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

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Date:   Mon, 6 May 2019 11:50:03 +0200
From:   Cédric Le Goater <clg@...d.org>
To:     Alexey Kardashevskiy <aik@...abs.ru>,
        Colin Ian King <colin.king@...onical.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        kvm@...r.kernel.org
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: KVM: Introduce a 'release' method for KVM devices

On 5/2/19 4:35 AM, Alexey Kardashevskiy wrote:
> 
> 
> 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.

Clearly.

>>
>> +
>> +       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

Yes. My bad :/ I will send a cleanup patch for 5.2

Thanks,

C.