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

1 files changed, 15 insertions, 3 deletions

diff --git a/Lib/pickle.py b/Lib/pickle.py
index 71aa57d500e..01d41422aa4 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):