netdev - Re: [PATCH net] net: sched: fix NULL pointer dereference in mq

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Date: Mon, 29 May 2023 17:17:24 -0700
From: Peilin Ye <yepeilin.cs@...il.com>
To: 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, pabeni@...hat.com,
	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, 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:
> > On Mon, May 29, 2023 at 09:10:23AM +0800, shaozhengchao wrote:
> > > On 2023/5/29 3:05, Jamal Hadi Salim wrote:
> > > > On Sat, May 27, 2023 at 5:30 AM Zhengchao Shao <shaozhengchao@...wei.com> wrote:
> > > > > When use the following command to test:
> > > > > 1)ip link add bond0 type bond
> > > > > 2)ip link set bond0 up
> > > > > 3)tc qdisc add dev bond0 root handle ffff: mq
> > > > > 4)tc qdisc replace dev bond0 parent ffff:fff1 handle ffff: mq
> > > >
> > > > This is fixed by Peilin in this ongoing discussion:
> > > > https://lore.kernel.org/netdev/cover.1684887977.git.peilin.ye@bytedance.com/
> > > >
> > >       Thank you for your reply. I have notice Peilin's patches before,
> > > and test after the patch is incorporated in local host. But it still
> > > triggers the problem.
> > >       Peilin's patches can be filtered out when the query result of
> > > qdisc_lookup is of the ingress type. Here is 4/6 patch in his patches.
> > > +if (q->flags & TCQ_F_INGRESS) {
> > > +     NL_SET_ERR_MSG(extack,
> > > +                    "Cannot regraft ingress or clsact Qdiscs");
> > > +     return -EINVAL;
> > > +}
> > >       However, the query result of my test case in qdisc_lookup is mq.
> > > Therefore, the patch cannot solve my problem.
> >
> > 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.

Thanks,
Peilin Ye