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

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Date: Thu, 23 May 2024 20:23:57 +0800
From: shichao lai <shichaorai@...il.com>
To: Greg KH <gregkh@...uxfoundation.org>
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 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().

 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.