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AJvYcCVpegVNFQMwLXfIlSKwVYOYmHhZDO47uJbXhWP7k+c0cnGrDGVECd0aqwCOtAWqF84QKXio8J4FGbf/ZwQyxFn89RibohOj X-Gm-Message-State: AOJu0YwurfiIOsw32ilatbcEqNFyhit7NUjFfT8uE9TgIOV1oo6sYmT7 IX59VTHXnueFYI8ijwJ2/HGo3Jh3wtk54BgMpSq7iIm0RxKF68VJ1PRGL+gxVdaGQDDxFaiON+d f6ld9XSDzyRe5geFrE7SVDaY0dGQjpILs7I/n X-Google-Smtp-Source: AGHT+IF+qgjURhYMWR8CuqJqM3wZsBDzYjCo431dW5yTIPonwd6ZA2vDeF2M9jhTSRYGe1x6IKm/EhIfWonJ6uEoJVU= X-Received: by 2002:a25:7483:0:b0:dc2:48af:bf17 with SMTP id p125-20020a257483000000b00dc248afbf17mr17238149ybc.62.1710955922883; Wed, 20 Mar 2024 10:32:02 -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: Wed, 20 Mar 2024 13:31:51 -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 Wed, Mar 20, 2024 at 12:58=E2=80=AFPM Eric Dumazet = wrote: > > On Tue, Mar 19, 2024 at 9:54=E2=80=AFPM Jamal Hadi Salim wrote: > > > > 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 <= jhs@mojatatu.com> 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 = filter attached to > > > > > > > > > > > a egress qdisc might cause a deadlock. To reproduce t= he problem, perform > > > > > > > > > > > the following steps: > > > > > > > > > > > (1)tc qdisc add dev eth0 root handle 1: htb default 3= 0 \n > > > > > > > > > > > (2)tc filter add dev eth2 protocol ip prio 2 flower v= erbose \ > > > > > > > > > > > action police rate 100mbit burst 12m conform-exc= eed jump 1 \ > > > > > > > > > > > / pipe mirred egress redirect dev eth2 action dr= op > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > I think you meant both to be the same device eth0 or et= h2? > > > > > > > > > > > > > > > > > > > > > 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_mirre= d] > > > > > > > > > > > [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_tabl= es] > > > > > > > > > > > [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_con= ntrack] > > > > > > > > > > > [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 loc= k in __dev_queue_xmit > > > > > > > > > > > before the egress packets are mirred, and it will att= empt to obtain the > > > > > > > > > > > spin lock again after packets are mirred, which cause= a deadlock. > > > > > > > > > > > > > > > > > > > > > > Fix the issue by forbidding assigning mirred action t= o 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_m= irred.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(struc= t net *net, struct nlattr *nla, > > > > > > > > > > > NL_SET_ERR_MSG_MOD(extack, "Mirred re= quires attributes to be passed"); > > > > > > > > > > > return -EINVAL; > > > > > > > > > > > } > > > > > > > > > > > + if (tp->chain->block->q->parent !=3D TC_H_ING= RESS) { > > > > > > > > > > > + NL_SET_ERR_MSG_MOD(extack, "Mirred ca= n 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. > > > > > > > > > > > > > > > > > > Ok, i looked at old notes - it did work at "some point" p= re-tdc. > > > > > > > > > Conclusion is things broke around this time frame: > > > > > > > > > https://lore.kernel.org/netdev/1431679850-31896-1-git-sen= d-email-fw@strlen.de/ > > > > > > > > > https://lore.kernel.org/netdev/1465095748.2968.45.camel@e= dumazet-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(str= uct 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 lo= ck then > > > > > > 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 sy= zkaller > > > > > > 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 0xf= f > > > > > > action mirred egress mirror dev $DEV > > > > > > > > > > > > Above example is essentially egress $DEV-> egress $DEV in both = cases > > > > > > "egress $DEV" grabs the root qdisc lock. You could also create = another > > > > > > example with egress($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 physic= al device. > > > > > > > > > > > > > > > > > > > If you have an example handy please send it. I am trying to ima= gine > > > > > > how those would have worked if they have to reenter the root qd= isc 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-devic= e. > > > > > > > > > > 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= context ? > > > > > > > > > > Perhaps safe-guard mirred, instead of adding more code to fast pa= th. > > > > > > > > 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-g= laptop3.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 befor= e. > > > > > > - i.e we had a trylock for the qdisc lock and if it failed we tagge= d > > > > 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= @strlen.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. > > Then it is fine, no qdisc spinlock is held at this point. > > The second time we would > > deadlock before we hit mirred. > > This is not how I see the trace. > > Mirred would detect that and either drop or queue the packet to a work > queue or something. > > diff --git a/net/sched/act_mirred.c b/net/sched/act_mirred.c > index 5b38143659249e66718348e0ec4ed3c7bc21c13d..a2c53e200629a17130f38246a= b3cdb8c89c6d30e > 100644 > --- a/net/sched/act_mirred.c > +++ b/net/sched/act_mirred.c > @@ -237,9 +237,15 @@ tcf_mirred_forward(bool at_ingress, bool > want_ingress, struct sk_buff *skb) > { > int err; > > - if (!want_ingress) > + if (!want_ingress) { > + if (__this_cpu_read(softnet_data.xmit.recursion) > 0) { > + // TODO increment a drop counter perhaps ? > + kfree_skb(skb); > + return -EINVAL; > + } > + > err =3D tcf_dev_queue_xmit(skb, dev_queue_xmit); > - else if (!at_ingress) > + } else if (!at_ingress) > err =3D netif_rx(skb); > else > err =3D netif_receive_skb(skb); I doubt this will work - who increments softnet_data.xmit.recursion? We enter __dev_xmit_skb (grab lock) --> qdisc_enq-->classify-->mirred (recursion is zero) which redirects entering back into __dev_xmit_skb again and deadlocks trying to grab lock. Maybe something is not clear to me, trying your suggestion... cheers, jamal