linux-kernel - Re: [REPORT] Use-after-free Read in __fdget

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Message-ID: <d503d5ff-4bc5-2bd0-00d3-cd7b0a0724cb@kernel.dk>
Date:   Tue, 17 May 2022 06:25:17 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Lee Jones <lee.jones@...aro.org>
Cc:     Pavel Begunkov <asml.silence@...il.com>, io-uring@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [REPORT] Use-after-free Read in __fdget_raw in v5.10.y

On 5/17/22 6:24 AM, Lee Jones wrote:
> On Tue, 17 May 2022, Jens Axboe wrote:
> 
>> On 5/17/22 5:41 AM, Lee Jones wrote:
>>> Good afternoon Jens, Pavel, et al.,
>>>
>>> Not sure if you are presently aware, but there appears to be a
>>> use-after-free issue affecting the io_uring worker driver (fs/io-wq.c)
>>> in Stable v5.10.y.
>>>
>>> The full sysbot report can be seen below [0].
>>>
>>> The C-reproducer has been placed below that [1].
>>>
>>> I had great success running this reproducer in an infinite loop.
>>>
>>> My colleague reverse-bisected the fixing commit to:
>>>
>>>   commit fb3a1f6c745ccd896afadf6e2d6f073e871d38ba
>>>   Author: Jens Axboe <axboe@...nel.dk>
>>>   Date:   Fri Feb 26 09:47:20 2021 -0700
>>>
>>>        io-wq: have manager wait for all workers to exit
>>>
>>>        Instead of having to wait separately on workers and manager, just have
>>>        the manager wait on the workers. We use an atomic_t for the reference
>>>        here, as we need to start at 0 and allow increment from that. Since the
>>>        number of workers is naturally capped by the allowed nr of processes,
>>>        and that uses an int, there is no risk of overflow.
>>>
>>>        Signed-off-by: Jens Axboe <axboe@...nel.dk>
>>>
>>>     fs/io-wq.c | 30 ++++++++++++++++++++++--------
>>>     1 file changed, 22 insertions(+), 8 deletions(-)
>>
>> Does this fix it:
>>
>> commit 886d0137f104a440d9dfa1d16efc1db06c9a2c02
>> Author: Jens Axboe <axboe@...nel.dk>
>> Date:   Fri Mar 5 12:59:30 2021 -0700
>>
>>     io-wq: fix race in freeing 'wq' and worker access
>>
>> Looks like it didn't make it into 5.10-stable, but we can certainly
>> rectify that.
> 
> Thanks for your quick response Jens.
> 
> This patch doesn't apply cleanly to v5.10.y.

This is probably why it never made it into 5.10-stable :-/

> I'll have a go at back-porting it.  Please bear with me.

Let me know if you into issues with that and I can help out.

-- 
Jens Axboe