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Most functions of audioop takes as input a byte string (audio data) and a size argument (number of bytes of a sample). Functions don't check that the byte string length is a multiple of the size. It leads to read and write from/to uninitialised memory and might crash.
Example on writing into uninitilized memory:
 $ python -c "import audioop; audioop.reverse('X', 2)"
 Fatal Python error: Inconsistent interned string state.
 Abandon
It allocates a string of 1 byte and write 2 bytes into this string => memory corruption.
Attached patch creates audioop_check_size() and audioop_check_parameters() functions.

http://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2010-2089 claims that this issue is about security vulnerability. This problem seems to also affect at least Python 2.6.

The patch looks fine to me.
- Please could you add some tests, to exercise the 'not a whole number of frames' errors?
- The patch obviously predates the grand reindenting, so its indentation needs fixing up
PEP 7 nits:
 - Please don't put spaces just inside the parens in an 'if' statement: i.e., use "if (size != 1 ...)", not "if ( size != 1 ...)" (I notice that the "if ( x == NULL )" style is already prevalent, though not universal, in the module, though.)
 - the 'else' clause of an if should be at the start of the line (i.e.,
on a new line below the closing brace of the 'if', if present)
Is there any particular reason that Python 3.1 is not included in the versions?

@Mark: Here is the updated version of the patch including all of your remarks. I fixed 3 bugs in my patch: the checks of adpcm2lin(), alaw2lin() and audioop.ulaw2lin() were incomplete (len was not checked).
I added 3.1 to the version field.

The new patch looks fine to me.
This is rather last minute for 2.7, and I'm very uncomfortable committing anything substantial this close to the release. Still, if it's really a security vulnerability then it would be good to get it in.
For what it's worth, the code looks fine to me, and I've tested thoroughly; I can't see any reasons this could cause problems.
Raising priority to release blocker just to alert Benjamin to the issue, and get his permission to go ahead (or not) before the release.

The following error messages looks strange to me:
+ if (((len / size) & 1) != 0) {
+ PyErr_SetString(AudioopError, "not a whole number of frames");
+ return NULL;
+ }
Perhaps you meant "not an even number of frames"?

Well, that would depend on how you define a 'frame', I guess.

This issue is a security vulnerability referenced as CVE-2010-2089.
Fixed in 2.7 (r82492), 2.6 (r82494), 3.2 (r82495) and 3.1 (r82496).
--
> Perhaps you meant "not an even number of frames"?
Hum, no: the input data is a stereo sound track. A "frame" includes left and right channels.

It seems you introduced a reference leak, Victor.
http://mail.python.org/pipermail/python-checkins/2010-July/094756.html 

Fixed in r82527 (py3k), r82528 (release31-maint).