Re: [patch 2/3] KVM: x86: disallow KVM_{SET,GET}_LAPIC without in kernel irqchip

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Oct 27, 2009 at 01:10:44PM -0200, Marcelo Tosatti wrote:
> Otherwise kvm might attempt to dereference a NULL pointer.
> 
> CC: stable@kernel.org
> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
> 
> Index: kvm/arch/x86/kvm/x86.c
> ===================================================================
> --- kvm.orig/arch/x86/kvm/x86.c
> +++ kvm/arch/x86/kvm/x86.c
> @@ -1815,6 +1815,9 @@ long kvm_arch_vcpu_ioctl(struct file *fi
>  
>  	switch (ioctl) {
>  	case KVM_GET_LAPIC: {
> +		r = -EINVAL;
> +		if (!irqchip_in_kernel(vcpu->kvm))
> +			goto out;
>  		lapic = kzalloc(sizeof(struct kvm_lapic_state), GFP_KERNEL);
>  
>  		r = -ENOMEM;
> @@ -1830,6 +1833,9 @@ long kvm_arch_vcpu_ioctl(struct file *fi
>  		break;
>  	}
>  	case KVM_SET_LAPIC: {
> +		r = -EINVAL;
> +		if (!irqchip_in_kernel(vcpu->kvm))
> +			goto out;
>  		lapic = kmalloc(sizeof(struct kvm_lapic_state), GFP_KERNEL);
>  		r = -ENOMEM;
>  		if (!lapic)
> 

Can the value of irqchip_in_kernel be changed by userspace
after we have checked it? If yes, this check won't help ...


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