linux-kernel - Re: [PATCH] tty:vt: Add check the return value of kzalloc to avoid oops

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Message-ID: <bee63793-e9f4-ecc4-7966-765207009c75@huawei.com>
Date:   Sat, 21 Sep 2019 15:26:38 +0800
From:   Xiaoming Ni <nixiaoming@...wei.com>
To:     Greg KH <gregkh@...uxfoundation.org>,
        Nicolas Pitre <nico@...xnic.net>
CC:     <penberg@...helsinki.fi>, <jslaby@...e.com>,
        <textshell@...uujin.de>, <sam@...nborg.org>,
        <daniel.vetter@...ll.ch>, <mpatocka@...hat.com>,
        <ghalat@...hat.com>, <linux-kernel@...r.kernel.org>,
        <yangyingliang@...wei.com>, <yuehaibing@...wei.com>,
        <zengweilin@...wei.com>
Subject: Re: [PATCH] tty:vt: Add check the return value of kzalloc to avoid
 oops


On 2019/9/20 14:04, Greg KH wrote:
> On Thu, Sep 19, 2019 at 10:56:15PM -0400, Nicolas Pitre wrote:
>> On Thu, 19 Sep 2019, Greg KH wrote:
>>
>>> On Thu, Sep 19, 2019 at 05:18:15PM +0800, Xiaoming Ni wrote:
>>>> Using kzalloc() to allocate memory in function con_init(), but not
>>>> checking the return value, there is a risk of null pointer references
>>>> oops.
>>>>
>>>> Signed-off-by: Xiaoming Ni <nixiaoming@...wei.com>
>>>
>>> We keep having this be "reported" :(
>>
>> Something probably needs to be "communicated" about that.
> 
> I know, but it's also kind of fun to see what these "automated" checkers
> find, sometimes the resulting patches almost work properly :)
> 
> This one is really close, I think if the likely/unlikely gets cleaned
> up, it is viable.
> 
>>>>  		vc_cons[currcons].d = vc = kzalloc(sizeof(struct vc_data), GFP_NOWAIT);
>>>> +		if (unlikely(!vc)) {
>>>> +			pr_warn("%s:failed to allocate memory for the %u vc\n",
>>>> +					__func__, currcons);
>>>> +			break;
>>>> +		}
>>>
>>> At init, this really can not happen.  Have you see it ever happen?
>>
>> This is maybe too subtle a fact. The "communication" could be done with 
>> some GFP_WONTFAIL flag, and have the allocator simply pannic() if it 
>> ever fails.
> 
> That's a good idea to do as well.
> 
> thanks,
> 
> greg k-h
> 
> .
> 
Thank you for your advice.

@ Nicolas Pitre
Can I make a v2 patch based on your advice ?
Or you will submit a patch for "GFP_WONTFAIL" yourself ?

thanks
Xiaoming Ni