linux-kernel - Re: [PATCHv2] Check whether divisor is non-zero before division

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Message-ID: <e1e593b2-fc50-4303-a01f-b7f7bf467c4e@rowland.harvard.edu>
Date: Fri, 24 May 2024 22:24:24 -0400
From: Alan Stern <stern@...land.harvard.edu>
To: shichao lai <shichaorai@...il.com>
Cc: gregkh@...uxfoundation.org, oneukum@...e.com, 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: [PATCHv2] Check whether divisor is non-zero before division

On Fri, May 24, 2024 at 10:13:45AM +0800, shichao lai wrote:
> On Fri, May 24, 2024 at 12:30 AM Alan Stern <stern@...land.harvard.edu> wrote:
> >
> > Good work!  So the problem is that the driver believes the status[0] &
> > 0x08 test.
> >
> > The way to fix this is to add an "initialized" flag to the alauda_info
> > structure.  Then alauda_check_media() should call alauda_init_media() if
> > the 0x08 bit is set in status[0] _or_ if info->initialized is 0.  And of
> > course, alauda_check_media() should then set info->initialized to 1 if
> > the alauda_init_media() call succeeds.
> >
> > Would you like to write and test a patch that does this?
> >
> > Alan Stern
> 
> I tried to do this. And the workflow can enter alauda_init_media(),
> but there are still many conditions to satisfy in alauda_init_media().
> Unfortunately alauda_init_media() stop and return here before
> initializing uzonesize:
> 
> if (data[0] != 0x14) {
>     usb_stor_dbg(us, "Media not ready after ack\n");
>     return USB_STOR_TRANSPORT_ERROR;
> }

That's an error return.

> The data[0] is status[0] showed before, and it was 0x0036.
> I am not familiar with the status code of alauda.
> How can I deal with this condition?
> Is it ok to pass this condition when info->initialized == false, even
> if the data[0] != 0x14?

If alauda_init_media() returns an error, leave info->initialized 
unchanged.  alauda_check_media() will return an error also, so the bad 
division won't take place.

Alan Stern