From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7C86BC2BA2B for ; Sat, 11 Apr 2020 12:12:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5594E20787 for ; Sat, 11 Apr 2020 12:12:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1586607139; bh=aoqivjAdPfLXCHPm7MVh9istfFKL/G+QKC2KQBc0cpY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=BIyBrCKTIT5AHkbbSHVrJOXdbSwGrPXK9fuVBdqtoMF7dsnZJpyHpejURVUW7kjHk DCtTz5xijlFbprKhZMmEckQOFHFSXeDBoqwhR6B+GAojV28yG9XK7pjtPpsdDqswb7 c0vwP9TydTGmIX9rPy54nUMmZDiq/5NDpP44XTjQ= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727199AbgDKMMR (ORCPT ); Sat, 11 Apr 2020 08:12:17 -0400 Received: from mail.kernel.org ([198.145.29.99]:44686 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727183AbgDKMMM (ORCPT ); Sat, 11 Apr 2020 08:12:12 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 098BD21744; Sat, 11 Apr 2020 12:12:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1586607131; bh=aoqivjAdPfLXCHPm7MVh9istfFKL/G+QKC2KQBc0cpY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=xz93EiA3+oS3Xbjz42bFENCZLlRgATkVwrICVGrU3sO0ICVVdm0EJV8mu8Q++gPuC UFsmcucmUvTCaK6fjdet/eWDn2vpjcCXqpfK/Iy+agTPfHG4HYPO9gisMZjtLKU1Bj JgTiSZIW3Pcgpl0jbECOjkBwV59cJ9T5DhMXrdiA= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Guillaume Nault , "David S. Miller" , Will Deacon Subject: [PATCH 4.9 02/32] l2tp: fix race between l2tp_session_delete() and l2tp_tunnel_closeall() Date: Sat, 11 Apr 2020 14:08:41 +0200 Message-Id: <20200411115419.004556589@linuxfoundation.org> X-Mailer: git-send-email 2.26.0 In-Reply-To: <20200411115418.455500023@linuxfoundation.org> References: <20200411115418.455500023@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Guillaume Nault commit b228a94066406b6c456321d69643b0d7ce11cfa6 upstream. 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 Signed-off-by: David S. Miller Signed-off-by: Will Deacon Signed-off-by: Greg Kroah-Hartman --- net/l2tp/l2tp_core.c | 6 ++++++ net/l2tp/l2tp_core.h | 1 + 2 files changed, 7 insertions(+) --- a/net/l2tp/l2tp_core.c +++ b/net/l2tp/l2tp_core.c @@ -1351,6 +1351,9 @@ again: hlist_del_init(&session->hlist); + if (test_and_set_bit(0, &session->dead)) + goto again; + if (session->ref != NULL) (*session->ref)(session); @@ -1799,6 +1802,9 @@ 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); --- a/net/l2tp/l2tp_core.h +++ b/net/l2tp/l2tp_core.h @@ -84,6 +84,7 @@ 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 */