File CVE-2020-36242-buffer-overflow.patch of Package python-cryptography.27852

From 3fe555d8e4fb52f21fc297dea88a03d52f319306 Mon Sep 17 00:00:00 2001
From: Paul Kehrer <paul.l.kehrer@gmail.com>
Date: Sun, 19 Jul 2020 00:00:18 -0500
Subject: [PATCH 1/3] chunked update_into

---
 .../hazmat/backends/openssl/ciphers.py        | 39 ++++++++++++-------
 tests/hazmat/primitives/test_ciphers.py       | 17 ++++++++
 2 files changed, 43 insertions(+), 13 deletions(-)

Index: cryptography-2.8/src/cryptography/hazmat/backends/openssl/ciphers.py
===================================================================
--- cryptography-2.8.orig/src/cryptography/hazmat/backends/openssl/ciphers.py
+++ cryptography-2.8/src/cryptography/hazmat/backends/openssl/ciphers.py
@@ -17,6 +17,7 @@ from cryptography.hazmat.primitives.ciph
 class _CipherContext(object):
     _ENCRYPT = 1
     _DECRYPT = 0
+    _MAX_CHUNK_SIZE = 2 ** 30 - 1
 
     def __init__(self, backend, cipher, mode, operation):
         self._backend = backend
@@ -125,22 +126,32 @@ class _CipherContext(object):
         return bytes(buf[:n])
 
     def update_into(self, data, buf):
-        if len(buf) < (len(data) + self._block_size_bytes - 1):
+        total_data_len = len(data)
+        if len(buf) < (total_data_len + self._block_size_bytes - 1):
             raise ValueError(
                 "buffer must be at least {} bytes for this "
                 "payload".format(len(data) + self._block_size_bytes - 1)
             )
 
-        buf = self._backend._ffi.cast(
-            "unsigned char *", self._backend._ffi.from_buffer(buf)
-        )
+        data_processed = 0
+        total_out = 0
         outlen = self._backend._ffi.new("int *")
-        res = self._backend._lib.EVP_CipherUpdate(
-            self._ctx, buf, outlen,
-            self._backend._ffi.from_buffer(data), len(data)
-        )
-        self._backend.openssl_assert(res != 0)
-        return outlen[0]
+        baseoutbuf = self._backend._ffi.from_buffer(buf)
+        baseinbuf = self._backend._ffi.from_buffer(data)
+
+        while data_processed != total_data_len:
+            outbuf = baseoutbuf + total_out
+            inbuf = baseinbuf + data_processed
+            inlen = min(self._MAX_CHUNK_SIZE, total_data_len - data_processed)
+
+            res = self._backend._lib.EVP_CipherUpdate(
+                self._ctx, outbuf, outlen, inbuf, inlen
+            )
+            self._backend.openssl_assert(res != 0)
+            data_processed += inlen
+            total_out += outlen[0]
+
+        return total_out
 
     def finalize(self):
         # OpenSSL 1.0.1 on Ubuntu 12.04 (and possibly other distributions)
Index: cryptography-2.8/tests/hazmat/primitives/test_ciphers.py
===================================================================
--- cryptography-2.8.orig/tests/hazmat/primitives/test_ciphers.py
+++ cryptography-2.8/tests/hazmat/primitives/test_ciphers.py
@@ -309,3 +309,20 @@ class TestCipherUpdateInto(object):
         buf = bytearray(5)
         with pytest.raises(ValueError):
             encryptor.update_into(b"testing", buf)
+
+    def test_update_into_auto_chunking(self, backend, monkeypatch):
+        key = b"\x00" * 16
+        c = ciphers.Cipher(AES(key), modes.ECB(), backend)
+        encryptor = c.encryptor()
+        # Lower max chunk size so we can test chunking
+        monkeypatch.setattr(encryptor._ctx, "_MAX_CHUNK_SIZE", 40)
+        buf = bytearray(527)
+        pt = b"abcdefghijklmnopqrstuvwxyz012345" * 16  # 512 bytes
+        processed = encryptor.update_into(pt, buf)
+        assert processed == 512
+        decryptor = c.decryptor()
+        # Change max chunk size to verify alternate boundaries don't matter
+        monkeypatch.setattr(decryptor._ctx, "_MAX_CHUNK_SIZE", 73)
+        decbuf = bytearray(527)
+        decprocessed = decryptor.update_into(buf[:processed], decbuf)
+        assert decbuf[:decprocessed] == pt