PKCS#7: Find intersection between PKCS#7 message and known, trusted keys

Find the intersection between the X.509 certificate chain contained in a PKCS#7
message and a set of keys that we already know and trust.

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
Reviewed-by: Kees Cook <keescook@chromium.org>

include/crypto/pkcs7.h

@@ -9,6 +9,7 @@
  * 2 of the Licence, or (at your option) any later version.
  */
 
+struct key;
 struct pkcs7_message;
 
 /*
@@ -22,6 +23,13 @@ extern int pkcs7_get_content_data(const struct pkcs7_message *pkcs7,
 				  const void **_data, size_t *_datalen,
 				  bool want_wrapper);
 
+/*
+ * pkcs7_trust.c
+ */
+extern int pkcs7_validate_trust(struct pkcs7_message *pkcs7,
+				struct key *trust_keyring,
+				bool *_trusted);
+
 /*
  * pkcs7_verify.c
  */