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

[duoming@zju.edu.cn]

On Fri, 6 Feb 2026 11:48:49 +0800 Jijie Shao wrote:
> > When the PCA-200E or SBA-200E adapters 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.
> >
> > Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> > Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>
> > ---
> >   drivers/atm/fore200e.c | 7 ++++++-
> >   1 file changed, 6 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/atm/fore200e.c b/drivers/atm/fore200e.c
> > index f62e3857144..7470daf9469 100644
> > --- a/drivers/atm/fore200e.c
> > +++ b/drivers/atm/fore200e.c
> > @@ -358,7 +358,12 @@ fore200e_shutdown(struct fore200e* fore200e)
> >       printk(FORE200E "removing device %s at 0x%lx, IRQ %s\n",
> >   	   fore200e->name, fore200e->phys_base,
> >   	   fore200e_irq_itoa(fore200e->irq));
> > -
> > +
> > +#ifdef FORE200E_USE_TASKLET
> > +	tasklet_kill(&fore200e->tx_tasklet);
> > +	tasklet_kill(&fore200e->rx_tasklet);
> > +#endif
> > +
> >       if (fore200e->state > FORE200E_STATE_RESET) {
> >   	/* first, reset the board to prevent further interrupts or data transfers */
> >   	fore200e_reset(fore200e, 0);
> 
> Hi,
> 
> I personally think that tasklet_kill() should be moved here.
> According to the code comments, there will be no data transfers or interrupts after fore200e_reset(),
> otherwise fore200e->tx_tasklet may be rescheduled again in fore200e_interrupt().

Thank you for your suggestions! I think you are right. I will send the v2 patch
and move the tasklet_kill() after fore200e_reset().

Best regards,
Duoming Zhou