Re: [REPORT] Use-after-free Read in __fdget_raw in v5.10.y

[Jens Axboe <axboe@kernel.dk>]

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@kernel.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@kernel.dk>
> 
>     fs/io-wq.c | 30 ++++++++++++++++++++++--------
>     1 file changed, 22 insertions(+), 8 deletions(-)

Does this fix it:

commit 886d0137f104a440d9dfa1d16efc1db06c9a2c02
Author: Jens Axboe <axboe@kernel.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.

-- 
Jens Axboe