[PATCH RFC v2 02/12] 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 (self-signed) or by being
vouched for by a key in either the built-in or the secondary trusted
keyrings.

Signed-off-by: Eric Snowberg <eric.snowberg@xxxxxxxxxx>
---
v1: Initial version
v2: Removed secondary keyring references
---
 certs/system_keyring.c            | 21 +++++++++++
 crypto/asymmetric_keys/restrict.c | 60 +++++++++++++++++++++++++++++++
 include/crypto/public_key.h       |  5 +++
 include/keys/system_keyring.h     |  6 ++++
 4 files changed, 92 insertions(+)

diff --git a/certs/system_keyring.c b/certs/system_keyring.c
index 692365dee2bd..0a7b16c28a72 100644
--- a/certs/system_keyring.c
+++ b/certs/system_keyring.c
@@ -21,6 +21,9 @@
 static struct key *builtin_trusted_keys;
 #ifdef CONFIG_SECONDARY_TRUSTED_KEYRING
 static struct key *secondary_trusted_keys;
+#define system_trusted_keys secondary_trusted_keys
+#else
+#define system_trusted_keys builtin_trusted_keys
 #endif
 #ifdef CONFIG_INTEGRITY_PLATFORM_KEYRING
 static struct key *platform_trusted_keys;
@@ -45,6 +48,24 @@ int restrict_link_by_builtin_trusted(struct key *dest_keyring,
 					  builtin_trusted_keys);
 }
 
+/**
+ * restrict_link_by_system_trusted_or_ca - Restrict keyring
+ *   addition by being a CA or vouched by the system trusted keyrings.
+ *
+ *  Restrict the addition of keys in a keyring based on the key-to-be-added
+ *  being a CA (self signed) or by being vouched for by a key in either
+ *  the built-in or the secondary system keyrings.
+ */
+int restrict_link_by_system_trusted_or_ca(
+	struct key *dest_keyring,
+	const struct key_type *type,
+	const union key_payload *payload,
+	struct key *restrict_key)
+{
+	return restrict_link_by_ca(dest_keyring, type, payload,
+				   system_trusted_keys);
+}
+
 #ifdef CONFIG_SECONDARY_TRUSTED_KEYRING
 /**
  * restrict_link_by_builtin_and_secondary_trusted - Restrict keyring
diff --git a/crypto/asymmetric_keys/restrict.c b/crypto/asymmetric_keys/restrict.c
index 84cefe3b3585..75e4379226e8 100644
--- a/crypto/asymmetric_keys/restrict.c
+++ b/crypto/asymmetric_keys/restrict.c
@@ -108,6 +108,66 @@ int restrict_link_by_signature(struct key *dest_keyring,
 	return ret;
 }
 
+/**
+ * restrict_link_by_ca - Restrict additions to a ring of public keys
+ * based on it being a CA
+ * @dest_keyring: Keyring being linked to.
+ * @type: The type of key being added.
+ * @payload: The payload of the new key.
+ * @trusted: A key or ring of keys that can be used to vouch for the new cert.
+ *
+ * Check if the new certificate is a CA or if they key can be vouched for
+ * by keys already linked in the destination keyring or the trusted
+ * keyring.  If one of those is the signing key or it is self signed, then
+ * mark the new certificate as being ok to link.
+ *
+ * Returns 0 if the new certificate was accepted, -ENOKEY if we could not find
+ * a matching parent certificate in the trusted list.  -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_signature *sig;
+	const struct public_key *pkey;
+	struct key *key;
+	int ret;
+
+	if (type != &key_type_asymmetric)
+		return -EOPNOTSUPP;
+
+	sig = payload->data[asym_auth];
+	if (!sig)
+		return -ENOPKG;
+
+	if (!sig->auth_ids[0] && !sig->auth_ids[1])
+		return -ENOKEY;
+
+	pkey = payload->data[asym_crypto];
+	if (!pkey)
+		return -ENOPKG;
+
+	ret = public_key_verify_signature(pkey, sig);
+	if (!ret)
+		return 0;
+
+	if (!trust_keyring)
+		return -ENOKEY;
+
+	key = find_asymmetric_key(trust_keyring,
+				  sig->auth_ids[0], sig->auth_ids[1],
+				  false);
+	if (IS_ERR(key))
+		return -ENOKEY;
+
+	ret = verify_signature(key, sig);
+	key_put(key);
+	return ret;
+}
+
 static bool match_either_id(const struct asymmetric_key_ids *pair,
 			    const struct asymmetric_key_id *single)
 {
diff --git a/include/crypto/public_key.h b/include/crypto/public_key.h
index 47accec68cb0..545af1ea57de 100644
--- a/include/crypto/public_key.h
+++ b/include/crypto/public_key.h
@@ -71,6 +71,11 @@ extern int restrict_link_by_key_or_keyring_chain(struct key *trust_keyring,
 						 const union key_payload *payload,
 						 struct key *trusted);
 
+extern int restrict_link_by_ca(struct key *dest_keyring,
+			       const struct key_type *type,
+			       const union key_payload *payload,
+			       struct key *trust_keyring);
+
 extern int query_asymmetric_key(const struct kernel_pkey_params *,
 				struct kernel_pkey_query *);
 
diff --git a/include/keys/system_keyring.h b/include/keys/system_keyring.h
index 6acd3cf13a18..2041254d74f4 100644
--- a/include/keys/system_keyring.h
+++ b/include/keys/system_keyring.h
@@ -28,6 +28,12 @@ static inline __init int load_module_cert(struct key *keyring)
 
 #endif
 
+extern int restrict_link_by_system_trusted_or_ca(
+	struct key *dest_keyring,
+	const struct key_type *type,
+	const union key_payload *payload,
+	struct key *restrict_key);
+
 #ifdef CONFIG_SECONDARY_TRUSTED_KEYRING
 extern int restrict_link_by_builtin_and_secondary_trusted(
 	struct key *keyring,
-- 
2.18.4