linux-kernel - Re: [PATCH] irqdomain: Fix NULL pointer dererence in irq_domain_free_irqs

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Message-ID: <546EA823.8030401@linux.intel.com>
Date:	Fri, 21 Nov 2014 10:49:07 +0800
From:	Jiang Liu <jiang.liu@...ux.intel.com>
To:	Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>,
	Thomas Gleixner <tglx@...utronix.de>
CC:	marc.zyngier@....com, linux-arm-kernel@...ts.infradead.org,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] irqdomain: Fix NULL pointer dererence in irq_domain_free_irqs_parent



On 2014/11/21 10:08, Suravee Suthikulpanit wrote:
> On 11/20/2014 07:32 PM, Thomas Gleixner wrote:
>> On Thu, 20 Nov 2014, suravee.suthikulpanit@....com wrote:
>>> This patch checks if the parent domain is NULL before recursively
>>> freeing
>>> irqs in the parent domains.
>>
>> Which is nonsense, because if the thing has not been allocated in the
>> first place, then it cannot explode in the free path magically, except
>> there is a missing check in the allocation path error handling.
>>
>> And that's obviously not the case simply because this originates from:
>>> [<fffffe0000449278>] pci_disable_msix+0x40/0x50
>>
> 
> Thomas,
> 
> In this case, I have the following irq domain hierarchy:
> 
> [GIC] -- [GICv2m] -- [MSI]
> 
> which recursively calling the freeing function:
> 
> In GIC domain, it currently defines the struct irq_domain_ops.free() with :
>   --> irq_domain_free_irqs_top()
>     |--> irq_domain_free_irqs_common()
>       |--> irq_domain_free_irq_parent()
>         |--> irq_domain_free_irqs_recursive()
> 
> and there is no check before passing the NULL domain->parent into the
> irq_domain_free_irqs_recursive(), which causes the error.
> 
> Since the GIC is the top most domain, it does not have parent domain.
> So, I'm not sure what is missing from the allocation path error
> handling, as you mentioned.
Hi Thomas,
	We have had a discussion about this issue in another thread.
Originally irq_domain_free_irqs_common() is designed to be used by
irqdomains with parent. But there are desires to reuse it to support
irqdomains without parent too for code reduction.
So I suggest to change irq_domain_free_irqs_common() instead of
irq_domain_free_irqs_parent() because caller of
irq_domain_free_irqs_parent() should guarantee current domain do have
a parent.
I'm preparing a patch for this:)
Regards!
Gerry
> 
> Thanks,
> 
> Suravee
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