mkv: detect parent overrun after the header parsing

symphonia-format-mkv/src/ebml.rs

@@ -544,9 +544,16 @@ impl<R: ReadEbml, S: EbmlSchema> EbmlIterator<R, S> {
             return Err(EbmlError::UnexpectedElement);
         }
 
-        // It is invalid for a child element's end position to exceed its parent's end position.
-        // The element may be discarded in such cases.
+        // perform checks after the header parsing
         if let Some(parent_end) = parent_end {
+            // The parent element was overrun. This can happen during header parsing
+            if self.reader.pos() > parent_end {
+                log::warn!("overran parent element by {} bytes", self.reader.pos() - parent_end);
+                return Err(EbmlError::Overrun);
+            }
+
+            // It is invalid for a child element's end position to exceed its parent's end position.
+            // The element may be discarded in such cases.
             if let Some(child_end) = header.end() {
                 if child_end > parent_end {
                     // TODO: Maybe scan for other elements instead of skipping to the end of the