From 6fd8904108f23810699d3a242e3612c4ec2f9cf2 Mon Sep 17 00:00:00 2001
From: Nick Wellnhofer <wellnhofer@aevum.de>
Date: Sun, 22 Jan 2023 19:42:41 +0100
Subject: [PATCH] malloc-fail: Fix use-after-free in xmlParseStartTag2

Fix error handling in xmlCtxtGrowAttrs.

Found with libFuzzer, see #344.

Reference:https://github.com/GNOME/libxml2/commit/6fd8904108f23810699d3a242e3612c4ec2f9cf2
Conflict:NA
---
 parser.c | 26 +++++++++++---------------
 1 file changed, 11 insertions(+), 15 deletions(-)

diff --git a/parser.c b/parser.c
index 88f04e4..3aea3e2 100644
--- a/parser.c
+++ b/parser.c
@@ -1715,25 +1715,21 @@ xmlCtxtGrowAttrs(xmlParserCtxtPtr ctxt, int nr) {
     int *attallocs;
     int maxatts;
 
-    if (ctxt->atts == NULL) {
-	maxatts = 55; /* allow for 10 attrs by default */
-	atts = (const xmlChar **)
-	       xmlMalloc(maxatts * sizeof(xmlChar *));
-	if (atts == NULL) goto mem_error;
-	ctxt->atts = atts;
-	attallocs = (int *) xmlMalloc((maxatts / 5) * sizeof(int));
-	if (attallocs == NULL) goto mem_error;
-	ctxt->attallocs = attallocs;
-	ctxt->maxatts = maxatts;
-    } else if (nr + 5 > ctxt->maxatts) {
-	maxatts = (nr + 5) * 2;
-	atts = (const xmlChar **) xmlRealloc((void *) ctxt->atts,
+    if (nr + 5 > ctxt->maxatts) {
+	maxatts = ctxt->maxatts == 0 ? 55 : (nr + 5) * 2;
+	atts = (const xmlChar **) xmlMalloc(
 				     maxatts * sizeof(const xmlChar *));
 	if (atts == NULL) goto mem_error;
-	ctxt->atts = atts;
 	attallocs = (int *) xmlRealloc((void *) ctxt->attallocs,
 	                             (maxatts / 5) * sizeof(int));
-	if (attallocs == NULL) goto mem_error;
+	if (attallocs == NULL) {
+            xmlFree(atts);
+            goto mem_error;
+        }
+        if (ctxt->maxatts > 0)
+            memcpy(atts, ctxt->atts, ctxt->maxatts * sizeof(const xmlChar *));
+        xmlFree(ctxt->atts);
+	ctxt->atts = atts;
 	ctxt->attallocs = attallocs;
 	ctxt->maxatts = maxatts;
     }
-- 
2.27.0