4.9-stable review patch. If anyone has any objections, please let me know.
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From: Paolo Bonzini pbonzini@redhat.com
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 syzkaller@googlegroups.com Cc: stable@vger.kernel.org Signed-off-by: Paolo Bonzini pbonzini@redhat.com Reviewed-by: David Hildenbrand david@redhat.com Signed-off-by: Sudip Mukherjee sudipm.mukherjee@gmail.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- 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 if (kvm_arch_has_irq_bypass()) { irqfd->consumer.token = (void *)irqfd->eventfd; @@ -425,6 +420,12 @@ 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: