exec: Only compute current once in flush_old_exec

Make it clear that current only needs to be computed once in
flush_old_exec.  This may have some efficiency improvements and it
makes the code easier to change.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Reviewed-by: Bernd Edlinger <bernd.edlinger@hotmail.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
Reviewed-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Signed-off-by: Bernd Edlinger <bernd.edlinger@hotmail.de>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

fs/exec.c

@@ -1260,13 +1260,14 @@ void __set_task_comm(struct task_struct *tsk, const char *buf, bool exec)
  */
 int flush_old_exec(struct linux_binprm * bprm)
 {
+	struct task_struct *me = current;
 	int retval;
 
 	/*
 	 * Make sure we have a private signal table and that
 	 * we are unassociated from the previous thread group.
 	 */
-	retval = de_thread(current);
+	retval = de_thread(me);
 	if (retval)
 		goto out;
 
@@ -1294,18 +1295,18 @@ int flush_old_exec(struct linux_binprm * bprm)
 	bprm->mm = NULL;
 
 	set_fs(USER_DS);
-	current->flags &= ~(PF_RANDOMIZE | PF_FORKNOEXEC | PF_KTHREAD |
+	me->flags &= ~(PF_RANDOMIZE | PF_FORKNOEXEC | PF_KTHREAD |
 					PF_NOFREEZE | PF_NO_SETAFFINITY);
 	flush_thread();
-	current->personality &= ~bprm->per_clear;
+	me->personality &= ~bprm->per_clear;
 
 	/*
 	 * We have to apply CLOEXEC before we change whether the process is
 	 * dumpable (in setup_new_exec) to avoid a race with a process in userspace
 	 * trying to access the should-be-closed file descriptors of a process
 	 * undergoing exec(2).
 	 */
-	do_close_on_exec(current->files);
+	do_close_on_exec(me->files);
 	return 0;
 
 out: