KVM: fix irqfd assign/deassign race

I think I see the following (theoretical) race:

During irqfd assign, we drop irqfds lock before we
schedule inject work. Therefore, deassign running
on another CPU could cause shutdown and flush to run
before inject, causing user after free in inject.

A simple fix it to schedule inject under the lock.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Gregory Haskins <ghaskins@novell.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
index 66cf65b510b11c1c245db3b6a435e040ac3606fc..c1f1e3c6298462f8ed4d672257dac3b4da081b33 100644 (file)
--- a/virt/kvm/eventfd.c
+++ b/virt/kvm/eventfd.c
@@ -218,7 +218,6 @@ kvm_irqfd_assign(struct kvm *kvm, int fd, int gsi)
        events = file->f_op->poll(file, &irqfd->pt);
 
        list_add_tail(&irqfd->list, &kvm->irqfds.items);
-       spin_unlock_irq(&kvm->irqfds.lock);
 
        /*
         * Check if there was an event already pending on the eventfd
@@ -227,6 +226,8 @@ kvm_irqfd_assign(struct kvm *kvm, int fd, int gsi)
        if (events & POLLIN)
                schedule_work(&irqfd->inject);
 
+       spin_unlock_irq(&kvm->irqfds.lock);
+
        /*
         * do not drop the file until the irqfd is fully initialized, otherwise
         * we might race against the POLLHUP