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Wed, 11 Aug 2021 01:30:08 -0700 (PDT) Subject: Re: [PATCH] net:sched fix array-index-out-of-bounds in taprio_change To: Eric Dumazet , tcs.kernel@gmail.com, vinicius.gomes@intel.com, jhs@mojatatu.com, xiyou.wangcong@gmail.com, jiri@resnulli.us, davem@davemloft.net, kuba@kernel.org, netdev@vger.kernel.org Cc: Haimin Zhang References: <1628658609-1208-1-git-send-email-tcs_kernel@tencent.com> <303b095e-3342-9461-16ae-86d0923b7dc7@gmail.com> From: Pavel Skripkin Message-ID: <1852afdd-7c93-fdbc-404f-a5c76b9bc5d7@gmail.com> Date: Wed, 11 Aug 2021 11:30:07 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.12.0 MIME-Version: 1.0 In-Reply-To: <303b095e-3342-9461-16ae-86d0923b7dc7@gmail.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 8/11/21 10:44 AM, Eric Dumazet wrote: > > > On 8/11/21 7:10 AM, tcs.kernel@gmail.com wrote: >> From: Haimin Zhang >> >> syzbot report an array-index-out-of-bounds in taprio_change >> index 16 is out of range for type '__u16 [16]' >> that's because mqprio->num_tc is lager than TC_MAX_QUEUE,so we check >> the return value of netdev_set_num_tc. >> >> Reported-by: syzbot+2b3e5fb6c7ef285a94f6@syzkaller.appspotmail.com >> Signed-off-by: Haimin Zhang >> --- >> net/sched/sch_taprio.c | 4 +++- >> 1 file changed, 3 insertions(+), 1 deletion(-) >> >> diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c >> index 9c79374..1ab2fc9 100644 >> --- a/net/sched/sch_taprio.c >> +++ b/net/sched/sch_taprio.c >> @@ -1513,7 +1513,9 @@ static int taprio_change(struct Qdisc *sch, struct nlattr *opt, >> taprio_set_picos_per_byte(dev, q); >> >> if (mqprio) { >> - netdev_set_num_tc(dev, mqprio->num_tc); >> + err = netdev_set_num_tc(dev, mqprio->num_tc); >> + if (err) >> + goto free_sched; >> for (i = 0; i < mqprio->num_tc; i++) >> netdev_set_tc_queue(dev, i, >> mqprio->count[i], >> > > When was the bug added ? > > Hint: Please provide a Fixes: tag > > taprio_parse_mqprio_opt() already checks : > > /* Verify num_tc is not out of max range */ > if (qopt->num_tc > TC_MAX_QUEUE) { > NL_SET_ERR_MSG(extack, "Number of traffic classes is outside valid range"); > return -EINVAL; > } > > So what is happening exactly ? > > Hi, Eric! I've looked into this bug, but I decided to write a reproducer for it first. Unfortunately, I didn't finish it yesterday, but I have an idea about what happened: taprio_parse_mqprio_opt() may return 0 before qopt->num_tc check: /* If num_tc is already set, it means that the user already * configured the mqprio part */ if (dev->num_tc) return 0; Then taprio_mqprio_cmp() fails here: if (!mqprio || mqprio->num_tc != dev->num_tc) return -1; That's why we won't get shift-out-of-bound in taprio_mqprio_cmp(). And finally taprio_change() gets to buggy for with wrong mqprio->num_tc. I don't know how to reproduce it, but I'll try to finish my reproducer this evening. Does above makes any sense? With regards, Pavel Skripkin