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, 8 insertions, 6 deletions

diff --git a/src/OpenSSL/crypto.py b/src/OpenSSL/crypto.py
index 7bb0cfa..4b86b95 100644
--- a/src/OpenSSL/crypto.py
+++ b/src/OpenSSL/crypto.py
@@ -2523,13 +2523,15 @@ class _PassphraseHelper(object):
             )
 
     def raise_if_problem(self, exceptionType=Error):
-        try:
-            _exception_from_error_queue(exceptionType)
-        except exceptionType as e:
-            from_queue = e
         if self._problems:
-            raise self._problems[0]
-        return from_queue
+
+            # Flush the OpenSSL error queue
+            try:
+                _exception_from_error_queue(exceptionType)
+            except exceptionType:
+                pass
+
+            raise self._problems.pop(0)
 
     def _read_passphrase(self, buf, size, rwflag, userdata):
         try: