Commit 4f3dbdf4 authored by Wanpeng Li's avatar Wanpeng Li Committed by Paolo Bonzini

KVM: eventfd: fix NULL deref irqbypass consumer

Reported syzkaller:

    BUG: unable to handle kernel NULL pointer dereference at 0000000000000008
    IP: irq_bypass_unregister_consumer+0x9d/0xb70 [irqbypass]
    PGD 0

    Oops: 0002 [#1] SMP
    CPU: 1 PID: 125 Comm: kworker/1:1 Not tainted 4.9.0+ #1
    Workqueue: kvm-irqfd-cleanup irqfd_shutdown [kvm]
    task: ffff9bbe0dfbb900 task.stack: ffffb61802014000
    RIP: 0010:irq_bypass_unregister_consumer+0x9d/0xb70 [irqbypass]
    Call Trace:
     irqfd_shutdown+0x66/0xa0 [kvm]
     ? process_one_work+0x480/0x480
     ? kthread_create_on_node+0x60/0x60
    RIP: irq_bypass_unregister_consumer+0x9d/0xb70 [irqbypass] RSP: ffffb61802017e20
    CR2: 0000000000000008

The syzkaller folks reported a NULL pointer dereference that due to
unregister an consumer which fails registration before. The syzkaller
creates two VMs w/ an equal eventfd occasionally. So the second VM
fails to register an irqbypass consumer. It will make irqfd as inactive
and queue an workqueue work to shutdown irqfd and unregister the irqbypass
consumer when eventfd is closed. However, the second consumer has been
initialized though it fails registration. So the token(same as the first
VM's) is taken to unregister the consumer through the workqueue, the
consumer of the first VM is found and unregistered, then NULL deref incurred
in the path of deleting consumer from the consumers list.

This patch fixes it by making irq_bypass_register/unregister_consumer()
looks for the consumer entry based on consumer pointer itself instead of
token matching.
Reported-by: default avatarDmitry Vyukov <>
Suggested-by: default avatarAlex Williamson <>
Cc: Paolo Bonzini <>
Cc: Radim Krčmář <>
Cc: Dmitry Vyukov <>
Cc: Alex Williamson <>
Signed-off-by: default avatarWanpeng Li <>
Signed-off-by: default avatarPaolo Bonzini <>
parent 129a72a0
......@@ -195,7 +195,7 @@ int irq_bypass_register_consumer(struct irq_bypass_consumer *consumer)
list_for_each_entry(tmp, &consumers, node) {
if (tmp->token == consumer->token) {
if (tmp->token == consumer->token || tmp == consumer) {
return -EBUSY;
......@@ -245,7 +245,7 @@ void irq_bypass_unregister_consumer(struct irq_bypass_consumer *consumer)
list_for_each_entry(tmp, &consumers, node) {
if (tmp->token != consumer->token)
if (tmp != consumer)
list_for_each_entry(producer, &producers, node) {
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