MySQL Bugs: #11909: mysql_stmt_attr_set CURSOR_TYPE_READ

Bug #11909	mysql_stmt_attr_set CURSOR_TYPE_READ_ONLY nested queries corrupt result
Submitted:	13 Jul 2005 11:24	Modified:	14 Aug 2005 0:39
Reporter:	Berto van de Kraats	Email Updates:
Status:	Closed	Impact on me:	None
Category:	MySQL Server	Severity:	S1 (Critical)
Version:	5.0.10-beta	OS:	Linux (Linux)
Assigned to:	Konstantin Osipov	CPU Architecture:	Any

Description:
If cursors are enabled, and queries on the same table are nested then the outer query returns corrupt data.

How to repeat:
Compile and run the attached program (which is an automatically generated trace of our mysql database driver). The problem reproduces if the program silently runs and has exit status 0.

The trace contains a call to mysql_stmt_fetch that returns corrupted data (search for pattern "ERROR:" in attached program).

Cpp trace of problem

Attachment: bug11909.cpp (text/plain), 29.68 KiB.

Another cpp trace of the problem

Attachment: bug11902.cpp (text/plain), 26.92 KiB.

Thanks for your excellent bug report Peter.  I was able to reproduce this bug using 5.0.10bk.

there is off-by-1 problem. the problem is that the pointer in the row advances one position more than needed and then the beginning of a text string is read as it's length and then the data is corrupted. when run in debugger and manually move the pointer with 1 byte behind everything is fine. I will continue investigating where exactly the problem is created.

assigning to me

A patch for this bug has been committed. After review, it may
be pushed to the relevant source trees for release in the next
version. You can access the patch from:

  http://lists.mysql.com/internals/27856

A patch for this bug has been committed. After review, it may
be pushed to the relevant source trees for release in the next
version. You can access the patch from:

  http://lists.mysql.com/internals/28000

Pushed into 5.0 tree, tagged 5.0.12

Noted in 5.0.12 changelog.