bug 1234417 - fix a leak in CreateECPublicKey r=rbarnes

Before this patch, CreateECPublicKey would create a SECKEYPublicKey allocated on
a scoped arena. It would then call CryptoKey::PublicKeyValid, which has the
side-effect of importing the key to the internal PKCS#11 slot. When the arena
went out of scope, the memory for the key would be released, but the reference
to the slot wouldn't, causing a leak.

This patch fixes the leak by making the SECKEYPublicKey a ScopedSECKEYPublicKey
(which ensures that the type-specific "destructor" SECKEY_DestroyPublicKey is
called, which releases the reference to the PKCS#11 slot).

--HG--
extra : rebase_source : 10ef3c0e6ade78ab8ec4c95464224ba2e38aa17b

dom/crypto/CryptoKey.cpp

@@ -974,11 +974,16 @@ CreateECPublicKey(const SECItem* aKeyData, const nsString& aNamedCurve)
     return nullptr;
   }
 
-  SECKEYPublicKey* key = PORT_ArenaZNew(arena, SECKEYPublicKey);
+  // It's important that this be a ScopedSECKEYPublicKey, as this ensures that
+  // SECKEY_DestroyPublicKey will be called on it. If this doesn't happen, when
+  // CryptoKey::PublicKeyValid is called on it and it gets moved to the internal
+  // PKCS#11 slot, it will leak a reference to the slot.
+  ScopedSECKEYPublicKey key(PORT_ArenaZNew(arena, SECKEYPublicKey));
   if (!key) {
     return nullptr;
   }
 
+  key->arena = nullptr; // key doesn't own the arena; it won't get double-freed
   key->keyType = ecKey;
   key->pkcs11Slot = nullptr;
   key->pkcs11ID = CK_INVALID_HANDLE;