Merge pull request #660 from reaperhulk/osrandom-more-robust

Cryptography_add_osrandom_engine should be safe to call multiple times

2 files changed, 13 insertions, 2 deletions

diff --git a/cryptography/hazmat/bindings/openssl/binding.py b/cryptography/hazmat/bindings/openssl/binding.py
index 714ecc07..0469a1ea 100644
--- a/cryptography/hazmat/bindings/openssl/binding.py
+++ b/cryptography/hazmat/bindings/openssl/binding.py
@@ -98,7 +98,7 @@ class Binding(object):
                                      _OSX_PRE_INCLUDE, _OSX_POST_INCLUDE,
                                      libraries)
         res = cls.lib.Cryptography_add_osrandom_engine()
-        assert res == 1
+        assert res != 0
 
     @classmethod
     def is_available(cls):
diff --git a/cryptography/hazmat/bindings/openssl/osrandom_engine.py b/cryptography/hazmat/bindings/openssl/osrandom_engine.py
index 23f2e17a..0903a4bf 100644
--- a/cryptography/hazmat/bindings/openssl/osrandom_engine.py
+++ b/cryptography/hazmat/bindings/openssl/osrandom_engine.py
@@ -174,8 +174,19 @@ static RAND_METHOD osrandom_rand = {
     osrandom_rand_status,
 };
 
+/* Returns 1 if successfully added, 2 if engine has previously been added,
+   and 0 for error. */
 int Cryptography_add_osrandom_engine(void) {
-    ENGINE *e = ENGINE_new();
+    ENGINE *e;
+    e = ENGINE_by_id(Cryptography_osrandom_engine_id);
+    if (e != NULL) {
+        ENGINE_free(e);
+        return 2;
+    } else {
+        ERR_clear_error();
+    }
+
+    e = ENGINE_new();
     if (e == NULL) {
         return 0;
     }