From: Sasha Levin <sasha.levin@oracle.com>
To: Tejun Heo <tj@kernel.org>
Cc: Greg KH <greg@kroah.com>, LKML <linux-kernel@vger.kernel.org>
Subject: Re: kernfs: possible deadlock between of->mutex and mmap_sem
Date: Mon, 03 Mar 2014 17:44:52 -0500 [thread overview]
Message-ID: <531505E4.8020802@oracle.com> (raw)
In-Reply-To: <20140303223933.GC26523@mtj.dyndns.org>
On 03/03/2014 05:39 PM, Tejun Heo wrote:
> On Fri, Feb 28, 2014 at 08:14:45PM -0500, Sasha Levin wrote:
>> Hi all,
>>
>> I've stumbled on the following while fuzzing with trinity inside a
>> KVM tools running the latest -next kernel.
>>
>> We deal with files that have an mmap op by giving them a different
>> locking class than the files which don't due to mmap_sem nesting
>> being different for those files.
>>
>> We assume that for mmap supporting files, of->mutex will be nested
>> inside mm->mmap_sem. However, this is not always the case. Consider
>> the following:
>>
>> kernfs_fop_write()
>> copy_from_user()
>> might_fault()
>>
>> might_fault() suggests that we may lock mm->mmap_sem, which causes a
>> reverse lock nesting of mm->mmap_sem inside of of->mutex.
>>
>> I'll send a patch to fix it some time next week unless someone beats me to it :)
>
> How are you planning to fix it? Prolly the right thing to do would be
> caching atomic_write_len in open_file and copy data before grabbing
> any locks.
I've actually didn't have a plan when I wrote that, was just planning on putting effort into it.
Thanks,
Sasha
next prev parent reply other threads:[~2014-03-03 22:44 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-03-01 1:14 kernfs: possible deadlock between of->mutex and mmap_sem Sasha Levin
2014-03-01 23:18 ` Dave Chinner
2014-03-03 22:39 ` Tejun Heo
2014-03-03 22:44 ` Sasha Levin [this message]
2014-03-03 22:46 ` Tejun Heo
2014-03-04 20:38 ` [PATCH driver-core-next] kernfs: cache atomic_write_len in kernfs_open_file Tejun Heo
2014-03-05 2:50 ` Greg KH
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