linux-kernel - Re: [PATCH 2/2] KVM: arm64: vgic-its: Fix memory leak on the error path of vgic_add

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Date:   Fri, 17 Apr 2020 14:40:31 +0800
From:   Zenghui Yu <yuzenghui@...wei.com>
To:     Marc Zyngier <maz@...nel.org>
CC:     <kvmarm@...ts.cs.columbia.edu>, <james.morse@....com>,
        <julien.thierry.kdev@...il.com>, <suzuki.poulose@....com>,
        <wanghaibin.wang@...wei.com>, <yezengruan@...wei.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] KVM: arm64: vgic-its: Fix memory leak on the error
 path of vgic_add_lpi()

On 2020/4/17 1:23, Marc Zyngier wrote:
> 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@...wei.com>
>>> Signed-off-by: Zenghui Yu <yuzenghui@...wei.com>
>>> ---
>>>   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.

Agreed. Thanks for the fix!


Zenghui