Re: [PATCH v2] watchdog: pcwd_usb: Fix attempting to access uninitialized memory

[Guenter Roeck <linux@roeck-us.net>]

On Wed, Nov 16, 2022 at 10:07:06AM +0800, Li Hua wrote:
> The stack variable msb and lsb may be used uninitialized in function
> usb_pcwd_get_temperature and usb_pcwd_get_timeleft when usb card no response.
> 
> The build waring is:
> drivers/watchdog/pcwd_usb.c:336:22: error: ‘lsb’ is used uninitialized in this function [-Werror=uninitialized]
>   *temperature = (lsb * 9 / 5) + 32;
>                   ~~~~^~~
> drivers/watchdog/pcwd_usb.c:328:21: note: ‘lsb’ was declared here
>   unsigned char msb, lsb;
>                      ^~~
> cc1: all warnings being treated as errors
> scripts/Makefile.build:250: recipe for target 'drivers/watchdog/pcwd_usb.o' failed
> make[3]: *** [drivers/watchdog/pcwd_usb.o] Error 1
> 
> Fixes: b7e04f8c61a4 ("mv watchdog tree under drivers")
> Signed-off-by: Li Hua <hucool.lihua@huawei.com>

Reviewed-by: Guenter Roeck <linux@roeck-us.net>

> ---
> v1 -> v2: just initialize lsb and msb with 0, but returning -EFAULT
> ---
>  drivers/watchdog/pcwd_usb.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/watchdog/pcwd_usb.c b/drivers/watchdog/pcwd_usb.c
> index 1bdaf17c1d38..8202f0a6b093 100644
> --- a/drivers/watchdog/pcwd_usb.c
> +++ b/drivers/watchdog/pcwd_usb.c
> @@ -325,7 +325,8 @@ static int usb_pcwd_set_heartbeat(struct usb_pcwd_private *usb_pcwd, int t)
>  static int usb_pcwd_get_temperature(struct usb_pcwd_private *usb_pcwd,
>  							int *temperature)
>  {
> -	unsigned char msb, lsb;
> +	unsigned char msb = 0x00;
> +	unsigned char lsb = 0x00;
>  
>  	usb_pcwd_send_command(usb_pcwd, CMD_READ_TEMP, &msb, &lsb);
>  
> @@ -341,7 +342,8 @@ static int usb_pcwd_get_temperature(struct usb_pcwd_private *usb_pcwd,
>  static int usb_pcwd_get_timeleft(struct usb_pcwd_private *usb_pcwd,
>  								int *time_left)
>  {
> -	unsigned char msb, lsb;
> +	unsigned char msb = 0x00;
> +	unsigned char lsb = 0x00;
>  
>  	/* Read the time that's left before rebooting */
>  	/* Note: if the board is not yet armed then we will read 0xFFFF */
> -- 
> 2.17.1
>