From: 陳偉銘 <jj251510319013@gmail.com>
To: Greg KH <gregkh@linuxfoundation.org>
Cc: linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org,
balbi@kernel.org, "Maciej Żenczykowski" <maze@google.com>
Subject: Re: [PATCH] usb: gadget: function: Fix returning incorrect PNP string
Date: Fri, 7 Jan 2022 10:37:19 +0800 [thread overview]
Message-ID: <CAJwFiG+caDOp48R+EMATi9W_hCt-SBoEeeeEK8XGuRWai=bYug@mail.gmail.com> (raw)
In-Reply-To: <Ydb+L+wXfKzXyma9@kroah.com>
Greg KH <gregkh@linuxfoundation.org> 於 2022年1月6日 週四 下午10:35寫道:
>
> On Wed, Jan 05, 2022 at 12:04:39PM +0800, Wei Ming Chen wrote:
> > There will be 2 leading bytes indicating the total length of
> > the PNP string, so I think we should add value by 2, otherwise
> > the PNP string copied to user will not contain the last 2 bytes
> >
> > Signed-off-by: Wei Ming Chen <jj251510319013@gmail.com>
> > ---
> > drivers/usb/gadget/function/f_printer.c | 4 +++-
> > 1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/usb/gadget/function/f_printer.c b/drivers/usb/gadget/function/f_printer.c
> > index abec5c58f525..3fb00fd0b5ee 100644
> > --- a/drivers/usb/gadget/function/f_printer.c
> > +++ b/drivers/usb/gadget/function/f_printer.c
> > @@ -1005,9 +1005,11 @@ static int printer_func_setup(struct usb_function *f,
> > break;
> > }
> > value = strlen(dev->pnp_string);
> > + memcpy(buf + 2, dev->pnp_string, value);
> > +
> > + value += 2;
> > buf[0] = (value >> 8) & 0xFF;
> > buf[1] = value & 0xFF;
> > - memcpy(buf + 2, dev->pnp_string, value);
> > DBG(dev, "1284 PNP String: %x %s\n", value,
> > dev->pnp_string);
> > break;
> > --
> > 2.25.1
> >
>
> Are you sure this is correct?
>
> How is this related to this recent thread:
> https://lore.kernel.org/all/CAKjGFBUdjXcZoVV4jdrgTz4rKThTfZAK4CqreKmBZ4KHE+K1GA@mail.gmail.com/#t
>
> your change is different from what is proposed there, why?
I didn’t notice this thread before I send this patch, I think the
concept of my change is similar to Volodymyr Lisivka’s change, he/she
introduced a separate variable for the PNP string length, I think it
may be clearer and more readable than just “value += 2”
Another thing that I am not too sure whether I am correct is this line of code
DBG(dev, "1284 PNP String: %x %s\n", value,
dev->pnp_string);
What Volodymyr Lisivka changed is like this
DBG(dev, "1284 PNP String: %x %s\n", pnp_length,
dev->pnp_string);
In my change, “value” equals to “pnp_length + 2” in Volodymyr
Lisivka’s change, and I think we should print “the PNP string length +
2” instead of “the PNP string length”?
>
> thanks,
>
> greg k-h
thanks,
Wei Ming Chen
next prev parent reply other threads:[~2022-01-07 2:37 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-05 4:04 [PATCH] usb: gadget: function: Fix returning incorrect PNP string Wei Ming Chen
2022-01-06 14:35 ` Greg KH
2022-01-07 2:37 ` 陳偉銘 [this message]
2022-01-26 12:21 ` Greg KH
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