linux-kernel - Re: [PATCH] KVM: Add separate helper for putting borrowed reference to kvm

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Message-ID: <6beeff56-7676-5dfd-a578-1732730f8963@redhat.com>
Date:   Wed, 27 Nov 2019 19:32:32 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Leonardo Bras <leonardo@...ux.ibm.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Paul Mackerras <paulus@...abs.org>,
        Radim Krčmář <rkrcmar@...hat.com>,
        kvm-ppc@...r.kernel.org, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: Add separate helper for putting borrowed reference
 to kvm

On 27/11/19 19:24, Leonardo Bras wrote:
> By what I could undestand up to now, these functions that use borrowed
> references can only be called while the reference (file descriptor)
> exists. 
> So, suppose these threads, where:
> - T1 uses a borrowed reference, and 
> - T2 is releasing the reference (close, release):

Nit: T2 is releasing the *last* reference (as implied by your reference
to close/release).

> 
> T1				| T2
> kvm_get_kvm()			|
> ...				| kvm_put_kvm()
> kvm_put_kvm_no_destroy()	|
> 
> The above would not trigger a use-after-free bug, but will cause a
> memory leak. Is my above understanding right?

Yes, this is correct.

Paolo



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