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Date:   Mon, 11 May 2020 08:35:07 +0200
From:   Greg KH <gregkh@linuxfoundation.org>
To:     Kyungtae Kim <kt0755@gmail.com>
Cc:     Joel Becker <jlbec@evilplan.org>, Christoph Hellwig <hch@lst.de>,
        syzkaller <syzkaller@googlegroups.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Dave Tian <dave.jing.tian@gmail.com>
Subject: Re: KASAN: use-after-free Write in config_item_get
Message-ID: <20200511063507.GA1275674@kroah.com>
References: <20200511055200.GA31686@pizza01>
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On Mon, May 11, 2020 at 05:52:16AM +0000, Kyungtae Kim wrote:
> We report a bug (in linux-5.6.8) found by FuzzUSB (a modified version
> of syzkaller)
> 
> kernel config: https://kt0755.github.io/etc/config_v5.6.8
> 
> 
> This bug happened when accessing a configfs_item instance right after being
> deallocated.
> Specifically, config_item_get() tries to access ci_kref element in a config_item instance. 
> But this led to memory access violation because that instance (held by a fsg_opts structure) 
> had been freed by fsg_free_inst() in another thread (PID: 2603).
> 
> To fix, it needs to check if the config_item instance is still in use 
> when trying to deallocate it.

Great, can you create a patch to fix this now that you have a solid test
for it?

thanks,

greg k-h