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

[Jiri Pirko <jiri@resnulli.us>]

Thu, Mar 14, 2024 at 12:17:13PM CET, 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
>
>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>

You are missing "Fixes" tag.


>---
> 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");

Hmm, that is quite restrictive. I'm pretty sure you would break some
valid usecases.


>+		return -EINVAL;
>+	}
> 	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
>
>