[PATCH v2 2/3] keys: add KEY_SPEC_IPE_KEYRING

@@ -373,6 +373,18 @@ process making the call::
 	KEY_SPEC_REQKEY_AUTH_KEY	-7	assumed request_key()
 						  authorisation key
 
+There are also values that refer to a specific kernel keyring rather than to
+anything belonging to the caller.  These well-known IDs allow userspace to
+name kernel keyrings directly even when they are not linked into a process
+keyring::
+
+	CONSTANT			VALUE	KEY REFERENCED
+	==============================	======	===========================
+	KEY_SPEC_IPE_KEYRING		-12	the ".ipe" keyring
+
+The availability of a subsystem keyring depends on its kernel configuration.
+Looking up an unavailable keyring returns ``ENOKEY``.
+
 
 The main syscalls are:
 

@@ -440,6 +440,8 @@ extern key_ref_t keyring_search(key_ref_t keyring,
 extern int keyring_restrict(key_ref_t keyring, const char *type,
 			    const char *restriction);
 
+extern void key_register_ipe_keyring(struct key *keyring);
+
 extern struct key *key_lookup(key_serial_t id);
 
 static inline key_serial_t key_serial(const struct key *key)

@@ -24,6 +24,7 @@
 #define KEY_SPEC_GROUP_KEYRING		-6	/* - key ID for GID-specific keyring */
 #define KEY_SPEC_REQKEY_AUTH_KEY	-7	/* - key ID for assumed request_key auth key */
 #define KEY_SPEC_REQUESTOR_KEYRING	-8	/* - key ID for request_key() dest keyring */
+#define KEY_SPEC_IPE_KEYRING		-12	/* - key ID for the .ipe keyring */
 
 /* request-key default keyrings */
 #define KEY_REQKEY_DEFL_NO_CHANGE		-1

@@ -26,5 +26,7 @@ int __init ipe_keyring_init(void)
 			      KEY_ALLOC_NOT_IN_QUOTA, NULL, NULL);
 	if (IS_ERR(ipe_keyring))
 		panic("failed to allocate \".ipe\" keyring");
+	key_register_ipe_keyring(ipe_keyring);
+
 	return 0;
 }

@@ -22,6 +22,9 @@
 /* Session keyring create vs join semaphore */
 static DEFINE_MUTEX(key_session_mutex);
 
+/* IPE keyring reachable through KEY_SPEC_IPE_KEYRING */
+static struct key *ipe_keyring __ro_after_init;
+
 /* The root user's tracking struct */
 struct key_user root_key_user = {
 	.usage		= REFCOUNT_INIT(3),

@@ -590,6 +593,18 @@ bool lookup_user_key_possessed(const struct key *key,
 	return key == match_data->raw_data;
 }
 
+/**
+ * key_register_ipe_keyring - Publish the IPE keyring
+ * @keyring: The keyring to publish
+ *
+ * Make @keyring reachable by userspace through the KEY_SPEC_IPE_KEYRING
+ * special key ID. Called once, from an initcall, and never undone.
+ */
+void key_register_ipe_keyring(struct key *keyring)
+{
+	ipe_keyring = keyring;
+}
+
 /*
  * Look up a key ID given us by userspace with a given permissions mask to get
  * the key it refers to.

@@ -741,6 +756,14 @@ key_ref_t lookup_user_key(key_serial_t id, unsigned long lflags,
 		key_ref = make_key_ref(key, 1);
 		break;
 
+	case KEY_SPEC_IPE_KEYRING:
+		key = ipe_keyring;
+		if (!key)
+			goto error;
+		__key_get(key);
+		key_ref = make_key_ref(key, 0);
+		break;
+
 	default:
 		key_ref = ERR_PTR(-EINVAL);
 		if (id < 1)