linux-kernel - Re: [PATCH] kvm: fix page struct leak in handle

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Date:   Wed, 25 Jan 2017 10:31:13 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     dvyukov@...gle.com
Subject: Re: [PATCH] kvm: fix page struct leak in handle_vmon

Am 24.01.2017 um 11:56 schrieb Paolo Bonzini:
> handle_vmon gets a reference on VMXON region page,
> but does not release it. Release the reference.
> 
> Found by syzkaller; based on a patch by Dmitry.
> 
> Reported-by: Dmitry Vyukov <dvyukov@...gle.com>
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>  arch/x86/kvm/vmx.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 42cc3d6f4d20..0f7345035210 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -7085,13 +7085,18 @@ static int nested_vmx_check_vmptr(struct kvm_vcpu *vcpu, int exit_reason,
>  		}
>  
>  		page = nested_get_page(vcpu, vmptr);
> -		if (page == NULL ||
> -		    *(u32 *)kmap(page) != VMCS12_REVISION) {
> +		if (page == NULL) {
>  			nested_vmx_failInvalid(vcpu);
> +			return kvm_skip_emulated_instruction(vcpu);
> +		}
> +		if (*(u32 *)kmap(page) != VMCS12_REVISION) {

shouldn't we also check if kmap even returned a valid pointer before
dereferencing it?

David thinks so.

>  			kunmap(page);
> +			nested_release_page_clean(page);
> +			nested_vmx_failInvalid(vcpu);
>  			return kvm_skip_emulated_instruction(vcpu);
>  		}
>  		kunmap(page);
> +		nested_release_page_clean(page);
>  		vmx->nested.vmxon_ptr = vmptr;
>  		break;
>  	case EXIT_REASON_VMCLEAR:
> 

-- 

David