From: Leonardo Bras <leonardo@linux.ibm.com>
To: Paolo Bonzini <pbonzini@redhat.com>,
Sean Christopherson <sean.j.christopherson@intel.com>
Cc: "Paul Mackerras" <paulus@ozlabs.org>,
"Radim Krčmář" <rkrcmar@redhat.com>,
kvm-ppc@vger.kernel.org, kvm@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] KVM: Add separate helper for putting borrowed reference to kvm
Date: Wed, 27 Nov 2019 15:24:35 -0300 [thread overview]
Message-ID: <bfa563e6a584bd85d3abe953ca088281dc0e167b.camel@linux.ibm.com> (raw)
In-Reply-To: <e1a4218f-2a70-3de3-1403-dbebf8a8abdf@redhat.com>
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On Wed, 2019-11-27 at 17:38 +0100, Paolo Bonzini wrote:
> On 26/11/19 18:53, Leonardo Bras wrote:
> > I agree an use-after-free more problem than a memory leak, but I
> > think
> > that there is a way to solve this without leaking the memory also.
> >
> > One option would be reordering the kvm_put_kvm(), like in this
> > patch:
> > https://lkml.org/lkml/2019/11/26/517
>
> It's a tradeoff between "fix one bug" and "mitigate all bugs of that
> class", both are good things to do. Reordering the kvm_put_kvm()
> fixes
> the bug. kvm_put_kvm_no_destroy() makes all bugs of that kind less
> severe, but it doesn't try to fix them.
>
> Paolo
>
I think I understand it better now, thanks Paolo and Sean.
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):
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?
Best regards,
Leonardo
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next prev parent reply other threads:[~2019-11-27 18:24 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-21 22:58 [PATCH] KVM: Add separate helper for putting borrowed reference to kvm Sean Christopherson
2019-10-22 13:49 ` Paolo Bonzini
2019-11-26 16:44 ` Leonardo Bras
2019-11-26 17:14 ` Sean Christopherson
2019-11-26 17:53 ` Leonardo Bras
2019-11-27 16:38 ` Paolo Bonzini
2019-11-27 18:24 ` Leonardo Bras [this message]
2019-11-27 18:32 ` Paolo Bonzini
2019-11-27 19:25 ` Leonardo Bras
2019-11-27 19:47 ` Sean Christopherson
2019-11-27 20:15 ` Leonardo Bras
2019-11-27 21:57 ` Leonardo Bras
2019-11-28 1:00 ` Sean Christopherson
2019-11-28 16:29 ` Leonardo Bras
2019-11-28 13:49 ` Paolo Bonzini
2019-11-28 16:04 ` Leonardo Bras
2019-11-26 17:57 ` Leonardo Bras
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