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gh-92888: Fix memoryview bad __index__ use after free #92946

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Jun 17, 2022
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gh-92888: Fix memoryview bad __index__ use after free #92946

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73ffb29
Fix memoryview bad `__index__` use after free
Fidget-Spinner May 19, 2022
3581de7
📜🤖 Added by blurb_it.
blurb-it[bot] May 19, 2022
43c66d6
stylistic nits
Fidget-Spinner May 19, 2022
18b921f
Merge branch 'fix_memoryview_auf' of https://github.com/Fidget-Spinne…
Fidget-Spinner May 20, 2022
2f3c04f
Fix whitespace
Fidget-Spinner May 21, 2022
a250b02
Use more comprehensive tests by Serhiy
Fidget-Spinner May 23, 2022
c818990
Add more tests by Serhiy
Fidget-Spinner May 23, 2022
42a706c
Fix newline
Fidget-Spinner May 23, 2022
b650764
Fix for tuple index
Fidget-Spinner May 23, 2022
47bd91f
Address review
Fidget-Spinner May 23, 2022
6890713
Address Victor's review
Fidget-Spinner May 29, 2022
d3edf74
re-add ba=None
Fidget-Spinner May 30, 2022
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96 changes: 96 additions & 0 deletions Lib/test/test_memoryview.py
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Original file line number Diff line number Diff line change
Expand Up @@ -545,6 +545,102 @@ def test_pickle(self):
with self.assertRaises(TypeError):
pickle.dumps(m, proto)

def test_use_released_memory(self):
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# gh-92888: Previously it was possible to use a memoryview even after
# backing buffer is freed in certain cases. This tests that those
# cases raise an exception.
size = 128
def release():
m.release()
nonlocal ba
ba = bytearray(size)
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That's useless, no?

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No, we need it for tests below that tests indexing into ba[].

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We allocate a bytearray of the same size as the bytearray just released in memoryview in hope that it will be allocated at the same memory. It helps to check that we do nor read/write a freed memory.

class MyIndex:
def __index__(self):
release()
return 4
class MyFloat:
def __float__(self):
release()
return 4.25
class MyBool:
def __bool__(self):
release()
return True

m = memoryview(bytearray(b'\xff'*size))
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In my PR, I tried to make the code more generic to test more cases: https://github.com/python/cpython/pull/93127/files#diff-d41c6bb40a1e03fea5a20d15c4077413e0ddde65651147922b625b03a66a2f16R399:

        tp = self.rw_type
        b = self.rw_type(self._source)
        view = self._view(b)

with self.assertRaises(ValueError):
m[MyIndex()]
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This test is very long. Can you try to factorize similar code and use loop with subTest(), and put pack operations in one test method and unpack in another test method?

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Then we will need to duplicate the definitions of internal classes.

The tested code is so different, that it is difficult to use a loop. And I think that the result will be more complicated.


m = memoryview(bytearray(b'\xff'*size))
self.assertEqual(list(m[:MyIndex()]), [255] * 4)

m = memoryview(bytearray(b'\xff'*size))
self.assertEqual(list(m[MyIndex():8]), [255] * 4)

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m = memoryview(bytearray(b'\xff'*size)).cast('B', (64, 2))
with self.assertRaisesRegex(ValueError, "operation forbidden"):
m[MyIndex(), 0]

m = memoryview(bytearray(b'\xff'*size)).cast('B', (2, 64))
with self.assertRaisesRegex(ValueError, "operation forbidden"):
m[0, MyIndex()]

ba = None
m = memoryview(bytearray(b'\xff'*size))
with self.assertRaisesRegex(ValueError, "operation forbidden"):
m[MyIndex()] = 42
self.assertEqual(ba[:8], b'\0'*8)

ba = None
m = memoryview(bytearray(b'\xff'*size))
with self.assertRaisesRegex(ValueError, "operation forbidden"):
m[:MyIndex()] = b'spam'
self.assertEqual(ba[:8], b'\0'*8)

ba = None
m = memoryview(bytearray(b'\xff'*size))
with self.assertRaisesRegex(ValueError, "operation forbidden"):
m[MyIndex():8] = b'spam'
self.assertEqual(ba[:8], b'\0'*8)

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ba = None
m = memoryview(bytearray(b'\xff'*size)).cast('B', (64, 2))
with self.assertRaisesRegex(ValueError, "operation forbidden"):
m[MyIndex(), 0] = 42
self.assertEqual(ba[8:16], b'\0'*8)
ba = None
m = memoryview(bytearray(b'\xff'*size)).cast('B', (2, 64))
with self.assertRaisesRegex(ValueError, "operation forbidden"):
m[0, MyIndex()] = 42
self.assertEqual(ba[:8], b'\0'*8)

ba = None
m = memoryview(bytearray(b'\xff'*size))
with self.assertRaisesRegex(ValueError, "operation forbidden"):
m[0] = MyIndex()
self.assertEqual(ba[:8], b'\0'*8)

for fmt in 'bhilqnBHILQN':
with self.subTest(fmt=fmt):
ba = None
m = memoryview(bytearray(b'\xff'*size)).cast(fmt)
with self.assertRaisesRegex(ValueError, "operation forbidden"):
m[0] = MyIndex()
self.assertEqual(ba[:8], b'\0'*8)

for fmt in 'fd':
with self.subTest(fmt=fmt):
ba = None
m = memoryview(bytearray(b'\xff'*size)).cast(fmt)
with self.assertRaisesRegex(ValueError, "operation forbidden"):
m[0] = MyFloat()
self.assertEqual(ba[:8], b'\0'*8)

ba = None
m = memoryview(bytearray(b'\xff'*size)).cast('?')
with self.assertRaisesRegex(ValueError, "operation forbidden"):
m[0] = MyBool()
self.assertEqual(ba[:8], b'\0'*8)

if __name__ == "__main__":
unittest.main()
2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Security/2022-05-19-08-53-07.gh-issue-92888.TLtR9W.rst
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@@ -0,0 +1,2 @@
Fix ``memoryview`` use after free when accessing the backing buffer in certain cases.
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I propose to mention more explicitly that the protection is about released views:

If a memoryview is released while getting or setting an item, raise an exception.
For example, converting an object to an index can execute arbitrary Python
code which can indirectly release the memoryview.

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Not always an exception is raised.

The bug was in reading or wring the freed memory. Now it is prevented -- you either get an exception or free the memory after reading. @Fidget-Spinner's description is more correct.

I am going to address such inconsistency in a separate issue.


55 changes: 36 additions & 19 deletions Objects/memoryobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -193,6 +193,11 @@ PyTypeObject _PyManagedBuffer_Type = {
return -1; \
}

/* See gh-92888. These macros signal that we need to check the memoryview
again due to possible read after frees. */
#define CHECK_RELEASED_AGAIN(mv) CHECK_RELEASED(mv)
#define CHECK_RELEASED_INT_AGAIN(mv) CHECK_RELEASED_INT(mv)

#define CHECK_LIST_OR_TUPLE(v) \
if (!PyList_Check(v) && !PyTuple_Check(v)) { \
PyErr_SetString(PyExc_TypeError, \
Expand Down Expand Up @@ -381,8 +386,9 @@ copy_rec(const Py_ssize_t *shape, Py_ssize_t ndim, Py_ssize_t itemsize,

/* Faster copying of one-dimensional arrays. */
static int
copy_single(const Py_buffer *dest, const Py_buffer *src)
copy_single(PyMemoryViewObject *self, const Py_buffer *dest, const Py_buffer *src)
{
CHECK_RELEASED_INT_AGAIN(self);
char *mem = NULL;

assert(dest->ndim == 1);
Expand Down Expand Up @@ -1677,7 +1683,7 @@ pylong_as_zu(PyObject *item)
module syntax. This function is very sensitive to small changes. With this
layout gcc automatically generates a fast jump table. */
static inline PyObject *
unpack_single(const char *ptr, const char *fmt)
unpack_single(PyMemoryViewObject *self, const char *ptr, const char *fmt)
{
unsigned long long llu;
unsigned long lu;
Expand All @@ -1689,6 +1695,8 @@ unpack_single(const char *ptr, const char *fmt)
unsigned char uc;
void *p;

CHECK_RELEASED_AGAIN(self);

switch (fmt[0]) {

/* signed integers and fast path for 'B' */
Expand Down Expand Up @@ -1767,7 +1775,7 @@ unpack_single(const char *ptr, const char *fmt)
/* Pack a single item. 'fmt' can be any native format character in
struct module syntax. */
static int
pack_single(char *ptr, PyObject *item, const char *fmt)
pack_single(PyMemoryViewObject *self, char *ptr, PyObject *item, const char *fmt)
{
unsigned long long llu;
unsigned long lu;
Expand All @@ -1784,6 +1792,7 @@ pack_single(char *ptr, PyObject *item, const char *fmt)
ld = pylong_as_ld(item);
if (ld == -1 && PyErr_Occurred())
goto err_occurred;
CHECK_RELEASED_INT_AGAIN(self);
switch (fmt[0]) {
case 'b':
if (ld < SCHAR_MIN || ld > SCHAR_MAX) goto err_range;
Expand All @@ -1804,6 +1813,7 @@ pack_single(char *ptr, PyObject *item, const char *fmt)
lu = pylong_as_lu(item);
if (lu == (unsigned long)-1 && PyErr_Occurred())
goto err_occurred;
CHECK_RELEASED_INT_AGAIN(self);
switch (fmt[0]) {
case 'B':
if (lu > UCHAR_MAX) goto err_range;
Expand All @@ -1824,12 +1834,14 @@ pack_single(char *ptr, PyObject *item, const char *fmt)
lld = pylong_as_lld(item);
if (lld == -1 && PyErr_Occurred())
goto err_occurred;
CHECK_RELEASED_INT_AGAIN(self);
PACK_SINGLE(ptr, lld, long long);
break;
case 'Q':
llu = pylong_as_llu(item);
if (llu == (unsigned long long)-1 && PyErr_Occurred())
goto err_occurred;
CHECK_RELEASED_INT_AGAIN(self);
PACK_SINGLE(ptr, llu, unsigned long long);
break;

Expand All @@ -1838,12 +1850,14 @@ pack_single(char *ptr, PyObject *item, const char *fmt)
zd = pylong_as_zd(item);
if (zd == -1 && PyErr_Occurred())
goto err_occurred;
CHECK_RELEASED_INT_AGAIN(self);
PACK_SINGLE(ptr, zd, Py_ssize_t);
break;
case 'N':
zu = pylong_as_zu(item);
if (zu == (size_t)-1 && PyErr_Occurred())
goto err_occurred;
CHECK_RELEASED_INT_AGAIN(self);
PACK_SINGLE(ptr, zu, size_t);
break;

Expand All @@ -1852,6 +1866,7 @@ pack_single(char *ptr, PyObject *item, const char *fmt)
d = PyFloat_AsDouble(item);
if (d == -1.0 && PyErr_Occurred())
goto err_occurred;
CHECK_RELEASED_INT_AGAIN(self);
if (fmt[0] == 'f') {
PACK_SINGLE(ptr, d, float);
}
Expand All @@ -1865,6 +1880,7 @@ pack_single(char *ptr, PyObject *item, const char *fmt)
ld = PyObject_IsTrue(item);
if (ld < 0)
return -1; /* preserve original error */
CHECK_RELEASED_INT_AGAIN(self);
PACK_SINGLE(ptr, ld, _Bool);
break;

Expand All @@ -1882,6 +1898,7 @@ pack_single(char *ptr, PyObject *item, const char *fmt)
p = PyLong_AsVoidPtr(item);
if (p == NULL && PyErr_Occurred())
goto err_occurred;
CHECK_RELEASED_INT_AGAIN(self);
PACK_SINGLE(ptr, p, void *);
break;

Expand Down Expand Up @@ -2048,7 +2065,7 @@ adjust_fmt(const Py_buffer *view)

/* Base case for multi-dimensional unpacking. Assumption: ndim == 1. */
static PyObject *
tolist_base(const char *ptr, const Py_ssize_t *shape,
tolist_base(PyMemoryViewObject *self, const char *ptr, const Py_ssize_t *shape,
const Py_ssize_t *strides, const Py_ssize_t *suboffsets,
const char *fmt)
{
Expand All @@ -2061,7 +2078,7 @@ tolist_base(const char *ptr, const Py_ssize_t *shape,

for (i = 0; i < shape[0]; ptr+=strides[0], i++) {
const char *xptr = ADJUST_PTR(ptr, suboffsets, 0);
item = unpack_single(xptr, fmt);
item = unpack_single(self, xptr, fmt);
if (item == NULL) {
Py_DECREF(lst);
return NULL;
Expand All @@ -2075,7 +2092,7 @@ tolist_base(const char *ptr, const Py_ssize_t *shape,
/* Unpack a multi-dimensional array into a nested list.
Assumption: ndim >= 1. */
static PyObject *
tolist_rec(const char *ptr, Py_ssize_t ndim, const Py_ssize_t *shape,
tolist_rec(PyMemoryViewObject *self, const char *ptr, Py_ssize_t ndim, const Py_ssize_t *shape,
const Py_ssize_t *strides, const Py_ssize_t *suboffsets,
const char *fmt)
{
Expand All @@ -2087,15 +2104,15 @@ tolist_rec(const char *ptr, Py_ssize_t ndim, const Py_ssize_t *shape,
assert(strides != NULL);

if (ndim == 1)
return tolist_base(ptr, shape, strides, suboffsets, fmt);
return tolist_base(self, ptr, shape, strides, suboffsets, fmt);

lst = PyList_New(shape[0]);
if (lst == NULL)
return NULL;

for (i = 0; i < shape[0]; ptr+=strides[0], i++) {
const char *xptr = ADJUST_PTR(ptr, suboffsets, 0);
item = tolist_rec(xptr, ndim-1, shape+1,
item = tolist_rec(self, xptr, ndim-1, shape+1,
strides+1, suboffsets ? suboffsets+1 : NULL,
fmt);
if (item == NULL) {
Expand Down Expand Up @@ -2129,15 +2146,15 @@ memoryview_tolist_impl(PyMemoryViewObject *self)
if (fmt == NULL)
return NULL;
if (view->ndim == 0) {
return unpack_single(view->buf, fmt);
return unpack_single(self, view->buf, fmt);
}
else if (view->ndim == 1) {
return tolist_base(view->buf, view->shape,
return tolist_base(self, view->buf, view->shape,
view->strides, view->suboffsets,
fmt);
}
else {
return tolist_rec(view->buf, view->ndim, view->shape,
return tolist_rec(self, view->buf, view->ndim, view->shape,
view->strides, view->suboffsets,
fmt);
}
Expand Down Expand Up @@ -2345,7 +2362,7 @@ memory_item(PyMemoryViewObject *self, Py_ssize_t index)
char *ptr = ptr_from_index(view, index);
if (ptr == NULL)
return NULL;
return unpack_single(ptr, fmt);
return unpack_single(self, ptr, fmt);
}

PyErr_SetString(PyExc_NotImplementedError,
Expand Down Expand Up @@ -2376,7 +2393,7 @@ memory_item_multi(PyMemoryViewObject *self, PyObject *tup)
ptr = ptr_from_tuple(view, tup);
if (ptr == NULL)
return NULL;
return unpack_single(ptr, fmt);
return unpack_single(self, ptr, fmt);
}

static inline int
Expand Down Expand Up @@ -2463,7 +2480,7 @@ memory_subscript(PyMemoryViewObject *self, PyObject *key)
const char *fmt = adjust_fmt(view);
if (fmt == NULL)
return NULL;
return unpack_single(view->buf, fmt);
return unpack_single(self, view->buf, fmt);
}
else if (key == Py_Ellipsis) {
Py_INCREF(self);
Expand Down Expand Up @@ -2538,7 +2555,7 @@ memory_ass_sub(PyMemoryViewObject *self, PyObject *key, PyObject *value)
if (key == Py_Ellipsis ||
(PyTuple_Check(key) && PyTuple_GET_SIZE(key)==0)) {
ptr = (char *)view->buf;
return pack_single(ptr, value, fmt);
return pack_single(self, ptr, value, fmt);
}
else {
PyErr_SetString(PyExc_TypeError,
Expand All @@ -2560,7 +2577,7 @@ memory_ass_sub(PyMemoryViewObject *self, PyObject *key, PyObject *value)
ptr = ptr_from_index(view, index);
if (ptr == NULL)
return -1;
return pack_single(ptr, value, fmt);
return pack_single(self, ptr, value, fmt);
}
/* one-dimensional: fast path */
if (PySlice_Check(key) && view->ndim == 1) {
Expand All @@ -2583,7 +2600,7 @@ memory_ass_sub(PyMemoryViewObject *self, PyObject *key, PyObject *value)
goto end_block;
dest.len = dest.shape[0] * dest.itemsize;

ret = copy_single(&dest, &src);
ret = copy_single(self, &dest, &src);

end_block:
PyBuffer_Release(&src);
Expand All @@ -2599,7 +2616,7 @@ memory_ass_sub(PyMemoryViewObject *self, PyObject *key, PyObject *value)
ptr = ptr_from_tuple(view, key);
if (ptr == NULL)
return -1;
return pack_single(ptr, value, fmt);
return pack_single(self, ptr, value, fmt);
}
if (PySlice_Check(key) || is_multislice(key)) {
/* Call memory_subscript() to produce a sliced lvalue, then copy
Expand Down Expand Up @@ -3200,7 +3217,7 @@ memoryiter_next(memoryiterobject *it)
if (ptr == NULL) {
return NULL;
}
return unpack_single(ptr, it->it_fmt);
return unpack_single(seq, ptr, it->it_fmt);
}

it->it_seq = NULL;
Expand Down