On 22/12/2017 03:10, Lan Tianyu wrote:
> 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 <dvyukov@xxxxxxxxxx>
> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Cc: Radim Krčmář <rkrcmar@xxxxxxxxxx>
> Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> Signed-off-by: Tianyu Lan <tianyu.lan@xxxxxxxxx>
> ---
> 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:
>
Queued, at last. Thanks,
Paolo
