Re: [PATCH net] net: airoha: Fix potential use-after-free in airoha_ppe_deinit()

[Lorenzo Bianconi <lorenzo@kernel.org>]

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> airoha_ppe_deinit() replaces the NPU pointer with NULL via
> rcu_replace_pointer() but does not wait for existing RCU readers
> to exit before calling ppe_deinit() and airoha_npu_put(). This can
> cause a use-after-free if a reader in an RCU read-side critical
> section still holds a reference to the NPU when it is freed.
> 
> The init path (airoha_ppe_init) already calls synchronize_rcu()
> after rcu_assign_pointer(), but the deinit path introduced in
> commit 6abcf751bc08 ("net: airoha: Fix schedule while atomic in
> airoha_ppe_deinit()") omitted the matching barrier when switching
> from rcu_read_lock()/rcu_dereference() to rcu_replace_pointer().
> 
> Add synchronize_rcu() before ppe_deinit() to ensure all existing
> RCU readers have completed before the NPU resources are released.
> 
> Fixes: 6abcf751bc084804a9e5b3051442e8a2ce67f48a ("net: airoha: Fix schedule while atomic in airoha_ppe_deinit()")
> Signed-off-by: Wayen Yan <win847@gmail.com>

Acked-by: Lorenzo Bianconi <lorenzo@kernel.org>

> ---
>  drivers/net/ethernet/airoha/airoha_ppe.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/net/ethernet/airoha/airoha_ppe.c b/drivers/net/ethernet/airoha/airoha_ppe.c
> index e7c78293002a..f6396925722d 100644
> --- a/drivers/net/ethernet/airoha/airoha_ppe.c
> +++ b/drivers/net/ethernet/airoha/airoha_ppe.c
> @@ -1659,6 +1659,7 @@ void airoha_ppe_deinit(struct airoha_eth *eth)
>  	npu = rcu_replace_pointer(eth->npu, NULL,
>  				  lockdep_is_held(&flow_offload_mutex));
>  	if (npu) {
> +		synchronize_rcu();
>  		npu->ops.ppe_deinit(npu);
>  		airoha_npu_put(npu);
>  	}
> -- 
> 2.51.0
> 
> 

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