linux-kernel - Re: [PATCH -next] arch/arm: use scnprintf() in l2x0_pmu_event

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Date:   Sun, 10 May 2020 08:14:22 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Chen Zhou <chenzhou10@...wei.com>
Cc:     linux@...linux.org.uk, alexios.zavras@...el.com,
        tglx@...utronix.de, allison@...utok.net,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -next] arch/arm: use scnprintf() in l2x0_pmu_event_show()

On Sat, May 09, 2020 at 04:35:39PM +0800, Chen Zhou wrote:
> snprintf() returns the number of bytes that would be written,
> which may be greater than the the actual length to be written.
> 
> show() methods should return the number of bytes printed into the
> buffer. This is the return value of scnprintf().
> 
> Signed-off-by: Chen Zhou <chenzhou10@...wei.com>
> ---
>  arch/arm/mm/cache-l2x0-pmu.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm/mm/cache-l2x0-pmu.c b/arch/arm/mm/cache-l2x0-pmu.c
> index 993fefdc167a..d20626451a2e 100644
> --- a/arch/arm/mm/cache-l2x0-pmu.c
> +++ b/arch/arm/mm/cache-l2x0-pmu.c
> @@ -343,7 +343,7 @@ static ssize_t l2x0_pmu_event_show(struct device *dev,
>  	struct l2x0_event_attribute *lattr;
>  
>  	lattr = container_of(attr, typeof(*lattr), attr);
> -	return snprintf(buf, PAGE_SIZE, "config=0x%x\n", lattr->config);
> +	return scnprintf(buf, PAGE_SIZE, "config=0x%x\n", lattr->config);

This should just be replaced with sprintf() as there's no way such a
string can go beyond PAGE_SIZE.

And the "config=" part could be dropped as well, but now userspace
probably requires it, that is sad.

thanks,

greg k-h