Re: [PATCH 1/1] can: bcm: prevent thrtimer UAF in rx path by checking RX_NO_AUTOTIMER

[Oliver Hartkopp]

On 24.04.26 21:08, Marc Kleine-Budde wrote:
> On 22.04.2026 14:55:50, Oliver Hartkopp wrote:
> > On 22.04.26 12:22, Lee Jones wrote:
> > > Commit f1b4e32aca08 ("can: bcm: use call_rcu() instead of costly
> > > synchronize_rcu()") removed the synchronize_rcu() call from
> > > bcm_delete_rx_op() and introduced the RX_NO_AUTOTIMER flag to prevent
> > > timers from being rearmed during deletion.  However, it only applied
> > > this check to op->timer via bcm_rx_starttimer().
> > >
> > > It missed the fact that op->thrtimer can also be rearmed by an
> > > in-flight bcm_rx_handler() (which runs as an RCU reader) via
> > > bcm_rx_update_and_send().  This allows op->thrtimer to be queued after
> > > bcm_remove_op() has already cancelled it, leading to a use-after-free
> > > when the timer fires on the deferred-freed struct bcm_op.
> > >
> > > Address the omission by checking the RX_NO_AUTOTIMER flag
> > > in bcm_rx_update_and_send() before starting op->thrtimer, effectively
> > > preventing it from being rearmed concurrently with teardown.
> > >
> > > Signed-off-by: Lee Jones <lee@xxxxxxxxxx>
> >
> > Many thanks for the investigation and the fix!
> >
> > Acked-by: Oliver Hartkopp <socketcan@xxxxxxxxxxxx>
>
> Can we add a Fixes: tag?

Yes, we should.

Thanks!

Signed-off-by: Oliver Hartkopp <socketcan@xxxxxxxxxxxx>

Best regards,
Oliver