Attempt to catch reads from a buffer that is relocated

* src/xml.c (parse_region): Add assertion to ensure buffer text is
not relocated while libxml2 is reading it.  (Bug#24764)

1 files changed, 9 insertions, 2 deletions

diff --git a/src/xml.c b/src/xml.c
index b1175d14a1a..1ef84bd917e 100644
--- a/src/xml.c
+++ b/src/xml.c
@@ -181,6 +181,7 @@ parse_region (Lisp_Object start, Lisp_Object end, Lisp_Object base_url,
   Lisp_Object result = Qnil;
   const char *burl = "";
   ptrdiff_t istart, iend, istart_byte, iend_byte;
+  unsigned char *buftext;
 
   xmlCheckVersion (LIBXML_VERSION);
 
@@ -200,18 +201,24 @@ parse_region (Lisp_Object start, Lisp_Object end, Lisp_Object base_url,
       burl = SSDATA (base_url);
     }
 
+  buftext = BYTE_POS_ADDR (istart_byte);
   if (htmlp)
-    doc = htmlReadMemory ((char *) BYTE_POS_ADDR (istart_byte),
+    doc = htmlReadMemory ((char *)buftext,
                           iend_byte - istart_byte, burl, "utf-8",
                           HTML_PARSE_RECOVER|HTML_PARSE_NONET|
                           HTML_PARSE_NOWARNING|HTML_PARSE_NOERROR|
                           HTML_PARSE_NOBLANKS);
   else
-    doc = xmlReadMemory ((char *) BYTE_POS_ADDR (istart_byte),
+    doc = xmlReadMemory ((char *)buftext,
                          iend_byte - istart_byte, burl, "utf-8",
                          XML_PARSE_NONET|XML_PARSE_NOWARNING|
                          XML_PARSE_NOBLANKS |XML_PARSE_NOERROR);
 
+  /* If the assertion below fails, malloc was called inside the above
+     libxml2 functions, and ralloc.c caused relocation of buffer text,
+     so we could have read from unrelated memory.  */
+  eassert (buftext == BYTE_POS_ADDR (istart_byte));
+
   if (doc != NULL)
     {
       Lisp_Object r = Qnil;