epub: add NULL guards to prevent crashes with malformed EPUBsHEADmaster

EPUB files with missing or incomplete metadata (like no title or missing
navigation elements) can cause NULL pointer dereferences in the XML
parsing functions. This adds NULL checks to xml_parse_children_of_node,
get_child_list, and the TOC text parsing loop.

Fixes #707

1 files changed, 8 insertions, 1 deletions

diff --git a/backend/epub/epub-document.c b/backend/epub/epub-document.c
index 91e33faa..10b13d91 100644
--- a/backend/epub/epub-document.c
+++ b/backend/epub/epub-document.c
@@ -549,6 +549,9 @@ xml_parse_children_of_node(xmlNodePtr parent,
                            xmlChar* attributename,
                            xmlChar* attributevalue )
 {
+    if ( parent == NULL )
+        return;
+
     xmlNodePtr child = parent->xmlChildrenNode ;
 
     while ( child != NULL )
@@ -612,6 +615,8 @@ xml_get_data_from_node(xmlNodePtr node,
                        xmlChar* attributename)
 {
     xmlChar* datastring ;
+    if ( node == NULL )
+        return NULL;
     if ( rettype == XML_ATTRIBUTE )
        datastring= xmlGetProp(node,attributename);
     else
@@ -1178,6 +1183,8 @@ static GList*
 get_child_list(xmlNodePtr ol,gchar* documentdir)
 {
     GList *childlist = NULL;
+    if (ol == NULL)
+        return NULL;
     xmlNodePtr li = ol->xmlChildrenNode;
 
     while (li != NULL) {
@@ -1302,7 +1309,7 @@ setup_document_index(EpubDocument *epub_document,gchar *containeruri)
             xml_parse_children_of_node(navLabel,(xmlChar*)"text",NULL,NULL);
             linknode *newnode = g_new0(linknode,1);
             newnode->linktext = NULL;
-            while (newnode->linktext == NULL) {
+            while (newnode->linktext == NULL && xmlretval != NULL) {
                 newnode->linktext = (gchar*)xml_get_data_from_node(xmlretval,XML_KEYWORD,NULL);
                 xmlretval = xmlretval->next;
             }