[PATCH v6 08/13] KEYS: Introduce link restriction for machine keys

[Eric Snowberg <eric.snowberg@oracle.com>]

Introduce a new link restriction that includes the trusted builtin,
secondary and machine keys. The restriction is based on the key to be
added being vouched for by a key in any of these three keyrings.

Suggested-by: Mimi Zohar <zohar@linux.ibm.com>
Signed-off-by: Eric Snowberg <eric.snowberg@oracle.com>
---
v3: Initial version
v4: moved code under CONFIG_INTEGRITY_MOK_KEYRING
v5: Rename to machine keyring
v6: Change subject name (suggested by Mimi)
    Rename restrict_link_by_builtin_secondary_and_ca_trusted
      to restrict_link_by_builtin_secondary_and_machine (suggested by
      Mimi)
---
 certs/system_keyring.c        | 23 +++++++++++++++++++++++
 include/keys/system_keyring.h |  6 ++++++
 2 files changed, 29 insertions(+)

diff --git a/certs/system_keyring.c b/certs/system_keyring.c
index bc7e44fc82c2..71a00add9805 100644
--- a/certs/system_keyring.c
+++ b/certs/system_keyring.c
@@ -99,6 +99,29 @@ void __init set_machine_trusted_keys(struct key *keyring)
 {
 	machine_trusted_keys = keyring;
 }
+
+/**
+ * restrict_link_by_builtin_secondary_and_machine
+ *
+ * Restrict the addition of keys into a keyring based on the key-to-be-added
+ * being vouched for by a key in either the built-in, the secondary, or
+ * the machine keyrings.
+ */
+int restrict_link_by_builtin_secondary_and_machine(
+	struct key *dest_keyring,
+	const struct key_type *type,
+	const union key_payload *payload,
+	struct key *restrict_key)
+{
+	if (machine_trusted_keys && type == &key_type_keyring &&
+	    dest_keyring == secondary_trusted_keys &&
+	    payload == &machine_trusted_keys->payload)
+		/* Allow the machine keyring to be added to the secondary */
+		return 0;
+
+	return restrict_link_by_builtin_and_secondary_trusted(dest_keyring, type,
+							      payload, restrict_key);
+}
 #endif
 
 /*
diff --git a/include/keys/system_keyring.h b/include/keys/system_keyring.h
index 98c9b10cdc17..2419a735420f 100644
--- a/include/keys/system_keyring.h
+++ b/include/keys/system_keyring.h
@@ -39,8 +39,14 @@ extern int restrict_link_by_builtin_and_secondary_trusted(
 #endif
 
 #ifdef CONFIG_INTEGRITY_MACHINE_KEYRING
+extern int restrict_link_by_builtin_secondary_and_machine(
+	struct key *dest_keyring,
+	const struct key_type *type,
+	const union key_payload *payload,
+	struct key *restrict_key);
 extern void __init set_machine_trusted_keys(struct key *keyring);
 #else
+#define restrict_link_by_builtin_secondary_and_machine restrict_link_by_builtin_trusted
 static inline void __init set_machine_trusted_keys(struct key *keyring)
 {
 }
-- 
2.18.4