Re: [PATCH] net/sched: Forbid assigning mirred action to a filter attached to the egress

[Jamal Hadi Salim <jhs@mojatatu.com>]

On Thu, Mar 14, 2024 at 1:14 PM Jamal Hadi Salim <jhs@mojatatu.com> wrote:
>
> On Thu, Mar 14, 2024 at 7:18 AM renmingshuai <renmingshuai@huawei.com> wrote:
> >
> > As we all know the mirred action is used to mirroring or redirecting the
> > packet it receives. Howerver, add mirred action to a filter attached to
> > a egress qdisc might cause a deadlock. To reproduce the problem, perform
> > the following steps:
> > (1)tc qdisc add dev eth0 root handle 1: htb default 30 \n
> > (2)tc filter add dev eth2 protocol ip prio 2 flower verbose \
> >      action police rate 100mbit burst 12m conform-exceed jump 1 \
> >      / pipe mirred egress redirect dev eth2 action drop
> >
>
> I think you meant both to be the same device eth0 or eth2?
>
> > The stack is show as below:
> > [28848.883915]  _raw_spin_lock+0x1e/0x30
> > [28848.884367]  __dev_queue_xmit+0x160/0x850
> > [28848.884851]  ? 0xffffffffc031906a
> > [28848.885279]  tcf_mirred_act+0x3ab/0x596 [act_mirred]
> > [28848.885863]  tcf_action_exec.part.0+0x88/0x130
> > [28848.886401]  fl_classify+0x1ca/0x1e0 [cls_flower]
> > [28848.886970]  ? dequeue_entity+0x145/0x9e0
> > [28848.887464]  ? newidle_balance+0x23f/0x2f0
> > [28848.887973]  ? nft_lookup_eval+0x57/0x170 [nf_tables]
> > [28848.888566]  ? nft_do_chain+0xef/0x430 [nf_tables]
> > [28848.889137]  ? __flush_work.isra.0+0x35/0x80
> > [28848.889657]  ? nf_ct_get_tuple+0x1cf/0x210 [nf_conntrack]
> > [28848.890293]  ? do_select+0x637/0x870
> > [28848.890735]  tcf_classify+0x52/0xf0
> > [28848.891177]  htb_classify+0x9d/0x1c0 [sch_htb]
> > [28848.891722]  htb_enqueue+0x3a/0x1c0 [sch_htb]
> > [28848.892251]  __dev_queue_xmit+0x2d8/0x850
> > [28848.892738]  ? nf_hook_slow+0x3c/0xb0
> > [28848.893198]  ip_finish_output2+0x272/0x580
> > [28848.893692]  __ip_queue_xmit+0x193/0x420
> > [28848.894179]  __tcp_transmit_skb+0x8cc/0x970
> >
> > In this case, the process has hold the qdisc spin lock in __dev_queue_xmit
> > before the egress packets are mirred, and it will attempt to obtain the
> > spin lock again after packets are mirred, which cause a deadlock.
> >
> > Fix the issue by forbidding assigning mirred action to a filter attached
> > to the egress.
> >
> > Signed-off-by: Mingshuai Ren <renmingshuai@huawei.com>
> > ---
> >  net/sched/act_mirred.c                        |  4 +++
> >  .../tc-testing/tc-tests/actions/mirred.json   | 32 +++++++++++++++++++
> >  2 files changed, 36 insertions(+)
> >
> > diff --git a/net/sched/act_mirred.c b/net/sched/act_mirred.c
> > index 5b3814365924..fc96705285fb 100644
> > --- a/net/sched/act_mirred.c
> > +++ b/net/sched/act_mirred.c
> > @@ -120,6 +120,10 @@ static int tcf_mirred_init(struct net *net, struct nlattr *nla,
> >                 NL_SET_ERR_MSG_MOD(extack, "Mirred requires attributes to be passed");
> >                 return -EINVAL;
> >         }
> > +       if (tp->chain->block->q->parent != TC_H_INGRESS) {
> > +               NL_SET_ERR_MSG_MOD(extack, "Mirred can only be assigned to the filter attached to ingress");
> > +               return -EINVAL;
> > +       }
>
> Sorry, this is too restrictive as Jiri said. We'll try to reproduce. I
> am almost certain this used to work in the old days.

Ok, i looked at old notes - it did work at "some point" pre-tdc.
Conclusion is things broke around this time frame:
https://lore.kernel.org/netdev/1431679850-31896-1-git-send-email-fw@strlen.de/
https://lore.kernel.org/netdev/1465095748.2968.45.camel@edumazet-glaptop3.roam.corp.google.com/

Looking further into it.

cheers,
jamal