we don't actually care about the errstack here, it's an invalid signature (#4325)

* we don't actually care about the errstack here, it's an invalid signature

We previously had no cases where we could error without getting errors
on the error stack, but wycheproof contains test cases that can error
without adding anything to the stack. Accordingly, we should clear the
stack but raise InvalidSignature no matter what (rather than
InternalError if we have no error msgs)

* add a test

2 files changed, 36 insertions, 2 deletions

diff --git a/src/cryptography/hazmat/backends/openssl/rsa.py b/src/cryptography/hazmat/backends/openssl/rsa.py
index e7a77312..9a7bfaa5 100644
--- a/src/cryptography/hazmat/backends/openssl/rsa.py
+++ b/src/cryptography/hazmat/backends/openssl/rsa.py
@@ -264,8 +264,7 @@ def _rsa_sig_verify(backend, padding, algorithm, public_key, signature, data):
     # occurs.
     backend.openssl_assert(res >= 0)
     if res == 0:
-        errors = backend._consume_errors()
-        backend.openssl_assert(errors)
+        backend._consume_errors()
         raise InvalidSignature
 
 
diff --git a/tests/hazmat/primitives/test_rsa.py b/tests/hazmat/primitives/test_rsa.py
index 217c6680..ec08eade 100644
--- a/tests/hazmat/primitives/test_rsa.py
+++ b/tests/hazmat/primitives/test_rsa.py
@@ -731,6 +731,41 @@ class TestRSAVerification(object):
                 hashes.SHA1()
             )
 
+    def test_invalid_signature_sequence_removed(self, backend):
+        """
+        This test comes from wycheproof
+        """
+        key_der = binascii.unhexlify(
+            b"30820122300d06092a864886f70d01010105000382010f003082010a02820101"
+            b"00a2b451a07d0aa5f96e455671513550514a8a5b462ebef717094fa1fee82224"
+            b"e637f9746d3f7cafd31878d80325b6ef5a1700f65903b469429e89d6eac88450"
+            b"97b5ab393189db92512ed8a7711a1253facd20f79c15e8247f3d3e42e46e48c9"
+            b"8e254a2fe9765313a03eff8f17e1a029397a1fa26a8dce26f490ed81299615d9"
+            b"814c22da610428e09c7d9658594266f5c021d0fceca08d945a12be82de4d1ece"
+            b"6b4c03145b5d3495d4ed5411eb878daf05fd7afc3e09ada0f1126422f590975a"
+            b"1969816f48698bcbba1b4d9cae79d460d8f9f85e7975005d9bc22c4e5ac0f7c1"
+            b"a45d12569a62807d3b9a02e5a530e773066f453d1f5b4c2e9cf7820283f742b9"
+            b"d50203010001"
+        )
+        sig = binascii.unhexlify(
+            b"498209f59a0679a1f926eccf3056da2cba553d7ab3064e7c41ad1d739f038249"
+            b"f02f5ad12ee246073d101bc3cdb563e8b6be61562056422b7e6c16ad53deb12a"
+            b"f5de744197753a35859833f41bb59c6597f3980132b7478fd0b95fd27dfad64a"
+            b"20fd5c25312bbd41a85286cd2a83c8df5efa0779158d01b0747ff165b055eb28"
+            b"80ea27095700a295593196d8c5922cf6aa9d7e29b5056db5ded5eb20aeb31b89"
+            b"42e26b15a5188a4934cd7e39cfe379a197f49a204343a493452deebca436ee61"
+            b"4f4daf989e355544489f7e69ffa8ccc6a1e81cf0ab33c3e6d7591091485a6a31"
+            b"bda3b33946490057b9a3003d3fd9daf7c4778b43fd46144d945d815f12628ff4"
+        )
+        public_key = serialization.load_der_public_key(key_der, backend)
+        with pytest.raises(InvalidSignature):
+            public_key.verify(
+                sig,
+                binascii.unhexlify(b"313233343030"),
+                padding.PKCS1v15(),
+                hashes.SHA256()
+            )
+
     @pytest.mark.supported(
         only_if=lambda backend: backend.rsa_padding_supported(
             padding.PKCS1v15()