Prevent _PassphraseHelper.raise_if_problem() from eating exceptions (#581)

* Modify tests to detect empty crypto.Errors from load_privatekey

This reproduces #119 and #456.

* Prevent _PassphraseHelper.raise_if_problem() from eating exceptions.

This resolves #119, resolves #456.

`_PassphraseHelper.raise_if_problem()` always flushes the OpenSSL
exception queue, but does not always raise an exception. In some cases,
other code attempts to raise an error from OpenSSL after
`raise_if_problem()` has flushed the queue, thus causing an empty
exception to be raised (i.e. `raise Error([])`).

This commit modifies `_PassphraseHelper.raise_if_problem` to flush the
OpenSSL error queue only if it has en exception to raise. Subsequent
code that detects an error should now be able to raise an non-empty
exception.

* Add CHANGELOG entry for #581.

1 files changed, 4 insertions, 5 deletions

diff --git a/src/OpenSSL/SSL.py b/src/OpenSSL/SSL.py
index 003ed43..d4158d4 100644
--- a/src/OpenSSL/SSL.py
+++ b/src/OpenSSL/SSL.py
@@ -771,11 +771,10 @@ class Context(object):
             _raise_current_error()
 
     def _raise_passphrase_exception(self):
-        if self._passphrase_helper is None:
-            _raise_current_error()
-        exception = self._passphrase_helper.raise_if_problem(Error)
-        if exception is not None:
-            raise exception
+        if self._passphrase_helper is not None:
+            self._passphrase_helper.raise_if_problem(Error)
+
+        _raise_current_error()
 
     def use_privatekey_file(self, keyfile, filetype=_UNSPECIFIED):
         """