Commit b5020a8e authored Dec 21, 2017 by Lan Tianyu Committed by Paolo Bonzini Jul 18, 2018

KVM/Eventfd: Avoid crash when assign and deassign specific eventfd in parallel.



Syzbot reports crashes in kvm_irqfd_assign(), caused by use-after-free
when kvm_irqfd_assign() and kvm_irqfd_deassign() run in parallel
for one specific eventfd. When the assign path hasn't finished but irqfd
has been added to kvm->irqfds.items list, another thead may deassign the
eventfd and free struct kvm_kernel_irqfd(). The assign path then uses
the struct kvm_kernel_irqfd that has been freed by deassign path. To avoid
such issue, keep irqfd under kvm->irq_srcu protection after the irqfd
has been added to kvm->irqfds.items 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@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Tianyu Lan <tianyu.lan@intel.com>
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

parent 94ffba48

virt/kvm/eventfd.c

+5 −1

Original line number	Diff line number	Diff line
		@@ -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: