netdev - Re: [PATCH] rt2x00: reset reg earlier in rt2500usb_register

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Date:   Thu, 21 Jan 2021 18:59:08 +0800
From:   慕冬亮 <mudongliangabcd@...il.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     davem@...emloft.net, helmut.schaa@...glemail.com,
        kvalo@...eaurora.org, linux-kernel <linux-kernel@...r.kernel.org>,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        sgruszka@...hat.com
Subject: Re: [PATCH] rt2x00: reset reg earlier in rt2500usb_register_read

On Thu, Jan 21, 2021 at 5:49 PM Greg KH <gregkh@...uxfoundation.org> wrote:
>
> 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@...500usb_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 <mudongliangabcd@...il.com>
> > ---
> >  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.

I've sent another patch.

BTW, I set "--subject-prefix="PATCH v2" in my git-send-mail command.
But it does not show "v2" in the subject of the new email.

>
> >       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?

First, I did not do any changes to this call. Second, the programming
style to pass the pointer of stack variable as arguments is not really
good. Third, I check this same code file, there are many code snippets
with such programming style. :(

>
> thanks,
>
> greg k-h