From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755184AbdLVISy (ORCPT ); Fri, 22 Dec 2017 03:18:54 -0500 Received: from mga11.intel.com ([192.55.52.93]:58825 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753417AbdLVISv (ORCPT ); Fri, 22 Dec 2017 03:18:51 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.45,439,1508828400"; d="scan'208";a="14787893" From: Lan Tianyu Cc: Lan Tianyu , pbonzini@redhat.com, rkrcmar@redhat.com, kvm@vger.kernel.org, dvyukov@google.com, linux-kernel@vger.kernel.org, david@redhat.com Subject: [PATCH V2] KVM/Eventfd: Avoid crash when assign and deassign specific eventfd in parallel. Date: Thu, 21 Dec 2017 21:10:36 -0500 Message-Id: <20171222021036.13107-1-tianyu.lan@intel.com> X-Mailer: git-send-email 2.15.1.433.g936d1b9.dirty MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit To: unlisted-recipients:; (no To-header on input) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Syzroot reports crash in kvm_irqfd_assign() is caused by use-after-free. Because kvm_irqfd_assign() and kvm_irqfd_deassign() can't run in parallel for one specific eventfd. When assign path hasn't been finished after irqfd has been added to kvm->irqfds.items list, another thead may deassign the eventfd and free struct kvm_kernel_irqfd(). This causes assign path still uses struct kvm_kernel_irqfd freed by deassign path. To avoid such issue, make irqfd's reference under kvm->irq_srcu protection after irqfd added to kvm->irqfds.iterms list and call synchronize_srcu() in irq_shutdown() to make sure that irqfd has been fully initialized in the assign path. Reported-by: Dmitry Vyukov Cc: Paolo Bonzini Cc: Radim Krčmář Cc: Dmitry Vyukov Signed-off-by: Tianyu Lan --- virt/kvm/eventfd.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c index a334399fafec..0abc2e9ddafb 100644 --- a/virt/kvm/eventfd.c +++ b/virt/kvm/eventfd.c @@ -119,8 +119,12 @@ irqfd_shutdown(struct work_struct *work) { struct kvm_kernel_irqfd *irqfd = container_of(work, struct kvm_kernel_irqfd, shutdown); + struct kvm *kvm = irqfd->kvm; u64 cnt; + /* Make sure irqfd has been initalized in assign path. */ + synchronize_srcu(&kvm->irq_srcu); + /* * Synchronize with the wait-queue and unhook ourselves to prevent * further events. @@ -387,7 +391,6 @@ kvm_irqfd_assign(struct kvm *kvm, struct kvm_irqfd *args) idx = srcu_read_lock(&kvm->irq_srcu); irqfd_update(kvm, irqfd); - srcu_read_unlock(&kvm->irq_srcu, idx); list_add_tail(&irqfd->list, &kvm->irqfds.items); @@ -421,6 +424,7 @@ kvm_irqfd_assign(struct kvm *kvm, struct kvm_irqfd *args) } #endif + srcu_read_unlock(&kvm->irq_srcu, idx); return 0; fail: -- 2.15.1.433.g936d1b9.dirty