Check for CaptureFileDialog::selectedFileType() failing.

Have it return WTAP_FILE_TYPE_SUBTYPE_UNKNOWN, rather than an
undecorated -1, if the hash table lookup fails.

Check for that as a return value, and pop up a "file an issue" dialog if
WTAP_FILE_TYPE_SUBTYPE_UNKNOWN is returned.

This should squelch Coverity CID 1473325; the error Coverity reports is
bogus, as negative file type/subtype values are check for before we try
to use them as suffixes, but this should catch the "this should not
happen" case that caused the error to pop up.

2 files changed, 51 insertions, 3 deletions

diff --git a/ui/qt/capture_file_dialog.cpp b/ui/qt/capture_file_dialog.cpp
index a5834cb2ca..51128a696d 100644
--- a/ui/qt/capture_file_dialog.cpp
+++ b/ui/qt/capture_file_dialog.cpp
@@ -625,7 +625,7 @@ void CaptureFileDialog::addMergeControls(QVBoxLayout &v_box) {
 }
 
 int CaptureFileDialog::selectedFileType() {
-    return type_hash_.value(selectedNameFilter(), -1);
+    return type_hash_.value(selectedNameFilter(), WTAP_FILE_TYPE_SUBTYPE_UNKNOWN);
 }
 
 wtap_compression_type CaptureFileDialog::compressionType() {
@@ -748,8 +748,22 @@ check_savability_t CaptureFileDialog::saveAs(QString &file_name, bool must_suppo
     connect(this, &QFileDialog::filterSelected, this, &CaptureFileDialog::fixFilenameExtension);
 
     if (WiresharkFileDialog::exec() && selectedFiles().length() > 0) {
+        int file_type;
+
         file_name = selectedFiles()[0];
-        return checkSaveAsWithComments(this, cap_file_, selectedFileType());
+        file_type = selectedFileType();
+        /* Is the file type bogus? */
+        if (file_type == WTAP_FILE_TYPE_SUBTYPE_UNKNOWN) {
+            /* This "should not happen". */
+            QMessageBox msg_dialog;
+
+            msg_dialog.setIcon(QMessageBox::Critical);
+            msg_dialog.setText(tr("Unknown file type returned by save as dialog."));
+            msg_dialog.setInformativeText(tr("Please report this as a Wireshark issue at https://gitlab.com/wireshark/wireshark/-/issues."));
+            msg_dialog.exec();
+            return CANCELLED;
+        }
+        return checkSaveAsWithComments(this, cap_file_, file_type);
     }
     return CANCELLED;
 }
@@ -784,8 +798,22 @@ check_savability_t CaptureFileDialog::exportSelectedPackets(QString &file_name,
     connect(this, &QFileDialog::filterSelected, this, &CaptureFileDialog::fixFilenameExtension);
 
     if (WiresharkFileDialog::exec() && selectedFiles().length() > 0) {
+        int file_type;
+
         file_name = selectedFiles()[0];
-        return checkSaveAsWithComments(this, cap_file_, selectedFileType());
+        file_type = selectedFileType();
+        /* Is the file type bogus? */
+        if (file_type == WTAP_FILE_TYPE_SUBTYPE_UNKNOWN) {
+            /* This "should not happen". */
+            QMessageBox msg_dialog;
+
+            msg_dialog.setIcon(QMessageBox::Critical);
+            msg_dialog.setText(tr("Unknown file type returned by save as dialog."));
+            msg_dialog.setInformativeText(tr("Please report this as a Wireshark issue at https://gitlab.com/wireshark/wireshark/-/issues."));
+            msg_dialog.exec();
+            return CANCELLED;
+        }
+        return checkSaveAsWithComments(this, cap_file_, file_type);
     }
     return CANCELLED;
 }
diff --git a/ui/qt/main_window.cpp b/ui/qt/main_window.cpp
index 9a13c1f901..24906c7ebd 100644
--- a/ui/qt/main_window.cpp
+++ b/ui/qt/main_window.cpp
@@ -1470,6 +1470,16 @@ bool MainWindow::saveAsCaptureFile(capture_file *cf, bool must_support_comments,
             return false;
         }
         file_type = save_as_dlg.selectedFileType();
+        if (file_type == WTAP_FILE_TYPE_SUBTYPE_UNKNOWN) {
+            /* This "should not happen". */
+            QMessageBox msg_dialog;
+
+            msg_dialog.setIcon(QMessageBox::Critical);
+            msg_dialog.setText(tr("Unknown file type returned by merge dialog."));
+            msg_dialog.setInformativeText(tr("Please report this as a Wireshark issue at https://gitlab.com/wireshark/wireshark/-/issues."));
+            msg_dialog.exec();
+            return false;
+	}
         compression_type = save_as_dlg.compressionType();
 
 #ifdef Q_OS_WIN
@@ -1604,6 +1614,16 @@ void MainWindow::exportSelectedPackets() {
         }
 
         file_type = esp_dlg.selectedFileType();
+        if (file_type == WTAP_FILE_TYPE_SUBTYPE_UNKNOWN) {
+            /* This "should not happen". */
+            QMessageBox msg_box;
+
+            msg_box.setIcon(QMessageBox::Critical);
+            msg_box.setText(tr("Unknown file type returned by export dialog."));
+            msg_box.setInformativeText(tr("Please report this as a Wireshark issue at https://gitlab.com/wireshark/wireshark/-/issues."));
+            msg_box.exec();
+            goto cleanup;
+	}
         compression_type = esp_dlg.compressionType();
 #ifdef Q_OS_WIN
         // the Windows dialog does not fixup extensions, do it manually here.