Re: [PATCH net] net/sched: act_api: fix TOCTOU NULL deref on a->goto_chain

On Sun,  9 Aug 2026 05:09:28 -0400 Jamal Hadi Salim wrote:
> tcf_action_exec() handles TC_ACT_GOTO_CHAIN by first checking
> rcu_access_pointer(a->goto_chain) and then calling
> tcf_action_goto_chain_exec(), which does a second, independent
> rcu_dereference_bh(a->goto_chain) read and immediately dereferences
> chain->filter_chain. A concurrent tcf_action_set_ctrlact() (e.g. the gact
> replace path) can clear a->goto_chain between the two reads, so the second
> read returns NULL and tcf_action_goto_chain_exec() dereferences NULL.

FWIW *shiko suggests another tweak but looks orthogonal, LMK if you
disagree:

https://netdev-ai.bots.linux.dev/sashiko/#/patchset/[email protected]

(the patch is "too fresh" for me to apply right now anyway)