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=-2.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,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 03F63ECDFB8 for ; Mon, 23 Jul 2018 12:26:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B394820854 for ; Mon, 23 Jul 2018 12:26:14 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B394820854 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linuxfoundation.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388309AbeGWN1J (ORCPT ); Mon, 23 Jul 2018 09:27:09 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:45186 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387882AbeGWN1J (ORCPT ); Mon, 23 Jul 2018 09:27:09 -0400 Received: from localhost (LFbn-1-12238-233.w90-92.abo.wanadoo.fr [90.92.53.233]) by mail.linuxfoundation.org (Postfix) with ESMTPSA id C8A77BE1; Mon, 23 Jul 2018 12:26:11 +0000 (UTC) From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, syzbot , Paolo Bonzini , David Hildenbrand Subject: [PATCH 4.17 06/63] KVM: irqfd: fix race between EPOLLHUP and irq_bypass_register_consumer Date: Mon, 23 Jul 2018 14:24:12 +0200 Message-Id: <20180723122446.617075797@linuxfoundation.org> X-Mailer: git-send-email 2.18.0 In-Reply-To: <20180723122446.351334162@linuxfoundation.org> References: <20180723122446.351334162@linuxfoundation.org> User-Agent: quilt/0.65 X-stable: review MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 4.17-stable review patch. If anyone has any objections, please let me know. ------------------ From: Paolo Bonzini commit 9432a3175770e06cb83eada2d91fac90c977cb99 upstream. A comment warning against this bug is there, but the code is not doing what the comment says. Therefore it is possible that an EPOLLHUP races against irq_bypass_register_consumer. The EPOLLHUP handler schedules irqfd_shutdown, and if that runs soon enough, you get a use-after-free. Reported-by: syzbot Cc: stable@vger.kernel.org Signed-off-by: Paolo Bonzini Reviewed-by: David Hildenbrand Signed-off-by: Greg Kroah-Hartman --- virt/kvm/eventfd.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) --- a/virt/kvm/eventfd.c +++ b/virt/kvm/eventfd.c @@ -405,11 +405,6 @@ kvm_irqfd_assign(struct kvm *kvm, struct if (events & EPOLLIN) schedule_work(&irqfd->inject); - /* - * do not drop the file until the irqfd is fully initialized, otherwise - * we might race against the EPOLLHUP - */ - fdput(f); #ifdef CONFIG_HAVE_KVM_IRQ_BYPASS if (kvm_arch_has_irq_bypass()) { irqfd->consumer.token = (void *)irqfd->eventfd; @@ -425,6 +420,12 @@ kvm_irqfd_assign(struct kvm *kvm, struct #endif srcu_read_unlock(&kvm->irq_srcu, idx); + + /* + * do not drop the file until the irqfd is fully initialized, otherwise + * we might race against the EPOLLHUP + */ + fdput(f); return 0; fail: