From: Date: August 12 2008 3:37pm
Subject: bzr commit into mysql-5.1 branch (mats:2669) Bug#37466
List-Archive: http://lists.mysql.com/commits/51416
X-Bug: 37466
Message-Id: <20080812133757.BF4F85BF30@mats-laptop>
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#At file:///home/bzr/b37466-mysql-5.1-bugteam/

 2669 Mats Kindahl	2008-08-12
      Bug #37466  	Adding field to Log_event header not backward compatible
      
      In order to be able to extend the common header, the length of the
      common header is given in the format description log event. This will
      allow any server reading an event to find the location of the post-
      header and data even if the common header is longer than expected by
      just adding the size of the common header given in the format
      description log event.
      
      However, in order to be read correctly, the common header of both
      the format description log event and rotate event has to be fixed
      at LOG_EVENT_MINIMAL_HEADER_LEN, which is 19. The value of LOG_
      EVENT_MINIMAL_HEADER_LEN may not change.
      
      If the common header is extended with new data, the header will grow
      beyond LOG_EVENT_MINIMAL_HEADER_LEN. However, the code for the format
      description and rotate event reads the size from the format description
      log event instead of just using the value LOG_EVENT_MINIMAL_HEADER_LEN,
      this subsequently will cause them to read bad data, leading to a crash or
      data corruption of some other form.
      
      This patch replace the read of the common header length from the format
      description log event with the constant LOG_EVENT_MINIMAL_HEADER_LEN in
      order to allow the common header to be extended with new fields.
modified:
  sql/log_event.cc

per-file messages:
  sql/log_event.cc
    Replacing the read of the common header length from the format description
    log events with the constant value LOG_EVENT_MINIMAL_HEADER_LEN.
=== modified file 'sql/log_event.cc'
--- a/sql/log_event.cc	2008-05-12 17:50:53 +0000
+++ b/sql/log_event.cc	2008-08-12 13:37:51 +0000
@@ -2696,7 +2696,13 @@ Start_log_event_v3::Start_log_event_v3(c
                                        *description_event)
   :Log_event(buf, description_event)
 {
-  buf+= description_event->common_header_len;
+  /*
+    The size of the common header for the Rotate_log_event,
+    Start_log_event_v3, and the Format_description_log_event has to be
+    fixed at LOG_EVENT_MINIMAL_HEADER_LEN and should not be read from
+    the description log event supplied.
+   */
+  buf+= LOG_EVENT_MINIMAL_HEADER_LEN;
   binlog_version= uint2korr(buf+ST_BINLOG_VER_OFFSET);
   memcpy(server_version, buf+ST_SERVER_VER_OFFSET,
 	 ST_SERVER_VER_LEN);
@@ -2947,7 +2953,13 @@ Format_description_log_event(const char*
                              description_event)
   :Start_log_event_v3(buf, description_event), event_type_permutation(0)
 {
-  DBUG_ENTER("Format_description_log_event::Format_description_log_event(char*,...)");
+  DBUG_ENTER("Format_description_log_event(char*,...)");
+  /*
+    The size of the common header for the Rotate_log_event,
+    Start_log_event_v3, and the Format_description_log_event has to be
+    fixed at LOG_EVENT_MINIMAL_HEADER_LEN and should not be read from
+    the description log event supplied.
+   */
   buf+= LOG_EVENT_MINIMAL_HEADER_LEN;
   if ((common_header_len=buf[ST_COMMON_HEADER_LEN_OFFSET]) < OLD_HEADER_LEN)
     DBUG_VOID_RETURN; /* sanity check */
@@ -4052,10 +4064,16 @@ Rotate_log_event::Rotate_log_event(const
   :Log_event(buf, description_event) ,new_log_ident(0), flags(DUP_NAME)
 {
   DBUG_ENTER("Rotate_log_event::Rotate_log_event(char*,...)");
-  // The caller will ensure that event_len is what we have at EVENT_LEN_OFFSET
-  uint8 header_size= description_event->common_header_len;
+  /*
+    The size of the common header for the Rotate_log_event,
+    Start_log_event_v3, and the Format_description_log_event has to be
+    fixed at LOG_EVENT_MINIMAL_HEADER_LEN and should not be read from
+    the description log event supplied.
+   */
+  uint8 header_size= LOG_EVENT_MINIMAL_HEADER_LEN;
   uint8 post_header_len= description_event->post_header_len[ROTATE_EVENT-1];
   uint ident_offset;
+  // The caller will ensure that event_len is what we have at EVENT_LEN_OFFSET
   if (event_len < header_size)
     DBUG_VOID_RETURN;
   buf += header_size;