Re: [PATCH] w1: Misuse of get_user()/put_user() reported by sparse

[Greg Kroah-Hartman]

On Fri, Nov 19, 2021 at 10:15:09AM +0100, Christophe Leroy wrote:
> sparse warnings: (new ones prefixed by >>)
> >> drivers/w1/slaves/w1_ds28e04.c:342:13: sparse: sparse: incorrect type in initializer (different address spaces) @@     expected char [noderef] __user *_pu_addr @@     got char *buf @@
>    drivers/w1/slaves/w1_ds28e04.c:342:13: sparse:     expected char [noderef] __user *_pu_addr
>    drivers/w1/slaves/w1_ds28e04.c:342:13: sparse:     got char *buf
> >> drivers/w1/slaves/w1_ds28e04.c:356:13: sparse: sparse: incorrect type in initializer (different address spaces) @@     expected char const [noderef] __user *_gu_addr @@     got char const *buf @@
>    drivers/w1/slaves/w1_ds28e04.c:356:13: sparse:     expected char const [noderef] __user *_gu_addr
>    drivers/w1/slaves/w1_ds28e04.c:356:13: sparse:     got char const *buf
> 
> The buffer buf is a failsafe buffer in kernel space, it's not user
> memory hence doesn't deserve the use of get_user() or put_user().
> 
> Access 'buf' content directly.
> 
> Reported-by: kernel test robot <lkp@xxxxxxxxx>
> Link: https://lore.kernel.org/lkml/202111190526.K5vb7NWC-lkp@xxxxxxxxx/T/
> Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
> ---
>  drivers/w1/slaves/w1_ds28e04.c | 10 ++--------
>  1 file changed, 2 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/w1/slaves/w1_ds28e04.c b/drivers/w1/slaves/w1_ds28e04.c
> index e4f336111edc..d75bb16fb7a1 100644
> --- a/drivers/w1/slaves/w1_ds28e04.c
> +++ b/drivers/w1/slaves/w1_ds28e04.c
> @@ -339,10 +339,7 @@ static BIN_ATTR_RW(pio, 1);
>  static ssize_t crccheck_show(struct device *dev, struct device_attribute *attr,
>  			     char *buf)
>  {
> -	if (put_user(w1_enable_crccheck + 0x30, buf))
> -		return -EFAULT;
> -
> -	return sizeof(w1_enable_crccheck);
> +	return sprintf(buf, "%d", w1_enable_crccheck);

This should be sysfs_emit(), right?

>  }
>  
>  static ssize_t crccheck_store(struct device *dev, struct device_attribute *attr,
> @@ -353,11 +350,8 @@ static ssize_t crccheck_store(struct device *dev, struct device_attribute *attr,
>  	if (count != 1 || !buf)
>  		return -EINVAL;
>  
> -	if (get_user(val, buf))
> -		return -EFAULT;
> -
>  	/* convert to decimal */
> -	val = val - 0x30;
> +	val = *buf - 0x30;

Why not use a proper function that can parse a string and turn it into a
number?

thanks,

greg k-h