bpo-38876: Raise pickle.UnpicklingError when loading an item from memo for invalid input (GH-17335)

The previous code was raising a `KeyError` for both the Python and C implementation.
This was caused by the specified index of an invalid input which did not exist
in the memo structure, where the pickle stores what objects it has seen.
The malformed input would have caused either a `BINGET` or `LONG_BINGET` load
from the memo, leading to a `KeyError` as the determined index was bogus.

https://bugs.python.org/issue38876



https://bugs.python.org/issue38876

4 files changed, 35 insertions, 8 deletions

diff --git a/Lib/pickle.py b/Lib/pickle.py
index 71aa57d500..01d41422aa 100644
--- a/Lib/pickle.py
+++ b/Lib/pickle.py
@@ -1604,17 +1604,29 @@ class _Unpickler:
 
     def load_get(self):
         i = int(self.readline()[:-1])
-        self.append(self.memo[i])
+        try:
+            self.append(self.memo[i])
+        except KeyError:
+            msg = f'Memo value not found at index {i}'
+            raise UnpicklingError(msg) from None
     dispatch[GET[0]] = load_get
 
     def load_binget(self):
         i = self.read(1)[0]
-        self.append(self.memo[i])
+        try:
+            self.append(self.memo[i])
+        except KeyError as exc:
+            msg = f'Memo value not found at index {i}'
+            raise UnpicklingError(msg) from None
     dispatch[BINGET[0]] = load_binget
 
     def load_long_binget(self):
         i, = unpack('<I', self.read(4))
-        self.append(self.memo[i])
+        try:
+            self.append(self.memo[i])
+        except KeyError as exc:
+            msg = f'Memo value not found at index {i}'
+            raise UnpicklingError(msg) from None
     dispatch[LONG_BINGET[0]] = load_long_binget
 
     def load_put(self):
diff --git a/Lib/test/pickletester.py b/Lib/test/pickletester.py
index c9f374678a..953fd5c5a2 100644
--- a/Lib/test/pickletester.py
+++ b/Lib/test/pickletester.py
@@ -1019,7 +1019,9 @@ class AbstractUnpickleTests(unittest.TestCase):
         self.assertEqual(self.loads(dumped), '\u20ac\x00')
 
     def test_misc_get(self):
-        self.check_unpickling_error(KeyError, b'g0\np0')
+        self.check_unpickling_error(pickle.UnpicklingError, b'g0\np0')
+        self.check_unpickling_error(pickle.UnpicklingError, b'jens:')
+        self.check_unpickling_error(pickle.UnpicklingError, b'hens:')
         self.assert_is_copy([(100,), (100,)],
                             self.loads(b'((Kdtp0\nh\x00l.))'))
 
diff --git a/Misc/NEWS.d/next/Library/2019-11-22-10-58-58.bpo-38876.qqy1Vp.rst b/Misc/NEWS.d/next/Library/2019-11-22-10-58-58.bpo-38876.qqy1Vp.rst
new file mode 100644
index 0000000000..43b25acc39
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2019-11-22-10-58-58.bpo-38876.qqy1Vp.rst
@@ -0,0 +1,9 @@
+Raise pickle.UnpicklingError when loading an item from memo for invalid
+input
+
+The previous code was raising a `KeyError` for both the Python and C
+implementation. This was caused by the specified index of an invalid input
+which did not exist in the memo structure, where the pickle stores what
+objects it has seen. The malformed input would have caused either a `BINGET`
+or `LONG_BINGET` load from the memo, leading to a `KeyError` as the
+determined index was bogus. Patch by Claudiu Popa
diff --git a/Modules/_pickle.c b/Modules/_pickle.c
index 7370be5938..baa0a27419 100644
--- a/Modules/_pickle.c
+++ b/Modules/_pickle.c
@@ -6174,8 +6174,10 @@ load_get(UnpicklerObject *self)
 
     value = _Unpickler_MemoGet(self, idx);
     if (value == NULL) {
-        if (!PyErr_Occurred())
-            PyErr_SetObject(PyExc_KeyError, key);
+        if (!PyErr_Occurred()) {
+           PickleState *st = _Pickle_GetGlobalState();
+           PyErr_Format(st->UnpicklingError, "Memo value not found at index %ld", idx);
+        }
         Py_DECREF(key);
         return -1;
     }
@@ -6201,7 +6203,8 @@ load_binget(UnpicklerObject *self)
     if (value == NULL) {
         PyObject *key = PyLong_FromSsize_t(idx);
         if (key != NULL) {
-            PyErr_SetObject(PyExc_KeyError, key);
+            PickleState *st = _Pickle_GetGlobalState();
+            PyErr_Format(st->UnpicklingError, "Memo value not found at index %ld", idx);
             Py_DECREF(key);
         }
         return -1;
@@ -6227,7 +6230,8 @@ load_long_binget(UnpicklerObject *self)
     if (value == NULL) {
         PyObject *key = PyLong_FromSsize_t(idx);
         if (key != NULL) {
-            PyErr_SetObject(PyExc_KeyError, key);
+            PickleState *st = _Pickle_GetGlobalState();
+            PyErr_Format(st->UnpicklingError, "Memo value not found at index %ld", idx);
             Py_DECREF(key);
         }
         return -1;