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

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Message-ID: <CAM0EoMm5vCmtQ8CS4zRZX3QDfB9zoEYZC_CDHO_tHug-okXHhQ@mail.gmail.com>
Date: Fri, 15 Mar 2024 18:34:30 -0400
From: Jamal Hadi Salim <jhs@...atatu.com>
To: renmingshuai <renmingshuai@...wei.com>
Cc: caowangbao@...wei.com, davem@...emloft.net, jiri@...nulli.us, 
	liaichun@...wei.com, netdev@...r.kernel.org, vladbu@...dia.com, 
	xiyou.wangcong@...il.com, yanan@...wei.com
Subject: Re: [PATCH] net/sched: Forbid assigning mirred action to a filter
 attached to the egress

On Thu, Mar 14, 2024 at 10:10 PM renmingshuai <renmingshuai@...wei.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?
>
> Sorry, a careless mistake. eth2 in step 2 should be eth0.
> (2)tc filter add dev eth0 protocol ip prio 2 flower verbose \
>      action police rate 100mbit burst 12m conform-exceed jump 1 \
>      / pipe mirred egress redirect dev eth0 action drop
>
> >> 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@...wei.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.
> >

> >cheers,
> >jamal
> >
> >PS:- thanks for the tdc test, you are a hero just for submitting that!
>
> As Jiri said, that is really quite restrictive. It might be better to forbid mirred attached to egress filter
> to mirror or redirect packets to the egress. Just like:
>

Please, no. You are continuing to restrict many valid use cases. We'll
look at it this weekend.

cheers,
jamal

> --- a/net/sched/act_mirred.c
> +++ b/net/sched/act_mirred.c
> @@ -152,6 +152,12 @@ static int tcf_mirred_init(struct net *net, struct nlattr *nla,
>                 return -EINVAL;
>         }
>
> +       if ((tp->chain->block->q->parent != TC_H_INGRESS) &&
> +           (parm->eaction == TCA_EGRESS_MIRROR || parm->eaction == TCA_EGRESS_REDIR)) {
> +               NL_SET_ERR_MSG_MOD(extack, "Mirred assigned to egress filter can only mirror or redirect to ingress");
> +               return -EINVAL;
> +       }
> +
>         switch (parm->eaction) {
>         case TCA_EGRESS_MIRROR:
>         case TCA_EGRESS_REDIR:
>