linux-kernel - Re: Re: [PATCH] iommu/intel: Fix memleak in intel_irq_remapping

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Message-ID: <577ae864.1df8f.176d0722e45.Coremail.dinghao.liu@zju.edu.cn>
Date:   Tue, 5 Jan 2021 10:48:32 +0800 (GMT+08:00)
From:   dinghao.liu@....edu.cn
To:     "Lu Baolu" <baolu.lu@...ux.intel.com>
Cc:     kjlu@....edu, "David Woodhouse" <dwmw2@...radead.org>,
        "Joerg Roedel" <joro@...tes.org>, "Will Deacon" <will@...nel.org>,
        "Jiang Liu" <jiang.liu@...ux.intel.com>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: Re: [PATCH] iommu/intel: Fix memleak in
 intel_irq_remapping_alloc

> On 1/3/21 2:22 PM, dinghao.liu@....edu.cn wrote:
> >> On 2021/1/3 12:08, dinghao.liu@....edu.cn wrote:
> >>>> Hi,
> >>>>
> >>>> On 2021/1/2 17:50, Dinghao Liu wrote:
> >>>>> When irq_domain_get_irq_data() or irqd_cfg() fails
> >>>>> meanwhile i == 0, data allocated by kzalloc() has not
> >>>>> been freed before returning, which leads to memleak.
> >>>>>
> >>>>> Fixes: b106ee63abccb ("irq_remapping/vt-d: Enhance Intel IR driver to support hierarchical irqdomains")
> >>>>> Signed-off-by: Dinghao Liu <dinghao.liu@....edu.cn>
> >>>>> ---
> >>>>>     drivers/iommu/intel/irq_remapping.c | 2 ++
> >>>>>     1 file changed, 2 insertions(+)
> >>>>>
> >>>>> diff --git a/drivers/iommu/intel/irq_remapping.c b/drivers/iommu/intel/irq_remapping.c
> >>>>> index aeffda92b10b..cdaeed36750f 100644
> >>>>> --- a/drivers/iommu/intel/irq_remapping.c
> >>>>> +++ b/drivers/iommu/intel/irq_remapping.c
> >>>>> @@ -1354,6 +1354,8 @@ static int intel_irq_remapping_alloc(struct irq_domain *domain,
> >>>>>     		irq_cfg = irqd_cfg(irq_data);
> >>>>>     		if (!irq_data || !irq_cfg) {
> >>>>>     			ret = -EINVAL;
> >>>>> +			kfree(data);
> >>>>> +			data = NULL;
> >>>>
> >>>> Do you need to check (i == 0) here? @data will not be used anymore as it
> >>>> goes to out branch, why setting it to NULL here?
> >>>>
> >>>
> >>> data will be passed to ire_data->chip_data when i == 0 and
> >>> intel_free_irq_resources() will free it on failure. Thus I
> >>
> >> Isn't it going to "goto out_free_data"? If "i == 0", the allocated @data
> >> won't be freed by intel_free_irq_resources(), hence memory leaking. Does
> >> this patch aim to fix this?
> >>
> >> Best regards,
> >> baolu
> >>
> > 
> > Correct, this is what I mean. When i > 0, data has been passed to
> > irq_data->chip_data, which will be freed in intel_free_irq_resources()
> > on failure. So there is no memleak in this case. The memleak only occurs
> > on failure when i == 0 (data has not been passed to irq_data->chip_data).
> 
> So how about
> 
> diff --git a/drivers/iommu/intel/irq_remapping.c 
> b/drivers/iommu/intel/irq_remapping.c
> index aeffda92b10b..685200a5cff0 100644
> --- a/drivers/iommu/intel/irq_remapping.c
> +++ b/drivers/iommu/intel/irq_remapping.c
> @@ -1353,6 +1353,8 @@ static int intel_irq_remapping_alloc(struct 
> irq_domain *domain,
>                  irq_data = irq_domain_get_irq_data(domain, virq + i);
>                  irq_cfg = irqd_cfg(irq_data);
>                  if (!irq_data || !irq_cfg) {
> +                       if (!i)
> +                               kfree(data);
>                          ret = -EINVAL;
>                          goto out_free_data;
>                  }
> 
> > I set data to NULL after kfree() in this patch to prevent double-free
> > when the failure occurs at i > 0.
> 
> if i>0, @data has been passed and will be freed by
> intel_free_irq_resources() on the failure path. No need to free or
> clear, right?

Right, this is clearer. Thank you for your advice and I will resend a
new patch soon.

Regards,
Dinghao

> 
> Best regards,
> baolu
> 
> > 
> > Regards,
> > Dinghao
> > 
> >>> set it to NULL to prevent double-free. However, if we add
> >>> a check (i == 0) here, we will not need to set it to NULL.
> >>> If this is better, I will resend a new patch soon.
> >>>
> >>> Regards,
> >>> Dinghao
> >>>