[PATCH v3 09/10] KEYS: CA link restriction

[Eric Snowberg]

Add a new link restriction.  Restrict the addition of keys in a keyring
based on the key to be added being a CA.

Signed-off-by: Eric Snowberg <eric.snowberg@xxxxxxxxxx>
---
 crypto/asymmetric_keys/restrict.c        | 35 ++++++++++++++++++++++++
 crypto/asymmetric_keys/x509_public_key.c |  5 +++-
 include/crypto/public_key.h              | 16 +++++++++++
 3 files changed, 55 insertions(+), 1 deletion(-)

diff --git a/crypto/asymmetric_keys/restrict.c b/crypto/asymmetric_keys/restrict.c
index 005cb28969e4..ca305ba1c0b5 100644
--- a/crypto/asymmetric_keys/restrict.c
+++ b/crypto/asymmetric_keys/restrict.c
@@ -108,6 +108,41 @@ int restrict_link_by_signature(struct key *dest_keyring,
 	return ret;
 }
 
+/**
+ * restrict_link_by_ca - Restrict additions to a ring of CA keys
+ * @dest_keyring: Keyring being linked to.
+ * @type: The type of key being added.
+ * @payload: The payload of the new key.
+ * @trust_keyring: Unused.
+ *
+ * Check if the new certificate is a CA. If it is a CA, then mark the new
+ * certificate as being ok to link.
+ *
+ * Returns 0 if the new certificate was accepted, -ENOKEY if the
+ * certificate is not a CA. -ENOPKG if the signature uses unsupported
+ * crypto, or some other error if there is a matching certificate but
+ * the signature check cannot be performed.
+ */
+int restrict_link_by_ca(struct key *dest_keyring,
+			const struct key_type *type,
+			const union key_payload *payload,
+			struct key *trust_keyring)
+{
+	const struct public_key *pkey;
+
+	if (type != &key_type_asymmetric)
+		return -EOPNOTSUPP;
+
+	pkey = payload->data[asym_crypto];
+	if (!pkey)
+		return -ENOPKG;
+
+	if (!pkey->key_is_ca)
+		return -ENOKEY;
+
+	return 0;
+}
+
 int restrict_link_by_ca_and_signature(struct key *dest_keyring,
 				       const struct key_type *type,
 				       const union key_payload *payload,
diff --git a/crypto/asymmetric_keys/x509_public_key.c b/crypto/asymmetric_keys/x509_public_key.c
index 75699987a6b1..88c6e9829224 100644
--- a/crypto/asymmetric_keys/x509_public_key.c
+++ b/crypto/asymmetric_keys/x509_public_key.c
@@ -209,8 +209,11 @@ static int x509_key_preparse(struct key_preparsed_payload *prep)
 	}
 
 	if (cert->kcs_set) {
-		if (cert->root_ca)
+		if (cert->root_ca) {
 			prep->payload_flags |= KEY_ALLOC_PECA;
+			cert->pub->key_is_ca = true;
+		}
+
 		/*
 		 * In this case it could be an Intermediate CA.  Set
 		 * KEY_MAYBE_PECA for now.  If the restriction check
diff --git a/include/crypto/public_key.h b/include/crypto/public_key.h
index e51bbc5ffe17..3de0f8a68914 100644
--- a/include/crypto/public_key.h
+++ b/include/crypto/public_key.h
@@ -26,6 +26,7 @@ struct public_key {
 	void *params;
 	u32 paramlen;
 	bool key_is_private;
+	bool key_is_ca;
 	const char *id_type;
 	const char *pkey_algo;
 };
@@ -76,6 +77,21 @@ extern int restrict_link_by_ca_and_signature(struct key *dest_keyring,
 					      const union key_payload *payload,
 					      struct key *unused);
 
+#if IS_REACHABLE(CONFIG_ASYMMETRIC_KEY_TYPE)
+extern int restrict_link_by_ca(struct key *dest_keyring,
+			       const struct key_type *type,
+			       const union key_payload *payload,
+			       struct key *trust_keyring);
+#else
+static inline int restrict_link_by_ca(struct key *dest_keyring,
+				      const struct key_type *type,
+				      const union key_payload *payload,
+				      struct key *trust_keyring)
+{
+	return 0;
+}
+#endif
+
 extern int query_asymmetric_key(const struct kernel_pkey_params *,
 				struct kernel_pkey_query *);
 
-- 
2.27.0