virtio-mmio: don't break lifecycle of vm_dev

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: virtio-mmio: don't break lifecycle of vm_dev vm_dev has a separate lifecycle because it has a 'struct device' embedded. Thus, having a release callback for it is correct. Allocating the vm_dev struct with devres totally breaks this protection, though. Instead of waiting for the vm_dev release callback, the memory is freed when the platform_device is removed. Resulting in a use-after-free when finally the callback is to be called. To easily see the problem, compile the kernel with CONFIG_DEBUG_KOBJECT_RELEASE and unbind with sysfs. The fix is easy, don't use devres in this case. Found during my research about object lifetime problems.

References

• https://git.kernel.org/stable/c/97a2d55ead76358245b446efd87818e919196d7a
• https://git.kernel.org/stable/c/b788ad3b2468512339c05f23692e36860264e674
• https://git.kernel.org/stable/c/3ff54d904fafabd0912796785e53cce4e69ca123
• https://git.kernel.org/stable/c/5b7d5c2dd664eb8b9a06ecbc06e28d39359c422e
• https://git.kernel.org/stable/c/af5818c35173e096085c6ae2e3aac605d3d15e41
• https://git.kernel.org/stable/c/2dcb368fe5a8eee498ca75c93a18ce2f3b0d6a8e
• https://git.kernel.org/stable/c/55c91fedd03d7b9cf0c5199b2eb12b9b8e95281a