Date:   Thu, 6 Jan 2022 15:35:27 +0100
From:   Greg KH <gregkh@linuxfoundation.org>
To:     Wei Ming Chen <jj251510319013@gmail.com>
Cc:     linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org,
        balbi@kernel.org, maze@google.com
Subject: Re: [PATCH] usb: gadget: function: Fix returning incorrect PNP string
Message-ID: <Ydb+L+wXfKzXyma9@kroah.com>
References: <20220105040439.3182-1-jj251510319013@gmail.com>
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In-Reply-To: <20220105040439.3182-1-jj251510319013@gmail.com>
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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?

thanks,

greg k-h