From 9432a3175770e06cb83eada2d91fac90c977cb99 Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Mon, 28 May 2018 13:31:13 +0200 Subject: [PATCH] KVM: irqfd: fix race between EPOLLHUP and irq_bypass_register_consumer 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 --- virt/kvm/eventfd.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c index decefe944b0f..fe6eb0fe07f6 100644 --- a/virt/kvm/eventfd.c +++ b/virt/kvm/eventfd.c @@ -405,11 +405,6 @@ kvm_irqfd_assign(struct kvm *kvm, struct kvm_irqfd *args) 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 kvm_irqfd *args) #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: