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([2620:10d:c093:600::2:2b02]) by smtp.gmail.com with ESMTPSA id c4sm11932896wrx.77.2021.05.24.03.16.47 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 24 May 2021 03:16:48 -0700 (PDT) To: "Zhang, Qiang" , Hillf Danton , "axboe@kernel.dk" Cc: "syzbot+6cb11ade52aa17095297@syzkaller.appspotmail.com" , "io-uring@vger.kernel.org" , "linux-kernel@vger.kernel.org" References: <20210524071844.24085-1-qiang.zhang@windriver.com> <20210524082536.2032-1-hdanton@sina.com> From: Pavel Begunkov Subject: =?UTF-8?B?UmU6IOWbnuWkjTogW1BBVENIXSBpby13cTogRml4IFVBRiB3aGVuIHdh?= =?UTF-8?Q?keup_wqe_in_hash_waitqueue?= Message-ID: <916ad789-c996-258f-d3b7-b41d749618d8@gmail.com> Date: Mon, 24 May 2021 11:16:40 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.10.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 -- Pavel Begunkov