Re: [PATCH] staging/lustre: Use proper number of bytes in copy_from_user

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Mon, Nov 21, 2016 at 12:46:48AM -0500, Oleg Drokin wrote:
> From: Jian Yu <jian.yu@intel.com>
> 
> This patch removes the usage of MAX_STRING_SIZE from
> copy_from_user() and just copies enough bytes to cover
> count passed in.
> 
> Signed-off-by: Jian Yu <jian.yu@intel.com>
> Reviewed-on: http://review.whamcloud.com/23462
> Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-8774
> Reviewed-by: John L. Hammond <john.hammond@intel.com>
> Signed-off-by: Oleg Drokin <green@linuxhacker.ru>
> ---
>  drivers/staging/lustre/lustre/obdclass/lprocfs_status.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/staging/lustre/lustre/obdclass/lprocfs_status.c b/drivers/staging/lustre/lustre/obdclass/lprocfs_status.c
> index 8a2f02f3..db49992 100644
> --- a/drivers/staging/lustre/lustre/obdclass/lprocfs_status.c
> +++ b/drivers/staging/lustre/lustre/obdclass/lprocfs_status.c
> @@ -400,10 +400,17 @@ int lprocfs_wr_uint(struct file *file, const char __user *buffer,
>  	char dummy[MAX_STRING_SIZE + 1], *end;
>  	unsigned long tmp;
>  
> -	dummy[MAX_STRING_SIZE] = '\0';
> -	if (copy_from_user(dummy, buffer, MAX_STRING_SIZE))
> +	if (count >= sizeof(dummy))
> +		return -EINVAL;
> +
> +	if (count == 0)
> +		return 0;
> +
> +	if (copy_from_user(dummy, buffer, count))
>  		return -EFAULT;
>  
> +	dummy[count] = '\0';
> +

You do know about simple_read_from_buffer(), right?  I suggest using
those simple_* functions where ever you are touching user buffers, like
this code.

thanks,

greg k-h