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 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.

cheers,
jamal

PS:- thanks for the tdc test, you are a hero just for submitting that!



>         ret = nla_parse_nested_deprecated(tb, TCA_MIRRED_MAX, nla,
>                                           mirred_policy, extack);
>         if (ret < 0)
> diff --git a/tools/testing/selftests/tc-testing/tc-tests/actions/mirred.json b/tools/testing/selftests/tc-testing/tc-tests/actions/mirred.json
> index b73bd255ea36..50c6153bf34c 100644
> --- a/tools/testing/selftests/tc-testing/tc-tests/actions/mirred.json
> +++ b/tools/testing/selftests/tc-testing/tc-tests/actions/mirred.json
> @@ -1052,5 +1052,37 @@
>              "$TC qdisc del dev $DEV1 ingress_block 21 clsact",
>              "$TC actions flush action mirred"
>          ]
> +    },
> +    {
> +        "id": "fdda",
> +        "name": "Add mirred mirror to the filter which attached to engress",
> +        "category": [
> +            "actions",
> +            "mirred"
> +        ],
> +        "plugins": {
> +            "requires": "nsPlugin"
> +        },
> +        "setup": [
> +            [
> +                "$TC actions flush action mirred",
> +                0,
> +                1,
> +                255
> +            ],
> +            [
> +                "$TC qdisc add dev $DEV1 root handle 1: htb default 1",
> +                0
> +            ]
> +        ],
> +        "cmdUnderTest": "$TC filter add dev $DEV1 protocol ip u32 match ip protocol 1 0xff action mirred egress mirror dev $DEV1",
> +        "expExitCode": "2",
> +        "verifyCmd": "$TC action list action mirred",
> +        "matchPattern": "^[ \t]+index [0-9]+ ref",
> +        "matchCount": "0",
> +        "teardown": [
> +            "$TC qdisc del dev $DEV1 root handle 1: htb default 1",
> +            "$TC actions flush action mirred"
> +        ]
>      }
>  ]
> --
> 2.33.0
>