Re: [PATCH 2/2] KVM: arm64: vgic-its: Fix memory leak on the error path of vgic_add_lpi()

[Marc Zyngier]

On 2020-04-16 02:17, Zenghui Yu wrote:
> On 2020/4/14 11:03, Zenghui Yu wrote:
> > If we're going to fail out the vgic_add_lpi(), let's make sure the
> > allocated vgic_irq memory is also freed. Though it seems that both
> > cases are unlikely to fail.
> >
> > Cc: Zengruan Ye <yezengruan@xxxxxxxxxx>
> > Signed-off-by: Zenghui Yu <yuzenghui@xxxxxxxxxx>
> > ---
> >   virt/kvm/arm/vgic/vgic-its.c | 8 ++++++--
> >   1 file changed, 6 insertions(+), 2 deletions(-)
> >
> > diff --git a/virt/kvm/arm/vgic/vgic-its.c 
> > b/virt/kvm/arm/vgic/vgic-its.c
> > index d53d34a33e35..3c3b6a0f2dce 100644
> > --- a/virt/kvm/arm/vgic/vgic-its.c
> > +++ b/virt/kvm/arm/vgic/vgic-its.c
> > @@ -98,12 +98,16 @@ static struct vgic_irq *vgic_add_lpi(struct kvm 
> > *kvm, u32 intid,
> >   	 * the respective config data from memory here upon mapping the 
> > LPI.
> >   	 */
> >   	ret = update_lpi_config(kvm, irq, NULL, false);
> > -	if (ret)
> > +	if (ret) {
> > +		kfree(irq);
> >   		return ERR_PTR(ret);
> > +	}
> >     	ret = vgic_v3_lpi_sync_pending_status(kvm, irq);
> > -	if (ret)
> > +	if (ret) {
> > +		kfree(irq);
> >   		return ERR_PTR(ret);
> > +	}
>
> Looking at it again, I realized that this error handling is still not
> complete. Maybe we should use a vgic_put_irq() instead so that we can
> also properly delete the vgic_irq from lpi_list.

Yes, this is a more correct fix indeed. There is still a bit of a 
bizarre
behaviour if you have two vgic_add_lpi() racing to create the same 
interrupt,
which is pretty dodgy anyway (it means we have two MAPI at the same 
time...).
You end-up with re-reading the state from memory... Oh well.

> Marc, what do you think? Could you please help to fix it, or I can
> resend it.

I've fixed it as such (with a comment for a good measure):

diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
index 3c3b6a0f2dce..c012a52b19f5 100644
--- a/virt/kvm/arm/vgic/vgic-its.c
+++ b/virt/kvm/arm/vgic/vgic-its.c
@@ -96,16 +96,19 @@ static struct vgic_irq *vgic_add_lpi(struct kvm 
*kvm, u32 intid,
 	 * We "cache" the configuration table entries in our struct 
vgic_irq's.
 	 * However we only have those structs for mapped IRQs, so we read in
 	 * the respective config data from memory here upon mapping the LPI.
+	 *
+	 * Should any of these fail, behave as if we couldn't create the LPI
+	 * by dropping the refcount and returning the error.
 	 */
 	ret = update_lpi_config(kvm, irq, NULL, false);
 	if (ret) {
-		kfree(irq);
+		vgic_put_irq(kvm, irq);
 		return ERR_PTR(ret);
 	}

 	ret = vgic_v3_lpi_sync_pending_status(kvm, irq);
 	if (ret) {
-		kfree(irq);
+		vgic_put_irq(kvm, irq);
 		return ERR_PTR(ret);
 	}


Let me know if you agree with that.

Thanks,

        M.
--
Jazz is not dead. It just smells funny...