Re: [PATCH] usb: core: hcd: fix bug: application of sizeof to pointer

[Guo Zhengkui]

On 2021/12/8 6:21, Alan Stern wrote:
> On Tue, Dec 07, 2021 at 03:40:37PM +0100, Greg Kroah-Hartman wrote:
> > On Tue, Dec 07, 2021 at 09:53:47PM +0800, Guo Zhengkui wrote:
> > > Fix following error:
> > > ./drivers/usb/core/hcd.c:1284:38-44: ERROR:
> > > application of sizeof to pointer.
> >
> > What generated this error?
> >
> > > Use sizeof(*vaddr) instead.
> > >
> > > Signed-off-by: Guo Zhengkui <guozhengkui@xxxxxxxx>
> > > ---
> > >   drivers/usb/core/hcd.c | 2 +-
> > >   1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c
> > > index 4d326ee12c36..996d5273cf60 100644
> > > --- a/drivers/usb/core/hcd.c
> > > +++ b/drivers/usb/core/hcd.c
> > > @@ -1281,7 +1281,7 @@ static int hcd_alloc_coherent(struct usb_bus *bus,
> > >   		return -EFAULT;
> > >   	}
> > >   
> > > -	vaddr = hcd_buffer_alloc(bus, size + sizeof(vaddr),
> > > +	vaddr = hcd_buffer_alloc(bus, size + sizeof(*vaddr),
> >
> > I think you just broke the code.
> >
> > Look at this closer and see what the function is doing with this buffer
> > and if you still think your patch is correct, please rewrite the
> > changelog text to explain why it is so (hint, just using the output of
> > coccinelle isn't ok.)

Sorry for my carelessness. It should be sizeof(vaddr).

> Although the patch is definitely wrong, the code could stand to be
> improved.  The value stored at the end of the buffer is *vaddr_handle
> converted to an unsigned long, but the space reserved for this value is
> sizeof(vaddr) -- which doesn't make much sense since vaddr is a pointer
> to unsigned char.  The code implicitly relies on the fact that unsigned
> long takes up the same amount of space as a pointer.
>
> Readers wouldn't have to stop and figure this out if the amount of
> reserved space was simply set to sizeof(unsigned long) rather than
> sizeof(vaddr).

OK, I will commit another patch to fix this problem. Do you mind I add a 
"Suggested-by" tag of your name (Alan Stern) in this new patch?

Zhengkui

> Alan Stern