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KVM: Destroy I/O bus devices on unregister failure _after_ sync'ing SRCU 

If allocating a new instance of an I/O bus fails when unregistering a
device, wait to destroy the device until after all readers are guaranteed
to see the new null bus.  Destroying devices before the bus is nullified
could lead to use-after-free since readers expect the devices on their
reference of the bus to remain valid.

Fixes: f65886606c ("KVM: fix memory leak in kvm_io_bus_unregister_dev()")
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210412222050.876100-2-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2021-04-12 15:20:48 -07:00 committed by Paolo Bonzini
parent 24e7475f93
commit 2ee3757424
1 changed files with 7 additions and 3 deletions
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10
virt/kvm/kvm_main.c
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@ -4646,7 +4646,13 @@ void kvm_io_bus_unregister_dev(struct kvm *kvm, enum kvm_bus bus_idx,
new_bus->dev_count--; new_bus->dev_count--;
memcpy(new_bus->range + i, bus->range + i + 1, memcpy(new_bus->range + i, bus->range + i + 1,
flex_array_size(new_bus, range, new_bus->dev_count - i)); flex_array_size(new_bus, range, new_bus->dev_count - i));
} else { }
rcu_assign_pointer(kvm->buses[bus_idx], new_bus);
synchronize_srcu_expedited(&kvm->srcu);
/* Destroy the old bus _after_ installing the (null) bus. */
if (!new_bus) {
pr_err("kvm: failed to shrink bus, removing it completely\n"); pr_err("kvm: failed to shrink bus, removing it completely\n");
for (j = 0; j < bus->dev_count; j++) { for (j = 0; j < bus->dev_count; j++) {
if (j == i) if (j == i)
@ -4655,8 +4661,6 @@ void kvm_io_bus_unregister_dev(struct kvm *kvm, enum kvm_bus bus_idx,
} }
} }
rcu_assign_pointer(kvm->buses[bus_idx], new_bus);
synchronize_srcu_expedited(&kvm->srcu);
kfree(bus); kfree(bus);
return; return;
} }