[libxml2] Handle dumps of corrupted documents more gracefully

[Nick Wellnhofer <nwellnhof src gnome org>]

commit 0b3c64d9f2f3e9ce1a98d8f19ee7a763c87e27d5
Author: Nick Wellnhofer <wellnhofer aevum de>
Date:   Tue Sep 29 18:08:37 2020 +0200

    Handle dumps of corrupted documents more gracefully
    
    Check parent pointers for NULL after the non-recursive rewrite of the
    serialization code. This avoids segfaults with corrupted documents
    which can apparently be seen with lxml, see issue #187.

 HTMLtree.c |  6 ++++++
 xmlsave.c  | 12 ++++++++++++
 2 files changed, 18 insertions(+)
---
diff --git a/HTMLtree.c b/HTMLtree.c
index cdb7f86a6..8d0c77957 100644
--- a/HTMLtree.c
+++ b/HTMLtree.c
@@ -903,6 +903,12 @@ htmlNodeDumpFormatOutput(xmlOutputBufferPtr buf, xmlDocPtr doc,
                 break;
             }
 
+            /*
+             * The parent should never be NULL here but we want to handle
+             * corrupted documents gracefully.
+             */
+            if (cur->parent == NULL)
+                return;
             cur = cur->parent;
 
             if ((cur->type == XML_HTML_DOCUMENT_NODE) ||
diff --git a/xmlsave.c b/xmlsave.c
index 2225628dc..61a40459b 100644
--- a/xmlsave.c
+++ b/xmlsave.c
@@ -1058,6 +1058,12 @@ xmlNodeDumpOutputInternal(xmlSaveCtxtPtr ctxt, xmlNodePtr cur) {
                 break;
             }
 
+            /*
+             * The parent should never be NULL here but we want to handle
+             * corrupted documents gracefully.
+             */
+            if (cur->parent == NULL)
+                return;
             cur = cur->parent;
 
             if (cur->type == XML_ELEMENT_NODE) {
@@ -1686,6 +1692,12 @@ xhtmlNodeDumpOutput(xmlSaveCtxtPtr ctxt, xmlNodePtr cur) {
                 break;
             }
 
+            /*
+             * The parent should never be NULL here but we want to handle
+             * corrupted documents gracefully.
+             */
+            if (cur->parent == NULL)
+                return;
             cur = cur->parent;
 
             if (cur->type == XML_ELEMENT_NODE) {