audit: Simply AUDIT_TTY_SET and AUDIT_TTY_GET

Use current instead of looking up the current up the current task by
process identifier.  Netlink requests are processed in trhe context of
the sending task so this is safe.

Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Eric Paris <eparis@redhat.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

kernel/audit.c

@@ -866,41 +866,29 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
 		break;
 	case AUDIT_TTY_GET: {
 		struct audit_tty_status s;
-		struct task_struct *tsk;
-		unsigned long flags;
-
-		rcu_read_lock();
-		tsk = find_task_by_vpid(pid);
-		if (tsk && lock_task_sighand(tsk, &flags)) {
-			s.enabled = tsk->signal->audit_tty != 0;
-			unlock_task_sighand(tsk, &flags);
-		} else
-			err = -ESRCH;
-		rcu_read_unlock();
-
-		if (!err)
-			audit_send_reply(NETLINK_CB(skb).pid, seq,
-					 AUDIT_TTY_GET, 0, 0, &s, sizeof(s));
+		struct task_struct *tsk = current;
+
+		spin_lock_irq(&tsk->sighand->siglock);
+		s.enabled = tsk->signal->audit_tty != 0;
+		spin_unlock_irq(&tsk->sighand->siglock);
+
+		audit_send_reply(NETLINK_CB(skb).pid, seq,
+				 AUDIT_TTY_GET, 0, 0, &s, sizeof(s));
 		break;
 	}
 	case AUDIT_TTY_SET: {
 		struct audit_tty_status *s;
-		struct task_struct *tsk;
-		unsigned long flags;
+		struct task_struct *tsk = current;
 
 		if (nlh->nlmsg_len < sizeof(struct audit_tty_status))
 			return -EINVAL;
 		s = data;
 		if (s->enabled != 0 && s->enabled != 1)
 			return -EINVAL;
-		rcu_read_lock();
-		tsk = find_task_by_vpid(pid);
-		if (tsk && lock_task_sighand(tsk, &flags)) {
-			tsk->signal->audit_tty = s->enabled != 0;
-			unlock_task_sighand(tsk, &flags);
-		} else
-			err = -ESRCH;
-		rcu_read_unlock();
+
+		spin_lock_irq(&tsk->sighand->siglock);
+		tsk->signal->audit_tty = s->enabled != 0;
+		spin_unlock_irq(&tsk->sighand->siglock);
 		break;
 	}
 	default: