[PATCH] Fix memory corruption in pygrub/fsimage python binding

["Daniel P. Berrange" <berrange@redhat.com>]

[-- Attachment #1: Type: text/plain, Size: 1456 bytes --]

In updating Fedora 7 to use Xen 3.0.4 we encountered a problem with the
use of pygrub - it would trigger a memory corruption report by glibc's 
free() routine having been given an invalid pointer. The pygrub process
is thus terminated with extreme prejudice by glibc with SIGABRT

After a little painful memory debugging in python I discovered that the
fsimage python binding is mistakenly using PyMem_DEL instead of PyObject_DEL
to deallocate its objects.

PyMem_DEL simply ends up in a #define to free(). The memory associated with
Python objects is not neccessarily allocated by malloc(), so calling free()
is bogus. Python keeps an internal memory pool from which it allocates
objects, so upon deallocation memory needs to be returned to this pool
rather than free'd.

As for why no one has hit this before I can only assume this is showing up
now because of ever stricted glibc memory checking, internal changes in 
python 2.5 memory handling, or a combo of both + a little good/bad luck

The attached patch corrects the fsimage binding to call PyObject_DEL.

   Signed-off-by: Daniel P. Berrange <berrange@redhat.com>

Regards,
Dan.
-- 
|=- Red Hat, Engineering, Emerging Technologies, Boston.  +1 978 392 2496 -=|
|=-           Perl modules: http://search.cpan.org/~danberr/              -=|
|=-               Projects: http://freshmeat.net/~danielpb/               -=|
|=-  GnuPG: 7D3B9505   F3C9 553F A1DA 4AC2 5648 23C1 B3DF F742 7D3B 9505  -=| 

[-- Attachment #2: pygrub-memcorruption.patch --]
[-- Type: text/plain, Size: 669 bytes --]

diff -r 82c306ad212e tools/pygrub/src/fsimage/fsimage.c
--- a/tools/pygrub/src/fsimage/fsimage.c	Thu Jan 25 10:34:17 2007 +0000
+++ b/tools/pygrub/src/fsimage/fsimage.c	Tue Jan 30 12:18:30 2007 -0500
@@ -125,7 +125,7 @@ fsimage_file_dealloc(fsimage_file_t *fil
 	if (file->file != NULL)
 		fsi_close_file(file->file);
 	Py_XDECREF(file->fs);
-	PyMem_DEL(file);
+	PyObject_DEL(file);
 }
 
 static char fsimage_file_type__doc__[] = "Filesystem image file";
@@ -226,7 +226,7 @@ fsimage_fs_dealloc (fsimage_fs_t *fs)
 {
 	if (fs->fs != NULL)
 		fsi_close_fsimage(fs->fs);
-	PyMem_DEL(fs);
+	PyObject_DEL(fs);
 }
 
 PyDoc_STRVAR(fsimage_fs_type__doc__, "Filesystem image");

[-- Attachment #3: Type: text/plain, Size: 138 bytes --]

_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xensource.com
http://lists.xensource.com/xen-devel