From mboxrd@z Thu Jan  1 00:00:00 1970
From: Radim =?utf-8?B?S3LEjW3DocWZ?= <rkrcmar@redhat.com>
Subject: Re: [PATCH v3] KVM: remove buggy vcpu id check on vcpu creation
Date: Wed, 20 Apr 2016 20:31:42 +0200
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Cc: James Hogan <james.hogan@imgtec.com>,
	Paolo Bonzini <pbonzini@redhat.com>, mingo@redhat.com,
	linux-mips@linux-mips.org, kvm@vger.kernel.org,
	linux-kernel@vger.kernel.org, qemu-ppc@nongnu.org,
	Cornelia Huck <cornelia.huck@de.ibm.com>,
	Paul Mackerras <paulus@samba.org>,
	David Gibson <david@gibson.dropbear.id.au>
To: Greg Kurz <gkurz@linux.vnet.ibm.com>
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2016-04-20 19:53+0200, Greg Kurz:
> On Wed, 20 Apr 2016 19:27:06 +0200
> Radim Kr=C4=8Dm=C3=A1=C5=99 <rkrcmar@redhat.com> wrote:
>> 2016-04-20 18:09+0100, James Hogan:
>> > On Wed, Apr 20, 2016 at 07:02:10PM +0200, Radim Kr=C4=8Dm=C3=A1=C5=
=99 wrote: =20
>> >> 2016-04-20 17:44+0200, Greg Kurz: =20
>> >> > diff --git a/arch/mips/kvm/mips.c b/arch/mips/kvm/mips.c
>> >> > index 70ef1a43c114..0278ea146db5 100644
>> >> > --- a/arch/mips/kvm/mips.c
>> >> > +++ b/arch/mips/kvm/mips.c
>> >> > @@ -248,9 +248,14 @@ struct kvm_vcpu *kvm_arch_vcpu_create(stru=
ct kvm *kvm, unsigned int id)
>> >> >  	int err, size, offset;
>> >> >  	void *gebase;
>> >> >  	int i;
>> >> > +	struct kvm_vcpu *vcpu;
>> >> > =20
>> >> > -	struct kvm_vcpu *vcpu =3D kzalloc(sizeof(struct kvm_vcpu), GF=
P_KERNEL);
>> >> > +	if (id >=3D KVM_MAX_VCPUS) {
>> >> > +		err =3D -EINVAL;
>> >> > +		goto out; =20
>> >>=20
>> >> 'vcpu' looks undefined at this point, so kfree in 'out:' may bug.=
 =20
>> >=20
>> > Thats out_free_cpu I think? =20
>>=20
>> My bad, it is.  Thank you!
>>=20
>=20
> I kept the goto based construct because it was done this way for kzal=
loc().
> but I agree that 'return ERR_PTR(-EINVAL)' may look more explicit.
>=20
> Worth a v4 ?

No, it is consistent with kzalloc fault handling this way.

I was going to queue it, but found an issue with kvm_get_vcpu_by_id()
that would allow the guest to create multiple VCPUs with the same id,
which led to an unfortunate discourse on KVM API.
(Please see a new thread.)