linux-kernel - Re: KVM: Introduce a 'release' method for KVM devices

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Message-ID: <2e7890d2-e433-8553-c466-5b42f7d7776e@ozlabs.ru>
Date:   Thu, 2 May 2019 12:35:33 +1000
From:   Alexey Kardashevskiy <aik@...abs.ru>
To:     Colin Ian King <colin.king@...onical.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        kvm@...r.kernel.org,
        Cédric Le Goater <clg@...d.org>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: KVM: Introduce a 'release' method for KVM devices



On 02/05/2019 00:42, Colin Ian King wrote:
> Hi,
> 
> Static analysis with Coverity picked up an issue in the following commit:
> 
> commit 2bde9b3ec8bdf60788e9e2ce8c07a2f8d6003dbd
> Author: Cédric Le Goater <clg@...d.org>
> Date:   Thu Apr 18 12:39:41 2019 +0200
> 
>     KVM: Introduce a 'release' method for KVM devices
> 
> 
>         struct kvm *kvm = dev->kvm;
> 
> +       if (!dev)
> +               return -ENODEV;
> 
> If dev is null then the dereference of dev->kvm when assigning pointer
> kvm will cause an null pointer dereference.  This is easily fixed by
> assigning kvm after the dev null check.

Yes, this is a bug.

> 
> +
> +       if (dev->kvm != kvm)
> +               return -EPERM;
> 
> I don't understand the logic of the above check. kvm is the same
> dev->kvm on the earlier assignment, so dev->kvm != kvm seems to be
> always false, so this check seems to be redundant. Am I missing
> something more fundamental here?

Nope. This looks like unfortunate cut-n-paste which slipped through out
reviewing process :-D


-- 
Alexey