[PATCH] usb: gadget: function: Fix returning incorrect PNP string

[PATCH] usb: gadget: function: Fix returning incorrect PNP string

[Wei Ming Chen]

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

Re: [PATCH] usb: gadget: function: Fix returning incorrect PNP string

[Greg KH]

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

Re: [PATCH] usb: gadget: function: Fix returning incorrect PNP string

[陳偉銘]

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

Re: [PATCH] usb: gadget: function: Fix returning incorrect PNP string

[Greg KH]

On Fri, Jan 07, 2022 at 10:37:19AM +0800, 陳偉銘 wrote:
> 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”?
> 

I do not know, I suggest you two work together to get the correct fix
submitted.

thanks,

greg k-h