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KVM: irqfd: fix race between EPOLLHUP and irq_bypass_register_consumer

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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>
This commit is contained in:
Paolo Bonzini 2018-05-28 13:31:13 +02:00
parent b5020a8e6b
commit 9432a31757
1 changed files with 6 additions and 5 deletions
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11
virt/kvm/eventfd.c
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@ -405,11 +405,6 @@ kvm_irqfd_assign(struct kvm *kvm, struct kvm_irqfd *args)
if (events & EPOLLIN) if (events & EPOLLIN)
schedule_work(&irqfd->inject); schedule_work(&irqfd->inject);
/*
* do not drop the file until the irqfd is fully initialized, otherwise
* we might race against the EPOLLHUP
*/
fdput(f);
#ifdef CONFIG_HAVE_KVM_IRQ_BYPASS #ifdef CONFIG_HAVE_KVM_IRQ_BYPASS
if (kvm_arch_has_irq_bypass()) { if (kvm_arch_has_irq_bypass()) {
irqfd->consumer.token = (void *)irqfd->eventfd; irqfd->consumer.token = (void *)irqfd->eventfd;
@ -425,6 +420,12 @@ kvm_irqfd_assign(struct kvm *kvm, struct kvm_irqfd *args)
#endif #endif
srcu_read_unlock(&kvm->irq_srcu, idx); srcu_read_unlock(&kvm->irq_srcu, idx);
/*
* do not drop the file until the irqfd is fully initialized, otherwise
* we might race against the EPOLLHUP
*/
fdput(f);
return 0; return 0;
fail: fail: