New submission from Richard Oudkerk:
A memoryview which does not own a reference to its base object can point to
freed or reallocated memory. For instance the following segfaults for me on
Windows and Linux.
import io
class File(io.RawIOBase):
def readinto(self, buf):
global view
view = buf
def readable(self):
return True
f = io.BufferedReader(File())
f.read(1) # get view of buffer used by BufferedReader
del f # deallocate buffer
view = view.cast('P')
L = [None] * len(view) # create list whose array has same size
# (this will probably coincide with view)
view[0] = 0 # overwrite first item with NULL
print(L[0]) # segfault: dereferencing NULL
I realize there are easier ways to make Python segfault, so maybe this should
not be considered a serious issue. But I think there should be some way of
guaranteeing that a memoryview will not try to access memory which has already
been freed.
In #15903 skrah proposed exposing memory_release() as PyBuffer_Release().
However, I don't think that would necessarily invalidate all exports of the
buffer.
Alternatively, one could incref the buffered reader object and set
mview->mbuf->obj to it. Maybe we could have
PyMemoryView_FromMemoryEx(char *mem, Py_ssize_t size, int flags, PyObject
*obj)
which guarantees that if obj is non-NULL then it will not be garbage collected
before the memoryview. This should *not* expose obj as an attribute of the
memoryview.
----------
messages: 170846
nosy: sbt, skrah
priority: normal
severity: normal
status: open
title: memoryview to freed memory can cause segfault
type: crash
versions: Python 3.4
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Python tracker <[email protected]>
<http://bugs.python.org/issue15994>
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