netdev - Re: [PATCH net] net/sched: act_mirred: use the backlog for mirred ingress

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Message-ID: <CAM0EoMnYyyf7Zpa9eUFBU1vzx5QrUhFfXSFH4_utXOPU4+YFxQ@mail.gmail.com>
Date: Mon, 12 Feb 2024 10:11:25 -0500
From: Jamal Hadi Salim <jhs@...atatu.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: davem@...emloft.net, netdev@...r.kernel.org, edumazet@...gle.com, 
	pabeni@...hat.com, Marcelo Ricardo Leitner <marcelo.leitner@...il.com>, 
	Davide Caratti <dcaratti@...hat.com>, xiyou.wangcong@...il.com, jiri@...nulli.us, 
	shmulik.ladkani@...il.com
Subject: Re: [PATCH net] net/sched: act_mirred: use the backlog for mirred ingress

On Mon, Feb 12, 2024 at 9:51 AM Jamal Hadi Salim <jhs@...atatu.com> wrote:
>
> On Fri, Feb 9, 2024 at 6:54 PM Jakub Kicinski <kuba@...nel.org> wrote:
> >
> > The test Davide added in commit ca22da2fbd69 ("act_mirred: use the backlog
> > for nested calls to mirred ingress") hangs our testing VMs every 10 or so
> > runs, with the familiar tcp_v4_rcv -> tcp_v4_rcv deadlock reported by
> > lockdep.
> >
> > In the past there was a concern that the backlog indirection will
> > lead to loss of error reporting / less accurate stats. But the current
> > workaround does not seem to address the issue.
> >
>
> Let us run some basic tests on this first - it's a hairy spot. Also,

Something broke.
Create a ns. Put one half of veth into the namespace. Create a filter
inside the net ns.
at_ns$ tc qdisc add dev port0 ingress_block 21 clsact
at_ns$ tc filter add block 21 egress protocol ip prio 10 matchall
action mirred ingress redirect dev port0

Send a ping from host:
at_host@ ping 10.0.0.2 -c 1 -I <vethportonhostside>

And.. hits uaf.... see attached.
Sorry, no time to look at it right now but one of us
(Victor/Pedro/myself) will look later unless someone else beats us to
it.

cheers,
jamal

> IIRC Cong had some reservations about this in the past. Can't remember
> what they were.


> cheers,
> jamal
>
>
> > Fixes: 53592b364001 ("net/sched: act_mirred: Implement ingress actions")
> > Cc: Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
> > Suggested-by: Davide Caratti <dcaratti@...hat.com>
> > Link: https://lore.kernel.org/netdev/33dc43f587ec1388ba456b4915c75f02a8aae226.1663945716.git.dcaratti@redhat.com/
> > Signed-off-by: Jakub Kicinski <kuba@...nel.org>
> > ---
> > CC: jhs@...atatu.com
> > CC: xiyou.wangcong@...il.com
> > CC: jiri@...nulli.us
> > CC: shmulik.ladkani@...il.com
> > ---
> >  net/sched/act_mirred.c                             | 14 +++++---------
> >  .../testing/selftests/net/forwarding/tc_actions.sh |  3 ---
> >  2 files changed, 5 insertions(+), 12 deletions(-)
> >
> > diff --git a/net/sched/act_mirred.c b/net/sched/act_mirred.c
> > index 93a96e9d8d90..35c366f043d9 100644
> > --- a/net/sched/act_mirred.c
> > +++ b/net/sched/act_mirred.c
> > @@ -232,18 +232,14 @@ static int tcf_mirred_init(struct net *net, struct nlattr *nla,
> >         return err;
> >  }
> >
> > -static bool is_mirred_nested(void)
> > -{
> > -       return unlikely(__this_cpu_read(mirred_nest_level) > 1);
> > -}
> > -
> > -static int tcf_mirred_forward(bool want_ingress, struct sk_buff *skb)
> > +static int
> > +tcf_mirred_forward(bool at_ingress, bool want_ingress, struct sk_buff *skb)
> >  {
> >         int err;
> >
> >         if (!want_ingress)
> >                 err = tcf_dev_queue_xmit(skb, dev_queue_xmit);
> > -       else if (is_mirred_nested())
> > +       else if (!at_ingress)
> >                 err = netif_rx(skb);
> >         else
> >                 err = netif_receive_skb(skb);
> > @@ -319,9 +315,9 @@ static int tcf_mirred_to_dev(struct sk_buff *skb, struct tcf_mirred *m,
> >
> >                 skb_set_redirected(skb_to_send, skb_to_send->tc_at_ingress);
> >
> > -               err = tcf_mirred_forward(want_ingress, skb_to_send);
> > +               err = tcf_mirred_forward(at_ingress, want_ingress, skb_to_send);
> >         } else {
> > -               err = tcf_mirred_forward(want_ingress, skb_to_send);
> > +               err = tcf_mirred_forward(at_ingress, want_ingress, skb_to_send);
> >         }
> >
> >         if (err) {
> > diff --git a/tools/testing/selftests/net/forwarding/tc_actions.sh b/tools/testing/selftests/net/forwarding/tc_actions.sh
> > index b0f5e55d2d0b..589629636502 100755
> > --- a/tools/testing/selftests/net/forwarding/tc_actions.sh
> > +++ b/tools/testing/selftests/net/forwarding/tc_actions.sh
> > @@ -235,9 +235,6 @@ mirred_egress_to_ingress_tcp_test()
> >         check_err $? "didn't mirred redirect ICMP"
> >         tc_check_packets "dev $h1 ingress" 102 10
> >         check_err $? "didn't drop mirred ICMP"
> > -       local overlimits=$(tc_rule_stats_get ${h1} 101 egress .overlimits)
> > -       test ${overlimits} = 10
> > -       check_err $? "wrong overlimits, expected 10 got ${overlimits}"
> >
> >         tc filter del dev $h1 egress protocol ip pref 100 handle 100 flower
> >         tc filter del dev $h1 egress protocol ip pref 101 handle 101 flower
> > --
> > 2.43.0
> >

View attachment "mirred_ingress_bug.txt" of type "text/plain" (26164 bytes)