________________________________________ 发件人: Pavel Begunkov <asml.silence@xxxxxxxxx> 发送时间: 2021年5月24日 18:16 收件人: Zhang, Qiang; Hillf Danton; axboe@xxxxxxxxx 抄送: syzbot+6cb11ade52aa17095297@xxxxxxxxxxxxxxxxxxxxxxxxx; io-uring@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx 主题: Re: 回复: [PATCH] io-wq: Fix UAF when wakeup wqe in hash waitqueue [Please note: This e-mail is from an EXTERNAL e-mail address] On 5/24/21 10:19 AM, Zhang, Qiang wrote: [...] >> Scratch scalp one inch off to work out how this is a cure given a) uaf makes >> no sense without free and b) how io workers could survive >> wait_for_completion(&wq->worker_done). >> >> If they could OTOH then this is not the pill for the leak in worker_refs. > > Hello Pavel Begunkov, Hillf Danton > > Sorry there is a problem with the calltrace described in my message. Please ignore this modification > >Haven't looked at the trace and description, but I do think >there is a problem it solves. > >1) io_wait_on_hash() -> __add_wait_queue(&hash->wait, &wqe->wait); >2) (note: wqe is a worker) wqe's workers exit dropping refs >3) refs are zero, free io-wq >4) @hash is shared, so other task/wq does wake_up(&wq->hash->wait); >5) it wakes freed wqe > >step 4) is a bit more trickier than that, tl;dr; >wq3:worker1 | locks bit1 >wq1:worker2 | waits bit1 >wq2:worker1 | waits bit1 >wq1:worker3 | waits bit1 > >wq3:worker1 | drop bit1 >wq1:worker2 | locks bit1 >wq1:worker2 | completes all wq1 bit1 work items >wq1:worker2 | drop bit1, exit and free io-wq > >wq2:worker1 | locks bit1 >wq1 | free complete >wq2:worker1 | drops bit1 >wq1:worker3 | waked up, even though freed > >Can be simplified, don't want to waste time on that Thanks Pavel Your description is better. I have another question: under what circumstances will three io-wq(wq1, wq2, wq3) be created to share this @hash? This kind of problem also occurs between two io-wq(wq1, wq2). Is the following description OK？ wq1:worker2 | locks bit1 wq2:worker1 | waits bit1 wq1:worker3 | waits bit1 wq1:worker2 | completes all wq1 bit1 work items wq1:worker2 | drop bit1, exit and free io-wq wq2:worker1 | locks bit1 wq1 | free complete wq2:worker1 | drops bit1 wq1:worker3 | waked up, even though freed Zhang > >-- >Pavel Begunkov
