From e42162a7f730481642bb063cf72274d002dc8c0b Mon Sep 17 00:00:00 2001
From: Paul Kehrer <paul.l.kehrer@gmail.com>
Date: Sun, 5 Nov 2023 19:18:50 +0800
Subject: [PATCH] raise an exception instead of returning an empty list for
 pkcs7 cert loading (#9947)

* raise an exception instead of returning an empty list

as davidben points out in #9926 we are calling a specific load
certificates function and an empty value doesn't necessarily mean empty
because PKCS7 contains multitudes. erroring is more correct.

* changelog

* Update CHANGELOG.rst

Co-authored-by: Alex Gaynor <alex.gaynor@gmail.com>

---------

Co-authored-by: Alex Gaynor <alex.gaynor@gmail.com>
---
 src/cryptography/hazmat/backends/openssl/backend.py | 7 +++++--
 tests/hazmat/primitives/test_pkcs7.py               | 6 +++---
 2 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/src/cryptography/hazmat/backends/openssl/backend.py b/src/cryptography/hazmat/backends/openssl/backend.py
index 1a1a6d1..485cf89 100644
--- a/src/cryptography/hazmat/backends/openssl/backend.py
+++ b/src/cryptography/hazmat/backends/openssl/backend.py
@@ -2189,12 +2189,15 @@ class Backend(BackendInterface):
                 _Reasons.UNSUPPORTED_SERIALIZATION,
             )
 
-        certs: list[x509.Certificate] = []
         if p7.d.sign == self._ffi.NULL:
-            return certs
+            raise ValueError(
+                "The provided PKCS7 has no certificate data, but a cert "
+                "loading method was called."
+            )
 
         sk_x509 = p7.d.sign.cert
         num = self._lib.sk_X509_num(sk_x509)
+        certs: list[x509.Certificate] = []
         for i in range(num):
             x509 = self._lib.sk_X509_value(sk_x509, i)
             self.openssl_assert(x509 != self._ffi.NULL)
diff --git a/tests/hazmat/primitives/test_pkcs7.py b/tests/hazmat/primitives/test_pkcs7.py
index e6dcd8e..96aa2f2 100644
--- a/tests/hazmat/primitives/test_pkcs7.py
+++ b/tests/hazmat/primitives/test_pkcs7.py
@@ -81,11 +81,11 @@ class TestPKCS7Loading(object):
                 mode="rb",
             )
 
-    def test_load_pkcs7_empty_certificates(self, backend):
+    def test_load_pkcs7_empty_certificates(self):
         der = b"\x30\x0B\x06\x09\x2A\x86\x48\x86\xF7\x0D\x01\x07\x02"
 
-        certificates = pkcs7.load_der_pkcs7_certificates(der)
-        assert certificates == []
+        with pytest.raises(ValueError):
+            pkcs7.load_der_pkcs7_certificates(der)
 
 
 # We have no public verification API and won't be adding one until we get
-- 
2.33.0

