From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, syzbot , Paolo Bonzini , David Hildenbrand , Sudip Mukherjee Subject: [PATCH 4.4 67/79] KVM: irqfd: fix race between EPOLLHUP and irq_bypass_register_consumer Date: Thu, 23 Aug 2018 09:53:43 +0200 Message-Id: <20180823074923.544978272@linuxfoundation.org> In-Reply-To: <20180823074918.641878835@linuxfoundation.org> References: <20180823074918.641878835@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: 4.4-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: Sudip Mukherjee 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 & POLLIN) schedule_work(&irqfd->inject); - /* - * do not drop the file until the irqfd is fully initialized, otherwise - * we might race against the POLLHUP - */ - fdput(f); #ifdef CONFIG_HAVE_KVM_IRQ_BYPASS irqfd->consumer.token = (void *)irqfd->eventfd; irqfd->consumer.add_producer = kvm_arch_irq_bypass_add_producer; @@ -423,6 +418,12 @@ 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 POLLHUP + */ + fdput(f); return 0; fail: