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 <[email protected]> > Cc: Paolo Bonzini <[email protected]> > Cc: Radim Krčmář <[email protected]> > Cc: Dmitry Vyukov <[email protected]> > Signed-off-by: Tianyu Lan <[email protected]> > --- > 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
