Fix for bug #39021: SELECT REGEXP BINARY NULL never returns

Problem: SELECT ... REGEXP BINARY NULL may lead to server crash/hang.

Fix: properly handle NULL regular expressions.

mysql-test/r/func_regexp.result

@@ -114,4 +114,16 @@ End of 4.1 tests
 SELECT 1 REGEXP NULL;
 1 REGEXP NULL
 NULL
+SELECT '' REGEXP BINARY NULL;
+'' REGEXP BINARY NULL
+NULL
+SELECT NULL REGEXP BINARY NULL;
+NULL REGEXP BINARY NULL
+NULL
+SELECT 'A' REGEXP BINARY NULL;
+'A' REGEXP BINARY NULL
+NULL
+SELECT "ABC" REGEXP BINARY NULL;
+"ABC" REGEXP BINARY NULL
+NULL
 End of 5.0 tests

mysql-test/t/func_regexp.test

@@ -64,4 +64,14 @@ drop table t1;
 
 SELECT 1 REGEXP NULL;
 
+
+#
+# Bug #39021: SELECT REGEXP BINARY NULL never returns
+#
+
+SELECT '' REGEXP BINARY NULL;
+SELECT NULL REGEXP BINARY NULL;
+SELECT 'A' REGEXP BINARY NULL;
+SELECT "ABC" REGEXP BINARY NULL;
+
 --echo End of 5.0 tests

sql/item_cmpfunc.cc

@@ -4341,8 +4341,20 @@ void Item_func_like::cleanup()
 
 #ifdef USE_REGEX
 
-bool
-Item_func_regex::regcomp(bool send_error)
+/**
+  @brief Compile regular expression.
+
+  @param[in]    send_error     send error message if any.
+
+  @details Make necessary character set conversion then 
+  compile regular expression passed in the args[1].
+
+  @retval    0     success.
+  @retval    1     error occurred.
+  @retval   -1     given null regular expression.
+ */
+
+int Item_func_regex::regcomp(bool send_error)
 {
   char buff[MAX_FIELD_WIDTH];
   String tmp(buff,sizeof(buff),&my_charset_bin);
@@ -4350,12 +4362,12 @@ Item_func_regex::regcomp(bool send_error)
   int error;
 
   if (args[1]->null_value)
-    return TRUE;
+    return -1;
 
   if (regex_compiled)
   {
     if (!stringcmp(res, &prev_regexp))
-      return FALSE;
+      return 0;
     prev_regexp.copy(*res);
     my_regfree(&preg);
     regex_compiled= 0;
@@ -4367,7 +4379,7 @@ Item_func_regex::regcomp(bool send_error)
     uint dummy_errors;
     if (conv.copy(res->ptr(), res->length(), res->charset(),
                   regex_lib_charset, &dummy_errors))
-      return TRUE;
+      return 1;
     res= &conv;
   }
 
@@ -4379,10 +4391,10 @@ Item_func_regex::regcomp(bool send_error)
       (void) my_regerror(error, &preg, buff, sizeof(buff));
       my_error(ER_REGEXP_ERROR, MYF(0), buff);
     }
-    return TRUE;
+    return 1;
   }
   regex_compiled= 1;
-  return FALSE;
+  return 0;
 }
 
 
@@ -4420,13 +4432,14 @@ Item_func_regex::fix_fields(THD *thd, Item **ref)
   const_item_cache=args[0]->const_item() && args[1]->const_item();
   if (!regex_compiled && args[1]->const_item())
   {
-    if (args[1]->null_value)
+    int comp_res= regcomp(TRUE);
+    if (comp_res == -1)
     {						// Will always return NULL
       maybe_null=1;
       fixed= 1;
       return FALSE;
     }
-    if (regcomp(TRUE))
+    else if (comp_res)
       return TRUE;
     regex_is_const= 1;
     maybe_null= args[0]->maybe_null;

sql/item_cmpfunc.h

@@ -1323,7 +1323,7 @@ class Item_func_regex :public Item_bool_func
   CHARSET_INFO *regex_lib_charset;
   int regex_lib_flags;
   String conv;
-  bool regcomp(bool send_error);
+  int regcomp(bool send_error);
 public:
   Item_func_regex(Item *a,Item *b) :Item_bool_func(a,b),
     regex_compiled(0),regex_is_const(0) {}