Enlarge _oid2txt buffer to handle larger OIDs (#3612)
The OpenSSL manual recommends a buffer size of 80 for OBJ_oid2txt:
https://www.openssl.org/docs/crypto/OBJ_nid2ln.html#return_values.
But OIDs longer than this occur in real life (e.g. Active Directory
makes some very long OIDs). If the length of the stringified OID
exceeds the buffer size, allocate a new buffer that is big enough to
hold the stringified OID, and re-do the conversion into the new
buffer.
diff --git a/docs/development/test-vectors.rst b/docs/development/test-vectors.rst
index 868619a..a1d8b11 100644
--- a/docs/development/test-vectors.rst
+++ b/docs/development/test-vectors.rst
@@ -156,6 +156,9 @@
RSA with SHA1.
* ``badssl-sct.pem`` - A certificate with the certificate transparency signed
certificate timestamp extension.
+* ``bigoid.pem`` - A certificate with a rather long OID in the
+ Certificate Policies extension. We need to make sure we can parse
+ long OIDs.
Custom X.509 Vectors
~~~~~~~~~~~~~~~~~~~~
diff --git a/src/cryptography/hazmat/backends/openssl/decode_asn1.py b/src/cryptography/hazmat/backends/openssl/decode_asn1.py
index 19df4c8..282e30f 100644
--- a/src/cryptography/hazmat/backends/openssl/decode_asn1.py
+++ b/src/cryptography/hazmat/backends/openssl/decode_asn1.py
@@ -24,9 +24,23 @@
def _obj2txt(backend, obj):
# Set to 80 on the recommendation of
# https://www.openssl.org/docs/crypto/OBJ_nid2ln.html#return_values
+ #
+ # But OIDs longer than this occur in real life (e.g. Active
+ # Directory makes some very long OIDs). So we need to detect
+ # and properly handle the case where the default buffer is not
+ # big enough.
+ #
buf_len = 80
buf = backend._ffi.new("char[]", buf_len)
+
+ # 'res' is the number of bytes that *would* be written if the
+ # buffer is large enough. If 'res' > buf_len - 1, we need to
+ # alloc a big-enough buffer and go again.
res = backend._lib.OBJ_obj2txt(buf, buf_len, obj, 1)
+ if res > buf_len - 1: # account for terminating null byte
+ buf_len = res + 1
+ buf = backend._ffi.new("char[]", buf_len)
+ res = backend._lib.OBJ_obj2txt(buf, buf_len, obj, 1)
backend.openssl_assert(res > 0)
return backend._ffi.buffer(buf, res)[:].decode()
diff --git a/tests/test_x509_ext.py b/tests/test_x509_ext.py
index eaf5a51..b89abdd 100644
--- a/tests/test_x509_ext.py
+++ b/tests/test_x509_ext.py
@@ -409,6 +409,7 @@
assert pi != object()
+@pytest.mark.requires_backend_interface(interface=X509Backend)
class TestCertificatePolicies(object):
def test_invalid_policies(self):
pq = [u"string"]
@@ -481,6 +482,26 @@
assert cp[-1] == cp[4]
assert cp[2:6:2] == [cp[2], cp[4]]
+ def test_long_oid(self, backend):
+ """
+ Test that parsing a CertificatePolicies ext with
+ a very long OID succeeds.
+ """
+ cert = _load_cert(
+ os.path.join("x509", "bigoid.pem"),
+ x509.load_pem_x509_certificate,
+ backend
+ )
+ ext = cert.extensions.get_extension_for_class(
+ x509.CertificatePolicies)
+
+ oid = x509.ObjectIdentifier(
+ "1.3.6.1.4.1.311.21.8.8950086.10656446.2706058"
+ ".12775672.480128.147.13466065.13029902"
+ )
+
+ assert ext.value[0].policy_identifier == oid
+
@pytest.mark.requires_backend_interface(interface=RSABackend)
@pytest.mark.requires_backend_interface(interface=X509Backend)
diff --git a/vectors/cryptography_vectors/x509/bigoid.pem b/vectors/cryptography_vectors/x509/bigoid.pem
new file mode 100644
index 0000000..7bf865b
--- /dev/null
+++ b/vectors/cryptography_vectors/x509/bigoid.pem
@@ -0,0 +1,32 @@
+-----BEGIN CERTIFICATE-----
+MIIFiTCCBHGgAwIBAgITSAAAAAd1bEC5lsOdnQAAAAAABzANBgkqhkiG9w0BAQsF
+ADBLMRUwEwYKCZImiZPyLGQBGRYFbG9jYWwxEjAQBgoJkiaJk/IsZAEZFgJhZDEe
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+CSc7sKqOf+fn3+fKITR2/DcSVvb0SGCr5fVVnjQ=
+-----END CERTIFICATE-----