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Subject: Re: [PATCH 14/22] [media] usbvision-i2c: fix format overflow warning
To: Arnd Bergmann <arnd@arndb.de>
References: <20170714120720.906842-1-arnd@arndb.de>
 <20170714120720.906842-15-arnd@arndb.de>
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 <CAK8P3a3BWBQMcbg0hOoZa+N86dsEN88p9Wh0_cHSmKEur1uJhg@mail.gmail.com>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
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        Networking <netdev@vger.kernel.org>,
        "David S . Miller" <davem@davemloft.net>,
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From: Hans Verkuil <hverkuil@xs4all.nl>
Message-ID: <f09172bd-50c7-f376-8958-52bf4b47b701@xs4all.nl>
Date: Mon, 17 Jul 2017 14:59:15 +0200
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On 17/07/17 14:57, Arnd Bergmann wrote:
> On Mon, Jul 17, 2017 at 2:53 PM, Hans Verkuil <hverkuil@xs4all.nl> wrote:
>> On 14/07/17 14:07, Arnd Bergmann wrote:
>>> gcc-7 notices that we copy a fixed length string into another
>>> string of the same size, with additional characters:
>>>
>>> drivers/media/usb/usbvision/usbvision-i2c.c: In function 'usbvision_i2c_register':
>>> drivers/media/usb/usbvision/usbvision-i2c.c:190:36: error: '%d' directive writing between 1 and 11 bytes into a region of size between 0 and 47 [-Werror=format-overflow=]
>>>   sprintf(usbvision->i2c_adap.name, "%s-%d-%s", i2c_adap_template.name,
>>>                                     ^~~~~~~~~~
>>> drivers/media/usb/usbvision/usbvision-i2c.c:190:2: note: 'sprintf' output between 4 and 76 bytes into a destination of size 48
>>>
>>> We know this is fine as the template name is always "usbvision", so
>>> we can easily avoid the warning by using this as the format string
>>> directly.
>>
>> Hmm, how about replacing sprintf by snprintf? That feels a lot safer (this is very
>> old code, it's not surprising it is still using sprintf).
> 
> With snprintf(), you will still get a -Wformat-truncation warning. One
> of my patches
> disables that warning by default, but Mauro likes build-testing with
> "make W=1", so
> it would still show up then.
> 
> However, we can do both: replace the string and use snprintf().

Yes please!

Regards,

	Hans