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=-6.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_PASS,URIBL_BLOCKED,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 671CFC43381 for ; Thu, 21 Feb 2019 14:37:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3779A2084D for ; Thu, 21 Feb 2019 14:37:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1550759864; bh=l93Evb8YqM0Tkmz6yNRBZOhB4d6bmHgDT8WwYma9qDM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=Wk++mtfZZI8JVag++Z48JLi54OgVH3QTzCPbztBZvLvbDknnuOFmXUoa55gqkVTbT tuEKDhn9vmMKpE8DB93MGVD5uXwGfnk043ZEmS/zpJOjYS1bJedcf1rtRWfzbqEpxL JWfKzaOEpme3KiRo1PjxWsV2wUv78YnYw9R2EQA4= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728447AbfBUOhi (ORCPT ); Thu, 21 Feb 2019 09:37:38 -0500 Received: from mail.kernel.org ([198.145.29.99]:58940 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725870AbfBUOhh (ORCPT ); Thu, 21 Feb 2019 09:37:37 -0500 Received: from localhost (5356596B.cm-6-7b.dynamic.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 B517E2084D; Thu, 21 Feb 2019 14:37:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1550759857; bh=l93Evb8YqM0Tkmz6yNRBZOhB4d6bmHgDT8WwYma9qDM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=r/4eGZd4QS9FZQ7mVUiahCeQHRBp60HwuYmiknC2f03mk1IzWgeL9nWSLWG5OYruj aqDASB58DX5hIYKlrRG6vbu7B4lXS4BYwxRqA3/r0U/B9W2agIEtMlMWWPt0KcRSLY UaX72JledjHzbeIvi+8PxisOEgcppwWps/dxoPug= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, stable@kernel.org, Jann Horn , Paolo Bonzini Subject: [PATCH 4.4 14/20] kvm: fix kvm_ioctl_create_device() reference counting (CVE-2019-6974) Date: Thu, 21 Feb 2019 15:35:44 +0100 Message-Id: <20190221141947.179218556@linuxfoundation.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190221141946.772985220@linuxfoundation.org> References: <20190221141946.772985220@linuxfoundation.org> User-Agent: quilt/0.65 X-stable: review X-Patchwork-Hint: ignore MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org 4.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Jann Horn commit cfa39381173d5f969daf43582c95ad679189cbc9 upstream. kvm_ioctl_create_device() does the following: 1. creates a device that holds a reference to the VM object (with a borrowed reference, the VM's refcount has not been bumped yet) 2. initializes the device 3. transfers the reference to the device to the caller's file descriptor table 4. calls kvm_get_kvm() to turn the borrowed reference to the VM into a real reference The ownership transfer in step 3 must not happen before the reference to the VM becomes a proper, non-borrowed reference, which only happens in step 4. After step 3, an attacker can close the file descriptor and drop the borrowed reference, which can cause the refcount of the kvm object to drop to zero. This means that we need to grab a reference for the device before anon_inode_getfd(), otherwise the VM can disappear from under us. Fixes: 852b6d57dc7f ("kvm: add device control API") Cc: stable@kernel.org Signed-off-by: Jann Horn Signed-off-by: Paolo Bonzini Signed-off-by: Greg Kroah-Hartman --- virt/kvm/kvm_main.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -2711,14 +2711,15 @@ static int kvm_ioctl_create_device(struc return ret; } + kvm_get_kvm(kvm); ret = anon_inode_getfd(ops->name, &kvm_device_fops, dev, O_RDWR | O_CLOEXEC); if (ret < 0) { + kvm_put_kvm(kvm); ops->destroy(dev); return ret; } list_add(&dev->vm_node, &kvm->devices); - kvm_get_kvm(kvm); cd->fd = ret; return 0; }