Item12084: CGI.pm has a private class called CGITempFile which is use…

…d to hold a handle to a temporary file. The idea is that when the CGI object is reaped, the temporary files are automatically unlinked. However, when Sandbox::sysCommand is invoked - for example, by loading a topic before the uploads have been processed - a subprocess is created that gets a copy of the parent process, including these objects. When the subprocess terminates, the CGITempFiles are DESTROYed and the external files unlinked, leaving the parent process with pointers to non- existant temporary files. We solve this problem by patching the DESTROY method on CGITempFile so that the temporary files are only ever destroyed by the parent process, and never by the child. We do this by comparing the PID with a PID recorded when the CGI object is constructed. git-svn-id: http://svn.foswiki.org/trunk@16968 0b4bb1d4-4e5a-0410-9cc4-b2b747904278
foswiki · Oct 24, 2013 · b8a8c31 · b8a8c31
1 parent da0a18f
commit b8a8c31
Showing 1 changed file with 39 additions and 1 deletion.
diff --git a/core/lib/Foswiki/Engine/CGI.pm b/core/lib/Foswiki/Engine/CGI.pm
@@ -23,11 +23,44 @@ use Foswiki::Request         ();
 use Foswiki::Request::Upload ();
 use Foswiki::Response        ();
 
+# ****
+# CGI.pm has a private class called CGITempFile which is used to hold
+# a handle to a temporary file. The idea is that when the CGI object
+# is reaped, the temporary files are automatically unlinked. However,
+# when Sandbox::sysCommand is invoked - for example, by loading a topic
+# before the uploads have been processed - a subprocess is created that
+# gets a copy of the parent process, including these objects. When the
+# subprocess terminates, the CGITempFiles are DESTROYed and the external
+# files unlinked, leaving the parent process with pointers to non-
+# existant temporary files.
+#
+# We solve this problem by patching the DESTROY method on CGITempFile so
+# that the temporary files are only ever destroyed by the parent process,
+# and never by the child. We do this by comparing the PID with a PID
+# recorded when the CGI object is constructed.
+
+our $CONSTRUCTOR_PID;
+our $SAVE_DESTROY;
+eval {
+    # In an eval in case it's ever removed from CGI
+    $SAVE_DESTROY = \&CGITempFile::DESTROY;
+};
+if ( defined $SAVE_DESTROY ) {
+    no warnings 'redefine';
+    *CGITempFile::DESTROY = sub {
+        if ( $$ == $CONSTRUCTOR_PID ) {
+
+            # Parent process, unlink the temp file
+            &$SAVE_DESTROY(@_);
+        }
+    };
+}
+
 sub run {
     my $this = shift;
     my $req  = $this->prepare;
     unless ( $Foswiki::cfg{isVALID}
-        || $req->http('x-requested-with') eq 'XMLHttpRequest' )
+        || ( $req->http('x-requested-with') || '' ) eq 'XMLHttpRequest' )
     {
         print STDOUT "Content-type: text/html\n\n";
         print STDOUT '<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"'
@@ -153,6 +186,11 @@ sub prepareBody {
     my ( $this, $req ) = @_;
 
     return unless $ENV{CONTENT_LENGTH};
+
+    # Record the master process so we don't reap temp files in
+    # sub-processes (see long comment ****)
+    $CONSTRUCTOR_PID = $$;
+
     my $cgi = new CGI();
     my $err = $cgi->cgi_error;
     throw Foswiki::EngineException( $1, $2 )