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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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