From patchwork Thu Jan 7 14:16:48 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg KH X-Patchwork-Id: 359710 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=-18.8 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_BLOCKED, 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 A80FDC4332D for ; Thu, 7 Jan 2021 14:19:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6F9CD208A9 for ; Thu, 7 Jan 2021 14:19:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729117AbhAGOR3 (ORCPT ); Thu, 7 Jan 2021 09:17:29 -0500 Received: from mail.kernel.org ([198.145.29.99]:39068 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729103AbhAGOR2 (ORCPT ); Thu, 7 Jan 2021 09:17:28 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id B450E23343; Thu, 7 Jan 2021 14:16:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1610029017; bh=ULK609EFnTBW8KsazZ5uOOaBEPQe7mf2MfJu790YcjI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=LrzKD112sDTzZptkLU4sJAxQ4Lv/cyntio1eMev/WJi0IVpf5+Usym/0uR5DuURzK 6xZ4NpibqenynyhwQIDgHDtEatJcxLeffRv6aRgT/3Rs3bArn8WXTSrBzbpz3Cs0HY MZFIewVr4CptIEfMymXkXFdtMRusRhUIYEG3o/ek= 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 4.9 28/32] xenbus/xenbus_backend: Disallow pending watch messages Date: Thu, 7 Jan 2021 15:16:48 +0100 Message-Id: <20210107140829.206117258@linuxfoundation.org> X-Mailer: git-send-email 2.30.0 In-Reply-To: <20210107140827.866214702@linuxfoundation.org> References: <20210107140827.866214702@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 @@ -181,6 +181,12 @@ static int xenbus_probe_backend(struct x return err; } +static bool frontend_will_handle(struct xenbus_watch *watch, + const char **vec, unsigned int len) +{ + return watch->nr_pending == 0; +} + static void frontend_changed(struct xenbus_watch *watch, const char **vec, unsigned int len) { @@ -192,6 +198,7 @@ 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",