linux-kernel - Re: [PATCH -next] irqchip/tango: Fix potential NULL pointer dereference

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Date:   Wed, 30 Jan 2019 14:25:04 +0800
From:   YueHaibing <yuehaibing@...wei.com>
To:     Måns Rullgård <mans@...sr.com>,
        Marc Zyngier <marc.zyngier@....com>
CC:     <tglx@...utronix.de>, <jason@...edaemon.net>,
        <marc.w.gonzalez@...e.fr>, <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH -next] irqchip/tango: Fix potential NULL pointer
 dereference

On 2019/1/29 20:20, Måns Rullgård wrote:
> Marc Zyngier <marc.zyngier@....com> writes:
> 
>> On Tue, 29 Jan 2019 08:01:22 +0000,
>> YueHaibing <yuehaibing@...wei.com> wrote:
>>>
>>> There is a potential NULL pointer dereference in case kzalloc()
>>> fails and returns NULL.
>>>
>>> Fixes: 4bba66899ac6 ("irqchip/tango: Add support for Sigma Designs SMP86xx/SMP87xx interrupt controller")
>>> Signed-off-by: YueHaibing <yuehaibing@...wei.com>
>>> ---
>>>  drivers/irqchip/irq-tango.c | 2 ++
>>>  1 file changed, 2 insertions(+)
>>>
>>> diff --git a/drivers/irqchip/irq-tango.c b/drivers/irqchip/irq-tango.c
>>> index ae28d86..a63b828 100644
>>> --- a/drivers/irqchip/irq-tango.c
>>> +++ b/drivers/irqchip/irq-tango.c
>>> @@ -191,6 +191,8 @@ static int __init tangox_irq_init(void __iomem *base, struct resource *baseres,
>>>  		panic("%pOFn: failed to get address", node);
>>>  
>>>  	chip = kzalloc(sizeof(*chip), GFP_KERNEL);
>>> +	if (!chip)
>>> +		return -ENOMEM;
>>>  	chip->ctl = res.start - baseres->start;
>>>  	chip->base = base;
>>>  
>>
>> This is a commendable effort, but given that the whole error handling
>> of this driver is just to simply panic, I have the ugly feeling that
>> this lack of check is more a feature than a bug... Not that I like it,
>> but at least it is consistent.
> 
> That seemed to be the norm for irqchip drivers when I wrote this one,
> and a fair number of them still panic on errors during init.  There's
> really not much else that can sanely be done since nothing will work
> without irq handling.
> 
> As for the error return added by this patch, nothing checks it, so a
> failure would merely result in the irqchip being silently skipped and
> nothing working.  Propagating the error back to of_irq_init() also has
> no effect, not even a warning.  Besides, kzalloc() is extremely unlikely
> to fail at this stage, and if it does, you have much bigger problems.

Thanks for your comment.

>