BUG#14629727: USER_VAR_EVENT IS MISSING RANGE CHECKS

This bug had two problems:
 P1) Reads out of bounds;
 P2) Writes out of bounds.

PROBLEM P1
----------
User_var_log_event unmarshalling from binlog was not performing range
checks when using name_len and val_len variables to walk on event
buffer.

Added range checks to User_var_log_event unmarshalling to prevent
unmarshalling errors.

PROBLEM P2
----------
User_var_log_event value was allocated on thread stack, what caused
stack frame errors when User_var_log_event value was bigger than thread
stack size.

Currently value is allocated on heap memory.

sql/log_event.cc

@@ -1286,7 +1286,7 @@ Log_event* Log_event::read_log_event(const char* buf, uint event_len,
       ev = new Rand_log_event(buf, description_event);
       break;
     case USER_VAR_EVENT:
-      ev = new User_var_log_event(buf, description_event);
+      ev = new User_var_log_event(buf, event_len, description_event);
       break;
     case FORMAT_DESCRIPTION_EVENT:
       ev = new Format_description_log_event(buf, event_len, description_event);
@@ -5685,18 +5685,34 @@ void User_var_log_event::pack_info(Protocol* protocol)
 
 
 User_var_log_event::
-User_var_log_event(const char* buf,
+User_var_log_event(const char* buf, uint event_len,
                    const Format_description_log_event* description_event)
   :Log_event(buf, description_event)
 #ifndef MYSQL_CLIENT
   , deferred(false)
 #endif
 {
+  bool error= false;
+  const char* buf_start= buf;
   /* The Post-Header is empty. The Variable Data part begins immediately. */
   buf+= description_event->common_header_len +
     description_event->post_header_len[USER_VAR_EVENT-1];
   name_len= uint4korr(buf);
   name= (char *) buf + UV_NAME_LEN_SIZE;
+
+  /*
+    We don't know yet is_null value, so we must assume that name_len
+    may have the bigger value possible, is_null= True and there is no
+    payload for val.
+  */
+  if (0 == name_len ||
+      !valid_buffer_range<uint>(name_len, buf_start, name,
+                                event_len - UV_VAL_IS_NULL))
+  {
+    error= true;
+    goto err;
+  }
+
   buf+= UV_NAME_LEN_SIZE + name_len;
   is_null= (bool) *buf;
   if (is_null)
@@ -5708,13 +5724,31 @@ User_var_log_event(const char* buf,
   }
   else
   {
+    if (!valid_buffer_range<uint>(UV_VAL_IS_NULL + UV_VAL_TYPE_SIZE
+                                  + UV_CHARSET_NUMBER_SIZE + UV_VAL_LEN_SIZE,
+                                  buf_start, buf, event_len))
+    {
+      error= true;
+      goto err;
+    }
+
     type= (Item_result) buf[UV_VAL_IS_NULL];
     charset_number= uint4korr(buf + UV_VAL_IS_NULL + UV_VAL_TYPE_SIZE);
     val_len= uint4korr(buf + UV_VAL_IS_NULL + UV_VAL_TYPE_SIZE + 
 		       UV_CHARSET_NUMBER_SIZE);
     val= (char *) (buf + UV_VAL_IS_NULL + UV_VAL_TYPE_SIZE +
 		   UV_CHARSET_NUMBER_SIZE + UV_VAL_LEN_SIZE);
+
+    if (!valid_buffer_range<uint>(val_len, buf_start, val, event_len))
+    {
+      error= true;
+      goto err;
+    }
   }
+
+err:
+  if (error)
+    name= 0;
 }
 
 
@@ -5860,8 +5894,9 @@ void User_var_log_event::print(FILE* file, PRINT_EVENT_INFO* print_event_info)
       char *hex_str;
       CHARSET_INFO *cs;
 
-      if (!(hex_str= (char *)my_alloca(2*val_len+1+2))) // 2 hex digits / byte
-        break; // no error, as we are 'void'
+      hex_str= (char *)my_malloc(2*val_len+1+2,MYF(MY_WME)); // 2 hex digits / byte
+      if (!hex_str)
+        return;
       str_to_hex(hex_str, val, val_len);
       /*
         For proper behaviour when mysqlbinlog|mysql, we need to explicitely
@@ -5879,7 +5914,7 @@ void User_var_log_event::print(FILE* file, PRINT_EVENT_INFO* print_event_info)
         my_b_printf(&cache, ":=_%s %s COLLATE `%s`%s\n",
                     cs->csname, hex_str, cs->name,
                     print_event_info->delimiter);
-      my_afree(hex_str);
+      my_free(hex_str, MYF(MY_WME));
     }
       break;
     case ROW_RESULT:

sql/log_event.h

@@ -2496,7 +2496,7 @@ class User_var_log_event: public Log_event
   void print(FILE* file, PRINT_EVENT_INFO* print_event_info);
 #endif
 
-  User_var_log_event(const char* buf,
+  User_var_log_event(const char* buf, uint event_len,
                      const Format_description_log_event *description_event);
   ~User_var_log_event() {}
   Log_event_type get_type_code() { return USER_VAR_EVENT;}
@@ -2510,7 +2510,7 @@ class User_var_log_event: public Log_event
   bool is_deferred() { return deferred; }
   void set_deferred() { deferred= true; }
 #endif
-  bool is_valid() const { return 1; }
+  bool is_valid() const { return name != 0; }
 
 private:
 #if !defined(MYSQL_CLIENT) && defined(HAVE_REPLICATION)

sql/mysql_priv.h

@@ -501,6 +501,50 @@ class Default_object_creation_ctx : public Object_creation_ctx
 */
 #define MAX_TIME_ZONE_NAME_LENGTH       (NAME_LEN + 1)
 
+/*
+  Check how many bytes are available on buffer.
+
+  @param buf_start    Pointer to buffer start.
+  @param buf_current  Pointer to the current position on buffer.
+  @param buf_len      Buffer length.
+
+  @return             Number of bytes available on event buffer.
+*/
+template <class T> T available_buffer(const char* buf_start,
+                                      const char* buf_current,
+                                      T buf_len)
+{
+  return buf_len - (buf_current - buf_start);
+}
+/* Explicit instantion to unsigned int. */
+template unsigned int available_buffer<unsigned int>(const char*,
+                                                     const char*,
+                                                     unsigned int);
+
+/*
+  Check if jump value is within buffer limits.
+
+  @param jump         Number of positions we want to advance.
+  @param buf_start    Pointer to buffer start
+  @param buf_current  Pointer to the current position on buffer.
+  @param buf_len      Buffer length.
+
+  @return      True   If jump value is within buffer limits.
+               False  Otherwise.
+*/
+template <class T> bool valid_buffer_range(T jump,
+                                           const char* buf_start,
+                                           const char* buf_current,
+                                           T buf_len)
+{
+  return (jump <= available_buffer(buf_start, buf_current, buf_len));
+}
+/* Explicit instantion to unsigned int. */
+template bool valid_buffer_range<unsigned int>(unsigned int,
+                                               const char*,
+                                               const char*,
+                                               unsigned int);
+
 /* The rest of the file is included in the server only */
 #ifndef MYSQL_CLIENT