Fix double-free crash under Perl ithreads

RSA.pm

@@ -93,6 +93,8 @@ sub get_key_parameters {
 
 *get_public_key_pkcs1_string = \&get_public_key_string;
 
+sub CLONE_SKIP { 1 }
+
 unless ( defined &use_sslv23_padding ) {
     *use_sslv23_padding = sub {
         croak(  "use_sslv23_padding is not available: "
@@ -487,6 +489,15 @@ Return true if this is a private key, and false if it is public only.
 
 =back
 
+=head1 THREAD SAFETY
+
+This module defines C<CLONE_SKIP>, which means that
+C<Crypt::OpenSSL::RSA> objects become undefined in child threads
+created via C<threads-E<gt>create()>.  Each thread must construct its
+own key objects.  This prevents double-free crashes that would
+otherwise occur when both parent and child threads destroy the same
+underlying OpenSSL key structure.
+
 =head1 AUTHOR
 
 Ian Robertson, C<iroberts@cpan.org>.  For support, please email

t/threads.t

@@ -0,0 +1,41 @@
+use strict;
+use warnings;
+use Test::More;
+use Config;
+
+BEGIN {
+    if (!$Config{useithreads}) {
+        plan skip_all => 'perl not built with ithreads';
+    }
+    eval 'require threads; threads->import()';
+    if ($@) {
+        plan skip_all => "threads not available: $@";
+    }
+}
+use Crypt::OpenSSL::Random;
+use Crypt::OpenSSL::RSA;
+
+plan tests => 4;
+
+Crypt::OpenSSL::Random::random_seed("OpenSSL needs at least 32 bytes.");
+Crypt::OpenSSL::RSA->import_random_seed();
+
+ok(Crypt::OpenSSL::RSA->can('CLONE_SKIP'),
+    "CLONE_SKIP is defined");
+is(Crypt::OpenSSL::RSA->CLONE_SKIP, 1,
+    "CLONE_SKIP returns 1");
+
+my $rsa = Crypt::OpenSSL::RSA->generate_key(2048);
+my $pub_pem = $rsa->get_public_key_x509_string();
+
+my $thr = threads->create(sub {
+    my $child_rsa = Crypt::OpenSSL::RSA->generate_key(2048);
+    return $child_rsa->get_public_key_x509_string();
+});
+
+my $child_pub = $thr->join();
+ok(defined $child_pub && $child_pub =~ /^-----BEGIN PUBLIC KEY-----/,
+    "child thread can independently generate and export keys");
+
+ok($rsa->get_public_key_x509_string() eq $pub_pem,
+    "parent RSA object undamaged after child thread exit");