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
