l2tp: don't mask errors in pppol2tp_getsockopt()

pppol2tp_getsockopt() doesn't take into account the error code returned
by pppol2tp_tunnel_getsockopt() or pppol2tp_session_getsockopt(). If
error occurs there, pppol2tp_getsockopt() continues unconditionally and
reports erroneous values.

Fixes: fd558d186df2 ("l2tp: Split pppol2tp patch into separate l2tp and ppp parts")
Signed-off-by: Guillaume Nault <g.nault@alphalink.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/l2tp/l2tp_ppp.c

@@ -1505,8 +1505,13 @@ static int pppol2tp_getsockopt(struct socket *sock, int level, int optname,
 
 		err = pppol2tp_tunnel_getsockopt(sk, tunnel, optname, &val);
 		sock_put(ps->tunnel_sock);
-	} else
+		if (err)
+			goto end_put_sess;
+	} else {
 		err = pppol2tp_session_getsockopt(sk, session, optname, &val);
+		if (err)
+			goto end_put_sess;
+	}
 
 	err = -EFAULT;
 	if (put_user(len, optlen))