Messages in this thread Patch in this message |  | | From | Lan Tianyu <> | Subject | [PATCH] KVM/Eventfd: Avoid crash when assign and deassign same eventfd in parallel. | Date | Sun, 17 Dec 2017 18:40:07 -0500 |
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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 same 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, add "initialized" flag in the struct kvm_kernel_irqfd and check the flag before deactivating irqfd. If irqfd is still in initialization, deassign path return fault.
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> Cc: Wanpeng Li <kernellwp@gmail.com> Signed-off-by: Tianyu Lan <tianyu.lan@intel.com> --- include/linux/kvm_irqfd.h | 1 + virt/kvm/eventfd.c | 11 +++++++++-- 2 files changed, 10 insertions(+), 2 deletions(-)
diff --git a/include/linux/kvm_irqfd.h b/include/linux/kvm_irqfd.h index 76c2fbc..be6b254 100644 --- a/include/linux/kvm_irqfd.h +++ b/include/linux/kvm_irqfd.h @@ -66,6 +66,7 @@ struct kvm_kernel_irqfd { struct work_struct shutdown; struct irq_bypass_consumer consumer; struct irq_bypass_producer *producer; + u8 initialized:1; }; #endif /* __LINUX_KVM_IRQFD_H */ diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c index a334399..80f06e6 100644 --- a/virt/kvm/eventfd.c +++ b/virt/kvm/eventfd.c @@ -421,6 +421,7 @@ int __attribute__((weak)) kvm_arch_update_irqfd_routing( } #endif + irqfd->initialized = 1; return 0; fail: @@ -525,6 +526,7 @@ void kvm_unregister_irq_ack_notifier(struct kvm *kvm, { struct kvm_kernel_irqfd *irqfd, *tmp; struct eventfd_ctx *eventfd; + int ret = 0; eventfd = eventfd_ctx_fdget(args->fd); if (IS_ERR(eventfd)) @@ -543,7 +545,12 @@ void kvm_unregister_irq_ack_notifier(struct kvm *kvm, write_seqcount_begin(&irqfd->irq_entry_sc); irqfd->irq_entry.type = 0; write_seqcount_end(&irqfd->irq_entry_sc); - irqfd_deactivate(irqfd); + + if (irqfd->initialized) + irqfd_deactivate(irqfd); + else + ret = -EFAULT; + } } @@ -557,7 +564,7 @@ void kvm_unregister_irq_ack_notifier(struct kvm *kvm, */ flush_workqueue(irqfd_cleanup_wq); - return 0; + return ret; } int -- 1.8.3.1
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