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

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Message-ID: <1ec5e02d.6d52a.19c337418d3.Coremail.duoming@zju.edu.cn>
Date: Fri, 6 Feb 2026 22:56:12 +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 Fri, 6 Feb 2026 18:48:38 +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.

Best regards,
Duoming Zhou