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

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Date:   Tue, 5 Jan 2021 09:51:31 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     dinghao.liu@....edu.cn
Cc:     baolu.lu@...ux.intel.com, 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: [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?

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
>>>