certs: Add wrapper function to check blacklisted binary hash

The -EKEYREJECTED error returned by existing is_hash_blacklisted() is
misleading when called for checking against blacklisted hash of a
binary.

This patch adds a wrapper function is_binary_blacklisted() to return
-EPERM error if binary is blacklisted.

Signed-off-by: Nayna Jain <nayna@linux.ibm.com>
Reviewed-by: Mimi Zohar <zohar@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/1572492694-6520-7-git-send-email-zohar@linux.ibm.com
diff --git a/certs/blacklist.c b/certs/blacklist.c
index ec00bf33..6514f9e 100644
--- a/certs/blacklist.c
+++ b/certs/blacklist.c
@@ -135,6 +135,15 @@ int is_hash_blacklisted(const u8 *hash, size_t hash_len, const char *type)
 }
 EXPORT_SYMBOL_GPL(is_hash_blacklisted);
 
+int is_binary_blacklisted(const u8 *hash, size_t hash_len)
+{
+	if (is_hash_blacklisted(hash, hash_len, "bin") == -EKEYREJECTED)
+		return -EPERM;
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(is_binary_blacklisted);
+
 /*
  * Initialise the blacklist
  */