linux-kernel - Re: [patch 0/3] Re: tty contention resulting from tty_open_by

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Message-ID: <20170717123145.GE24503@kroah.com>
Date:   Mon, 17 Jul 2017 14:31:45 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Okash Khawaja <okash.khawaja@...il.com>
Cc:     Alan Cox <gnomes@...rguk.ukuu.org.uk>,
        Jiri Slaby <jslaby@...e.com>,
        Samuel Thibault <samuel.thibault@...-lyon.org>,
        linux-kernel@...r.kernel.org, William Hubbs <w.d.hubbs@...il.com>,
        Chris Brannon <chris@...-brannons.com>,
        Kirk Reiser <kirk@...sers.ca>, speakup@...ux-speakup.org,
        devel@...verdev.osuosl.org
Subject: Re: [patch 0/3] Re: tty contention resulting from tty_open_by_device
 export

On Thu, Jul 13, 2017 at 12:29:54PM +0100, Okash Khawaja wrote:
> On Wed, Jul 12, 2017 at 07:20:28PM +0100, Alan Cox wrote:
> > 
> > > When opening from kernel, we don't use file pointer. The count mismatch
> > > is between tty->count and #fd's. So opening from kernel leads to #fd's
> > > being less than tty->count. I thought this difference is relevant to
> > > user-space opening of tty, and not to kernel opening of tty. Can you
> > > suggest how to address this mismatch?
> > 
> > Your kernel reference is the same as having a file open reference so I
> > think this actually needs addressing in the maths. In other words count
> > the number of kernel references and also add that into the test for
> > check_tty_count (kernel references + #fds == count).
> > 
> > I'd really like to keep this right because that check has a long history
> > of catching really nasty race conditions in the tty code. The
> > open/close/hangup code is really fragile so worth the debugability.
> 
> I see. Okay based this, check_tty_count can be easily updated to take
> into account kernel references.

Ok, I'll drop this series from my "to-apply" queue and wait for you to
redo it.

thanks,

greg k-h