From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-ed1-f47.google.com (mail-ed1-f47.google.com [209.85.208.47]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id EF4BC69DF7 for ; Wed, 20 Mar 2024 16:58:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.208.47 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1710953887; cv=none; b=aHFlR52v9Tt6zywfp4WrJ7pbAFU3OnhU3gJtILhKQHgjUmykX3WK2uMDRI2FTNZb4S6NEVQ5V0DjOi/TkN70PdRUbDaJZVNDaH/87ojlXVrF/XVqcSXtqG5x5VZ+CoyMndIjClJNjiF7JxSNC48h3eZeza/5sCmqU36960lGVPw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1710953887; c=relaxed/simple; bh=mJrymtDICi7bFPltbPdz2gu7QDCeDyi2aNoLDRK3u2o=; h=MIME-Version:References:In-Reply-To:From:Date:Message-ID:Subject: To:Cc:Content-Type; b=a9uqJwnoRzzOw7dB9r+Z0d46IR09biNT3bSw8rb8bmEnGSGnJOmg9jlEaUtiqqmPBbnx6XDixV/B/L5Ub/pii2MFtocxc+Ji6HjNwvjh3f9KQZokHsGOc8ifEiy/o8m4Lh+aDEnjcyPNtZyqSn5AOuOZoSUjrCygTUh2WQwPcLk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=va8cuuFg; arc=none smtp.client-ip=209.85.208.47 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="va8cuuFg" Received: by mail-ed1-f47.google.com with SMTP id 4fb4d7f45d1cf-56b9dac4e6cso310a12.1 for ; Wed, 20 Mar 2024 09:58:04 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1710953883; x=1711558683; darn=vger.kernel.org; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:from:to:cc:subject:date :message-id:reply-to; bh=tzPodG4qFomJO8EjbK+loR6z9eNmrS/kvFeMe1pqOxg=; b=va8cuuFgWChWq9anC9kEUlY+hJRsS6KzTS3VAMb6RkGw8k6czYlS6i7A6Jq3HF8goR EJNvg0D27+AAPA31e4od1RI4X6R2ILOFHWqE7xlCuNC26hpoHN9S9J/fThnKBVMe5EAa RQ3LMUFD0mofm9aSXNFC3XJFnLuPotiDKup7DpUbS7/P2VlgeoWhStCMUckgzIoIApWb VOqMq+FBNCcV1Cll5fNhudV7V7YPyMCu23NXhACGyJvbppw3URz36zYDkQfJg+5zoAmZ w/G73KV37sZBQEvYvBdzIGz5OdtKrzOLPSVT0fIDfHnOIMQBpT6GtbLVXpRudfF2JXE/ oLfg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1710953883; x=1711558683; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=tzPodG4qFomJO8EjbK+loR6z9eNmrS/kvFeMe1pqOxg=; b=Zb/2r3ypulKy4TZykEuMFkECTRVzxicCeoJNMzIreUIzAyrf/OJSj30kwXdRkDI82W MpYyRoU9arZEkFx2N6N59Rx+quSVfTJM6rR40Lpu+23Fe84wyzGolLA9DEp8qmp+2fbU siTsrlmf1tK3aUDyelkGvfi+ZeD+chbP9cMS05VgEWc2I7QuRYRH97U/VlDpVcSrLU9A 51It2gy8SUp1OZ7y8QgoHjIVffl0BgzgAgoS62ZkqHmennH+IfyUPBgC0us+36F+U8XN qpsk6Cc9rFfiWKwjQ0Zy4UFu4FRnWtcBHa+ha7VePn14sYCeuweSYmZYUFvA/YvhnLYr RnkQ== X-Forwarded-Encrypted: i=1; AJvYcCU67mtIl+kZipj6davGOCUnJ+xqtFRmymSUMQp/dwOi+xV1ivitOImVytMc0HSKmlSmmscNOBGgEN5I/+qSSbtxurwgu/zd X-Gm-Message-State: AOJu0Yw27zx3eQtsLw2NUz6B7LTak0h00/jeVDk3zNX2kDsxi/7ApMaH IAS7E3kHGwN0CtCCJ/0PsEzO407rqsqEej4INQbIdld/4T4G1vFFYw07AgDhV9llWr51lOgodzZ m+Hb59sdtzX15+SYitvuxgUUrB1UBmwvhgdjR X-Google-Smtp-Source: AGHT+IHp9rpPNLc7D04a2Vlegq+BarNCT0eDwVjBHcW3jFj+1I/j4pCFnbEipACZrmhKgZC99ZKmx2zW+xfSlFRiicE= X-Received: by 2002:a05:6402:1d08:b0:56b:b856:7eb5 with SMTP id dg8-20020a0564021d0800b0056bb8567eb5mr90332edb.4.1710953882883; Wed, 20 Mar 2024 09:58:02 -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: Eric Dumazet Date: Wed, 20 Mar 2024 17:57:51 +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 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 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 o= r redirecting the > > > > > > > > > > packet it receives. Howerver, add mirred action to a fi= lter 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 ver= bose \ > > > > > > > > > > action police rate 100mbit burst 12m conform-excee= d 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_connt= rack] > > > > > > > > > > [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 attem= pt 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 > > > > > > > > > > --- > > > > > > > > > > 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_mir= red.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 requ= ires attributes to be passed"); > > > > > > > > > > return -EINVAL; > > > > > > > > > > } > > > > > > > > > > + if (tp->chain->block->q->parent !=3D TC_H_INGRE= SS) { > > > > > > > > > > + 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. > > > > > > > > > > > > > > > > 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-= email-fw@strlen.de/ > > > > > > > > https://lore.kernel.org/netdev/1465095748.2968.45.camel@edu= mazet-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(struc= t 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 qd= isc > > > > > attached to it more than once. > > > > > Essentially entering __dev_xmit_skb() we grab the root qdisc lock= then > > > > > run some action which requires it to grab the root qdisc lock (ag= ain). > > > > > This is easy to show with mirred (although i am wondering if syzk= aller > > > > > 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 ca= ses > > > > > "egress $DEV" grabs the root qdisc lock. You could also create an= other > > > > > example with egress($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= device. > > > > > > > > > > > > > > > > If you have an example handy please send it. I am trying to imagi= ne > > > > > how those would have worked if they have to reenter the root qdis= c of > > > > > the same dev multiple times.. > > > > > > > > Any virtual device like a GRE/SIT/IPIP/... tunnel, add a qdisc on i= t ? > > > > > > > > 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 t= o > > > > 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 f= or > > > > ingress (via netif_rx() / netif_receive_skb()), > > > > but thinks it is okay to call dev_queue_xmit(), regardless of the c= ontext ? > > > > > > > > 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 th= e > > > 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-gla= ptop3.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@s= trlen.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..a2c53e200629a17130f38246ab3= cdb8c89c6d30e 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);