The patch below does not apply to the 4.4-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@xxxxxxxxxxxxxxx>.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
>From 2ee3757424be7c1cd1d0bbfa6db29a7edd82a250 Mon Sep 17 00:00:00 2001
From: Sean Christopherson <seanjc@xxxxxxxxxx>
Date: Mon, 12 Apr 2021 15:20:48 -0700
Subject: [PATCH] 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: f65886606c2d ("KVM: fix memory leak in kvm_io_bus_unregister_dev()")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Message-Id: <20210412222050.876100-2-seanjc@xxxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 529cff1050d7..c771d40737c9 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -4646,7 +4646,13 @@ void kvm_io_bus_unregister_dev(struct kvm *kvm, enum kvm_bus bus_idx,
new_bus->dev_count--;
memcpy(new_bus->range + i, bus->range + i + 1,
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");
for (j = 0; j < bus->dev_count; j++) {
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);
return;
}
