Re: [PATCH v2] w1: Misuse of get_user()/put_user() reported by sparse

[Greg Kroah-Hartman]

On Fri, Nov 26, 2021 at 05:47:58PM +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>
> ---
> v2: Use sysfs_emit() and kstrtobool()
> ---
>  drivers/w1/slaves/w1_ds28e04.c | 25 +++----------------------
>  1 file changed, 3 insertions(+), 22 deletions(-)
> 
> diff --git a/drivers/w1/slaves/w1_ds28e04.c b/drivers/w1/slaves/w1_ds28e04.c
> index e4f336111edc..98f80f412cfd 100644
> --- a/drivers/w1/slaves/w1_ds28e04.c
> +++ b/drivers/w1/slaves/w1_ds28e04.c
> @@ -32,7 +32,7 @@ static int w1_strong_pullup = 1;
>  module_param_named(strong_pullup, w1_strong_pullup, int, 0);
>  
>  /* enable/disable CRC checking on DS28E04-100 memory accesses */
> -static char w1_enable_crccheck = 1;
> +static bool w1_enable_crccheck = true;
>  
>  #define W1_EEPROM_SIZE		512
>  #define W1_PAGE_COUNT		16
> @@ -339,32 +339,13 @@ 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 sysfs_emit(buf, "%d\n", w1_enable_crccheck);
>  }
>  
>  static ssize_t crccheck_store(struct device *dev, struct device_attribute *attr,
>  			      const char *buf, size_t count)
>  {
> -	char val;
> -
> -	if (count != 1 || !buf)
> -		return -EINVAL;
> -
> -	if (get_user(val, buf))
> -		return -EFAULT;
> -
> -	/* convert to decimal */
> -	val = val - 0x30;
> -	if (val != 0 && val != 1)
> -		return -EINVAL;
> -
> -	/* set the new value */
> -	w1_enable_crccheck = val;
> -
> -	return sizeof(w1_enable_crccheck);
> +	return kstrtobool(buf, &w1_enable_crccheck) ? : count;

Please spell this line out, using ? : is unreadable at times.

thanks,

greg k-h