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

[Jijie Shao]

on 2026/2/6 22:56, duoming@xxxxxxxxxx wrote:
> 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@xxxxxxxxxx>
> > > ---
> > > 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.

Jijie Shao