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patch #3347: Double free and memory loss probing partition table

Submitter:  Neal H. Walfield <neal>
Submitted:  Tue 07 Sep 2004 03:10:06 PM UTC
   
 
Category:  GNU Mach Priority:  7 - High
Status:  Done Privacy:  Public
Assigned to:  None Open/Closed:  Closed
Planned Release:  None
Wiki-like text discussion box: 


Tue 07 Sep 2004 03:10:06 PM UTC, original submission:  

While GNU Mach reads the partition table, the second assert in
linux/dev/glue:free_pages is triggered.  This particular assert checks
for double frees.
I have traced the problem back to getblk and __brelse: if linux_auto_config
is true (which it is when partitions are being probed), a static buffer
is used to hold the BH structure.  If getblk is called a second time
(i.e. before the first block is released), the buffer is overriden.
This results in a double free, a memory leak (as the buffer in the
first BH is never released) and a consistency problem as code which
uses the first buffer will now see different data.  This is the case
in linux/dev/drivers/block/genhd.c:msdos_partition which calls bread
then, before freeing the block, calls extended_partition which also
calls bread.  In reality, there is no reason to not use kalloc and
kfree here.  In kern/statup.c:setup_main, we see that vm_mem_bootstrap
which calls kmem_init is called long before
linux/dev/init/main.c:linux_init is invoked by i386/i386at/machine_init:machine_init.

This attached patch changes getblk and __brelse to always use kalloc
and kfree and adds asserts to kern/kalloc.c to make sure that kalloc,
kfree and kget are only called after kmem_init has been called.

Apply the patch using -p0

ChangeLog:

2004-09-07  Neal H. Walfield  <neal@cs.uml.edu>

  • linux/dev/glue/block.c (__brelse): Unconditionally kfree BH.

(getblk): Unconditionally kalloc BH.

  • kern/kalloc.c [!NDEBUG] (kalloc_init_called): New static

variable.
(kalloc_init): Assert that kalloc_init_called is zero.
[! NDEBUG] Set kalloc_init_called to 1 on success.
(kalloc): Assert that kalloc_init_called is non-zero.
(kget): Likewise.
(kfree): Likewise.


Neal H. Walfield <neal>
Group administrator

 

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Attached Files
file #7842:  double-free.diff added by neal (3KiB - text/x-patch)

 

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Follow 3 latest changes.

Date Changed by Updated Field Previous Value => Replaced by
2004-12-03 neal StatusNone Done
    Open/ClosedOpen Closed
2004-09-07 neal Attached File- Added double-free.diff, #3647

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