CRED: Rename cred_exec_mutex to reflect that it's a guard against ptrace

Rename cred_exec_mutex to reflect that it's a guard against foreign
intervention on a process's credential state, such as is made by ptrace().  The
attachment of a debugger to a process affects execve()'s calculation of the new
credential state - _and_ also setprocattr()'s calculation of that state.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: James Morris <jmorris@namei.org>
diff --git a/include/linux/init_task.h b/include/linux/init_task.h
index d87247d..7f54ba9 100644
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -145,8 +145,8 @@
 	.group_leader	= &tsk,						\
 	.real_cred	= &init_cred,					\
 	.cred		= &init_cred,					\
-	.cred_exec_mutex =						\
-		 __MUTEX_INITIALIZER(tsk.cred_exec_mutex),		\
+	.cred_guard_mutex =						\
+		 __MUTEX_INITIALIZER(tsk.cred_guard_mutex),		\
 	.comm		= "swapper",					\
 	.thread		= INIT_THREAD,					\
 	.fs		= &init_fs,					\
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 3fa82b3..5932ace 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1247,7 +1247,9 @@
 					 * credentials (COW) */
 	const struct cred *cred;	/* effective (overridable) subjective task
 					 * credentials (COW) */
-	struct mutex cred_exec_mutex;	/* execve vs ptrace cred calculation mutex */
+	struct mutex cred_guard_mutex;	/* guard against foreign influences on
+					 * credential calculations
+					 * (notably. ptrace) */
 
 	char comm[TASK_COMM_LEN]; /* executable name excluding path
 				     - access with [gs]et_task_comm (which lock