From patchwork Mon Dec 28 12:51:02 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg KH X-Patchwork-Id: 353206 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=-18.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_RED, USER_AGENT_GIT autolearn=unavailable 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 F1EBEC433E0 for ; Mon, 28 Dec 2020 15:55:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B0550206E5 for ; Mon, 28 Dec 2020 15:55:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390801AbgL1Pyi (ORCPT ); Mon, 28 Dec 2020 10:54:38 -0500 Received: from mail.kernel.org ([198.145.29.99]:37046 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2390802AbgL1Ngt (ORCPT ); Mon, 28 Dec 2020 08:36:49 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id BA23F207C9; Mon, 28 Dec 2020 13:36:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1609162568; bh=+pSnwWsCMByYdsFsfpHiPyCaC6g7YzUC9AlAXhW96sA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=CjLKl+Ou0xXMCiQFEhzqRFqPjAt393Hu6nUbb+65vl9Iwab+1afgux2uLXDOYYHcY VZ94CRYRIQoIJteIqMLBLgrBYg3zIiJ1J57geGD5Cai6po04xdMmn1poWodBbsm1ms cWvuKiXm8PfEda7Hlvoallpy9LBGj2IgC05pxmyg= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, SeongJae Park , Michael Kurth , Pawel Wieczorkiewicz , Juergen Gross Subject: [PATCH 4.19 343/346] xenbus/xenbus_backend: Disallow pending watch messages Date: Mon, 28 Dec 2020 13:51:02 +0100 Message-Id: <20201228124936.337727453@linuxfoundation.org> X-Mailer: git-send-email 2.29.2 In-Reply-To: <20201228124919.745526410@linuxfoundation.org> References: <20201228124919.745526410@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: SeongJae Park commit 9996bd494794a2fe393e97e7a982388c6249aa76 upstream. 'xenbus_backend' watches 'state' of devices, which is writable by guests. Hence, if guests intensively updates it, dom0 will have lots of pending events that exhausting memory of dom0. In other words, guests can trigger dom0 memory pressure. This is known as XSA-349. However, the watch callback of it, 'frontend_changed()', reads only 'state', so doesn't need to have the pending events. To avoid the problem, this commit disallows pending watch messages for 'xenbus_backend' using the 'will_handle()' watch callback. This is part of XSA-349 Cc: stable@vger.kernel.org Signed-off-by: SeongJae Park Reported-by: Michael Kurth Reported-by: Pawel Wieczorkiewicz Reviewed-by: Juergen Gross Signed-off-by: Juergen Gross Signed-off-by: Greg Kroah-Hartman --- drivers/xen/xenbus/xenbus_probe_backend.c | 7 +++++++ 1 file changed, 7 insertions(+) --- a/drivers/xen/xenbus/xenbus_probe_backend.c +++ b/drivers/xen/xenbus/xenbus_probe_backend.c @@ -180,6 +180,12 @@ static int xenbus_probe_backend(struct x return err; } +static bool frontend_will_handle(struct xenbus_watch *watch, + const char *path, const char *token) +{ + return watch->nr_pending == 0; +} + static void frontend_changed(struct xenbus_watch *watch, const char *path, const char *token) { @@ -191,6 +197,7 @@ static struct xen_bus_type xenbus_backen .levels = 3, /* backend/type// */ .get_bus_id = backend_bus_id, .probe = xenbus_probe_backend, + .otherend_will_handle = frontend_will_handle, .otherend_changed = frontend_changed, .bus = { .name = "xen-backend",