Merge pull request #541 from public/fix-466

Handle multiple errors on the stack

1 files changed, 10 insertions, 2 deletions

diff --git a/cryptography/hazmat/backends/openssl/backend.py b/cryptography/hazmat/backends/openssl/backend.py
index cf931dab..e842f078 100644
--- a/cryptography/hazmat/backends/openssl/backend.py
+++ b/cryptography/hazmat/backends/openssl/backend.py
@@ -182,12 +182,20 @@ class Backend(object):
         if not code and isinstance(mode, GCM):
             raise InvalidTag
         assert code != 0
+
+        # consume any remaining errors on the stack
+        ignored_code = None
+        while ignored_code != 0:
+            ignored_code = self._lib.ERR_get_error()
+
+        # raise the first error we found
+        return self._handle_error_code(code)
+
+    def _handle_error_code(self, code):
         lib = self._lib.ERR_GET_LIB(code)
         func = self._lib.ERR_GET_FUNC(code)
         reason = self._lib.ERR_GET_REASON(code)
-        return self._handle_error_code(lib, func, reason)
 
-    def _handle_error_code(self, lib, func, reason):
         if lib == self._lib.ERR_LIB_EVP:
             if func == self._lib.EVP_F_EVP_ENCRYPTFINAL_EX:
                 if reason == self._lib.EVP_R_DATA_NOT_MULTIPLE_OF_BLOCK_LENGTH: