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AJvYcCXWH0AOnqv/pvLE48bdS2lQAylLFBq2/ijrY4rWm12Bhgimsm2BV8I33Zc2ZJYSrNzDTiyCdtk5Bb1Nw7TvkpqlXtrsB062 X-Gm-Message-State: AOJu0Yy0/DQs8rBzCTYGreP5Gsf9D+utRTKK7Ojw0U2FEOpA+ogHEv2r r8qU30boiJzischYJcOM372FUOr1kUZrgln5vz8sXjLOdoOehycctQbj39eA6OULbjrX973xY2y spSKZqbq3WSERb3+4z+WbdZOV18iwmA9vLF02 X-Google-Smtp-Source: AGHT+IFebxuEfKJRNI8lOsQ3ctqXear4d66BeJTuiGpb89ZZefz3oVUOmI1LI+SpV3KaliRfiZvN4s1uGepvBAO0258= X-Received: by 2002:aa7:c3d0:0:b0:568:ce1e:94e5 with SMTP id l16-20020aa7c3d0000000b00568ce1e94e5mr110369edr.5.1710841125151; Tue, 19 Mar 2024 02:38:45 -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: Eric Dumazet Date: Tue, 19 Mar 2024 10:38:31 +0100 Message-ID: Subject: Re: [PATCH] net/sched: Forbid assigning mirred action to a filter attached to the egress To: Jamal Hadi Salim 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 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 re= directing the > > > > > > > > packet it receives. Howerver, add mirred action to a filter= attached to > > > > > > > > a egress qdisc might cause a deadlock. To reproduce the pro= blem, 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 ju= mp 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 t= o obtain the > > > > > > > > spin lock again after packets are mirred, which cause a dea= dlock. > > > > > > > > > > > > > > > > Fix the issue by forbidding assigning mirred action to a fi= lter 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_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 !=3D 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 rep= roduce. 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-emai= l-fw@strlen.de/ > > > > > > https://lore.kernel.org/netdev/1465095748.2968.45.camel@edumaze= t-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 qdisc > > > attached to it more than once. > > > Essentially entering __dev_xmit_skb() we grab the root qdisc lock the= n > > > run some action which requires it to grab the root qdisc lock (again)= . > > > This is easy to show with mirred (although i am wondering if syzkalle= r > > > 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 cases > > > "egress $DEV" grabs the root qdisc lock. You could also create anothe= r > > > example with egress($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 dev= ice. > > > > > > > > > > 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 conte= xt ? > > > > 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-glaptop= 3.roam.corp.google.com/) spin_trylock() had to go. There is no way we could keep this. > - 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@strle= n.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 This can be done from net/sched/act_mirred.c with no additional change in net/core/dev.c, and no new skb field.