linux-kernel - Re: [PATCH v2] usb-storage: Check whether divisor is non-zero before division

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Message-ID: <2024052354-snorkel-drainer-d328@gregkh>
Date: Thu, 23 May 2024 14:37:18 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: shichao lai <shichaorai@...il.com>
Cc: oneukum@...e.com, stern@...land.harvard.edu, linux-usb@...r.kernel.org,
	usb-storage@...ts.one-eyed-alien.net, linux-kernel@...r.kernel.org,
	xingwei lee <xrivendell7@...il.com>,
	yue sun <samsun1006219@...il.com>
Subject: Re: [PATCH v2] usb-storage: Check whether divisor is non-zero before
 division

On Thu, May 23, 2024 at 08:23:57PM +0800, shichao lai wrote:
> On Thu, May 23, 2024 at 7:47 PM Greg KH <gregkh@...uxfoundation.org> wrote:
> >
> > On Thu, May 23, 2024 at 07:34:10PM +0800, Shichao Lai wrote:
> > > Since uzonesize may be zero, so judgements for non-zero
> > > are necessary in both place.
> > >
> > > Changes since v1:
> > > - Add one more check in alauda_write_lba().
> > > - Move check ahead of loop in alauda_read_data().
> >
> > Nit, this changes list should go below the --- line, as the
> > documentation asks for.
> 
> Sorry for my inexperience. I have read the document and found some
> examples but I am still a little confused about this.
> I guess this is what you mean?
> 
> Since uzonesize may be zero ... (context)
> 
> Reported-by: xingwei lee <xrivendell7@...il.com>
> Reported-by: yue sun <samsun1006219@...il.com>
> Signed-off-by: Shichao Lai <shichaorai@...il.com>
> ---
> Changes since v1:
> - Add one more check in alauda_write_lba().
> - Move check ahead of loop in alauda_read_data().

Yes.

> 
>  drivers/usb/storage/alauda.c | 4 ++++
>  1 file changed, 4 insertions(+)
> ...
> 
> 
> 
> > Check after the list of variables please, not in the middle of them.  I
> > think checkpatch will complain about this, right?
> 
> In fact this script doesn't warn about these problems, but I will
> adjust my code style later.
> But the check in alauda_write_lba() is due to some variable like
> lba_offset and zone will perform modulo and divide operations,
> which may throw divide errors when uzonesize is 0.
> So I think I prefer to adjust the order of the variable list later.
> Changes like this.
> ```c
> unsigned int uzonesize = MEDIA_INFO(us).uzonesize;
> unsigned int zonesize = MEDIA_INFO(us).zonesize;
> unsigned int pagesize = MEDIA_INFO(us).pagesize;
> unsigned int blocksize = MEDIA_INFO(us).blocksize;
> unsigned int new_pba_offset;
> if (!uzonesize)
>     return USB_STOR_TRANSPORT_ERROR;
> unsigned int lba_offset = lba % uzonesize;
> unsigned int zone = lba / uzonesize;
> ```
> If it's ok, I will post the patch v3 soon.

That works, thanks!

greg k-h