KEYS: Introduce sig restriction that validates root of trust

The current keyring restrictions validate if a key can be vouched for by
another key already contained in a keyring.  Add a new restriction called
restrict_link_by_rot_and_signature that both vouches for the new key and
validates the vouching key contains the builtin root of trust flag.

Two new system keyring restrictions are added to use
restrict_link_by_rot_and_signature.  The first restriction called
restrict_link_by_rot_builtin_trusted  uses the builtin_trusted_keys as
the restricted keyring.  The second system keyring restriction called
restrict_link_by_rot_builtin_and_secondary_trusted uses the
secondary_trusted_keys as the restricted keyring.  Should the machine
keyring be defined, it shall be validated too, since it is linked to
the secondary_trusted_keys keyring.

Signed-off-by: Eric Snowberg <eric.snowberg@oracle.com>

certs/system_keyring.c

@@ -48,6 +48,14 @@ int restrict_link_by_builtin_trusted(struct key *dest_keyring,
 					  builtin_trusted_keys);
 }
 
+int restrict_link_by_rot_builtin_trusted(struct key *dest_keyring,
+					 const struct key_type *type,
+					 const union key_payload *payload,
+					 struct key *unused)
+{
+	return restrict_link_by_rot_and_signature(dest_keyring, type, payload,
+						  builtin_trusted_keys);
+}
 #ifdef CONFIG_SECONDARY_TRUSTED_KEYRING
 /**
  * restrict_link_by_builtin_and_secondary_trusted - Restrict keyring
@@ -76,6 +84,16 @@ int restrict_link_by_builtin_and_secondary_trusted(
 					  secondary_trusted_keys);
 }
 
+int restrict_link_by_rot_builtin_and_secondary_trusted(
+	struct key *dest_keyring,
+	const struct key_type *type,
+	const union key_payload *payload,
+	struct key *unused)
+{
+	return restrict_link_by_rot_and_signature(dest_keyring, type, payload,
+						  secondary_trusted_keys);
+}
+
 /**
  * Allocate a struct key_restriction for the "builtin and secondary trust"
  * keyring. Only for use in system_trusted_keyring_init().

crypto/asymmetric_keys/restrict.c

@@ -108,6 +108,48 @@ int restrict_link_by_signature(struct key *dest_keyring,
 	return ret;
 }
 
+int restrict_link_by_rot_and_signature(struct key *dest_keyring,
+				       const struct key_type *type,
+				       const union key_payload *payload,
+				       struct key *trust_keyring)
+{
+	const struct public_key_signature *sig;
+	struct key *key;
+	int ret;
+
+	if (!trust_keyring)
+		return -ENOKEY;
+
+	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] && !sig->auth_ids[2])
+		return -ENOKEY;
+
+	if (ca_keyid && !asymmetric_key_id_partial(sig->auth_ids[1], ca_keyid))
+		return -EPERM;
+
+	/* See if we have a key that signed this one. */
+	key = find_asymmetric_key(trust_keyring,
+				  sig->auth_ids[0], sig->auth_ids[1],
+				  sig->auth_ids[2], false);
+	if (IS_ERR(key))
+		return -ENOKEY;
+
+	if (!test_bit(KEY_FLAG_BUILTIN_ROT, &key->flags))
+		ret = -ENOKEY;
+	else if (use_builtin_keys && !test_bit(KEY_FLAG_BUILTIN, &key->flags))
+		ret = -ENOKEY;
+	else
+		ret = verify_signature(key, sig);
+	key_put(key);
+	return ret;
+}
+
+
 static bool match_either_id(const struct asymmetric_key_id **pair,
 			    const struct asymmetric_key_id *single)
 {

include/keys/system_keyring.h

@@ -17,9 +17,18 @@ extern int restrict_link_by_builtin_trusted(struct key *keyring,
 					    const union key_payload *payload,
 					    struct key *restriction_key);
 extern __init int load_module_cert(struct key *keyring);
-
+extern int restrict_link_by_rot_builtin_trusted(struct key *keyring,
+						const struct key_type *type,
+						const union key_payload *payload,
+						struct key *unused);
+extern int restrict_link_by_rot_and_signature(struct key *dest_keyring,
+					      const struct key_type *type,
+					      const union key_payload *payload,
+					      struct key *unused);
 #else
 #define restrict_link_by_builtin_trusted restrict_link_reject
+#define restrict_link_by_rot_and_signature restrict_link_reject
+#define restrict_link_by_rot_builtin_trusted restrict_link_reject
 
 static inline __init int load_module_cert(struct key *keyring)
 {
@@ -34,8 +43,14 @@ extern int restrict_link_by_builtin_and_secondary_trusted(
 	const struct key_type *type,
 	const union key_payload *payload,
 	struct key *restriction_key);
+extern int restrict_link_by_rot_builtin_and_secondary_trusted(
+	struct key *dest_keyring,
+	const struct key_type *type,
+	const union key_payload *payload,
+	struct key *restrict_key);
 #else
 #define restrict_link_by_builtin_and_secondary_trusted restrict_link_by_builtin_trusted
+#define restrict_link_by_rot_builtin_and_secondary_trusted restrict_link_by_builtin_trusted
 #endif
 
 #ifdef CONFIG_INTEGRITY_MACHINE_KEYRING