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AJvYcCUN6fAAIARvJOPEP30OcXyt0RRgoPE7ebHfi46PEbeER/eaatgXXPUI9eUMBTFMM4R9rJXOg6/Hl8xlKUXiWFcotE8x2YeZ X-Gm-Message-State: AOJu0Yyh6JYLlfakqcVOgjZ1wOuFUTN7CO0rtGf/oTGKVayz2bINIx7w ajFbyfYTCh01qW1T3bv+YJCZRxC4VG5PiKgXJmvOHk84hw134gpXHQ+/YHZz8VrjZZbpzvthRcS g6i1gDbdyDkRSO/8teYp86ns8d2KaHSSs5ueW X-Google-Smtp-Source: AGHT+IHjjhW9Mkc3MLi6AOXsxcvpZLuQOJNY5GEHtIJTZ5uVt1mdDCC/RFDainqjKD6ddgbeQDnoyNq4EjeHd53ZWV8= X-Received: by 2002:a81:dd06:0:b0:610:bc71:43ab with SMTP id e6-20020a81dd06000000b00610bc7143abmr8114088ywn.44.1710881692500; Tue, 19 Mar 2024 13:54:52 -0700 (PDT) Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 References: <20240314111713.5979-1-renmingshuai@huawei.com> In-Reply-To: From: Jamal Hadi Salim Date: Tue, 19 Mar 2024 16:54:41 -0400 Message-ID: Subject: Re: [PATCH] net/sched: Forbid assigning mirred action to a filter attached to the egress To: Eric Dumazet Cc: renmingshuai , xiyou.wangcong@gmail.com, jiri@resnulli.us, davem@davemloft.net, vladbu@nvidia.com, netdev@vger.kernel.org, yanan@huawei.com, liaichun@huawei.com, caowangbao@huawei.com, Eric Dumazet , Jakub Kicinski , Paolo Abeni , Victor Nogueira , Pedro Tammela , Davide Caratti Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Tue, Mar 19, 2024 at 5:38=E2=80=AFAM Eric Dumazet = wrote: > > On Mon, Mar 18, 2024 at 11:05=E2=80=AFPM Jamal Hadi Salim wrote: > > > > On Mon, Mar 18, 2024 at 3:11=E2=80=AFPM Eric Dumazet wrote: > > > > > > On Mon, Mar 18, 2024 at 6:36=E2=80=AFPM Jamal Hadi Salim wrote: > > > > > > > > On Mon, Mar 18, 2024 at 11:46=E2=80=AFAM Eric Dumazet wrote: > > > > > > > > > > On Mon, Mar 18, 2024 at 3:27=E2=80=AFPM Jamal Hadi Salim wrote: > > > > > > > > > > > > On Sun, Mar 17, 2024 at 12:10=E2=80=AFPM Jamal Hadi Salim wrote: > > > > > > > > > > > > > > On Thu, Mar 14, 2024 at 1:14=E2=80=AFPM Jamal Hadi Salim wrote: > > > > > > > > > > > > > > > > On Thu, Mar 14, 2024 at 7:18=E2=80=AFAM renmingshuai wrote: > > > > > > > > > > > > > > > > > > As we all know the mirred action is used to mirroring or = redirecting the > > > > > > > > > packet it receives. Howerver, add mirred action to a filt= er attached to > > > > > > > > > a egress qdisc might cause a deadlock. To reproduce the p= roblem, 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 verbo= se \ > > > > > > > > > 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_conntra= ck] > > > > > > > > > [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 d= eadlock. > > > > > > > > > > > > > > > > > > Fix the issue by forbidding assigning mirred action to a = filter attached > > > > > > > > > to the egress. > > > > > > > > > > > > > > > > > > Signed-off-by: Mingshuai Ren > > > > > > > > > --- > > > > > > > > > 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_mirre= d.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 ne= t *net, struct nlattr *nla, > > > > > > > > > NL_SET_ERR_MSG_MOD(extack, "Mirred requir= es attributes to be passed"); > > > > > > > > > return -EINVAL; > > > > > > > > > } > > > > > > > > > + if (tp->chain->block->q->parent !=3D TC_H_INGRESS= ) { > > > > > > > > > + NL_SET_ERR_MSG_MOD(extack, "Mirred can on= ly be assigned to the filter attached to ingress"); > > > > > > > > > + return -EINVAL; > > > > > > > > > + } > > > > > > > > > > > > > > > > Sorry, this is too restrictive as Jiri said. We'll try to r= eproduce. 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-t= dc. > > > > > > > Conclusion is things broke around this time frame: > > > > > > > https://lore.kernel.org/netdev/1431679850-31896-1-git-send-em= ail-fw@strlen.de/ > > > > > > > https://lore.kernel.org/netdev/1465095748.2968.45.camel@eduma= zet-glaptop3.roam.corp.google.com/ > > > > > > > > > > > > > > Looking further into it. > > > > > > > > > > > > This is what we came up with. Eric, please take a look... > > > > > > > > > > > > cheers, > > > > > > jamal > > > > > > > > > > > > > > > > > > --- a/net/core/dev.c > > > > > > +++ b/net/core/dev.c > > > > > > @@ -3789,7 +3789,14 @@ static inline int __dev_xmit_skb(struct = sk_buff > > > > > > *skb, struct Qdisc *q, > > > > > > if (unlikely(contended)) > > > > > > spin_lock(&q->busylock); > > > > > > > > > > > > + if (dev_recursion_level()) { > > > > > > > > > > I am not sure what your intent is, but this seems wrong to me. > > > > > > > > > > > > > There is a deadlock if you reenter the same device which has a qdis= c > > > > attached to it more than once. > > > > Essentially entering __dev_xmit_skb() we grab the root qdisc lock t= hen > > > > run some action which requires it to grab the root qdisc lock (agai= n). > > > > This is easy to show with mirred (although i am wondering if syzkal= ler > > > > may have produced this at some point).. > > > > $TC qdisc add dev $DEV root handle 1: htb default 1 > > > > $TC filter add dev $DEV protocol ip u32 match ip protocol 1 0xff > > > > action mirred egress mirror dev $DEV > > > > > > > > Above example is essentially egress $DEV-> egress $DEV in both case= s > > > > "egress $DEV" grabs the root qdisc lock. You could also create anot= her > > > > example with egress($DEV1->$DEV2->back to $DEV1). > > > > > > > > > Some valid setup use : > > > > > > > > > > A bonding device, with HTB qdisc (or other qdisc) > > > > > (This also could be a tunnel device with a qdisc) > > > > > > > > > > -> one or multiple physical NIC, wth FQ or other qdisc. > > > > > > > > > > Packets would be dropped here when we try to reach the physical d= evice. > > > > > > > > > > > > > If you have an example handy please send it. I am trying to imagine > > > > how those would have worked if they have to reenter the root qdisc = of > > > > the same dev multiple times.. > > > > > > Any virtual device like a GRE/SIT/IPIP/... tunnel, add a qdisc on it = ? > > > > > > dev_xmit_recursion_inc() is global (per-cpu), it is not per-device. > > > > > > A stack of devices A -> B -> C would elevate the recursion level to > > > three just fine. > > > > > > After your patch, a stack of devices would no longer work. > > > > > > It seems mirred correctly injects packets to the top of the stack for > > > ingress (via netif_rx() / netif_receive_skb()), > > > but thinks it is okay to call dev_queue_xmit(), regardless of the con= text ? > > > > > > Perhaps safe-guard mirred, instead of adding more code to fast path. > > > > I agree not to penalize everybody for a "bad config" like this > > (surprising syzkaller hasnt caught this). But i dont see how doing the > > checking within mirred will catch this (we cant detect the A->B->A > > case). > > I think you are suggesting a backlog-like queue for mirred? Not far > > off from that is how it used to work before > > (https://lore.kernel.org/netdev/1465095748.2968.45.camel@edumazet-glapt= op3.roam.corp.google.com/) > > > spin_trylock() had to go. There is no way we could keep this. > Not asking for it to come back... just pointing out why it worked before. > > - i.e we had a trylock for the qdisc lock and if it failed we tagged > > the rx softirq for a reschedule. That in itself is insufficient, we > > would need a loop check which is per-skb (which we had before > > https://lore.kernel.org/netdev/1431679850-31896-1-git-send-email-fw@str= len.de/). > > There are other gotchas there, potentially packet reordering. > > If we want to make sure dev_queue_xmit() is called from the top (no > spinlock held), > then we need a queue, serviced from another context. > > This extra queueing could happen if > __this_cpu_read(softnet_data.xmit.recursion) > 0 > I dont see a way to detect softnet_data.xmit.recursion > 0 at mirred level. The first time we enter it will be 0. The second time we would deadlock before we hit mirred. I am also worried about packet reordering avoidance logic code amount needed just to deal with a buggy configuration. Dropping the packet for this exact config should be ok. How about adding a per-qdisc per-cpu recursion counter? Incremented when we enter the cpu from the top, decremented when we leave. If we detect __this_cpu_read(qdisc.xmit_recursion) > 0 we drop as per that patch? cheers, jamal > This can be done from net/sched/act_mirred.c with no additional change > in net/core/dev.c, > and no new skb field.