Subject: Re: [PATCH] rt2x00: reset reg earlier in rt2500usb_register_read

From: Greg KH <[email-masked]>
Date: Thu, 21 Jan 2021 10:49:56 +0100

On Thu, Jan 21, 2021 at 05:20:26PM +0800, Dongliang Mu wrote:
> In the function rt2500usb_register_read(_lock), reg is uninitialized
> in some situation. Then KMSAN reports uninit-value at its first memory
> access. To fix this issue, add one reg initialization in the function
> rt2500usb_register_read and rt2500usb_register_read_lock
> 
> BUG: KMSAN: uninit-value in rt2500usb_init_eeprom rt2500usb.c:1443 [inline]
> BUG: KMSAN: uninit-value in rt2500usb_probe_hw+0xb5e/0x22a0 rt2500usb.c:1757
> CPU: 0 PID: 3369 Comm: kworker/0:2 Not tainted 5.3.0-rc7+ #0
> Hardware name: Google Compute Engine
> Workqueue: usb_hub_wq hub_event
> Call Trace:
>  __dump_stack lib/dump_stack.c:77 [inline]
>  dump_stack+0x191/0x1f0 lib/dump_stack.c:113
>  kmsan_report+0x162/0x2d0 mm/kmsan/kmsan_report.c:109
>  __msan_warning+0x75/0xe0 mm/kmsan/kmsan_instr.c:294
>  rt2500usb_init_eeprom wireless/ralink/rt2x00/rt2500usb.c:1443 [inline]
>  rt2500usb_probe_hw+0xb5e/0x22a0 wireless/ralink/rt2x00/rt2500usb.c:1757
>  rt2x00lib_probe_dev+0xba9/0x3260 wireless/ralink/rt2x00/rt2x00dev.c:1427
>  rt2x00usb_probe+0x7ae/0xf60 wireless/ralink/rt2x00/rt2x00usb.c:842
>  rt2500usb_probe+0x50/0x60 wireless/ralink/rt2x00/rt2500usb.c:1966
>  ......
> 
> Local variable description: ----reg.i.i@rt2500usb_probe_hw
> Variable was created at:
>  rt2500usb_register_read wireless/ralink/rt2x00/rt2500usb.c:51 [inline]
>  rt2500usb_init_eeprom wireless/ralink/rt2x00/rt2500usb.c:1440 [inline]
>  rt2500usb_probe_hw+0x774/0x22a0 wireless/ralink/rt2x00/rt2500usb.c:1757
>  rt2x00lib_probe_dev+0xba9/0x3260 wireless/ralink/rt2x00/rt2x00dev.c:1427
> 
> Signed-off-by: Dongliang Mu <[email-masked]>
> ---
>  drivers/net/wireless/ralink/rt2x00/rt2500usb.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/net/wireless/ralink/rt2x00/rt2500usb.c b/drivers/net/wireless/ralink/rt2x00/rt2500usb.c
> index fce05fc88aaf..f6c93a25b18c 100644
> --- a/drivers/net/wireless/ralink/rt2x00/rt2500usb.c
> +++ b/drivers/net/wireless/ralink/rt2x00/rt2500usb.c
> @@ -48,6 +48,7 @@ static u16 rt2500usb_register_read(struct rt2x00_dev *rt2x00dev,
>  				   const unsigned int offset)
>  {
>  	__le16 reg;
> +	memset(&reg, 0, sizeof(reg));

As was pointed out, just set reg = 0 on the line above please.

>  	rt2x00usb_vendor_request_buff(rt2x00dev, USB_MULTI_READ,
>  				      USB_VENDOR_REQUEST_IN, offset,
>  				      &reg, sizeof(reg));

Are you sure this is valid to call this function with a variable on the
stack like this?  How did you test this change?

thanks,

greg k-h