netdev - Re: [PATCH RFC 1/6] net: rfkill: gpio: fix gpio name buffer size off by 1

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Message-ID: <CAGb2v67L__kusyfSxSc1Rmb6mtJ_VQQF+rCfr1AiUxCemaXMqA@mail.gmail.com>
Date:	Fri, 17 Jan 2014 17:59:30 +0800
From:	Chen-Yu Tsai <wens@...e.org>
To:	David Laight <David.Laight@...lab.com>
Cc:	Johannes Berg <johannes@...solutions.net>,
	"David S. Miller" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-sunxi@...glegroups.com" <linux-sunxi@...glegroups.com>,
	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	"linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>
Subject: Re: [PATCH RFC 1/6] net: rfkill: gpio: fix gpio name buffer size off
 by 1

On Fri, Jan 17, 2014 at 5:46 PM, David Laight <David.Laight@...lab.com> wrote:
> From: Chen-Yu Tsai
>> snprintf should be passed the complete size of the buffer, including
>> the space for '\0'. The previous code resulted in the *_reset and
>> *_shutdown strings being truncated.
> ...
>> diff --git a/net/rfkill/rfkill-gpio.c b/net/rfkill/rfkill-gpio.c
> ...
>> -     snprintf(rfkill->reset_name, len + 6 , "%s_reset", rfkill->name);
>> -     snprintf(rfkill->shutdown_name, len + 9, "%s_shutdown", rfkill->name);
>> +     snprintf(rfkill->reset_name, len + 7 , "%s_reset", rfkill->name);
>> +     snprintf(rfkill->shutdown_name, len + 10, "%s_shutdown", rfkill->name);
>
> I can't find the context for the above, but they look very dubious.
> I'd expect: snprintf(foo, sizeof foo, ...).
> If you are trying to truncate rfkill->name you need to use %.*s.

The driver allocates these buffers on the fly, a few lines above:

        len = strlen(rfkill->name);
        rfkill->reset_name = devm_kzalloc(&pdev->dev, len + 7, GFP_KERNEL);
        rfkill->shutdown_name = devm_kzalloc(&pdev->dev, len + 10, GFP_KERNEL);

I am not trying to truncate rfkill->name. Rather, the buffer length passed
to snprintf was wrong, so the resulting name was truncated by one character.


Thanks,
ChenYu
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