netdev - Re: [PATCH] atm/fore200e: Consolidate available cell rate update to prevent race condition

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Date: Fri, 14 Jun 2024 13:23:41 +0100
From: Simon Horman <horms@...nel.org>
To: Gui-Dong Han <hanguidong02@...look.com>
Cc: 3chas3@...il.com, linux-atm-general@...ts.sourceforge.net,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	baijiaju1990@...il.com
Subject: Re: [PATCH] atm/fore200e: Consolidate available cell rate update to
 prevent race condition

On Tue, Jun 11, 2024 at 11:54:10AM +0800, Gui-Dong Han wrote:
> In fore200e_change_qos, there is a race condition due to two consecutive
> updates to the 'available_cell_rate' variable. If a read operation 
> occurs between these updates, an intermediate value might be read, 
> leading to potential bugs.
> 
> To fix this issue, 'available_cell_rate' should be adjusted in a single 
> operation, ensuring consistency and preventing any intermediate states 
> from being read.
> 
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Signed-off-by: Gui-Dong Han <hanguidong02@...look.com>

Hi Gui-Dong Han,

If there is a race involving writing and reading available_cell_rate,
then I believe there is still a race after your patch: if nothing protects
to protect available_cell_rate from being read while it is written then
that is true both before and after this patch.

Also, I would suggest that this is a very old and possibly unused driver.
If you wish to spend time on it I'd suggest that time go into
investigating if it is appropriate to remove the driver entirely.