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@vger.kernel.org.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 2ee3757424be7c1cd1d0bbfa6db29a7edd82a250 Mon Sep 17 00:00:00 2001
From: Sean Christopherson seanjc@google.com 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@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
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; }