linux-kernel - Re: [PATCH] usb: core: hcd: fix bug: application of sizeof to pointer

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Date:   Wed, 8 Dec 2021 11:00:41 +0800
From:   Guo Zhengkui <guozhengkui@...o.com>
To:     Alan Stern <stern@...land.harvard.edu>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Li Jun <jun.li@....com>, Kishon Vijay Abraham I <kishon@...com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Peter Chen <peter.chen@....com>,
        "open list:USB SUBSYSTEM" <linux-usb@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        kernel <kernel@...o.com>
Subject: Re: [PATCH] usb: core: hcd: fix bug: application of sizeof to pointer

On 2021/12/8 6:21, Alan Stern wrote:
> On Tue, Dec 07, 2021 at 03:40:37PM +0100, Greg Kroah-Hartman wrote:
>> On Tue, Dec 07, 2021 at 09:53:47PM +0800, Guo Zhengkui wrote:
>>> Fix following error:
>>> ./drivers/usb/core/hcd.c:1284:38-44: ERROR:
>>> application of sizeof to pointer.
>>
>> What generated this error?
>>
>>>
>>> Use sizeof(*vaddr) instead.
>>>
>>> Signed-off-by: Guo Zhengkui <guozhengkui@...o.com>
>>> ---
>>>   drivers/usb/core/hcd.c | 2 +-
>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c
>>> index 4d326ee12c36..996d5273cf60 100644
>>> --- a/drivers/usb/core/hcd.c
>>> +++ b/drivers/usb/core/hcd.c
>>> @@ -1281,7 +1281,7 @@ static int hcd_alloc_coherent(struct usb_bus *bus,
>>>   		return -EFAULT;
>>>   	}
>>>   
>>> -	vaddr = hcd_buffer_alloc(bus, size + sizeof(vaddr),
>>> +	vaddr = hcd_buffer_alloc(bus, size + sizeof(*vaddr),
>>
>> I think you just broke the code.
>>
>> Look at this closer and see what the function is doing with this buffer
>> and if you still think your patch is correct, please rewrite the
>> changelog text to explain why it is so (hint, just using the output of
>> coccinelle isn't ok.)
> 

Sorry for my carelessness. It should be sizeof(vaddr).

> Although the patch is definitely wrong, the code could stand to be
> improved.  The value stored at the end of the buffer is *vaddr_handle
> converted to an unsigned long, but the space reserved for this value is
> sizeof(vaddr) -- which doesn't make much sense since vaddr is a pointer
> to unsigned char.  The code implicitly relies on the fact that unsigned
> long takes up the same amount of space as a pointer.
> 
> Readers wouldn't have to stop and figure this out if the amount of
> reserved space was simply set to sizeof(unsigned long) rather than
> sizeof(vaddr).

OK, I will commit another patch to fix this problem. Do you mind I add a 
"Suggested-by" tag of your name (Alan Stern) in this new patch?

Zhengkui

> 
> Alan Stern
>