Re: [PATCH] can: bcm: delay release of struct bcm_op after synchronize_rcu

[Marc Kleine-Budde]

On 19.06.2021 13:18:13, Thadeu Lima de Souza Cascardo wrote:
> can_rx_register callbacks may be called concurrently to the call to
> can_rx_unregister. The callbacks and callback data, though, are protected by
> RCU and the struct sock reference count.
> 
> So the callback data is really attached to the life of sk, meaning that it
> should be released on sk_destruct. However, bcm_remove_op calls tasklet_kill,
> and RCU callbacks may be called under RCU softirq, so that cannot be used on
> kernels before the introduction of HRTIMER_MODE_SOFT.
> 
> However, bcm_rx_handler is called under RCU protection, so after calling
> can_rx_unregister, we may call synchronize_rcu in order to wait for any RCU
> read-side critical sections to finish. That is, bcm_rx_handler won't be called
> anymore for those ops. So, we only free them, after we do that synchronize_rcu.
> 
> Reported-by: syzbot+0f7e7e5e2f4f40fa89c0@xxxxxxxxxxxxxxxxxxxxxxxxx
> Reported-by: Norbert Slusarek <nslusarek@xxxxxxx>
> Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@xxxxxxxxxxxxx>

Added to linux-can/testing.

Thanks,
Marc

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