MDEV-12982 JSON_EXTRACT returns data for invalid JSON.

        Let's check the validity to the end of the JSON.

mysql-test/r/func_json.result

@@ -669,3 +669,8 @@ JSON_EXTRACT('{\"asdf\":true}', "$.\"asdf\"") = 1
 select JSON_EXTRACT('{\"input1\":\"\\u00f6\"}', '$.\"input1\"');
 JSON_EXTRACT('{\"input1\":\"\\u00f6\"}', '$.\"input1\"')
 "\u00f6"
+select JSON_EXTRACT('{"foo": "bar" foobar foo invalid ', '$.foo');
+JSON_EXTRACT('{"foo": "bar" foobar foo invalid ', '$.foo')
+NULL
+Warnings:
+Warning	4038	Syntax error in JSON text in argument 1 to function 'json_extract' at position 15

mysql-test/t/func_json.test

@@ -317,3 +317,8 @@ select JSON_EXTRACT('{\"asdf\":true}', "$.\"asdf\"") = false;
 select JSON_EXTRACT('{\"asdf\":true}', "$.\"asdf\"") = 1;
 select JSON_EXTRACT('{\"input1\":\"\\u00f6\"}', '$.\"input1\"');
 
+#
+# MDEV-129892 JSON_EXTRACT returns data for invalid JSON
+#
+select JSON_EXTRACT('{"foo": "bar" foobar foo invalid ', '$.foo');
+

sql/item_jsonfunc.cc

@@ -821,7 +821,11 @@ String *Item_func_json_extract::read_json(String *str,
     not_first_value= 1;
 
     if (!possible_multiple_values)
+    {
+      /* Loop to the end of the JSON just to make sure it's valid. */
+      while (json_get_path_next(&je, &p) == 0) {}
       break;
+    }
   }
 
   if (je.s.error)