linux-kernel - Re: [PATCH] fs: sysfs: don't pass count == 0 to bin file readers

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Message-ID: <20150521221423.GK4914@htj.duckdns.org>
Date:	Thu, 21 May 2015 18:14:23 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Vladimir Zapolskiy <vz@...ia.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fs: sysfs: don't pass count == 0 to bin file readers

Hello,

On Fri, May 22, 2015 at 12:21:16AM +0300, Vladimir Zapolskiy wrote:
> If count == 0 bytes are requested by a reader, sysfs_kf_bin_read()
> deliberately returns 0 without passing a potentially harmful value to
> some externally defined underlying battr->read() function.
> 
> However in case of (pos == size && count) the next clause always sets
> count to 0 and this value is handed over to battr->read().
> 
> The change intends to make obsolete (and remove later) a redundant
> sanity check in battr->read(), if it is present, or add more
> protection to struct bin_attribute users, who does not care about
> input arguments.
> 
> Signed-off-by: Vladimir Zapolskiy <vz@...ia.com>
> ---
>  fs/sysfs/file.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
> index 7c2867b..6c95628 100644
> --- a/fs/sysfs/file.c
> +++ b/fs/sysfs/file.c
> @@ -90,7 +90,7 @@ static ssize_t sysfs_kf_bin_read(struct kernfs_open_file *of, char *buf,
>  		return 0;
>  
>  	if (size) {
> -		if (pos > size)
> +		if (pos >= size)
>  			return 0;
>  		if (pos + count > size)
>  			count = size - pos;

Hmmm... maybe just move that test upwards?

	if (!count || pos >= size)
		return 0;

	count = min(count, size - pos);

-- 
tejun
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