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

[Jakub Kicinski <kuba@kernel.org>]

On Tue, 11 Aug 2026 06:43:32 -0400 Jamal Hadi Salim wrote:
> On Mon, Aug 10, 2026 at 7:45 PM Jakub Kicinski <kuba@kernel.org> wrote:
> >
> > 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/20260809090928.868186-1-jhs@mojatatu.com
> >
> > (the patch is "too fresh" for me to apply right now anyway)  
> 
> The concern is valid but pre-existing and orthogonal to this patch
> (and a lot less severe than the posted fix)
> I had this discussion with Paolo: When the sashikos raise a concern on
> "pre-existing" issues, what should be the reaction?
> In general the conclusion was to follow up later if worth it; however,
> sometimes we need to make a judgement call - if the pointed to issue
> is serious (and yes, the AI bots are now reading what Sashikos are
> saying  and constructing bug reports) then a v2 is needed.
> In this case, I was planning to follow up. I will start more actively
> looking at sashiko reports and analyzing if worth a followup or a v2.
> I dont know how to do these pw signals, but in case i see it as "needs
> v2" it won't be worth waiting for one of you guys to comment.

Right, I was hoping my question was clear enough. I don't think v2 was
needed here either. But we had time to confirm...

> Do we need a written policy somewhere?

The only written policy should be that everyone who asks for a written
policy in this rapidly changing environment owes maintainers a beer :)

More seriously I tried to float two written policies recently - for net
vs net-next and requirements for information in fixes. And each time
there was a long discussion and questions. So y'all need to either
stop making written policies so painful, or stop asking for the
policies. *%$#.