Qt: fix crash on dragging in packet dialog

"packet_dialog.cpp" does not use setCaptureFile, resulting in a NULL
dereference while trying to obtain the dissection context. Apply a fix
similar to v2.5.1rc0-121-g9198448f9d (pass a fixed dissection context to
ProtoTree). Additionally, fix a memleak and correct documentation.

Why not add "proto_tree_->setCaptureFile(cap_file_.capFile())" in
PacketDialog? Well, it also uses "proto_tree_->setRootNode(edt_.tree)"
which means that "cf_->edt" would be different from "edt_". If that is
the case, then "proto_construct_match_selected_string" will not return a
filter for FT_NONE fields (see the call chain in proto.c).

Bug: 14620
Change-Id: I6eeaf32b650a2095e15f64bbe64b54cdd545c7a9
Fixes: v2.5.0rc0-1608-g4d6454e180 ("Qt: Drag n Drop Filter expression from Packet Tree")
Reviewed-on: https://code.wireshark.org/review/27160
Petri-Dish: Peter Wu <peter@lekensteyn.nl>
Reviewed-by: Roland Knall <rknall@gmail.com>
Tested-by: Petri Dish Buildbot
Reviewed-by: Peter Wu <peter@lekensteyn.nl>

3 files changed, 17 insertions, 6 deletions

diff --git a/ui/qt/packet_dialog.cpp b/ui/qt/packet_dialog.cpp
index 3d6a4fc375..e35ec88885 100644
--- a/ui/qt/packet_dialog.cpp
+++ b/ui/qt/packet_dialog.cpp
@@ -69,7 +69,9 @@ PacketDialog::PacketDialog(QWidget &parent, CaptureFile &cf, frame_data *fdata)
                      fdata, &(cap_file_.capFile()->cinfo));
     epan_dissect_fill_in_columns(&edt_, TRUE, TRUE);
 
-    proto_tree_ = new ProtoTree(ui->packetSplitter);
+    proto_tree_ = new ProtoTree(ui->packetSplitter, &edt_);
+    // Do not call proto_tree_->setCaptureFile, ProtoTree only needs the
+    // dissection context.
     proto_tree_->setRootNode(edt_.tree);
 
     byte_view_tab_ = new ByteViewTab(ui->packetSplitter, &edt_);
diff --git a/ui/qt/proto_tree.cpp b/ui/qt/proto_tree.cpp
index 5d5f7509ac..26ffa2d38a 100644
--- a/ui/qt/proto_tree.cpp
+++ b/ui/qt/proto_tree.cpp
@@ -33,12 +33,13 @@
 // To do:
 // - Fix "apply as filter" behavior.
 
-ProtoTree::ProtoTree(QWidget *parent) :
+ProtoTree::ProtoTree(QWidget *parent, epan_dissect_t *edt_fixed) :
     QTreeView(parent),
     proto_tree_model_(new ProtoTreeModel(this)),
     decode_as_(NULL),
     column_resize_timer_(0),
-    cap_file_(NULL)
+    cap_file_(NULL),
+    edt_(edt_fixed)
 {
     setAccessibleName(tr("Packet details"));
     // Leave the uniformRowHeights property as-is (false) since items might
@@ -518,12 +519,16 @@ const QString ProtoTree::toString(const QModelIndex &start_idx) const
 
 void ProtoTree::setCaptureFile(capture_file *cf)
 {
+    // For use by the main view, set the capture file which will later have a
+    // dissection (EDT) ready.
+    // The packet dialog sets a fixed EDT context and MUST NOT use this.
+    Q_ASSERT(edt_ == NULL);
     cap_file_ = cf;
 }
 
 bool ProtoTree::eventFilter(QObject * obj, QEvent * event)
 {
-    if ( cap_file_ && event->type() != QEvent::MouseButtonPress && event->type() != QEvent::MouseMove )
+    if ( event->type() != QEvent::MouseButtonPress && event->type() != QEvent::MouseMove )
         return QTreeView::eventFilter(obj, event);
 
     /* Mouse was over scrollbar, ignoring */
@@ -554,7 +559,10 @@ bool ProtoTree::eventFilter(QObject * obj, QEvent * event)
                 emit fieldSelected(&finfo);
                 selectionModel()->select(idx, QItemSelectionModel::ClearAndSelect);
 
-                QString filter = QString(proto_construct_match_selected_string(finfo.fieldInfo(), cap_file_->edt));
+                epan_dissect_t *edt = cap_file_ ? cap_file_->edt : edt_;
+                char *field_filter = proto_construct_match_selected_string(finfo.fieldInfo(), edt);
+                QString filter(field_filter);
+                wmem_free(NULL, field_filter);
 
                 if ( filter.length() > 0 )
                 {
diff --git a/ui/qt/proto_tree.h b/ui/qt/proto_tree.h
index 9dada379eb..6ed2e6ebb5 100644
--- a/ui/qt/proto_tree.h
+++ b/ui/qt/proto_tree.h
@@ -29,7 +29,7 @@ class ProtoTree : public QTreeView
 {
     Q_OBJECT
 public:
-    explicit ProtoTree(QWidget *parent = 0);
+    explicit ProtoTree(QWidget *parent = 0, epan_dissect_t *edt_fixed = 0);
     QMenu *colorizeMenu() { return &colorize_menu_; }
     void setRootNode(proto_node *root_node);
     void emitRelatedFrame(int related_frame, ft_framenum_type_t framenum_type = FT_FRAMENUM_NONE);
@@ -62,6 +62,7 @@ private:
     QPoint drag_start_position_;
 
     capture_file *cap_file_;
+    epan_dissect_t *edt_;
 
     void saveSelectedField(QModelIndex &index);
     static void foreachTreeNode(proto_node *node, gpointer proto_tree_ptr);