Bug#44332 my_xml_scan reads behind the end of buffer

Problem: the scanner function tested for strings "<![CDATA[" and
"-->" without checking input string boundaries, which led to valgrind's
"Conditional jump or move depends on uninitialised value(s)" error.

Fix: Adding boundary checking.

  @ mysql-test/r/xml.result
  @ mysql-test/t/xml.test
  Adding test

  @ strings/xml.c
  Adding a helper function my_xml_parser_prefix_cmp(),
  with input string boundary check.

1 files changed, 17 insertions, 6 deletions

diff --git a/strings/xml.c b/strings/xml.c
index f3cfaad54fa..dee9da2864c 100644
--- a/strings/xml.c
+++ b/strings/xml.c
@@ -106,6 +106,13 @@ static void my_xml_norm_text(MY_XML_ATTR *a)
 }
 
 
+static inline my_bool
+my_xml_parser_prefix_cmp(MY_XML_PARSER *p, const char *s, size_t slen)
+{
+  return (p->cur + slen > p->end) || memcmp(p->cur, s, slen);
+}
+
+
 static int my_xml_scan(MY_XML_PARSER *p,MY_XML_ATTR *a)
 {
   int lex;
@@ -123,16 +130,20 @@ static int my_xml_scan(MY_XML_PARSER *p,MY_XML_ATTR *a)
   a->beg=p->cur;
   a->end=p->cur;
   
-  if ((p->end - p->cur > 3) && !memcmp(p->cur,"<!--",4))
+  if (!my_xml_parser_prefix_cmp(p, C_STRING_WITH_LEN("<!--")))
   {
-    for (; (p->cur < p->end) && memcmp(p->cur, "-->", 3); p->cur++)
-    {}
-    if (!memcmp(p->cur, "-->", 3))
-      p->cur+=3;
+    for (; p->cur < p->end; p->cur++)
+    {
+      if (!my_xml_parser_prefix_cmp(p, C_STRING_WITH_LEN("-->")))
+      {
+        p->cur+= 3;
+        break;
+      }
+    }
     a->end=p->cur;
     lex=MY_XML_COMMENT;
   }
-  else if (!memcmp(p->cur, "<![CDATA[",9))
+  else if (!my_xml_parser_prefix_cmp(p, C_STRING_WITH_LEN("<![CDATA[")))
   {
     p->cur+= 9;
     for (; p->cur < p->end - 2 ; p->cur++)