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

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Date: Thu, 23 May 2024 12:30:52 -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 Thu, May 23, 2024 at 11:13:08PM +0800, shichao lai wrote:
> Thanks for your comprehensive analysis.
> I added some pr_info() to check the workflow, and I found that the
> uzonesize was not initialized in fact!
> 
> The workflow is shown as below.
> Before alauda_read_data(), there are in fact many alauda_check_media(),
> but none of them enter the branch of alauda_init_media(), where
> uzonesize is set to nonzero value.
> The key branch condition is "status[0] & 0x08", which is always
> unsatisfied in this repro.
> 
> ```
> alauda_transport
>     alauda_check_media
>         if (status[0] & 0x08) // not satisfied
>             alauda_init_media()
>                 // initialize uzonesize
>     alauda_read_data
> ```

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