENV or die $!;

diff --git a/src/pl/plperl/sql/plperl_env.sql b/src/pl/plperl/sql/plperl_env.sql
new file mode 100644 (file)
index 0000000..4108f39
--- /dev/null
+++ b/src/pl/plperl/sql/plperl_env.sql
@@ -0,0 +1,58 @@
+--
+-- Test the environment setting
+--
+
+-- directory path and dlsuffix are passed to us in environment variables
+\getenv libdir PG_LIBDIR
+\getenv dlsuffix PG_DLSUFFIX
+
+\set regresslib :libdir '/regress' :dlsuffix
+
+CREATE FUNCTION get_environ()
+   RETURNS text[]
+   AS :'regresslib', 'get_environ'
+   LANGUAGE C STRICT;
+
+-- fetch the process environment
+
+CREATE FUNCTION process_env () RETURNS text[]
+LANGUAGE plpgsql AS
+$$
+
+declare
+   res text[];
+   tmp text[];
+   f record;
+begin
+    for f in select unnest(get_environ()) as t loop
+         tmp := regexp_split_to_array(f.t, '=');
+         if array_length(tmp, 1) = 2 then
+            res := res || tmp;
+         end if;
+    end loop;
+    return res;
+end
+
+$$;
+
+-- plperl should not be able to affect the process environment
+
+DO
+$$
+   $ENV{TEST_PLPERL_ENV_FOO} = "shouldfail";
+   untie %ENV;
+   $ENV{TEST_PLPERL_ENV_FOO} = "testval";
+   my $penv = spi_exec_query("select unnest(process_env()) as pe");
+   my %received;
+   for (my $f = 0; $f < $penv->{processed}; $f += 2)
+   {
+      my $k = $penv->{rows}[$f]->{pe};
+      my $v = $penv->{rows}[$f+1]->{pe};
+      $received{$k} = $v;
+   }
+   unless (exists $received{TEST_PLPERL_ENV_FOO})
+   {
+      elog(NOTICE, "environ unaffected")
+   }
+
+$$ LANGUAGE plperl;

diff --git a/src/test/regress/regress.c b/src/test/regress/regress.c
index ba3532a51e852b99d1ad8e6c520283474c3cbd71..6764589418e8197cf626ef42fe9cf052678275c4 100644 (file)
--- a/src/test/regress/regress.c
+++ b/src/test/regress/regress.c
@@ -639,6 +639,29 @@ make_tuple_indirect(PG_FUNCTION_ARGS)
        PG_RETURN_POINTER(newtup->t_data);
 }
 
+PG_FUNCTION_INFO_V1(get_environ);
+
+Datum
+get_environ(PG_FUNCTION_ARGS)
+{
+       extern char **environ;
+       int                     nvals = 0;
+       ArrayType  *result;
+       Datum      *env;
+
+       for (char **s = environ; *s; s++)
+               nvals++;
+
+       env = palloc(nvals * sizeof(Datum));
+
+       for (int i = 0; i < nvals; i++)
+               env[i] = CStringGetTextDatum(environ[i]);
+
+       result = construct_array(env, nvals, TEXTOID, -1, false, TYPALIGN_INT);
+
+       PG_RETURN_POINTER(result);
+}
+
 PG_FUNCTION_INFO_V1(regress_setenv);
 
 Datum