path: root/virt/lib
diff options
authorWanpeng Li <>2017-01-05 17:39:42 -0800
committerPaolo Bonzini <>2017-01-12 14:42:34 +0100
commit4f3dbdf47e150016aacd734e663347fcaa768303 (patch)
tree63b5cbad9d56038c76aaf061a3095769320ed853 /virt/lib
parent129a72a0d3c8e139a04512325384fe5ac119e74d (diff)
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+0x16b/0x480 worker_thread+0x4b/0x500 kthread+0x101/0x140 ? process_one_work+0x480/0x480 ? kthread_create_on_node+0x60/0x60 ret_from_fork+0x25/0x30 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: Dmitry Vyukov <> Suggested-by: Alex Williamson <> Cc: Cc: Paolo Bonzini <> Cc: Radim Krčmář <> Cc: Dmitry Vyukov <> Cc: Alex Williamson <> Signed-off-by: Wanpeng Li <> Signed-off-by: Paolo Bonzini <>
Diffstat (limited to 'virt/lib')
1 files changed, 2 insertions, 2 deletions
diff --git a/virt/lib/irqbypass.c b/virt/lib/irqbypass.c
index 52abac4bb6a2..6d2fcd6fcb25 100644
--- a/virt/lib/irqbypass.c
+++ b/virt/lib/irqbypass.c
@@ -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) {