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From: Pavel Begunkov <[email protected]>
To: "Zhang, Qiang" <[email protected]>,
	Hillf Danton <[email protected]>,
	"[email protected]" <[email protected]>
Cc: "[email protected]" 
	<[email protected]>,
	"[email protected]" <[email protected]>,
	"[email protected]" <[email protected]>
Subject: Re: 回复: [PATCH] io-wq: Fix UAF when wakeup wqe in hash waitqueue
Date: Mon, 24 May 2021 11:16:40 +0100	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <DM6PR11MB4202B442C4C27740B6EE2D64FF269@DM6PR11MB4202.namprd11.prod.outlook.com>

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

  reply	other threads:[~2021-05-24 10:16 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-24  7:18 [PATCH] io-wq: Fix UAF when wakeup wqe in hash waitqueue qiang.zhang
     [not found] ` <[email protected]>
2021-05-24  9:19   ` 回复: " Zhang, Qiang
2021-05-24 10:16     ` Pavel Begunkov [this message]
2021-05-25  2:01       ` 回复: " Zhang, Qiang
2021-06-07 17:38         ` Pavel Begunkov
2021-06-10  1:49           ` Zhang, Qiang
2021-05-24 10:18     ` Pavel Begunkov

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