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

[Alan Stern <stern@rowland.harvard.edu>]

On Wed, Dec 08, 2021 at 11:00:41AM +0800, Guo Zhengkui wrote:
> 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@vivo.com>
> > > > ---
> > > >   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?

That's fine.

Alan Stern