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From: Luis Chamberlain <>
To: Greg KH <>, Tejun Heo <>
Subject: Re: [PATCH v4] sysfs: fix kobject refcount to address races with kobject removal
Date: Thu, 1 Jul 2021 15:48:16 -0700	[thread overview]
Message-ID: <20210701224816.pkzeyo4uqu3kbqdo@garbanzo> (raw)
In-Reply-To: <20210625215558.xn4a24ts26bdyfzo@garbanzo>

On Fri, Jun 25, 2021 at 02:56:03PM -0700, Luis Chamberlain wrote:
> On Thu, Jun 24, 2021 at 01:09:03PM +0200, Greg KH wrote:
> > thanks for making this change and sticking with it!
> > 
> > Oh, and with this change, does your modprobe/rmmod crazy test now work?
> It does but I wrote a test_syfs driver and I believe I see an issue with
> this. I'll debug a bit more and see what it was, and I'll then also use
> the driver to demo the issue more clearly, and then verification can be
> an easy selftest test.

OK my conclusion based on a new selftest driver I wrote is we can drop
this patch safely. The selftest will cover this corner case well now.

In short: the kernfs active reference will ensure the store operation
still exists. The kernfs mutex is not enough, but if the driver removes
the operation prior to getting the active reference, the write will just
fail. The deferencing inside of the sysfs operation is abstract to
kernfs, and while kernfs can't do anything to prevent a driver from
doing something stupid, it at least can ensure an open file ensure the
op is not removed until the operation completes.


  reply	other threads:[~2021-07-01 22:48 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-23 21:50 [PATCH v4] sysfs: fix kobject refcount to address races with kobject removal Luis Chamberlain
2021-06-23 22:59 ` Kees Cook
2021-06-24  1:09   ` Luis Chamberlain
2021-06-24 11:06   ` Greg KH
2021-06-24 11:09 ` Greg KH
2021-06-25 21:55   ` Luis Chamberlain
2021-07-01 22:48     ` Luis Chamberlain [this message]
2021-07-02  1:04       ` Luis Chamberlain
2021-07-21 11:30       ` Greg KH
2021-07-22 21:31         ` Luis Chamberlain
2021-07-23 11:14           ` Greg KH
2021-07-23 17:35             ` Luis Chamberlain

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