netdev - Re: [PATCH net v2] atm: fore200e: fix use-after-free in tasklets during device removal

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Message-ID: <6a1f4a65.6fced.19c41863ba9.Coremail.duoming@zju.edu.cn>
Date: Mon, 9 Feb 2026 16:30:42 +0800 (GMT+08:00)
From: duoming@....edu.cn
To: "Jijie Shao" <shaojijie@...wei.com>
Cc: netdev@...r.kernel.org, linux-atm-general@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org, 3chas3@...il.com
Subject: Re: [PATCH net v2] atm: fore200e: fix use-after-free in tasklets
 during device removal

On Mon, 9 Feb 2026 14:41:52 +0800 Jijie Shao wrote:
> >>> When the PCA-200E or SBA-200E adapter is being detached, the fore200e
> >>> is deallocated. However, the tx_tasklet or rx_tasklet may still be running
> >>> or pending, leading to use-after-free bug when the already freed fore200e
> >>> is accessed again in fore200e_tx_tasklet() or fore200e_rx_tasklet().
> >>>
> >>> One of the race conditions can occur as follows:
> >>>
> >>> CPU 0 (cleanup)           | CPU 1 (tasklet)
> >>> fore200e_pca_remove_one() | fore200e_interrupt()
> >>>     fore200e_shutdown()     |   tasklet_schedule()
> >>>       kfree(fore200e)       | fore200e_tx_tasklet()
> >>>                             |   fore200e-> // UAF
> >>>
> >>> Fix this by ensuring tx_tasklet or rx_tasklet is properly canceled before
> >>> the fore200e is released. Add tasklet_kill() in fore200e_shutdown() to
> >>> synchronize with any pending or running tasklets. Moreover, since
> >>> fore200e_reset() could prevent further interrupts or data transfers,
> >>> the tasklet_kill() should be placed after fore200e_reset() to prevent
> >>> the tasklet from being rescheduled in fore200e_interrupt().
> >>>
> >>> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> >>> Signed-off-by: Duoming Zhou <duoming@....edu.cn>
> >>> ---
> >>> Changes in v2:
> >>>     - Move tasklet_kill() after fore200e_reset().
> >>>
> >>>    drivers/atm/fore200e.c | 4 ++++
> >>>    1 file changed, 4 insertions(+)
> >>>
> >>> diff --git a/drivers/atm/fore200e.c b/drivers/atm/fore200e.c
> >>> index f62e3857144..de04c407921 100644
> >>> --- a/drivers/atm/fore200e.c
> >>> +++ b/drivers/atm/fore200e.c
> >>> @@ -362,6 +362,10 @@ fore200e_shutdown(struct fore200e* fore200e)
> >>>        if (fore200e->state > FORE200E_STATE_RESET) {
> >>>    	/* first, reset the board to prevent further interrupts or data transfers */
> >>>    	fore200e_reset(fore200e, 0);
> >>> +#ifdef FORE200E_USE_TASKLET
> >>> +	tasklet_kill(&fore200e->tx_tasklet);
> >>> +	tasklet_kill(&fore200e->rx_tasklet);
> >>> +#endif
> >>>        }
> >> I'm sorry if I gave you a confusing comment.
> >>
> >> If (fore200e->state <= FORE200E_STATE_RESET), is there no need to do tasklet_kill()?
> > The following four states that are preceding FORE200E_STATE_RESET are only set
> > during device initialization: FORE200E_STATE_BLANK, FORE200E_STATE_REGISTER,
> > FORE200E_STATE_CONFIGURE, and FORE200E_STATE_MAP.
> >
> > If the device is in any of these states, it means the initialization is
> > not complete and interrupts have not been registered. Therefore, tasklet
> > could not be scheduled through fore200e_interrupt().
> >
> > If the device is in FORE200E_STATE_RESET state, the fore200e_reset() has
> > already reset the device, which could prevent further interrupts and
> > tasklet scheduling.
> >
> > So there is no need to do tasklet_kill() if the state of fore200e is
> > less than or equal to FORE200E_STATE_RESET.
> 
> Yeah, I agree.
> But I reviewed the fore200e_init() again, and it only needs to do tasklet_kill()
> when "fore200e->state >= fFORE200E_STATE_IRQ"(in fore200e_irq_request());
> otherwise, "fore200e->tx_tasklet" has not been initialized.

Thank you for your time and suggestions! You are right, I will adopt your 
suggestions in the v3 patch.

Best regards,
Duoming Zhou