linux-kernel - Re: [PATCH] drivers: isdn: capi: Fix data-race bug

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Date:   Fri, 24 Jul 2020 08:57:47 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Madhuparna Bhowmik <madhuparnabhowmik10@...il.com>
Cc:     David Miller <davem@...emloft.net>, isdn@...ux-pingi.de,
        arnd@...db.de, edumazet@...gle.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, andrianov@...ras.ru,
        ldv-project@...uxtesting.org
Subject: Re: [PATCH] drivers: isdn: capi: Fix data-race bug

On Fri, Jul 24, 2020 at 10:18:07AM +0530, Madhuparna Bhowmik wrote:
> On Thu, Jul 23, 2020 at 03:11:58PM -0700, David Miller wrote:
> > From: madhuparnabhowmik10@...il.com
> > Date: Wed, 22 Jul 2020 22:53:29 +0530
> > 
> > > From: Madhuparna Bhowmik <madhuparnabhowmik10@...il.com>
> > > 
> > > In capi_init(), after register_chrdev() the file operation callbacks
> > > can be called. However capinc_tty_init() is called later.
> > > Since capiminors and capinc_tty_driver are initialized in
> > > capinc_tty_init(), their initialization can race with their usage
> > > in various callbacks like in capi_release().
> > > 
> > > Therefore, call capinc_tty_init() before register_chrdev to avoid
> > > such race conditions.
> > > 
> > > Found by Linux Driver Verification project (linuxtesting.org).
> > > 
> > > Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik10@...il.com>
> > 
> > I agree with Arnd that this just exchanges one set of problems for
> > another.
> 
> Thanks Arnd and David, for reviewing the patch.
> Do you have any suggestions on how to fix this correctly?

Based on the installed base of ISDN systems, and the fact that no one
has ever actually hit this race and reported it ever, I wouldn't worry
about it :)

thanks,

greg k-h