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

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Date:   Sun, 3 Jan 2021 14:22:11 +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 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).
I set data to NULL after kfree() in this patch to prevent double-free
when the failure occurs at i > 0.

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
> >