Re: [PATCH net] ppp: fix race conditions in ppp_fill_forward_path

[Pablo Neira Ayuso]

On Tue, Aug 12, 2025 at 05:38:02PM +0800, Qingfang Deng wrote:
> On Mon, Aug 11, 2025 at 5:35 PM Qingfang Deng <dqfext@xxxxxxxxx> wrote:
> >
> > On Mon, Aug 11, 2025 at 5:19 PM Eric Dumazet <edumazet@xxxxxxxxxx> wrote:
> > >
> > > On Mon, Aug 11, 2025 at 1:44 AM Qingfang Deng <dqfext@xxxxxxxxx> wrote:
> > > It is unclear if rcu_read_lock() is held at this point.
> > >
> > > list_first_or_null_rcu() does not have a builtin __list_check_rcu()
> >
> > ndo_fill_forward_path() is called by nf_tables chains, which is inside
> > an RCU critical section.
> 
> Update: mtk_flow_get_wdma_info() in mtk_ppe_offload.c calls
> dev_fill_forward_path() in process context without RCU, so
> ppp_fill_forward_path() can be called from two different contexts.
> Should I add rcu_read_lock() to mtk_flow_get_wdma_info() or
> ppp_fill_forward_path()?

mtk_flow_get_wdma_info() seems to be the exception at this point, so
I'm inclined to add rcu_read_lock() to mtk_flow_get_wdma_info().