linux-kernel - Re: [syzbot] KASAN: use-after-free Read in srcu_invoke

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Date:   Fri, 14 Jan 2022 23:54:48 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     Boqun Feng <boqun.feng@...il.com>
Cc:     "Paul E. McKenney" <paulmck@...nel.org>,
        Hillf Danton <hdanton@...a.com>,
        syzbot <syzbot+4f789823c1abc5accf13@...kaller.appspotmail.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Lai Jiangshan <laijs@...ux.alibaba.com>,
        linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com,
        quic_neeraju@...cinc.com, frederic@...nel.org, urezki@...il.com,
        Jens Axboe <axboe@...nel.dk>
Subject: Re: [syzbot] KASAN: use-after-free Read in srcu_invoke_callbacks

On Fri, Jan 14, 2022 at 10:38:42PM +0800, Boqun Feng wrote:
> Hi,
> 
> On Tue, Jan 11, 2022 at 11:05:00AM -0800, Paul E. McKenney wrote:
> [...]
> > > > The buggy address belongs to the object at ffff8880189b5c70
> > > >  which belongs to the cache request_queue_srcu of size 3816
> 
> This cache name drew my attention when I was trying to look into this,
> because I couldn't find it in v5.16, later on I realized the UAF was
> found in linux-next and the commit introducing the cache was merged into
> mainline if 5.17 merge window:
> 
> 	704b914f15fb blk-mq: move srcu from blk_mq_hw_ctx to request_queue
> 
> I think the UAF is actually a bug introduced by the commit, because in
> that commit srcu structure was moved from blk_mq_hw_ctx to
> request_queue, and therefore the cleanup_srcu_struct() should be moved
> from blk_mq_hw_sysfs_release() to blk_release_queue(), however the above
> commit only deleted the one in blk_mq_hw_sysfs_release() but didn't add
> a new one in blk_release_queue(). As a result when a request queue is
> freed, the srcu structure is not fully clean up, therefore the UAF.
> 
> IOW, something like below (untested) should fix this. Copy the auther
> and block maintainers.
> 
> Regards,
> Boqun
> 
> diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
> index e20eadfcf5c8..10f59416376e 100644
> --- a/block/blk-sysfs.c
> +++ b/block/blk-sysfs.c
> @@ -812,6 +812,10 @@ static void blk_release_queue(struct kobject *kobj)
>         bioset_exit(&q->bio_split);
> 
>         ida_simple_remove(&blk_queue_ida, q->id);
> +
> +       if (test_bit(QUEUE_FLAG_HAS_SRCU, &q->queue_flags)) {
> +               cleanup_srcu_struct(q->srcu);
> +       }
>         call_rcu(&q->rcu_head, blk_free_queue_rcu);
>  }

Yes, this fix has been posted days ago:

https://lore.kernel.org/linux-block/20220111123401.520192-1-ming.lei@redhat.com/T/#u


Thanks,
Ming