linux-kernel - Re: [PATCH] KVM: x86: fix for missing initialization of return status variable

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Message-ID: <87ee6q6r1p.fsf@redhat.com>
Date:   Mon, 06 Dec 2021 10:06:26 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Ameer Hamza <amhamza.mgc@...il.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        amhamza.mgc@...il.com, pbonzini@...hat.com, seanjc@...gle.com,
        wanpengli@...cent.com, jmattson@...gle.com, joro@...tes.org,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com
Subject: Re: [PATCH] KVM: x86: fix for missing initialization of return
 status variable

Ameer Hamza <amhamza.mgc@...il.com> writes:

> If undefined ioctl number is passed to the kvm_vcpu_ioctl_device_attr
> function, it should return with error status.
>
> Addresses-Coverity: 1494124 ("Uninitialized scalar variable")
>
> Signed-off-by: Ameer Hamza <amhamza.mgc@...il.com>
> ---
>  arch/x86/kvm/x86.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index e0aa4dd53c7f..55b90c185717 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -5001,7 +5001,7 @@ static int kvm_vcpu_ioctl_device_attr(struct kvm_vcpu *vcpu,
>  				      void __user *argp)
>  {
>  	struct kvm_device_attr attr;
> -	int r;
> +	int r = -EINVAL;
>  
>  	if (copy_from_user(&attr, argp, sizeof(attr)))
>  		return -EFAULT;

The reported issue is not real, kvm_vcpu_ioctl_device_attr() is never
called with anything but [KVM_HAS_DEVICE_ATTR, KVM_GET_DEVICE_ATTR,
KVM_SET_DEVICE_ATTR] as 'ioctl' and the switch below covers all
three. Instead of initializing 'r' we could've added a 'default' case to
the switch, either returning something like EINVAL or just BUG(). Hope
it'll silence coverity.

-- 
Vitaly