Fix signature buffer size for RSA keys

src/OpenSSL/crypto.py

@@ -2583,9 +2583,9 @@ def sign(pkey, data, digest):
     _lib.EVP_SignInit(md_ctx, digest_obj)
     _lib.EVP_SignUpdate(md_ctx, data, len(data))
 
-    signature_buffer = _ffi.new("unsigned char[]", 512)
+    pkey_length = (PKey.bits(pkey) + 7) // 8
+    signature_buffer = _ffi.new("unsigned char[]", pkey_length)
     signature_length = _ffi.new("unsigned int*")
-    signature_length[0] = len(signature_buffer)
     final_result = _lib.EVP_SignFinal(
         md_ctx, signature_buffer, signature_length, pkey._pkey)
 

tests/test_crypto.py

@@ -420,6 +420,60 @@ def normalize_privatekey_pem(pem):
 RFEIPQsFZRLrtnCAiEhyT8bC2s/Njlu6ly9gtJZWSV46Q3ZjBL4q9sHKqZQ=
 -----END CERTIFICATE-----""")
 
+large_key_pem = b("""-----BEGIN RSA PRIVATE KEY-----
+MIIJYgIBAAKCAg4AtRua8eIeevRfsj+fkcHr1vmse7Kgb+oX1ssJAvCb1R7JQMnH
+hNDjDP6b3vEkZuPUzlDHymP+cNkXvvi4wJ4miVbO3+SeU4Sh+jmsHeHzGIXat9xW
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+vYeU7Ab/
+-----END RSA PRIVATE KEY-----""")
+
 
 class X509ExtTests(TestCase):
     """
@@ -3484,6 +3538,20 @@ def test_sign_nulls(self):
         sig = sign(priv_key, content, "sha1")
         verify(good_cert, sig, content, "sha1")
 
+    def test_sign_with_large_key(self):
+        """
+        :py:obj:`sign` produces a signature for a string when using a long key.
+        """
+        content = b(
+            "It was a bright cold day in April, and the clocks were striking "
+            "thirteen. Winston Smith, his chin nuzzled into his breast in an "
+            "effort to escape the vile wind, slipped quickly through the "
+            "glass doors of Victory Mansions, though not quickly enough to "
+            "prevent a swirl of gritty dust from entering along with him.")
+
+        priv_key = load_privatekey(FILETYPE_PEM, large_key_pem)
+        sign(priv_key, content, "sha1")
+
 
 class EllipticCurveTests(TestCase):
     """