This code crashes Python:

import io, mmap
io.BytesIO(b' ').readinto(memoryview(mmap.mmap(-1, 1, prot=mmap.PROT_READ)))

From what I can see, this issue is in memoryview and allows memoryview to export a readonly buffer as writable (because memoryview.getbuffer() removes the writable flag from flags before calling the underlying buffer).

This causes segfaults when using mmap. 

If a bytes object is used as the underlying buffer, it allows the bytes object to be changed.

Given this code:

import io
b=b"XXXX"
m=memoryview(b)
i=io.BytesIO(b'ZZZZ')
i.readinto(m)
print(b)
print(b == b"XXXX")

The output is:
b'ZZZZ'
True

I think this is due to interning.

Anyway, attached is a patch which hopefully fixes the issue + a test.

The patch produces a failure in test_getargs2, but that test is wrong and should be fixed:

======================================================================
ERROR: test_w_star (test.test_getargs2.Bytes_TestCase)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/antoine/py3k/__svn__/Lib/test/test_getargs2.py", line 385, in test_w_star
    self.assertEqual(getargs_w_star(memoryview(b'memoryview')), b'[emoryvie]')
TypeError: must be read-write buffer, not memoryview


I'm surprised no other test failures arise. I did add that line (which I commented with "XXX for whatever reason...") for a reason, but I don't remember which one. It seemed necessary at the time, I'm glad it isn't anymore.

So, about the patch itself: you should simply use assertRaises. There's no reason for readinto() not to fail with a TypeError (silent failure is wrong). Thank you.

Attached is an updated patch with a simpler test.

And a simple fix for the test_getargs2 test - it wraps the memoryview around a bytearray.

So, does "critical" mean "should be release blocker"?

> So, does "critical" mean "should be release blocker"?

It's up to you to decide. It's not a new bug AFAICT.

The patch looks trivial enough.  You're the memoryview guru, so if you have no doubts about it, I would say it can go in.

Patch with modified tests committed in r88097 (3.2), r88098 (3.1) and r88099 (2.7). Thank you!