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Message-ID: <9cf98c8ae48c99850a0a25ae7919420ce5dfa7b4.camel@redhat.com>
Date: Tue, 30 May 2023 12:16:10 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Peilin Ye <yepeilin.cs@...il.com>, Jamal Hadi Salim <jhs@...atatu.com>
Cc: shaozhengchao <shaozhengchao@...wei.com>, netdev@...r.kernel.org,
xiyou.wangcong@...il.com, jiri@...nulli.us, davem@...emloft.net,
edumazet@...gle.com, kuba@...nel.org, weiyongjun1@...wei.com,
yuehaibing@...wei.com, wanghai38@...wei.com, peilin.ye@...edance.com,
cong.wang@...edance.com
Subject: Re: [PATCH net] net: sched: fix NULL pointer dereference in
mq_attach
On Mon, 2023-05-29 at 17:17 -0700, Peilin Ye wrote:
> On Mon, May 29, 2023 at 09:53:28AM -0400, Jamal Hadi Salim wrote:
> > On Mon, May 29, 2023 at 4:59 AM Peilin Ye <yepeilin.cs@...il.com> wrote:
> > > Ack, they are different: patch [4/6] prevents ingress (clsact) Qdiscs
> > > from being regrafted (to elsewhere), and Zhengchao's patch prevents other
> > > Qdiscs from being regrafted to ffff:fff1.
> >
> > Ok, at first glance it was not obvious.
> > Do we catch all combinations? for egress (0xffffffff) allowed minor is
> > 0xfff3 (clsact::) and 0xffff. For ingress (0xfffffff1) allowed minor
> > is 0xfff1 and 0xfff2(clsact).
>
> ffff:fff1 is special in tc_modify_qdisc(); if minor isn't fff1,
> tc_modify_qdisc() thinks user wants to graft a Qdisc under existing ingress
> or clsact Qdisc:
>
> if (clid != TC_H_INGRESS) { /* ffff:fff1 */
> p = qdisc_lookup(dev, TC_H_MAJ(clid));
> if (!p) {
> NL_SET_ERR_MSG(extack, "Failed to find specified qdisc");
> return -ENOENT;
> }
> q = qdisc_leaf(p, clid);
> } else if (dev_ingress_queue_create(dev)) {
> q = dev_ingress_queue(dev)->qdisc_sleeping;
> }
>
> This will go to the "parent != NULL" path in qdisc_graft(), and
> sch_{ingress,clsact} doesn't implement cl_ops->graft(), so -EOPNOTSUPP will
> be returned.
>
> In short, yes, I think ffff:fff1 is the only case should be fixed.
>
> By the way I just noticed that currently it is possible to create a e.g.
> HTB class with a class ID of ffff:fff1...
>
> $ tc qdisc add dev eth0 root handle ffff: htb default fff1
> $ tc class add dev eth0 \
> parent ffff: classid ffff:fff1 htb rate 100%
>
> Regrafting a Qdisc to such classes won't work as intended at all. It's a
> separate issue though.
Jamal, are you ok with the above explanation? Perhaps it would be
worthy to add a specific test-case under tc-testing for this issue?
Thanks!
Paolo
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