I came across this by making a mistake, but it shouldn't crash:

rdmurray@hey:~/python/p32>touch temp
rdmurray@hey:~/python/p32>./python  
Python 3.2.3+ (3.2:e6952acd5a55+, Feb  2 2013, 15:04:21) 
[GCC 4.6.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> from email import message_from_binary_file as mb
>>> m = mb(open('temp'))
python: ./Modules/_io/textio.c:1454: textiowrapper_read_chunk: Assertion `((((((PyObject*)(input_chunk))->ob_type))->tp_flags & ((1L<<27))) != 0)' failed.
zsh: abort      ./python


This is a regression relative to 3.2.3:

Python 3.2.3 (default, Sep 16 2012, 16:35:39) 
[GCC 4.5.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> from email import message_from_binary_file as mb
>>> m = mb(open('temp'))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3.2/email/__init__.py", line 63, in
message_from_binary_file
    return BytesParser(*args, **kws).parse(fp)
  File "/usr/lib/python3.2/email/parser.py", line 124, in parse
    return self.parser.parse(fp, headersonly)
  File "/usr/lib/python3.2/email/parser.py", line 68, in parse
    data = fp.read(8192)
  File "/usr/lib/python3.2/encodings/ascii.py", line 26, in decode
    return codecs.ascii_decode(input, self.errors)[0]
TypeError: 'str' does not support the buffer interface

I see "TypeError: 'str' does not support the buffer interface" on current 3.2 and default.

It might not crash on a debug build.  I haven't tried that.

I mean, non-debug build.

OK, this happens in debug mode in 3.2.3, so it is not a regression.  Still something to be looked in to, since that assert presumably has a purpose.

There is a simpler crasher:

import io
io.TextIOWrapper(io.StringIO()).read(1)

Well, if a proper type check is made later, then the assert can go.
Also, the PyBytes_Size() result should be checked for error, which incidentally ensures the argument is a bytes object.

Crash is possible not only when reading from text files, but also when decoder 
returns a non-string or when decoder's state is not a bytes object. This is 
possible with malicious decoder and perhaps with some old not bytes-to-string 
decoder in stdlib codecs registry.

Here are patches for different versions.

Blocker for 3.2.4.

This bug exists also in 2.7.

I doubt about an exception type. On one hand, TypeError looks naturally here and exception of this type implicitly raised by Python implementation. On other hand, there is a precedent in __iter__() which raises IOError when readline() returns non-string.

TypeError should be the right exception here.

Yet one crasher, not fixed by my patch yet.

io.TextIOWrapper(io.BytesIO(b'a'), newline='\n', encoding='quopri_codec').read(1)

Sometimes it crashes (on non-debug build), sometimes raises an exception: "ValueError: character U+82228c0 is not in range [U+0000; U+10ffff]".

Here is an updated patch for 3.3+. An exception type changed to TypeError, fixed some new crashes, added tests. If it is good, I'll backport it to 3.2 and 2.7.

> Here is an updated patch for 3.3+. An exception type changed to
> TypeError, fixed some new crashes, added tests. If it is good, I'll
> backport it to 3.2 and 2.7.

Looks ok to me.

Here are patches for 3.2 and 2.7.

Note that due to unicode-str autoconversions 2.7 not always raises TypeError 
(sometimes it can do nor raise an exception, sometimes it raises 
UnicodeEncodeError). 2.7 tests are not so strong as 3.x tests.

New changeset 5655cdd3c010 by Serhiy Storchaka in branch '3.2':
Issue #17106: Fix a segmentation fault in io.TextIOWrapper when an underlying
http://hg.python.org/cpython/rev/5655cdd3c010

New changeset 0c4cc967a733 by Serhiy Storchaka in branch '3.3':
Issue #17106: Fix a segmentation fault in io.TextIOWrapper when an underlying
http://hg.python.org/cpython/rev/0c4cc967a733

New changeset 398bcdf55f92 by Serhiy Storchaka in branch 'default':
Issue #17106: Fix a segmentation fault in io.TextIOWrapper when an underlying
http://hg.python.org/cpython/rev/398bcdf55f92

New changeset 19a33ef3821d by Serhiy Storchaka in branch '2.7':
Issue #17106: Fix a segmentation fault in io.TextIOWrapper when an underlying
http://hg.python.org/cpython/rev/19a33ef3821d