CRED: Separate per-task-group keyrings from signal_struct

Separate per-task-group keyrings from signal_struct and dangle their anchor
from the cred struct rather than the signal_struct.

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: James Morris <jmorris@namei.org>
Signed-off-by: James Morris <jmorris@namei.org>
diff --git a/include/linux/cred.h b/include/linux/cred.h
index 166ce4d..62b9e53 100644
--- a/include/linux/cred.h
+++ b/include/linux/cred.h
@@ -72,6 +72,21 @@
 extern int in_egroup_p(gid_t);
 
 /*
+ * The common credentials for a thread group
+ * - shared by CLONE_THREAD
+ */
+#ifdef CONFIG_KEYS
+struct thread_group_cred {
+	atomic_t	usage;
+	pid_t		tgid;			/* thread group process ID */
+	spinlock_t	lock;
+	struct key	*session_keyring;	/* keyring inherited over fork */
+	struct key	*process_keyring;	/* keyring private to this process */
+	struct rcu_head	rcu;			/* RCU deletion hook */
+};
+#endif
+
+/*
  * The security context of a task
  *
  * The parts of the context break down into two categories:
@@ -114,6 +129,7 @@
 					 * keys to */
 	struct key	*thread_keyring; /* keyring private to this thread */
 	struct key	*request_key_auth; /* assumed request_key authority */
+	struct thread_group_cred *tgcred; /* thread-group shared credentials */
 #endif
 #ifdef CONFIG_SECURITY
 	void		*security;	/* subjective LSM security */