From patchwork Fri Sep 22 13:39:24 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Guillaume Nault X-Patchwork-Id: 817513 X-Patchwork-Delegate: davem@davemloft.net Return-Path: X-Original-To: patchwork-incoming@ozlabs.org Delivered-To: patchwork-incoming@ozlabs.org Authentication-Results: ozlabs.org; spf=none (mailfrom) smtp.mailfrom=vger.kernel.org (client-ip=209.132.180.67; helo=vger.kernel.org; envelope-from=netdev-owner@vger.kernel.org; receiver=) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by ozlabs.org (Postfix) with ESMTP id 3xzF2h69qDz9s06 for ; Fri, 22 Sep 2017 23:39:40 +1000 (AEST) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752376AbdIVNje (ORCPT ); Fri, 22 Sep 2017 09:39:34 -0400 Received: from zimbra.alphalink.fr ([217.15.80.77]:52471 "EHLO zimbra.alphalink.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752340AbdIVNjc (ORCPT ); Fri, 22 Sep 2017 09:39:32 -0400 Received: from localhost (localhost [127.0.0.1]) by mail-2-cbv2.admin.alphalink.fr (Postfix) with ESMTP id A27432B5206F; Fri, 22 Sep 2017 15:39:31 +0200 (CEST) Received: from zimbra.alphalink.fr ([127.0.0.1]) by localhost (mail-2-cbv2.admin.alphalink.fr [127.0.0.1]) (amavisd-new, port 10032) with ESMTP id IY2cYXijsnPW; Fri, 22 Sep 2017 15:39:24 +0200 (CEST) Received: from localhost (localhost [127.0.0.1]) by mail-2-cbv2.admin.alphalink.fr (Postfix) with ESMTP id D5D462B5212C; Fri, 22 Sep 2017 15:39:24 +0200 (CEST) X-Virus-Scanned: amavisd-new at mail-2-cbv2.admin.alphalink.fr Received: from zimbra.alphalink.fr ([127.0.0.1]) by localhost (mail-2-cbv2.admin.alphalink.fr [127.0.0.1]) (amavisd-new, port 10026) with ESMTP id 7mNNWR1AH840; Fri, 22 Sep 2017 15:39:24 +0200 (CEST) Received: from c-dev-0.admin.alphalink.fr (94-84-15-217.reverse.alphalink.fr [217.15.84.94]) by mail-2-cbv2.admin.alphalink.fr (Postfix) with ESMTP id AD5CA2B52057; Fri, 22 Sep 2017 15:39:24 +0200 (CEST) Received: by c-dev-0.admin.alphalink.fr (Postfix, from userid 1000) id 92A3660179; Fri, 22 Sep 2017 15:39:24 +0200 (CEST) Date: Fri, 22 Sep 2017 15:39:24 +0200 From: Guillaume Nault To: netdev@vger.kernel.org Cc: James Chapman , Tom Parkin , Sabrina Dubroca Subject: [PATCH net 2/2] l2tp: fix race between l2tp_session_delete() and l2tp_tunnel_closeall() Message-ID: <11b04a711e0c263d3d7626961cd211464360d314.1506086081.git.g.nault@alphalink.fr> References: MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-Mutt-Fcc: =Sent User-Agent: NeoMutt/20170609 (1.8.3) Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org There are several ways to remove L2TP sessions: * deleting a session explicitly using the netlink interface (with L2TP_CMD_SESSION_DELETE), * deleting the session's parent tunnel (either by closing the tunnel's file descriptor or using the netlink interface), * closing the PPPOL2TP file descriptor of a PPP pseudo-wire. In some cases, when these methods are used concurrently on the same session, the session can be removed twice, leading to use-after-free bugs. This patch adds a 'dead' flag, used by l2tp_session_delete() and l2tp_tunnel_closeall() to prevent them from stepping on each other's toes. The session deletion path used when closing a PPPOL2TP file descriptor doesn't need to be adapted. It already has to ensure that a session remains valid for the lifetime of its PPPOL2TP file descriptor. So it takes an extra reference on the session in the ->session_close() callback (pppol2tp_session_close()), which is eventually dropped in the ->sk_destruct() callback of the PPPOL2TP socket (pppol2tp_session_destruct()). Still, __l2tp_session_unhash() and l2tp_session_queue_purge() can be called twice and even concurrently for a given session, but thanks to proper locking and re-initialisation of list fields, this is not an issue. Signed-off-by: Guillaume Nault --- net/l2tp/l2tp_core.c | 6 ++++++ net/l2tp/l2tp_core.h | 1 + 2 files changed, 7 insertions(+) diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c index ee485df73ccd..d8c2a89a76e1 100644 --- a/net/l2tp/l2tp_core.c +++ b/net/l2tp/l2tp_core.c @@ -1314,6 +1314,9 @@ void l2tp_tunnel_closeall(struct l2tp_tunnel *tunnel) hlist_del_init(&session->hlist); + if (test_and_set_bit(0, &session->dead)) + goto again; + if (session->ref != NULL) (*session->ref)(session); @@ -1750,6 +1753,9 @@ EXPORT_SYMBOL_GPL(__l2tp_session_unhash); */ int l2tp_session_delete(struct l2tp_session *session) { + if (test_and_set_bit(0, &session->dead)) + return 0; + if (session->ref) (*session->ref)(session); __l2tp_session_unhash(session); diff --git a/net/l2tp/l2tp_core.h b/net/l2tp/l2tp_core.h index a305e0c5925a..70a12df40a5f 100644 --- a/net/l2tp/l2tp_core.h +++ b/net/l2tp/l2tp_core.h @@ -76,6 +76,7 @@ struct l2tp_session_cfg { struct l2tp_session { int magic; /* should be * L2TP_SESSION_MAGIC */ + long dead; struct l2tp_tunnel *tunnel; /* back pointer to tunnel * context */