linux-kernel - Re: [PATCH -next v2 7/9] blk-iocost: fix UAF in ioc_pd

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Date:   Wed, 30 Nov 2022 10:42:14 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Li Nan <linan122@...wei.com>
Cc:     josef@...icpanda.com, axboe@...nel.dk, cgroups@...r.kernel.org,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        yukuai3@...wei.com, yi.zhang@...wei.com
Subject: Re: [PATCH -next v2 7/9] blk-iocost: fix UAF in ioc_pd_free

On Wed, Nov 30, 2022 at 09:21:54PM +0800, Li Nan wrote:
> 	T1		     T2			T3
>   //delete device
>   del_gendisk
>    bdi_unregister
>     bdi_remove_from_list
>      synchronize_rcu_expedited
> 
> 		         //rmdir cgroup
> 		         blkcg_destroy_blkgs
> 		          blkg_destroy
> 		           percpu_ref_kill
> 		            blkg_release
> 		             call_rcu
>    rq_qos_exit
>     ioc_rqos_exit
>      kfree(ioc)
> 					   __blkg_release
> 					    blkg_free
> 					     blkg_free_workfn
> 					      pd_free_fn
> 					       ioc_pd_free
> 						spin_lock_irqsave
> 						 ->ioc is freed
> 
> Fix the problem by moving the operation on ioc in ioc_pd_free() to
> ioc_pd_offline(), and just free resource in ioc_pd_free() like iolatency
> and throttle.
> 
> Signed-off-by: Li Nan <linan122@...wei.com>

I wonder what we really wanna do is pinning ioc while blkgs are still around
but I think this should work too.

Acked-by: Tejun Heo <tj@...nel.org>

Thanks.

-- 
tejun